U.S. patent application number 12/826161 was filed with the patent office on 2010-12-30 for device and method for advanced low-power management of a sensor to measure a parameter of the muscular-skeletal system.
This patent application is currently assigned to OrthoSensor. Invention is credited to Andrew Kelly, Marc Stein.
Application Number | 20100331682 12/826161 |
Document ID | / |
Family ID | 43379281 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100331682 |
Kind Code |
A1 |
Stein; Marc ; et
al. |
December 30, 2010 |
DEVICE AND METHOD FOR ADVANCED LOW-POWER MANAGEMENT OF A SENSOR TO
MEASURE A PARAMETER OF THE MUSCULAR-SKELETAL SYSTEM
Abstract
A sensing insert device (100) is disclosed for measuring a
parameter of the muscular-skeletal system. The sensing insert
device (100) can be temporary or permanent. Used intra-operatively,
the sensing insert device (100) comprises an insert dock (202) and
a sensing module (200). The sensing module (200) is a
self-contained encapsulated measurement device having at least one
contacting surface that couples to the muscular-skeletal system.
The sensing module (200) comprises one or more sensors (303),
electronic circuitry (307), a capacitor (1410), and communication
circuitry (320). The capacitor (1410) powers the sensing module
during a measurement process. An application specific integrated
circuit (ASIC) increases power efficiency while reducing a form
factor of the sensing module (200). The ASIC comprises power
management circuitry (1412) and operational circuitry (1414). The
power management circuitry (1412) couples a low-power energy source
(1400) and operational circuitry (1414) to operate in one or more
power conservation modes.
Inventors: |
Stein; Marc; (Chandler,
AZ) ; Kelly; Andrew; (Scottsdale, AZ) |
Correspondence
Address: |
Orthosensor, Inc.
1560 Sawgrass Corporate Pkwy, 4th Floor
Sunrise
FL
33323
US
|
Assignee: |
OrthoSensor
Sunrise
FL
|
Family ID: |
43379281 |
Appl. No.: |
12/826161 |
Filed: |
June 29, 2010 |
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Application
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61221761 |
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Current U.S.
Class: |
600/437 ;
307/64 |
Current CPC
Class: |
A61B 5/7239 20130101;
A61B 5/6878 20130101; A61B 5/4509 20130101; A61B 5/6846 20130101;
A61B 8/15 20130101; A61B 5/4528 20130101 |
Class at
Publication: |
600/437 ;
307/64 |
International
Class: |
A61B 8/00 20060101
A61B008/00; H02J 9/00 20060101 H02J009/00 |
Claims
1. A system to measure a parameter of the muscular-skeletal system
comprising: a sensing module including: one or more sensors for
coupling to the muscular-skeletal system; a compact low-power
energy source to power the sensing module; and an application
specific integrated circuit (ASIC) comprising: partitioned
operational circuitry coupled to the one or more sensors; power
management circuitry operatively coupled to the compact low-power
energy source and operational circuitry to operate in one or more
power conservation modes.
2. The system of claim 1 where the power management circuitry
reduces a frequency of operation to lower power dissipation in a
power conservation mode.
3. The system of claim 1 where the power management circuitry
operably controls a partitioned block of the operational circuitry
to lower power dissipation in a power conservation mode.
4. The system of claim 1 where the compact low-power energy source
comprises a capacitor to power the sensing module to perform at
least one parameter measurement.
5. The system of claim 4 where the compact low-power energy source
further comprises: an induction coil; a rectifier coupled to the
induction coil; the capacitor coupled to the rectifier; and a
regulator coupled to the capacitor.
6. The system of claim 4 where the capacitor is decoupled from
remaining components of the compact low-power energy source when a
power signal charging the capacitor is no longer detected.
7. The system of claim 5 where the regulator is step-up or step
down voltage converter circuit.
8. The system of claim 1 where the power management circuitry
enables sequential channel operation in a power conservation
mode.
9. The system of claim 1 where the power management circuitry
delays transmission of measured parameter data if the charge on the
capacitor falls below a predetermined level in a power conservation
mode.
10. The system of claim 1 where the power management circuitry
performs an orderly shut down of the partitioned blocks of the
operational circuitry if the charge on the capacitor falls below a
predetermined level in a power conservation mode.
11. A method of measuring a parameter of the muscular-skeletal
system comprising the steps of: charging a capacitor prior to
measuring one or more parameters of the muscular-skeletal system;
and enabling one or more power conservation modes to reduce power
consumption prior to or during measurement of the muscular-skeletal
system where one or more sensors are powered solely by the
capacitor.
12. The method of claim 11 further including a step of enabling a
sleep mode after a predetermined time when no operations are being
performed.
13. The method of claim 11 further including a step of reducing a
frequency of operation to conserve power.
14. The method of claim 11 further including a step of decoupling a
compact low-power energy source from the capacitor when energy
coupling is inadequate or intermittent.
15. The method of claim 11 further including a step of disabling
one or more partitioned blocks of an ASIC coupled to the one or
more sensors to reduce power during measurement of the
muscular-skeletal system.
16. A method of providing backup power to measure a parameter of
the muscular-skeletal system comprising: interrupting power
provided to a sensing module; decoupling an energy source from a
capacitor; and powering the sensing module from the capacitor to
continue parameter measurements.
17. The method of claim 16 further including the steps of:
monitoring a level of charge on the capacitor; and providing power
to the sensing module while a capacitor voltage is above a
predetermined threshold.
18. The method of claim 17 further including a step of powering
down the sensing module when the capacitor voltage falls below the
predetermined threshold.
19. The method of claim 17 further including the steps of:
detecting the energy source; powering the sensing module with the
energy source; and charging the capacitor.
20. The method of claim 16 further including the steps of:
detecting when two or more energy sources are present where one of
the two or more energy sources is a wired energy source; and
selecting the wired energy source to power the sensing module.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S.
provisional patent applications No. 61/221,761, 61/221,767,
61/221,779, 61/221,788, 61/221,793, 61/221,801, 61/221,808,
61/221,817, 61/221,867, 61/221,874, 61/221,879, 61/221,881,
61/221,886, 61/221,889, 61/221,894, 61/221,901, 61/221,909,
61/221,916, 61/221,923, and 61/221,929 all filed 30 Jun. 2009; the
disclosures of which are hereby incorporated herein by reference in
their entirety.
FIELD
[0002] The present relates generally to the communication of data,
and more particularly, but not exclusively, to secure communication
of data and measurements in real-time.
BACKGROUND
[0003] The skeletal system of a mammal is subject to variations
among species. Further changes can occur due to environmental
factors, degradation through use, and aging. An orthopedic joint of
the skeletal system typically comprises two or more bones that move
in relation to one another. Movement is enabled by muscle tissue
and tendons attached to the skeletal system of the joint. Ligaments
hold and stabilize the one or more joint bones positionally.
Cartilage is a wear surface that prevents bone-to-bone contact,
distributes load, and lowers friction.
[0004] There has been substantial growth in the repair of the human
skeletal system. In general, orthopedic joints have evolved using
information from simulations, mechanical prototypes, and patient
data that is collected and used to initiate improved designs.
Similarly, the tools being used for orthopedic surgery have been
refined over the years but have not changed substantially. Thus,
the basic procedure for replacement of an orthopedic joint has been
standardized to meet the general needs of a wide distribution of
the population. Although the tools, procedure, and artificial joint
meet a general need, each replacement procedure is subject to
significant variation from patient to patient. The correction of
these individual variations relies on the skill of the surgeon to
adapt and fit the replacement joint using the available tools to
the specific circumstance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Various features of the system are set forth with
particularity in the appended claims. The embodiments herein, can
be understood by reference to the following description, taken in
conjunction with the accompanying drawings, in which:
[0006] FIG. 1 is an illustration of an application of sensing
insert device in accordance with an exemplary embodiment;
[0007] FIG. 2 is an illustration of a sensing insert device placed
in a joint of the muscular-skeletal system for measuring a
parameter in accordance with an exemplary embodiment;
[0008] FIG. 3 is a perspective view of a medical sensing platform
comprising an encapsulating enclosure in accordance with one
embodiment;
[0009] FIG. 4 is a perspective view of a medical sensing device
suitable for use as a bi-compartmental implant and comprising an
encapsulating enclosure in accordance with one embodiment;
[0010] FIG. 5 is an exemplary block diagram of the components of
the sensing module in accordance with an exemplary embodiment;
[0011] FIG. 6 is a diagram of an exemplary communications system
for short-range telemetry according to one embodiment;
[0012] FIG. 7 is an illustration of a block model diagram of the
sensing module in accordance with an exemplary embodiment;
[0013] FIG. 8 is an exemplary assemblage that illustrates
propagation of ultrasound waves within the waveguide in the
bi-directional mode of operation of this assemblage in accordance
with one embodiment;
[0014] FIG. 9 is an exemplary cross-sectional view of an ultrasound
waveguide to illustrate changes in the propagation of ultrasound
waves with changes in the length of the waveguide in accordance
with one embodiment;
[0015] FIG. 10 is an exemplary block diagram of a propagation tuned
oscillator (PTO) to maintain positive closed-loop feedback in
accordance with an exemplary embodiment;
[0016] FIG. 11 is a cross-sectional view of a layout architecture
of the sensing module in accordance with an exemplary
embodiment;
[0017] FIG. 12 is a simplified cross-sectional view of an
embodiment of the load sensing platform in accordance with an
exemplary embodiment;
[0018] FIG. 13 is an illustration of an exemplary data packet
containing sensor data;
[0019] FIG. 14 is an exemplary block diagram schematic of a compact
low-power energy source integrated into an exemplary electronic
assembly of the sensing module in accordance with one
embodiment;
[0020] FIG. 15 are exemplary methods for power conservation to
enable the capacitor power source in accordance with one or more
embodiments; and
[0021] FIG. 16 are exemplary methods for power conservation to
enable the capacitor power source in accordance with one or more
embodiments.
DETAILED DESCRIPTION
[0022] Embodiments of the invention are broadly directed to
measurement of physical parameters. Many physical parameters of
interest within physical systems or bodies can be measured by
evaluating changes in the characteristics of energy waves or
pulses. As one example, changes in the transit time or shape of an
energy wave or pulse propagating through a changing medium can be
measured to determine the forces acting on the medium and causing
the changes. The propagation velocity of the energy waves or pulses
in the medium is affected by physical changes in of the medium. The
physical parameter or parameters of interest can include, but are
not limited to, measurement of load, force, pressure, displacement,
density, viscosity, localized temperature. These parameters can be
evaluated by measuring changes in the propagation time of energy
pulses or waves relative to orientation, alignment, direction, or
position as well as movement, rotation, or acceleration along an
axis or combination of axes by wireless sensing modules or devices
positioned on or within a body, instrument, appliance, vehicle,
equipment, or other physical system.
[0023] In all of the examples illustrated and discussed herein, any
specific materials, temperatures, times, energies, etc. for process
steps or specific structure implementations should be interpreted
to illustrative only and non-limiting. Processes, techniques,
apparatus, and materials as known by one of ordinary skill in the
art may not be discussed in detail but are intended to be part of
an enabling description where appropriate.
[0024] Note that similar reference numerals and letters refer to
similar items in the following figures. In some cases, numbers from
prior illustrations will not be placed on subsequent figures for
purposes of clarity. In general, it should be assumed that
structures not identified in a figure are the same as previous
prior figures.
[0025] In the present invention these parameters are measured with
an integrated wireless sensing module or device comprising an i)
encapsulating structure that supports sensors and contacting
surfaces and ii) an electronic assemblage that integrates a power
supply, sensing elements, ultrasound resonator or resonators or
transducer or transducers and ultrasound waveguide or waveguides,
biasing spring or springs or other form of elastic members, an
accelerometer, antennas and electronic circuitry that processes
measurement data as well as controls all operations of energy
conversion, propagation, and detection and wireless communications.
The wireless sensing module or device can be positioned on or
within, or engaged with, or attached or affixed to or within, a
wide range of physical systems including, but not limited to
instruments, appliances, vehicles, equipments, or other physical
systems as well as animal and human bodies, for sensing and
communicating parameters of interest in real time.
[0026] FIG. 1 is an illustration of an application of sensing
insert device 100 in accordance with an exemplary embodiment. The
illustration shows the device 100 measuring a force, pressure, or
load applied by the muscular-skeletal system. The insert device 100
includes a compact low-power energy source 117. By way of the
compact low-power energy source 117 and associated integrated
electronics, the load sensor insert device 100 can transmit
measured load data to a receiver for permitting visualization of
the level and distribution of load at various points on the
prosthetic components. This can aid the surgeon in making any
adjustments needed to achieve optimal joint balancing.
[0027] In general, device 100 has at least one contacting surface
that couples to the muscular-skeletal system. As shown, a first and
a second contacting surface respectively couple to a femoral
prosthetic component 104 and a tibial prosthetic component 106.
Device 100 is designed to be used in the normal flow of an
orthopedic surgical procedure without special procedures,
equipment, or components. Typically, one or more natural components
of the muscular-skeletal system are replaced when joint
functionality substantially reduces a patient quality of life. A
joint replacement is a common procedure in later life because it is
prone to wear over time, can be damaged during physical activity,
or by accident.
[0028] A joint of the muscular-skeletal system provides movement of
bones in relation to one another that can comprise angular and
rotational motion. The joint can be subjected to loading and torque
throughout the range of motion. The joint typically comprises two
bones that move in relation to one another with a low friction
flexible connective tissue such as cartilage between the bones. The
joint also generates a natural lubricant that works in conjunction
with the cartilage to aid in ease of movement. Sensing insert
device 100 mimics the natural structure between the bones of the
joint. Insert device 100 has a contacting surface on which a bone
or a prosthetic component can moveably couple. A knee joint is
disclosed for illustrative purposes but sensing insert device 100
is applicable to other joints of the muscular-skeletal system. For
example, the hip, spine, and shoulder have similar structures
comprising two or more bones that move in relation to one another.
In general, insert device 100 can be used between two or more bones
allowing movement of the bones during measurement or maintaining
the bones in a fixed position.
[0029] The load sensor insert device 100 and the receiver station
110 forms a communication system for conveying data via secure
wireless transmission within a broadcasting range over short
distances on the order of a few meters to protect against any form
of unauthorized or accidental query. In one embodiment, the
transmission range is five meters or less which is approximately a
dimension of an operating room. In practice, it can be a shorter
distance 1-2 meters to transmit to a display outside the sterile
field. The transmit distance will be even shorter when device 100
is used in a prosthetic implanted component. Transmission occurs
through the skin of the patient and is likely limited to less than
0.5 meters. A combination of cyclic redundancy checks and a high
repetition rate of transmission during data capture permits
discarding of corrupted data without materially affecting display
of data
[0030] In the illustration, a surgical procedure is performed to
place a femoral prosthetic component 104 onto a prepared distal end
of the femur 102. Similarly, a tibial prosthetic component 106 is
placed to a prepared proximal end of the tibia 108. The tibial
prosthetic component 106 can be a tray or plate affixed to a
planarized proximal end of the tibia 108. The sensing insert device
100 is a third prosthetic component that is placed between the
plate of the tibial prosthetic component 106 and the femoral
prosthetic component 104. The three prosthetic components enable
the prostheses to emulate the functioning of a natural knee joint.
In one embodiment, sensing insert device 100 is used during surgery
and replaced with a final insert after quantitative measurements
are taken to ensure optimal fit, balance, and loading of the
prosthesis.
[0031] In one embodiment, sensing insert device 100 is a mechanical
replica of a final insert. In other words, sensing insert device
100 has substantially equal dimensions to the final insert. The
substantially equal dimensions ensure that the final insert when
placed in the reconstructed joint will have similar loading and
balance as that measured by sensing insert device 100 during the
trial phase of the surgery. Moreover, passive trial inserts are
commonly used during surgery to determine the appropriate final
insert. Thus, the procedure remains the same. It can measure loads
at various points (or locations) on the femoral prosthetic
component 104 and transmit the measured data to a receiving station
110 by way of an integrated loop antenna. The receiving station 110
can include data processing, storage, or display, or combination
thereof and provide real time graphical representation of the level
and distribution of the load.
[0032] As one example, the sensing insert device 100 can measure
forces (Fx, Fy, and Fz) with corresponding locations and torques
(e.g. Tx, Ty, and Tz) on the femoral prosthetic component 104 and
the tibial prosthetic component 106. It can then transmit this data
to the receiving station 110 to provide real-time visualization for
assisting the surgeon in identifying any adjustments needed to
achieve optimal joint balancing.
[0033] In a further example, an external wireless energy source 125
can be placed in proximity to the medical sensing device 100 to
initiate a wireless power recharging operation. As an example, the
external wireless energy source 125 generates energy transmissions
that are wirelessly directed to the medical sensing device 100 and
received as energy waves via resonant inductive coupling. The
external wireless energy source 125 can modulate a power signal
generating the energy transmissions to convey downlink data that is
then demodulated from the energy waves at the medical sensing
device 100. As described above, the sensing insert device 100 is a
sensing insert device 100 suitable for use in knee joint
replacement surgery. The external wireless energy source 125 can be
used to power the sensing insert device 100 during the surgical
procedure or thereafter when the surgery is complete and the
sensing insert device 100 is implanted for long-term use. The
method can also be used to provide power and communication where
the sensing insert device 100 is in a final insert that is part of
the final prosthesis implanted in the patient.
[0034] In one system embodiment, the sensing insert device 100
transmits measured parameter data to a receiver 110 via one-way
data communication over the up-link channel for permitting
visualization of the level and distribution of the parameter at
various points on the prosthetic components. This, combined with
cyclic redundancy check error checking, provides high security and
protection against any form of unauthorized or accidental
interference with a minimum of added circuitry and components. This
can aid the surgeon in making any adjustments needed to optimize
the installation. In addition to transmitting one-way data
communications over the up-link channel to the receiver station
110, the sensing insert device 100 can receive downlink data from
the external wireless energy source 125 during the wireless power
recharging operation. The downlink data can include component
information, such as a serial number, or control information, for
controlling operation of the sensing insert device 100. This data
can then be uploaded to the receiving system 110 upon request via
the one-way up-link channel, in effect providing two-way data
communications over separate channels.
[0035] Separating uplink and downlink telemetry eliminates the need
for transmit--receive circuitry within the sensing insert device
100. Two unidirectional telemetry channels operating on different
frequencies or with different forms of energy enables simultaneous
up and downlink telemetry. Modulating energy emissions from the
external wireless energy source 125 as a carrier for instructions
achieves these benefits with a minimum of additional circuitry and
components by leveraging existing circuitry and antenna, induction
loop, or piezoelectric components on the load sensor insert device
100. The frequencies of operation of the up and downlink telemetry
channels can also be selected and optimized to interface with other
devices, instruments, or equipment as needed. Separating uplink and
downlink telemetry also enables addition of downlink telemetry
without altering or upgrading existing chip-set telemetry for the
one-way transmit. That is, existing chip-set telemetry can be used
for encoding and packaging data and error checking without
modification, yet remain communicatively coupled to the separate
wireless power down-link telemetry operation for download
operations herein contemplated.
[0036] As shown, the wireless energy source 125 can include a power
supply 126, a modulation circuit 127, and a data input 128. The
power supply 126 can be a battery, a charging device, a capacitor,
a power connection, or other energy source for generating wireless
power signals to power the sensing insert device 100. The external
wireless energy source can transmit energy in the form of, but not
limited to, electromagnetic induction, or other electromagnetic or
ultrasound emissions. In at least one exemplary embodiment, the
wireless energy source 125 includes a coil to electromagnetically
couple with an induction coil in sensing device 100 when placed in
close proximity. The data input 128 can be a user interface
component (e.g., keyboard, keypad, or touchscreen) that receives
input information (e.g., serial number, control codes) to be
downloaded to the load sensor insert device 100. The data input 128
can also be an interface or port to receive the input information
from another data source, such as from a computer via a wired or
wireless connection (e.g., USB, IEEE802.16, etc.). The modulation
circuitry 127 can modulate the input information onto the power
signals generated by the power supply 126.
[0037] FIG. 2 is an illustration of a sensing insert device 100
placed in a joint of the muscular-skeletal system for measuring a
parameter in accordance with an exemplary embodiment. In
particular, sensing insert device 100 is placed in contact between
a femur 102 and a tibia 108 for measuring a parameter. In the
example, a force, pressure, or load is being measured. The device
100 in this example can intra-operatively assess a load on
prosthetic components during the surgical procedure. As mentioned
previously, sensing insert device 100 collects data for real-time
viewing of the load forces over various applied loads and angles of
flexion. It can measure the level and distribution of load at
various points on the prosthetic component and transmit the
measured load data by way data communication to a receiver station
110 for permitting visualization. This can aid the surgeon in
making any adjustments needed to achieve optimal joint
balancing.
[0038] A proximal end of tibia 108 is prepared to receive tibial
prosthetic component 106. Tibial prosthetic component 106 is a
support structure that is fastened to the proximal end of the tibia
and is usually made of a metal or metal alloy. The tibial
prosthetic component 106 also retains the insert in a fixed
position with respect to tibia 108. Similarly, a distal end of
femur 102 is prepared to receive femoral prosthetic component 104.
The femoral prosthetic component 104 is generally shaped to have an
outer condylar articulating surface. The preparation of femur 102
and tibia 108 is aligned to the mechanical axis of the leg. The
sensing insert device 100 provides a concave or flat surface
against which the outer condylar articulating surface of the
femoral prosthetic component 104 rides relative to the tibia
prosthetic component 106. In particular, the top surface of the
sensing module 200 faces the condylar articulating surface of the
femoral prosthetic component 104, and the bottom surface of the
insert dock 202 faces the top surface of the tibial prosthetic
component 106.
[0039] A final insert is subsequently fitted between femoral
prosthetic component 104 and tibial prosthetic component 106 that
has a bearing surface that couples to femoral component 104
allowing the leg a natural range of motion. The final insert is has
a wear surface that is typically made of a low friction polymer
material. Ideally, the prosthesis has an appropriate loading,
alignment, and balance that mimics the natural leg and maximizes
the life of the artificial components. It should be noted that
sensing module 200 can be placed a final insert and operated
similarly as disclosed herein. The sensing module 200 can be used
to periodically monitor status of the permanent joint.
[0040] The sensing insert device 100 is used to measure, adjust,
and test the reconstructed joint prior to installing the final
insert. As mentioned previously, the sensing insert device 100 is
placed between the femur 102 and tibia 108. The condyle surface of
femoral component 104 contacts a major surface of device 100. The
major surface of device 100 approximates a surface of a final
insert. Tibial prosthetic component 106 can include a cavity or
tray on the major surface that receives and retains an insert dock
202 and a sensing module 200 during a measurement process. It
should be noted that sensing insert device 100 is coupled to and
provides measurement data in conjunction with other implanted
prosthetic components. In other words, the prosthetic components
are the permanent installed components of the patient.
[0041] Insert dock 202 is provided in different sizes and shapes.
Insert dock 202 can comprise many different sizes and shapes to
interface appropriately with different manufacturer prosthetic
components. Prosthetic components are made in different sizes to
accommodate anatomical differences over a wide population range.
Insert dock 202 is designed for different prosthetic sizes within
the same manufacturer. In at least one embodiment, multiple docks
of different dimensions are provided for a surgery. For example,
the thickness of the final insert is determined by the surgical
cuts to the muscular-skeletal system and measurements provided by
sensing module 200. The surgeon may try two insert docks 202 of
different thicknesses before making a final decision. In one
embodiment, sensing insert device 100 selected by the surgeon has
substantially equal dimensions to the final insert used. In
general, insert dock 202 allows standardization on a single sensing
module 200 for different prosthetic platforms. Thus, the sensing
module 200 is common to the different insert docks 202 allowing
improved quality, reliability, and performance.
[0042] In one embodiment, one or more insert docks 202 are used to
determine an appropriate thickness that yields an optimal loading.
In general, the absolute loading over the range of motion is kept
within a predetermined range. Soft tissue tensioning can be used to
adjust the absolute loading. The knee balance can also be adjusted
within a predetermined range if a total knee reconstruction is
being performed and a sensing module 202 is used in each
compartment. Tibial prosthetic component 106 and device 100 have a
combined thickness that represents a combined thickness of tibial
prosthetic component 106 and a final (or chronic) insert of the
knee joint. Thus, the final insert thickness or depth is chosen
based on the trial performed using device 100. Typically, the final
insert thickness is identical to the device 100 to maintain the
measured loading and balance. In one embodiment, sensing module 200
and insert docks 202 are disposed of after surgery. Alternatively,
the sensing module 200 and insert docks 202 can be cleaned,
sterilized, and packaged for reuse.
[0043] The prosthesis incorporating device 100 emulates the
function of a natural knee joint. Device 100 can measure loads or
other parameters at various points throughout the range of motion.
Data from device 100 is transmitted to a receiving station 110 via
wired or wireless communications. In a first embodiment, device 100
is a disposable system. Device 100 can be disposed of after using
the sensing insert device 100 to optimally fit the joint implant.
Device 100 is a low cost disposable system that reduces capital
costs, operating costs, facilitates rapid adoption of quantitative
measurement, and initiates evidentiary based orthopedic medicine.
In a second embodiment, a methodology can be put in place to clean
and sterilize device 100 for reuse. In a third embodiment, device
100 can be incorporated in a tool instead of being a component of
the replacement joint. The tool can be disposable or be cleaned and
sterilized for reuse. In a fourth embodiment, device 100 can be a
permanent component of the replacement joint. Device 100 can be
used to provide both short term and long term post-operative data
on the implanted joint. In a fifth embodiment, device 100 can be
coupled to the muscular-skeletal system. In all of the embodiments,
receiving station 110 can include data processing, storage, or
display, or combination thereof and provide real time graphical
representation of the level and distribution of the load. Receiving
station 110 can record and provide accounting information of device
100 to an appropriate authority.
[0044] The sensing insert device 100, in one embodiment, comprises
a load sensing platform 121, an accelerometer 122, and sensing
assemblies 123. This permits the sensing device 100 to assess a
total load on the prosthetic components when it is being moved. The
system accounts for forces due to gravity and motion. In one
embodiment, load sensing platform 121 includes two or more load
bearing surfaces, at least one energy transducer, at least one
compressible energy propagating structure, and at least one member
for elastic support. The accelerometer 122 can measure
acceleration. Acceleration can occur when the sensing device 100 is
moved or put in motion. Accelerometer 122 can sense orientation,
vibration, and impact. In another embodiment, the femoral component
104 can similarly include an accelerometer 135, which by way of a
communication interface to the sensing insert device 100, can
provide reference position and acceleration data to determine an
exact angular relationship between the femur and tibia. The sensing
assemblies 123 can reveal changes in length or compression of the
energy propagating structure or structures by way of the energy
transducer or transducers. Together the load sensing platform 121,
accelerometer 122 (and in certain cases accelerometer 135), and
sensing assemblies 123 measure force or pressure external to the
load sensing platform 121 or displacement produced by contact with
the prosthetic components.
[0045] In at least one exemplary embodiment, an energy pulse is
directed within one or more waveguides in device 100 by way of
pulse mode operations and pulse shaping. The waveguide is a conduit
that directs the energy pulse in a predetermined direction. The
energy pulse is typically confined within the waveguide. In one
embodiment, the waveguide comprises a polymer material. For
example, urethane or polyethylene are polymers suitable for forming
a waveguide. The polymer waveguide can be compressed and has little
or no hysteresis in the system. Alternatively, the energy pulse can
be directed through the muscular-skeletal system. In one
embodiment, the energy pulse is directed through bone of the
muscular-skeletal system to measure bone density. A transit time of
an energy pulse is related to the material properties of a medium
through which it traverses. This relationship is used to generate
accurate measurements of parameters such as distance, weight,
strain, pressure, wear, vibration, viscosity, and density to name
but a few.
[0046] Incorporating data from the accelerometer 122 with data from
the other sensing components 121 and 123 assures accurate
measurement of the applied load, force, pressure, or displacement
by enabling computation of adjustments to offset this external
motion. This capability can be required in situations wherein the
body, instrument, appliance, vehicle, equipment, or other physical
system, is itself operating or moving during sensing of load,
pressure, or displacement. This capability can also be required in
situations wherein the body, instrument, appliance, vehicle,
equipment, or other physical system, is causing the portion of the
body, instrument, appliance, vehicle, equipment, or other physical
system being measured to be in motion during sensing of load,
pressure, or displacement.
[0047] The accelerometer 122 can operate singly, as an integrated
unit with the load sensing platform 121, and/or as an integrated
unit with the sensing assemblies 123. Integrating one or more
accelerometers 122 within the sensing assemblages 123 to determine
position, attitude, movement, or acceleration of sensing
assemblages 123 enables augmentation of presentation of data to
accurately identify, but not limited to, orientation or spatial
distribution of load, force, pressure, displacement, density, or
viscosity, or localized temperature by controlling the load and
position sensing assemblages to measure the parameter or parameters
of interest relative to specific orientation, alignment, direction,
or position as well as movement, rotation, or acceleration along
any axis or combination of axes. Measurement of the parameter or
parameters of interest may also be made relative to the earth's
surface and thus enable computation and presentation of spatial
distributions of the measured parameter or parameters relative to
this frame of reference.
[0048] In one embodiment, the accelerometer 122 includes direct
current (DC) sensitivity to measure static gravitational pull with
load and position sensing assemblages to enable capture of, but not
limited to, distributions of load, force, pressure, displacement,
movement, rotation, or acceleration by controlling the sensing
assemblages to measure the parameter or parameters of interest
relative to orientations with respect to the earths surface or
center and thus enable computation and presentation of spatial
distributions of the measured parameter or parameters relative to
this frame of reference.
[0049] Embodiments of device 100 are broadly directed to
measurement of physical parameters, and more particularly, to
evaluating changes in the transit time of a pulsed energy wave
propagating through a medium. In-situ measurements during
orthopedic joint implant surgery would be of substantial benefit to
verify an implant is in balance and under appropriate loading or
tension. In one embodiment, the instrument is similar to and
operates familiarly with other instruments currently used by
surgeons. This will increase acceptance and reduce the adoption
cycle for a new technology. The measurements will allow the surgeon
to ensure that the implanted components are installed within
predetermined ranges that maximize the working life of the joint
prosthesis and reduce costly revisions. Providing quantitative
measurement and assessment of the procedure using real-time data
will produce results that are more consistent. A further issue is
that there is little or no implant data generated from the implant
surgery, post-operatively, and long term. Device 100 can provide
implant status data to the orthopedic manufacturers and surgeons.
Moreover, data generated by direct measurement of the implanted
joint itself would greatly improve the knowledge of implanted joint
operation and joint wear thereby leading to improved design and
materials.
[0050] As mentioned previously, device 100 can be used for other
joint surgeries; it is not limited to knee replacement implant or
implants. Moreover, device 100 is not limited to trial
measurements. Device 100 can be incorporated into the final joint
system to provide data post-operatively to determine if the
implanted joint is functioning correctly. Early determination of a
problem using device 100 can reduce catastrophic failure of the
joint by bringing awareness to a problem that the patient cannot
detect. The problem can often be rectified with a minimal invasive
procedure at lower cost and stress to the patient. Similarly,
longer term monitoring of the joint can determine wear or
misalignment that if detected early can be adjusted for optimal
life or replacement of a wear surface with minimal surgery thereby
extending the life of the implant. In general, device 100 can be
shaped such that it can be placed or engaged or affixed to or
within load bearing surfaces used in many orthopedic applications
(or used in any orthopedic application) related to the
musculoskeletal system, joints, and tools associated therewith.
Device 100 can provide information on a combination of one or more
performance parameters of interest such as wear, stress,
kinematics, kinetics, fixation strength, ligament balance,
anatomical fit and balance.
[0051] FIG. 3 is a perspective view of a medical sensing platform
comprising an encapsulating enclosure in accordance with one
embodiment. In general, parameters of the muscular-skeletal system
can be measured with a sensing module 200 that in one embodiment is
an integral part of a complete sensing insert device 100. The
sensing module 200 is a self-contained sensor within an
encapsulating enclosure that integrates sensing assemblages, an
electronic assemblage that couples to the sensing assemblages, a
power source, signal processing, and wireless communication. All
components required for the measurement are contained in the
sensing module 200. The sensing module 200 has at least one
contacting surface for coupling to the muscular-skeletal system. A
parameter of the muscular-skeletal system is applied to the contact
surfaces to be measured by the one or more sensing assemblages
therein. As will be disclosed in further detail herein, the sensing
module 200 is part of a system that allows intra-operative and
post-operative sensing of a joint of the muscular-skeletal system.
More specifically, sensing module 200 is placed within a temporary
or permanent prosthetic component that has a similar form factor as
the passive prosthetic component currently being used. This has a
benefit of rapid adoption because the sensing platform is inserted
identically to the commonly used passive component but can provide
much needed quantitative measurements with little or no procedural
changes.
[0052] As shown, the sensing insert device 100 comprises an insert
dock 202 and the sensing module 200. Sensing insert device 100 is a
non-permanent or temporary measurement device that is used
intra-operatively to provide quantitative data related to the
installation of prosthetic components such as in joint replacement
surgery. The combination of the insert dock 202 and sensing module
202 has a form factor substantially equal to a final insert device.
The final insert device can be a passive component or sensored
incorporating sensing module 200. The substantially equal form
factor of sensing insert device 100 results in no extraneous
structures in the surgical field that can interfere with the
procedure. For example, a final insert device is designed to mimic
the function of the natural component it is replacing. The final
insert device allows natural movement of the muscular-skeletal
system and does not interfere with ligaments, tendons, tissue,
muscles, and other components of the muscular-skeletal system.
Similarly, sensing insert device 100 allows exposure of the
surgical field around the joint by having the similar form factor
as the final insert thereby allowing the surgeon to make
adjustments during the installation in a natural setting with
quantitative measurements to support the modifications.
[0053] In one embodiment, insert dock 202 is an adaptor. Insert
dock 202 is made in different sizes. In general, prosthetic
components are manufactured in different sizes to accommodate
variation in the muscular-skeletal system from person to person. In
the example, the size of insert dock 202 is chosen to mate with the
selected prosthetic implant components. In particular, a feature
204 aligns with and retains insert dock 202 in a fixed position to
a prosthetic or natural component of the muscular-skeletal system.
The insert dock 202 is a passive component having an opening for
receiving sensing module 200. The opening is positioned to place
the contacting surfaces in a proper orientation to measure the
parameter when used in conjunction with other prosthetic
components. The insert dock 202 as an adaptor can be manufactured
at low cost. Moreover, insert dock 202 can be formed for adapting
to different prosthetic manufacturers thereby increasing system
flexibility. This allows a standard sensing module 200 to be
provided but customized for appropriate size and dimensions through
dock 202 for the specific application and manufacturer
component.
[0054] The one or more sensing assemblages within sensing module
200 couple to the contacting surfaces of sensing module 200 for
receiving the applied parameter of the muscular-skeletal system. In
one embodiment, a sensing assemblage comprises one or more energy
transducers coupled to an elastic structure. The elastic structure
allows the propagation of energy waves. The forms of energy
propagated through the elastic energy propagating structures may
include, but is not limited to, sound, ultrasound, or
electromagnetic radiation including radio frequency, infrared, or
light. A change in the parameter applied to the contacting surfaces
results in a change a dimension of the elastic structure. The
dimension of the elastic structure can be measured precisely using
continuous wave, pulsed, or pulsed echo measurement. The dimension
and material properties of the elastic structure have a known
relationship to the parameter being measured. Thus, the dimension
is precisely measured and converted to the parameter. Other factors
such as movement or acceleration can be taken into account in the
calculation. As an example, a force, pressure, or load applied to
the one or more contacting surfaces of sensing module 200 is used
to illustrate a parameter measurement hereinbelow. It should be
noted that this is for illustration purposes and that the sensing
module 200 can be used to measure other parameters.
[0055] As will be shown ahead, the encapsulating enclosure can
serve in a first embodiment as a trial implant for orthopedic
surgical procedures, namely, for determining load forces on
prosthetic components and the musculoskeletal system. In a second
embodiment, the encapsulating enclosure can be placed within a
permanent prosthetic component for long term monitoring. The
encapsulating enclosure supports and protects internal mechanical
and electronic components from external physical, mechanical,
chemical, and electrical, and electromagnetic intrusion that might
compromise sensing or communication operations of the module or
device. The integration of the internal components is designed to
minimize adverse physical, mechanical, electrical, and ultrasonic
interactions that might compromise sensing or communication
operations of the module or device.
[0056] FIG. 4 is a perspective view of a medical sensing device
suitable for use as a bi-compartmental implant and comprising an
encapsulating enclosure in accordance with one embodiment. As
shown, the sensing insert device 100 comprises two sensing modules
200. Each sensing module 200 is a self-contained encapsulated
enclosure that can make individual or coordinated parameter
measurements. For example, the sensing insert device 100 can be
used to assess load forces on a bi-compartmental knee joint
implant. In particular, both sensing modules 200 can individually,
or in combination, report applied loading forces. Bi-compartmental
sensing provides the benefit of providing quantitative measurement
to balance each compartment in relation to one another.
[0057] Similar to that described above, insert dock 202 is an
adaptor having two openings instead of one. Insert dock 202 can be
made in different sizes to accommodated different sized prosthetic
components and different manufacturers. The insert dock 202 with
two openings is a passive component for receiving two separate
sensing modules 200. The opening is positioned to place the
contacting surfaces in a proper orientation to measure the
parameter when used in conjunction with other prosthetic
components. In general, encapsulated enclosures can be positioned
on or within, or engaged with, or attached or affixed to or within,
a wide range of physical systems including, but not limited to
instruments, appliances, vehicles, equipments, or other physical
systems as well as animal and human bodies, for sensing and
communicating the parameter or parameters of interest in real time.
Similar to that described above, insert dock 202 as an adaptor can
be manufactured at low cost providing design flexibility and
allowing rapid adoption of quantitative measurement.
[0058] FIG. 5 is an exemplary block diagram of the components of
the sensing module 200 in accordance with an exemplary embodiment.
It should be noted that the sensing module could comprise more or
less than the number of components shown. As illustrated, the
sensing module includes one or more sensing assemblages 303, a
transceiver 320, an energy storage 330, electronic circuitry 307,
one or more mechanical supports 315 (e.g., springs), and an
accelerometer 302. In the non-limiting example, an applied
compressive force can be measured by the sensing module.
[0059] The sensing assemblage 303 can be positioned, engaged,
attached, or affixed to the contact surfaces 306. Mechanical
supports 315 serve to provide proper balancing of contact surfaces
306. In at least one exemplary embodiment, contact surfaces 306 are
load-bearing surfaces. In general, the propagation structure 305 is
subject to the parameter being measured. Surfaces 306 can move and
tilt with changes in applied load; actions which can be transferred
to the sensing assemblages 303 and measured by the electronic
circuitry 307. The electronic circuitry 307 measures physical
changes in the sensing assemblage 303 to determine parameters of
interest, for example a level, distribution and direction of forces
acting on the contact surfaces 306. In general, the sensing module
is powered by the energy storage 330.
[0060] As one example, the sensing assemblage 303 can comprise an
elastic or compressible propagation structure 305 between a
transducer 304 and a transducer 314. In the current example,
transducer 304 can be an ultrasound (or ultrasonic) resonator, and
the elastic or compressible propagation structure 305 can be an
ultrasound (or ultrasonic) waveguide (or waveguides). The
electronic circuitry 307 is electrically coupled to the sensing
assemblages 303 and translates changes in the length (or
compression or extension) of the sensing assemblages 303 to
parameters of interest, such as force. It measures a change in the
length of the propagation structure 305 (e.g., waveguide)
responsive to an applied force and converts this change into
electrical signals which can be transmitted via the transceiver 320
to convey a level and a direction of the applied force. In other
arrangements herein contemplated, the sensing assemblage 303 may
require only a single transducer. In yet other arrangements, the
sensing assemblage 303 can include piezoelectric, capacitive,
optical or temperature sensors or transducers to measure the
compression or displacement. It is not limited to ultrasonic
transducers and waveguides.
[0061] The accelerometer 302 can measure acceleration and static
gravitational pull. Accelerometer 302 can be single-axis and
multi-axis accelerometer structures that detect magnitude and
direction of the acceleration as a vector quantity. Accelerometer
302 can also be used to sense orientation, vibration, impact and
shock. The electronic circuitry 307 in conjunction with the
accelerometer 302 and sensing assemblies 303 can measure parameters
of interest (e.g., distributions of load, force, pressure,
displacement, movement, rotation, torque and acceleration) relative
to orientations of the sensing module with respect to a reference
point. In such an arrangement, spatial distributions of the
measured parameters relative to a chosen frame of reference can be
computed and presented for real-time display.
[0062] The transceiver 320 comprises a transmitter 309 and an
antenna 310 to permit wireless operation and telemetry functions.
In various embodiments, the antenna 310 can be configured by design
as an integrated loop antenna. As will be explained ahead, the
integrated loop antenna is configured at various layers and
locations on the electronic substrate with electrical components
and by way of electronic control circuitry to conduct efficiently
at low power levels. Once initiated the transceiver 320 can
broadcast the parameters of interest in real-time. The telemetry
data can be received and decoded with various receivers, or with a
custom receiver. The wireless operation can eliminate distortion
of, or limitations on, measurements caused by the potential for
physical interference by, or limitations imposed by, wiring and
cables connecting the sensing module with a power source or with
associated data collection, storage, display equipment, and data
processing equipment.
[0063] The transceiver 320 receives power from the energy storage
330 and can operate at low power over various radio frequencies by
way of efficient power management schemes, for example,
incorporated within the electronic circuitry 307. As one example,
the transceiver 320 can transmit data at selected frequencies in a
chosen mode of emission by way of the antenna 310. The selected
frequencies can include, but are not limited to, ISM bands
recognized in International Telecommunication Union regions 1, 2
and 3. A chosen mode of emission can be, but is not limited to,
Gaussian Frequency Shift Keying, (GFSK), Amplitude Shift Keying
(ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK),
Frequency Modulation (FM), Amplitude Modulation (AM), or other
versions of frequency or amplitude modulation (e.g., binary,
coherent, quadrature, etc.).
[0064] The antenna 310 can be integrated with components of the
sensing module to provide the radio frequency transmission. The
substrate for the antenna 310 and electrical connections with the
electronic circuitry 307 can further include a matching network.
This level of integration of the antenna and electronics enables
reductions in the size and cost of wireless equipment. Potential
applications may include, but are not limited to any type of
short-range handheld, wearable, or other portable communication
equipment where compact antennas are commonly used. This includes
disposable modules or devices as well as reusable modules or
devices and modules or devices for long-term use.
[0065] The energy storage 330 provides power to electronic
components of the sensing module. It can be charged by wired energy
transfer, short-distance wireless energy transfer or a combination
thereof. External power sources can include, but are not limited
to, a battery or batteries, an alternating current power supply, a
radio frequency receiver, an electromagnetic induction coil, a
photoelectric cell or cells, a thermocouple or thermocouples, or an
ultrasound transducer or transducers. By way of the energy storage
330, the sensing module can be operated with a single charge until
the internal energy is drained. It can be recharged periodically to
enable continuous operation. The energy storage 330 can utilize
power management technologies such as replaceable batteries, supply
regulation technologies, and charging system technologies for
supplying energy to the components of the sensing module to
facilitate wireless applications.
[0066] The energy storage 330 minimizes additional sources of
energy radiation required to power the sensing module during
measurement operations. In one embodiment, as illustrated, the
energy storage 330 can include a capacitive energy storage device
308 and an induction coil 311. External source of charging power
can be coupled wirelessly to the capacitive energy storage device
308 through the electromagnetic induction coil or coils 311 by way
of inductive charging. The charging operation can be controlled by
power management systems designed into, or with, the electronic
circuitry 307. As one example, during operation of electronic
circuitry 307, power can be transferred from capacitive energy
storage device 308 by way of efficient step-up and step-down
voltage conversion circuitry. This conserves operating power of
circuit blocks at a minimum voltage level to support the required
level of performance.
[0067] In one configuration, the energy storage 330 can further
serve to communicate downlink data to the transceiver 320 during a
recharging operation. For instance, downlink control data can be
modulated onto the energy source signal and thereafter demodulated
from the induction coil 311 by way of electronic control circuitry
307. This can serve as a more efficient way for receiving downlink
data instead of configuring the transceiver 320 for both uplink and
downlink operation. As one example, downlink data can include
updated control parameters that the sensing module uses when making
a measurement, such as external positional information, or for
recalibration purposes, such as spring biasing. It can also be used
to download a serial number or other identification data.
[0068] The electronic circuitry 307 manages and controls various
operations of the components of the sensing module, such as
sensing, power management, telemetry, and acceleration sensing. It
can include analog circuits, digital circuits, integrated circuits,
discrete components, or any combination thereof. In one
arrangement, it can be partitioned among integrated circuits and
discrete components to minimize power consumption without
compromising performance. Partitioning functions between digital
and analog circuit enhances design flexibility and facilitates
minimizing power consumption without sacrificing functionality or
performance. Accordingly, the electronic circuitry 307 can comprise
one or more Application Specific Integrated Circuit (ASIC) chips,
for example, specific to a core signal processing algorithm.
[0069] In another arrangement, the electronic circuitry can
comprise a controller such as a programmable processor, a Digital
Signal Processor (DSP), a microcontroller, or a microprocessor,
with associated storage memory and logic. The controller can
utilize computing technologies with associated storage memory such
a Flash, ROM, RAM, SRAM, DRAM or other like technologies for
controlling operations of the aforementioned components of the
sensing module. In one arrangement, the storage memory may store
one or more sets of instructions (e.g., software) embodying any one
or more of the methodologies or functions described herein. The
instructions may also reside, completely or at least partially,
within other memory, and/or a processor during execution thereof by
another processor or computer system.
[0070] The electronics assemblage also supports testability and
calibration features that assure the quality, accuracy, and
reliability of the completed wireless sensing module or device. A
temporary bi-directional interconnect assures a high level of
electrical observability and controllability of the electronics.
The test interconnect also provides a high level of electrical
observability of the sensing subsystem, including the transducers,
waveguides, and mechanical spring or elastic assembly. Carriers or
fixtures emulate the final enclosure of the completed wireless
sensing module or device during manufacturing processing thus
enabling capture of accurate calibration data for the calibrated
parameters of the finished wireless sensing module or device. These
calibration parameters are stored within the on-board memory
integrated into the electronics assemblage.
[0071] Applications for sensing module 200 may include, but are not
limited to, disposable modules or devices as well as reusable
modules or devices and modules or devices for long-term use. In
addition to non-medical applications, examples of a wide range of
potential medical applications may include, but are not limited to,
implantable devices, modules within implantable devices,
intra-operative implants or modules within intra-operative implants
or trial inserts, modules within inserted or ingested devices,
modules within wearable devices, modules within handheld devices,
modules within instruments, appliances, equipment, or accessories
of all of these, or disposables within implants, trial inserts,
inserted or ingested devices, wearable devices, handheld devices,
instruments, appliances, equipment, or accessories to these
devices, instruments, appliances, or equipment.
[0072] FIG. 6 is a diagram of an exemplary communications system
400 for short-range telemetry according to one embodiment. As
illustrated, the exemplary communications system 400 comprises
medical device communications components 410 of the sensing insert
device 100 (see FIG. 1) and receiving system communications
components 450 of the receiving system 110 (see FIG. 1). The
medical device communications components 410 are inter-operatively
coupled to include, but not limited to, the antenna 412, a matching
network 414, the telemetry transceiver 416, a CRC circuit 418, a
data packetizer 422, a data input 424, a power source 426, and an
application specific integrated circuit (ASIC) 420. The medical
device communications components 410 may include more or less than
the number of components shown and are not limited to those shown
or the order of the components.
[0073] The receiving station communications components 450 comprise
an antenna 452, the matching network 454, the telemetry receiver
456, the CRC circuit 458, the data packetizer 460, and optionally a
USB interface 462. Notably, other interface systems can be directly
coupled to the data packetizer 460 for processing and rendering
sensor data.
[0074] With respect to FIG. 1, in view of the communication
components of FIG. 6, the sensing insert device 100 acquires sensor
data by way of the data input to the ASIC 420. Referring briefly to
FIG. 5, the ASIC 420 is operatively coupled to sensing assemblies
303. In one embodiment, a change in the parameter being measured by
device 100 produces a change in a length of a compressible
propagation structure 305. ASIC 420 controls the emission of energy
waves into propagation structure 305 and the detection of
propagated energy waves. ASIC 420 generates data related to transit
time, frequency, or phase of propagated energy waves. The data
corresponds to the length of propagation structure 305, which can
be translated to the parameter of interest by way of a known
function or relationship. Similarly, the data can comprise voltage
or current measurements from a MEMS structure, piezo-resistive
sensor, strain gauge, or other sensor type that is used to measure
the parameter. The data packetizer 422 assembles the sensor data
into packets; this includes sensor information received or
processed by ASIC 420. The ASIC 420 can comprise specific modules
for efficiently performing core signal processing functions of the
medical device communications components 410. The ASIC 420 provides
the further benefit of reducing the form factor of sensing insert
device 100 to meet dimensional requirements for integration into
temporary or permanent prosthetic components.
[0075] The CRC circuit 418 applies error code detection on the
packet data. The cyclic redundancy check is based on an algorithm
that computes a checksum for a data stream or packet of any length.
These checksums can be used to detect interference or accidental
alteration of data during transmission. Cyclic redundancy checks
are especially good at detecting errors caused by electrical noise
and therefore enable robust protection against improper processing
of corrupted data in environments having high levels of
electromagnetic activity. The telemetry transmitter 416 then
transmits the CRC encoded data packet through the matching network
414 by way of the antenna 412. The matching networks 414 and 454
provide an impedance match for achieving optimal communication
power efficiency.
[0076] The receiving system communications components 450 receive
transmission sent by medical device communications components 410.
In one embodiment, telemetry transmitter 416 is operated in
conjunction with a dedicated telemetry receiver 456 that is
constrained to receive a data stream broadcast on the specified
frequencies in the specified mode of emission. The telemetry
receiver 456 by way of the receiving station antenna 452 detects
incoming transmissions at the specified frequencies. The antenna
452 can be a directional antenna that is directed to a directional
antenna of components 410. Using at least one directional antenna
can reduce data corruption while increasing data security by
further limiting where the data is radiated. A matching network 454
couples to antenna 452 to provide an impedance match that
efficiently transfers the signal from antenna 452 to telemetry
receiver 456. Telemetry receiver 456 can reduce a carrier frequency
in one or more steps and strip off the information or data sent by
components 410. Telemetry receiver 456 couples to CRC circuit 458.
CRC circuit 458 verifies the cyclic redundancy checksum for
individual packets of data. CRC circuit 458 is coupled to data
packetizer 460. Data packetizer 460 processes the individual
packets of data. In general, the data that is verified by the CRC
circuit 458 is decoded (e.g., unpacked) and forwarded to an
external data processing device, such as an external computer, for
subsequent processing, display, or storage or some combination of
these.
[0077] The telemetry receiver 456 is designed and constructed to
operate on very low power such as, but not limited to, the power
available from the powered USB port 462, or a battery. In another
embodiment, the telemetry receiver 456 is designed for use with a
minimum of controllable functions to limit opportunities for
inadvertent corruption or malicious tampering with received data.
The telemetry receiver 456 can be designed and constructed to be
compact, inexpensive, and easily manufactured with standard
manufacturing processes while assuring consistently high levels of
quality and reliability.
[0078] In one configuration, the communication system 400 operates
in a transmit-only operation with a broadcasting range on the order
of a few meters to provide high security and protection against any
form of unauthorized or accidental query. The transmission range
can be controlled by the transmitted signal strength, antenna
selection, or a combination of both. A high repetition rate of
transmission can be used in conjunction with the Cyclic Redundancy
Check (CRC) bits embedded in the transmitted packets of data during
data capture operations thereby enabling the receiving system 110
to discard corrupted data without materially affecting display of
data or integrity of visual representation of data, including but
not limited to measurements of load, force, pressure, displacement,
flexion, attitude, and position within operating or static physical
systems.
[0079] By limiting the operating range to distances on the order of
a few meters the telemetry transmitter 416 can be operated at very
low power in the appropriate emission mode or modes for the chosen
operating frequencies without compromising the repetition rate of
the transmission of data. This mode of operation also supports
operation with compact antennas, such as an integrated loop
antenna. The combination of low power and compact antennas enables
the construction of, but is not limited to, highly compact
telemetry transmitters that can be used for a wide range of
non-medical and medical applications. Examples of potential medical
applications may include, but are not limited to, implantable
devices, modules within implantable devices, intra-operative
implants or modules within intra-operative implants or trial
inserts, modules within inserted or ingested devices, modules
within wearable devices, modules within handheld devices, modules
within instruments, appliances, equipment, or accessories of all of
these, or disposables within implants, trial inserts, inserted or
ingested devices, wearable devices, handheld devices, instruments,
appliances, equipment, or accessories to these devices,
instruments, appliances, or equipment.
[0080] The transmitter security as well as integrity of the
transmitted data is assured by operating the telemetry system
within predetermined conditions. The security of the transmitter
cannot be compromised because it is operated in a transmit-only
mode and there is no pathway to hack into medical device
communications components 410. The integrity of the data is assured
with the use of the CRC algorithm and the repetition rate of the
measurements. The risk of unauthorized reception of the data is
minimized by the limited broadcast range of the device. Even if
unauthorized reception of the data packets should occur there are
counter measures in place that further mitigate data access. A
first measure is that the transmitted data packets contain only
binary bits from a counter along with the CRC bits. A second
measure is that no data is available or required to interpret the
significance of the binary value broadcast at any time. A third
measure that can be implemented is that no patient or device
identification data is broadcast at any time.
[0081] The telemetry transmitter 416 can also operate in accordance
with some FCC regulations. According to section 18.301 of the FCC
regulations the ISM bands within the USA include 6.78, 13.56,
27.12, 30.68, 915, 2450, and 5800 MHz as well as 24.125, 61.25,
122.50, and 245 GHz. Globally other ISM bands, including 433 MHz,
are defined by the International Telecommunications Union in some
geographic locations. The list of prohibited frequency bands
defined in 18.303 are "the following safety, search and rescue
frequency bands is prohibited: 490-510 kHz, 2170-2194 kHz,
8354-8374 kHz, 121.4-121.6 MHz, 156.7-156.9 MHz, and 242.8-243.2
MHz." Section 18.305 stipulates the field strength and emission
levels ISM equipment must not exceed when operated outside defined
ISM bands. In summary, it may be concluded that ISM equipment may
be operated worldwide within ISM bands as well as within most other
frequency bands above 9 KHz given that the limits on field
strengths and emission levels specified in section 18.305 are
maintained by design or by active control. As an alternative,
commercially available ISM transceivers, including commercially
available integrated circuit ISM transceivers, may be designed to
fulfill these field strengths and emission level requirements when
used properly.
[0082] In one configuration, the telemetry transmitter 416 can also
operate in unlicensed ISM bands or in unlicensed operation of low
power equipment, wherein the ISM equipment (e.g., telemetry
transmitter 416) may be operated on ANY frequency above 9 kHz
except as indicated in Section 18.303 of the FCC code.
[0083] Wireless operation eliminates distortion of, or limitations
on, measurements caused by the potential for physical interference
by, or limitations imposed by, wiring and cables connecting the
wireless sensing module or device with a power source or with data
collection, storage, or display equipment. Power for the sensing
components and electronic circuits is maintained within the
wireless sensing module or device on an internal energy storage
device. This energy storage device is charged with external power
sources including, but not limited to, a battery or batteries,
super capacitors, capacitors, an alternating current power supply,
a radio frequency receiver, an electromagnetic induction coil, a
photoelectric cell or cells, a thermocouple or thermocouples, or an
ultrasound transducer or transducers. The wireless sensing module
may be operated with a single charge until the internal energy
source is drained or the energy source may be recharged
periodically to enable continuous operation. The embedded power
supply minimizes additional sources of energy radiation required to
power the wireless sensing module or device during measurement
operations. Telemetry functions are also integrated within the
wireless sensing module or device. Once initiated the telemetry
transmitter continuously broadcasts measurement data in real time.
Telemetry data may be received and decoded with commercial
receivers or with a simple, low cost custom receiver.
[0084] A method can be practiced with more or less than the number
of steps shown and is not limited to the order shown. To describe
the method, reference will be made to the components of FIG. 5,
although it is understood that the method can be implemented in any
other manner using other suitable components. Generally, method is
directed to non-secure applications for one-way transmission
communications, for example, where an implanted medical device or
sensor transmits data to a receiving station (e.g., 110 see FIG. 1)
but does not receive confirmation from the receiving station,
although in various embodiments, the implanted medical device
includes an integrated receiver for receiving confirmation and
acknowledgement communications.
[0085] The method can start in a state wherein the sensing insert
device 100 has been inserted and powered on, for example, within a
knee prosthesis implant. The medical device can be powered on via
manual intervention, for example, by the surgeon or technician
implanting the medical device during a surgical procedure, or the
device can turn on automatically after a duration of time or at
certain time intervals, for example, 1 hour after manual
activation, or every 10 seconds after power up, depending on an
operating mode.
[0086] In a first step, the medical device acquires sensor data
such as load information (e.g., force, location, duration, etc.)
from the sensing module 200. The electronic circuitry 307 generates
the load data by way of the sensing assemblies 303, for instance,
by converting changes in length of ultrasonic propagation
structures (waveguides) to force data. In a second step, the
sensing module 200 evaluates data bounds on the load data. In a
third step, sensing module 200 assigns priorities based on the data
bounds. Sensor data outside a predetermined range or above a
predefined threshold can be flagged with a priority or discarded.
For example, sensor data that falls outside a safe range or exceeds
a safe level (e.g., applied force level, angle of flexion,
excessive rotation) is prioritized accordingly.
[0087] In a fourth step, the sensing module 200 generates a packet
of data including the sensor data, priority, and any corresponding
information. In a fifth step, the sensing module 200 determines its
communications mode based on operating mode and priority level. The
operating mode indicates whether the sensing module 200 is
operating in a power saving mode (e.g., standby) or other power
management mode and takes into account information such as
remaining battery life and drain. In a sixth step, a Cyclic
Redundancy Check (CRC) can be appended to the data packed. In other
embodiments, more sophisticated forward error correction schemes
(e.g., block coding, convolutional coding) can be applied along
with secure encryption or key-exchange cryptographic protocols.
[0088] The cyclic redundancy check (CRC) is a non-secure form of
message digest designed to detect accidental changes to raw
computer data. The CRC step comprises calculating a short,
fixed-length sequence, known as the CRC code, for each block of
data and sends or stores them both together. When a block is read
or received the receiving station 110 (FIG. 1) repeats the
calculation; if the new CRC does not match the one sent (or in some
cases, cancel it out) then the block contains a data error and the
receiving station 110 may take corrective action such as rereading
or requesting the block be sent again. Briefly, FIG. 13,
illustrates an exemplary data packet 1300 containing sensor data
(e.g., Fx, duration, location), a priority level (e.g., 1 to 10),
and a CRC.
[0089] In a seventh step, the transceiver 320 then transmits the
data packet based on the priority level and operating mode. For
instance, a low priority data packet can be appended with previous
low-priority data packets and then transmitted over a single
communication channel as a data stream, or at staggered time
intervals to conserve power (e.g., scheduled to transmit every 10
seconds). The bundled packet data can then be decoded at the
receiving station 110 and thereafter processed accordingly.
Alternatively, a high priority packet can be transmitted
immediately instead of a delayed time or the scheduled transmit
intervals. Depending on the communication mode (e.g., priority
level, operating mode), the transceiver may transmit the same high
priority packet multiple times in a redundant manner to guarantee
receipt. This ensures that the data is received and processed at
the receiving station 110 in the event an immediate course of
action or response is necessary, for example, to ensure the
patient's safety or to report a warning.
[0090] The sensor data can be transmitted at the selected
frequencies in the chosen mode of emission by way of the antenna
310. In certain configurations, the antenna 310 is an integrated
loop antenna designed into a substrate of the sensing module 200
for maximizing power efficiency. As an example the chosen
frequencies can include, but are not limited to, ISM bands
recognized in International Telecommunication Union regions 1, 2,
and 3 and the chosen mode of emission may be, but is not limited
to, Gaussian Frequency Shift Keying, (GFSK) or others version of
frequency or amplitude shift keying or modulation.
[0091] The receiving station 110 (see FIG. 1) 110 receives packets
of data broadcast in the specified mode of emission on the
specified frequencies and verifies the cyclic redundancy check
checksum for individual packets of data or bundled packet data.
Data that cannot be verified may be discarded. Data that are
verified are forward to an external data processing device, such as
an external computer, for subsequent processing, display, or
storage or combination thereof.
[0092] FIG. 7 is an illustration of a block model diagram 500 of
the sensing module 200 in accordance with an exemplary embodiment.
In particular, the diagram 500 shows where certain components are
replaced or supplemented with one or more Application Specific
Integrated Circuits (ASICs). Referring briefly to FIG. 5,
electronic circuitry 307 is coupled to the one or more sensing
assemblages and includes circuitry that can control sensor
operations. Electronic circuitry 307 includes multiple channels
that can operate more than one device. Sensing module 200 is
optimized to operate under severe power constraints. Electronic
circuitry 307 includes power management circuitry that controls
power up, power down, and minimizes power usage through the control
of individual blocks. The architecture is designed to enable only
blocks required for the current operation.
[0093] Referring back to FIG. 7, the ASIC provides significant
benefit in reducing power requirements allowing the module 200 to
be powered by a temporary power source such as a super capacitor or
capacitor. The ASIC and super capacitor have a small form factor
allowing module 200 to be integrated within a temporary or
permanent prosthetic component. Module 200 incorporates one or more
sensors comprising at least one transducer and a compressible
media, the operation of which is disclosed in detail herein. As
shown, a sensing assemblage comprises a transducer 502,
compressible propagation structure 504, and a transducer 506. It
should be noted that other sensors such as MEMS devices, strain
gauges, and piezo-resistive sensors can be used with the ASIC. In
particular, the ASIC incorporates A/D and D/A circuitry (not shown)
to digitize current and voltage output from these types of sensing
components. Transducers 502 and 506 operatively couple to
compressible propagation structure 504. In a non-limiting example,
transducer 506 to emits energy waves into compressible structure
504 while transducer 502 detects propagated energy waves.
Compressible propagation structure 504 is coupled to a load bearing
or contacting surface 508 and an encapsulating enclosure 510 of
sensing module 200. A parameter to be measured is applied to either
contacting surface 508, encapsulating enclosure 510, or both. In
one embodiment, springs 560 couple to contacting surface 508 and
encapsulating enclosure 510 to support compressible propagation
structure 504. In particular, springs 560 prevent cantilevering of
contacting surface 508, reduce hysteresis caused by material
properties of compressible propagation structure 504, and improve
sensor response time to changes in the applied parameter.
[0094] In one embodiment, a first ASIC includes a charging circuit
514 and power management circuitry 518. The power management
circuitry 518 couples to the charging circuit, other blocks of the
ASIC and external components/circuitry to minimize power
consumption of the integrated circuit. The charging circuit 514
operatively couples to an induction coil 512 and energy storage
516. In a non-limiting example, induction coil 512 couples to an
external coil that provides energy to charge energy storage 516.
Induction coil 512 and the external coil are placed in proximity to
each other thereby electro-magnetically coupling to one another.
Induction coil 512 is coupled to energy storage 516. Charging
circuit 514 controls the charging of energy storage 516. Charging
circuit 514 can determine when charging is complete, monitor power
available, and regulate a voltage provided to the operational
circuitry. Charging circuit 514 can charge a battery in sensing
module 200. Alternatively, a capacitor or super capacitor can be
used to power the first ASIC for a time sufficient to acquire the
desired measurements. A capacitor has the benefit of a long or
indefinite shelf life and fast charge time. In either charging
scenario, energy from the external coil is coupled to the induction
coil 512. The energy from induction coil 512 is then stored in a
medium such as a battery or capacitor.
[0095] Benefits of ultracapacitors, ultra capacitors, or super
capacitors, or other form of capacitors as a power source instead
or, or in conjunction with, other power sources or rechargeable
technologies include, but are not limited to, enabling a high level
of miniaturization as ultracapacitors, ultra capacitors, or super
capacitors are smaller than smallest available battery for the same
level of energy and power for many low power applications or
applications that require power only intermittently or as a
short-term backup for other power sources.
[0096] For applications that require power only intermittently,
capacitors enable rapid recharge that is much faster than battery
technologies and rechargeable chemistries regardless of their
energy capacity. A charge time, from a completely uncharged state
takes minutes because no chemical processes are involved in
charging capacitors. This may be compared to charge times on the
order of hours for many battery technologies that cannot be charged
at a rate faster that one-half the energy storage capacity of the
battery within one hour. In practice, many battery applications
charge at a much slower rate. Many capacitors have the added
benefit of almost indefinite lifetimes. There is no deterioration
of a capacitor's storage capacity when uncharged, regardless of
length of time at zero charge. Another benefit is that overcharging
capacitors may pose less risk to electronics within an electronic
module or device than overcharging batteries might pose.
Furthermore, capacitors eliminate storage and disposal limitations
of batteries with no risk of chemical leakage. In addition,
capacitors can have a smaller form factor, are surface-mountable,
and integrate well into the electronics assemblies and standard
surface-mount electronic assembly processes.
[0097] Use capacitors to provide operating power for wireless
devices, telemetry devices, or medical devices provides design,
construction, and operating flexibility over a wide range of
potential applications. Capacitors can be charged by connecting
them to other power sources such as, but not limited to, a battery
or batteries, an alternating current (AC) power supply, a radio
frequency (RF) receiver, or an electromagnetic induction coil or
coils, a photoelectric cell or cells, a thermocouple or
thermocouples, capacitors, or an ultrasound transducer or
transducers. For compact electronic modules or devices,
ultracapacitors, super capacitors, or other form of capacitors
provide many benefits over other rechargeable technologies.
[0098] The first ASIC further includes circuitry to operate and
capture data from the sensing assemblages. A parameter to be
measured is applied to compressible propagation structure 504. As
an example of parameter measurement, a force, pressure, or load is
applied across contacting surface 508 and encapsulating enclosure
510. The force, pressure, or load affects the length of the
compressible propagation structure 504. The circuitry on the first
ASIC forms a positive closed loop feedback circuit that maintains
the emission, propagation, and detection of energy waves in the
compressible propagation structure 504. The first ASIC operatively
couples to transducers 502 and 506 to control the positive closed
loop feedback circuit that is herein called a propagation tuned
oscillator (PTO). The first ASIC measures a transit time,
frequency, or phase of propagated energy waves. The measurement is
used to determine the length of compressible propagation structure
504. The energy waves emitted into compressible propagation
structure 504 can be continuous or pulsed. The energy waves can
propagate by a direct path or be reflected.
[0099] The first ASIC comprises an oscillator 520, a switch 522,
driver 524, matching network 526, MUX 528, and control circuit 536.
The oscillator 520 is used as a reference clock for the ASIC and
enables the PTO to begin emission of energy waves into the
compressible propagation structure 504. Oscillator 520 in the first
ASIC can be coupled to an external component such as a crystal
oscillator to define and provide a stable frequency of operation.
Switch 522 couples the oscillator 520 to MUX 528. Control circuit
536 operatively enables MUX 528 and switch 522 to couple oscillator
520 to driver 524 during a startup sequence. Driver 524 and
matching network 526 couple to transducer 506. Driver 524 drives
transducer 506 to emit an energy wave. Matching network 526
impedance matches driver 524 to the transducer 506 to reduce power
consumption during energy wave emission.
[0100] In one embodiment, transducer 506 emits one or more energy
waves into the compressible propagation structure 504 at a first
location. Transducer 506 is located at a second location of
compressible propagation structure 504. Transducer 506 detects
propagated energy waves at the second location and generates a
signal corresponding to the propagated energy waves. The first ASIC
further comprises a MUX 530, pre-amplifier 532 (e.g. preamp 532)
and a zero-crossing receiver or edge detect receiver. Zero-crossing
receiver or edge-detect receiver comprise detect circuit 534.
Control circuit 536 enables MUX 530 to couple transducer 502 to
preamp 532. Preamp 532 amplifies a signal output by transducer 502
corresponding to a propagated energy wave. In a non-limiting
example, the first ASIC comprises both a zero-crossing receiver and
an edge detect receiver. More multiplexing circuitry in conjunction
with control circuit 536 can be incorporated on the first ASIC to
select between the circuits. Similarly, multiplexing circuitry can
be used to couple and operate more than one sensor. The amplified
signal from preamp 532 is coupled to detection circuit 534.
Zero-crossing receiver is a detection circuit that identifies a
propagated energy wave by sensing a transition of the signal. A
requirement of detection can be that the signal has certain
transition and magnitude characteristics. The edge-detect receiver
detects a propagated energy wave by identifying a wave front of the
propagated energy wave. The zero-crossing receiver or edge-detect
receiver outputs a pulse in response to the detection of a
propagated energy wave.
[0101] Positive closed loop feedback is applied upon detection of
an energy wave after the startup sequence. Control circuit 536
decouples oscillator 520 from driver 524 through switch 522 and MUX
528. Control circuit 536 operatively enables switch 558 and MUX 528
to couple detection circuit 534 to driver 524. A pulse generated by
detection circuit 534 initiates the emission of a new energy wave
into compressible propagation structure 504. The pulse from
detection circuit 534 is provided to driver 524. The positive
closed loop feedback of the circuitry maintains the emission,
propagation, and detection of energy waves in propagation structure
504.
[0102] The first ASIC further comprises a loop counter 538, time
counter 540, register 542, and ADC 556. Loop counter 538, time
counter 540, and register 542 are operatively coupled to control
circuit 536 to generate a precise measurement of the transit time,
frequency, or phase of propagated energy waves during a measurement
sequence. In one embodiment, a measurement comprises a
predetermined number of energy waves propagating through the
compressible propagation structure 504. The predetermined number is
set in the loop counter 538. The loop counter 538 is decremented by
each pulse output by detection circuit 534 that corresponds to a
detected propagated energy wave. The positive closed loop feedback
is broken when counter 538 decrements to zero thereby stopping the
measurement. Time counter 540 measures a total propagation time of
the predetermined number of propagated energy waves set in loop
counter 538. The measured total propagation time divided by the
predetermined number of propagated energy waves is a measured
transit time of an energy wave. The measured transit time can be
precisely converted to a length of compressible propagation
structure 504 under a stable condition of the applied parameter on
the sensing assemblage. The applied parameter value can be
calculated by known relationship between the length of compressible
propagation structure 504 and the parameter. A result of the
measurement is stored in register 542 when loop counter 538
decrements to zero. More than one measurement can be performed and
stored. In one embodiment, the precision can be increased by
raising the number of propagated energy waves being measured in
loop counter 538.
[0103] In the example, energy waves are propagated from transducer
506 to transducer 5. Alternatively, control circuit 536 can direct
the propagation of energy waves from transducer 502 to transducer
506 whereby transducer 502 emits energy waves and transducer 506
detects propagated energy waves. An analog to digital converter
(ADC) 556 is shown coupled to an accelerometer 554. ADC 556 is a
circuit on the first ASIC. It can be used to digitize an output
from a circuit such as accelerometer 554. Accelerometer 554 can be
used to detect and measure when sensing module 200 is in motion.
Data from accelerometer 554 can be used to correct the measured
result to account for module 200 acceleration. ADC 556 can also be
used to provide measurement data from other sensor types by
providing a digitized output corresponding to voltage or current
magnitude.
[0104] A second ASIC can comprise CRC circuit 546, telemetry
transmitter 548, and matching network 508. The CRC circuit 546
applies error code detection on the packet data such as data stored
in register 542. The cyclic redundancy check computes a checksum
for a data stream or packet of any length. The checksums are used
to detect interference or accidental alteration of data during
transmission. Transmitter 548 is coupled to CRC 546 and sends the
data wirelessly. Matching network 550 couples telemetry transmitter
512 to antenna 552 to provide an impedance match to efficiently
transfer the signal to the antenna 552. As disclosed above, the
integration of the telemetry transmitter and sensor modules enables
construction of a wide range of sizes of the sensing module 200.
This facilitates capturing data, measuring parameters of interest
and digitizing that data, and subsequently communicating that data
to external equipment with minimal disturbance to the operation of
the body, instrument, appliance, vehicle, equipment, or physical
system for a wide range of applications. Moreover, the level of
accuracy and resolution achieved by the total integration of
communication components, transducers, waveguides, and oscillators
to control the operating frequency of the ultrasound transducers
enables the compact, self-contained measurement module
construction. In a further embodiment, the circuitry on the first
and second ASICs can be combined on a single ASIC to further reduce
form factor, power, and cost.
[0105] FIG. 8 is an exemplary assemblage 800 that illustrates
propagation of ultrasound waves 810 within the waveguide 806 in the
bi-directional mode of operation of this assemblage. In this mode,
the selection of the roles of the two individual ultrasound
resonators (802, 804) or transducers affixed to interfacing
material 820 and 822, if required, are periodically reversed. In
the bi-directional mode the transit time of ultrasound waves
propagating in either direction within the waveguide 806 can be
measured. This can enable adjustment for Doppler effects in
applications where the sensing module 808 is operating while in
motion 816. Furthermore, this mode of operation helps assure
accurate measurement of the applied load, force, pressure, or
displacement by capturing data for computing adjustments to offset
this external motion 816. An advantage is provided in situations
wherein the body, instrument, appliance, vehicle, equipment, or
other physical system 814, is itself operating or moving during
sensing of load, pressure, or displacement. Similarly, the
capability can also correct in situation where the body,
instrument, appliance, vehicle, equipment, or other physical
system, is causing the portion 812 of the body, instrument,
appliance, vehicle, equipment, or other physical system being
measured to be in motion 816 during sensing of load, force,
pressure, or displacement. Other adjustments to the measurement for
physical changes to system 814 are contemplated and can be
compensated for in a similar fashion. For example, temperature of
system 814 can be measured and a lookup table or equation having a
relationship of temperature versus transit time can be used to
normalize measurements. Differential measurement techniques can
also be used to cancel many types of common factors as is known in
the art.
[0106] The use of waveguide 806 enables the construction of low
cost sensing modules and devices over a wide range of sizes,
including highly compact sensing modules, disposable modules for
bio-medical applications, and devices, using standard components
and manufacturing processes. The flexibility to construct sensing
modules and devices with very high levels of measurement accuracy,
repeatability, and resolution that can scale over a wide range of
sizes enables sensing modules and devices to the tailored to fit
and collect data on the physical parameter or parameters of
interest for a wide range of medical and non-medical
applications.
[0107] Referring back to FIG. 2, although not explicitly
illustrated, it should be noted that the load insert sensing device
100 and associated internal components move in accordance with
motion of the femur 108 as shown. The bi-directional operating mode
of the waveguide mitigates the Doppler effects resulting from the
motion. As previously indicated, incorporating data from the
accelerometer 121 with data from the other components of the
sensing module 200 helps assure accurate measurement of the applied
load, force, pressure, displacement, density, localized
temperature, or viscosity by enabling computation of adjustments to
offset this external motion.
[0108] For example, sensing modules or devices may be placed on or
within, or attached or affixed to or within, a wide range of
physical systems including, but not limited to instruments,
appliances, vehicles, equipments, or other physical systems as well
as animal and human bodies, for sensing the parameter or parameters
of interest in real time without disturbing the operation of the
body, instrument, appliance, vehicle, equipment, or physical
system.
[0109] In addition to non-medical applications, examples of a wide
range of potential medical applications may include, but are not
limited to, implantable devices, modules within implantable
devices, modules or devices within intra-operative implants or
trial inserts, modules within inserted or ingested devices, modules
within wearable devices, modules within handheld devices, modules
within instruments, appliances, equipment, or accessories of all of
these, or disposables within implants, trial inserts, inserted or
ingested devices, wearable devices, handheld devices, instruments,
appliances, equipment, or accessories to these devices,
instruments, appliances, or equipment. Many physiological
parameters within animal or human bodies may be measured including,
but not limited to, loading within individual joints, bone density,
movement, various parameters of interstitial fluids including, but
not limited to, viscosity, pressure, and localized temperature with
applications throughout the vascular, lymph, respiratory, and
digestive systems, as well as within or affecting muscles, bones,
joints, and soft tissue areas. For example, orthopedic applications
may include, but are not limited to, load bearing prosthetic
components, or provisional or trial prosthetic components for, but
not limited to, surgical procedures for knees, hips, shoulders,
elbows, wrists, ankles, and spines; any other orthopedic or
musculoskeletal implant, or any combination of these.
[0110] FIG. 9 is an exemplary cross-sectional view of a sensor
element 900 to illustrate changes in the propagation of ultrasound
waves 914 with changes in the length of a waveguide 906. In
general, the measurement of a parameter is achieved by relating
displacement to the parameter. In one embodiment, the displacement
required over the entire measurement range is measured in microns.
For example, an external force 908 compresses waveguide 906 thereby
changing the length of waveguide 906. Sensing circuitry (not shown)
measures propagation characteristics of ultrasonic signals in the
waveguide 906 to determine the change in the length of the
waveguide 906. These changes in length change in direct proportion
to the parameters of interest thus enabling the conversion of
changes in the parameter or parameters of interest into electrical
signals.
[0111] As previously discussed, external forces applied to the
sensing module 200 compress the waveguide(s) thereby changing the
length of the waveguide(s). The sensing module 200 measures
propagation characteristics of ultrasonic signals in the
waveguide(s) to determine the change in the length of the
waveguide(s). These changes in length change in direct proportion
to the parameters of interest thus enabling the conversion of
changes in the parameter or parameters of interest into load (or
force) information.
[0112] As illustrated, external force 908 compresses waveguide 906
and pushes the transducers 902 and 904 closer to one another by a
distance 910. This changes the length of waveguide 906 by distance
912 of the waveguide propagation path between transducers 902 and
904. Depending on the operating mode, the sensing circuitry
measures the change in length of the waveguide 906 by analyzing
characteristics of the propagation of ultrasound waves within the
waveguide.
[0113] One interpretation of FIG. 9 illustrates waves emitting from
transducer 902 at one end of waveguide 906 and propagating to
transducer 904 at the other end of the waveguide 906. The
interpretation includes the effect of movement of waveguide 906 and
thus the velocity of waves propagating within waveguide 906
(without changing shape or width of individual waves) and therefore
the transit time between transducers 902 and 904 at each end of the
waveguide. The interpretation further includes the opposite effect
on waves propagating in the opposite direction and is evaluated to
estimate the velocity of the waveguide and remove it by averaging
the transit time of waves propagating in both directions.
[0114] Changes in the parameter or parameters of interest are
measured by measuring changes in the transit time of energy pulses
or waves within the propagating medium. Closed loop measurement of
changes in the parameter or parameters of interest is achieved by
modulating the repetition rate of energy pulses or the frequency of
energy waves as a function of the propagation characteristics of
the elastic energy propagating structure.
[0115] In a continuous wave mode of operation, a phase detector
(not shown) evaluates the frequency and changes in the frequency of
resonant ultrasonic waves in the waveguide 906. As will be
described below, positive feedback closed-loop circuit operation in
continuous wave (CW) mode adjusts the frequency of ultrasonic waves
914 in the waveguide 906 to maintain a same number or integer
number of periods of ultrasonic waves in the waveguide 906. The CW
operation persists as long as the rate of change of the length of
the waveguide is not so rapid that changes of more than a quarter
wavelength occur before the frequency of the propagation tuned
oscillator (PTO) can respond. This restriction exemplifies one
advantageous difference between the performance of a PTO and a
Phase Locked Loop (PLL). Assuming the transducers are producing
ultrasonic waves, for example, at 2.4 MHz, the wavelength in air,
assuming a velocity of 343 microns per microsecond, is about
143.mu., although the wavelength within a waveguide may be longer
than in unrestricted air.
[0116] In a pulse mode of operation, the phase detector measures a
time of flight (TOF) between when an ultrasonic pulse is
transmitted by transducer 902 and received at transducer 904. The
time of flight determines the length of the waveguide propagating
path, and accordingly reveals the change in length of the waveguide
906. In another arrangement, differential time of flight
measurements (or phase differences) can be used to determine the
change in length of the waveguide 906. A pulse consists of a pulse
of one or more waves. The waves may have equal amplitude and
frequency (square wave pulse) or they may have different
amplitudes, for example, decaying amplitude (trapezoidal pulse) or
some other complex waveform. The PTO is holding the phase of the
leading edge of the pulses propagating through the waveguide
constant. In pulse mode operation the PTO detects the leading edge
of with an edge-detect receiver rather than a zero-crossing or
transition as detected by a zero-crossing receiver used in CW
mode.
[0117] It should be noted that ultrasound energy pulses or waves,
the emission of ultrasound pulses or waves by ultrasound resonators
or transducers, transmitted through ultrasound waveguides, and
detected by ultrasound resonators or transducers are used merely as
examples of energy pulses, waves, and propagation structures and
media. Other embodiments herein contemplated can utilize other wave
forms, such as, light.
[0118] FIG. 10 is an exemplary block diagram 1000 of a propagation
tuned oscillator (PTO) 4 to maintain positive closed-loop feedback
in accordance with an exemplary embodiment. The measurement system
includes a sensing assemblage 1 and propagation tuned oscillator
(PTO) 4 that detects energy waves 2 in one or more waveguides 3 of
the sensing assemblage 1. In one embodiment, energy waves 2 are
ultrasound waves. A pulse 11 is generated in response to the
detection of energy waves 2 to initiate a propagation of a new
energy wave in waveguide 3. It should be noted that ultrasound
energy pulses or waves, the emission of ultrasound pulses or waves
by ultrasound resonators or transducers, transmitted through
ultrasound waveguides, and detected by ultrasound resonators or
transducers are used merely as examples of energy pulses, waves,
and propagation structures and media. Other embodiments herein
contemplated can utilize other wave forms, such as, light.
[0119] Recall that the sensing insert device 100 when in motion
measures forces on the sensing assemblies by evaluating propagation
times of energy waves within the waveguides in conjunction with the
accelerometer data. The propagation tuned oscillator (PTO) 4
measures a transit time of ultrasound waves 2 within the waveguide
3 in a closed-loop configuration. The digital counter 20 determines
the physical change in the length of the waveguide. Referring to
FIG. 5, the one or more accelerometers 302 determines the changes
along x, y and z dimensions. The electronic circuitry 307 in view
of the accelerometer data from accelerometer 302 and the physical
changes in length of the sensing assemblage 1 determines the
applied loading (or forces).
[0120] The sensing assemblage 1 comprises transducer 5, transducer
6, and a waveguide 3 (or energy propagating structure). In a
non-limiting example, sensing assemblage 1 is affixed to load
bearing or contacting surfaces 8. External forces applied to the
contacting surfaces 8 compress the waveguide 3 and change the
length of the waveguide 3. Under compression, transducers 5 and 6
will also be moved closer together. The change in distance affects
the transit time 7 of energy waves 2 transmitted and received
between transducers 5 and 6. The propagation tuned oscillator 4 in
response to these physical changes will detect each energy wave
sooner (e.g. shorter transit time) and initiate the propagation of
new energy waves associated with the shorter transit time. As will
be explained below, this is accomplished by way of PTO 4 in
conjunction with the pulse generator 10, the mode control 12, and
the phase detector 14.
[0121] Notably, changes in the waveguide 3 (energy propagating
structure or structures) alter the propagation properties of the
medium of propagation (e.g. transit time 7). The energy wave can be
a continuous wave or a pulsed energy wave. A pulsed energy wave
approach reduces power dissipation allowing for a temporary power
source such as a battery or capacitor to power the system during
the course of operation. In at least one exemplary embodiment, a
continuous wave energy wave or a pulsed energy wave is provided by
transducer 5 to a first surface of waveguide 3. Transducer 5
generates energy waves 2 that are coupled into waveguide 3. In a
non-limiting example, transducer 5 is a piezo-electric device
capable of transmitting and receiving acoustic signals in the
ultrasonic frequency range.
[0122] Transducer 6 is coupled to a second surface of waveguide 3
to receive the propagated pulsed signal and generates a
corresponding electrical signal. The electrical signal output by
transducer 6 is coupled to phase detector 14. In general, phase
detector 14 compares the timing of a selected point on the waveform
of the detected energy wave with respect to the timing of the same
point on the waveform of other propagated energy waves. In a first
embodiment, phase detector 14 can be a zero-crossing receiver. In a
second embodiment, phase detector 14 can be an edge-detect
receiver. In the example where sensing assemblage 1 is compressed,
the detection of the propagated energy waves 2 occurs earlier (due
to the length/distance reduction of waveguide 3) than a signal
prior to external forces being applied to contacting surfaces.
Pulse generator 10 generates a new pulse in response to detection
of the propagated energy waves 2 by phase detector 14. The new
pulse is provided to transducer 5 to initiate a new energy wave
sequence. Thus, each energy wave sequence is an individual event of
energy wave propagation, energy wave detection, and energy wave
emission that maintains energy waves 2 propagating in waveguide
3.
[0123] The transit time 7 of a propagated energy wave is the time
it takes an energy wave to propagate from the first surface of
waveguide 3 to the second surface. There is delay associated with
each circuit described above. Typically, the total delay of the
circuitry is significantly less than the propagation time of an
energy wave through waveguide 3. In addition, under equilibrium
conditions variations in circuit delay are minimal. Multiple pulse
to pulse timings can be used to generate an average time period
when change in external forces occur relatively slowly in relation
to the pulsed signal propagation time such as in a physiologic or
mechanical system. The digital counter 20 in conjunction with
electronic components counts the number of propagated energy waves
to determine a corresponding change in the length of the waveguide
3. These changes in length change in direct proportion to the
external force thus enabling the conversion of changes in parameter
or parameters of interest into electrical signals.
[0124] The block diagram 1000 further includes counting and timing
circuitry. More specifically, the timing, counting, and clock
circuitry comprises a digital counter 20, a digital timer 22, a
digital clock 24, and a data register 26. The digital clock 24
provides a clock signal to digital counter 20 and digital timer 22
during a measurement sequence. The digital counter 20 is coupled to
the propagation tuned oscillator 4. Digital timer 22 is coupled to
data register 26. Digital timer 20, digital timer, 22, digital
clock 24 and data register 26 capture transit time 7 of energy
waves 2 emitted by ultrasound resonator or transducer 5, propagated
through waveguide 3, and detected by or ultrasound resonator or
transducer 5 or 6 depending on the mode of the measurement of the
physical parameters of interest applied to surfaces 8. The
operation of the timing and counting circuitry is disclosed in more
detail hereinbelow.
[0125] The measurement data can be analyzed to achieve accurate,
repeatable, high precision and high resolution measurements. This
method enables the setting of the level of precision or resolution
of captured data to optimize trade-offs between measurement
resolution versus frequency, including the bandwidth of the sensing
and data processing operations, thus enabling a sensing module or
device to operate at its optimal operating point without
compromising resolution of the measurements. This is achieved by
the accumulation of multiple cycles of excitation and transit time
instead of averaging transit time of multiple individual excitation
and transit cycles. The result is accurate, repeatable, high
precision and high resolution measurements of parameters of
interest in physical systems.
[0126] In at least one exemplary embodiment, propagation tuned
oscillator 4 in conjunction with one or more sensing assemblages 1
are used to take measurements on a muscular-skeletal system. In a
non-limiting example, sensing assemblage 1 is placed between a
femoral prosthetic component and tibial prosthetic component to
provide measured load information that aids in the installation of
an artificial knee joint. Sensing assemblage 1 can also be a
permanent component or a muscular-skeletal joint or artificial
muscular-skeletal joint to monitor joint function. The measurements
can be made in extension and in flexion. In the example, assemblage
1 is used to measure the condyle loading to determine if it falls
within a predetermined range and location. Based on the
measurement, the surgeon can select the thickness of the insert
such that the measured loading and incidence with the final insert
in place will fall within the predetermined range. Soft tissue
tensioning can be used by a surgeon to further optimize the force
or pressure. Similarly, two assemblages 1 can be used to measure
both condyles simultaneously or multiplexed. The difference in
loading (e.g. balance) between condyles can be measured. Soft
tissue tensioning can be used to reduce the force on the condyle
having the higher measured loading to reduce the measured pressure
difference between condyles.
[0127] One method of operation holds the number of energy waves
propagating through waveguide 3 as a constant integer number. A
time period of an energy wave corresponds to energy wave
periodicity. A stable time period is one in which the time period
changes very little over a number of energy waves. This occurs when
conditions that affect sensing assemblage 1 stay consistent or
constant. Holding the number of energy waves propagating through
waveguide 3 to an integer number is a constraint that forces a
change in the time between pulses when the length of waveguide 3
changes. The resulting change in time period of each energy wave
corresponds to a change in aggregate energy wave time period that
is captured using digital counter 20 as a measurement of changes in
external forces or conditions applied to contacting surfaces 8.
[0128] A further method of operation according to one embodiment is
described hereinbelow for energy waves 2 propagating from
transducer 5 and received by transducer 6. In at least one
exemplary embodiment, energy waves 2 is an ultrasonic energy wave.
Transducers 5 and 6 are piezo-electric resonator transducers.
Although not described, wave propagation can occur in the opposite
direction being initiated by transducer 6 and received by
transducer 5. Furthermore, detecting ultrasound resonator
transducer 6 can be a separate ultrasound resonator as shown or
transducer 5 can be used solely depending on the selected mode of
propagation (e.g. reflective sensing). Changes in external forces
or conditions applied to contacting surfaces 8 affect the
propagation characteristics of waveguide 3 and alter transit time
7. As mentioned previously, propagation tuned oscillator 4 holds
constant an integer number of energy waves 2 propagating through
waveguide 3 (e.g. an integer number of pulsed energy wave time
periods) thereby controlling the repetition rate. As noted above,
once PTO 4 stabilizes, the digital counter 20 digitizes the
repetition rate of pulsed energy waves, for example, by way of
edge-detection, as will be explained hereinbelow in more
detail.
[0129] In an alternate embodiment, the repetition rate of pulsed
energy waves 2 emitted by transducer 5 can be controlled by pulse
generator 10. The operation remains similar where the parameter to
be measured corresponds to the measurement of the transit time 7 of
pulsed energy waves 2 within waveguide 3. It should be noted that
an individual ultrasonic pulse can comprise one or more energy
waves with a damping wave shape. The energy wave shape is
determined by the electrical and mechanical parameters of pulse
generator 10, interface material or materials, where required, and
ultrasound resonator or transducer 5. The frequency of the energy
waves within individual pulses is determined by the response of the
emitting ultrasound resonator 4 to excitation by an electrical
pulse 11. The mode of the propagation of the pulsed energy waves 2
through waveguide 3 is controlled by mode control circuitry 12
(e.g., reflectance or uni-directional). The detecting ultrasound
resonator or transducer may either be a separate ultrasound
resonator or transducer 6 or the emitting resonator or transducer 5
depending on the selected mode of propagation (reflectance or
unidirectional).
[0130] In general, accurate measurement of physical parameters is
achieved at an equilibrium point having the property that an
integer number of pulses are propagating through the energy
propagating structure at any point in time. Measurement of changes
in the "time-of-flight" or transit time of ultrasound energy waves
within a waveguide of known length can be achieved by modulating
the repetition rate of the ultrasound energy waves as a function of
changes in distance or velocity through the medium of propagation,
or a combination of changes in distance and velocity, caused by
changes in the parameter or parameters of interest.
[0131] It should be noted that ultrasound energy pulses or waves,
the emission of ultrasound pulses or waves by ultrasound resonators
or transducers, transmitted through ultrasound waveguides, and
detected by ultrasound resonators or transducers are used merely as
examples of energy pulses, waves, and propagation structures and
media. Other embodiments herein contemplated can utilize other wave
forms, such as, light. Furthermore, the velocity of ultrasound
waves within a medium may be higher than in air. With the present
dimensions of the initial embodiment of a propagation tuned
oscillator the waveguide is approximately three wavelengths long at
the frequency of operation.
[0132] Measurement by propagation tuned oscillator 4 and sensing
assemblage 1 enables high sensitivity and high signal-to-noise
ratio. The time-based measurements are largely insensitive to most
sources of error that may influence voltage or current driven
sensing methods and devices. The resulting changes in the transit
time of operation correspond to frequency, which can be measured
rapidly, and with high resolution. This achieves the required
measurement accuracy and precision thus capturing changes in the
physical parameters of interest and enabling analysis of their
dynamic and static behavior.
[0133] These measurements may be implemented with an integrated
wireless sensing module or device having an encapsulating structure
that supports sensors and load bearing or contacting surfaces and
an electronic assemblage that integrates a power supply, sensing
elements, energy transducer or transducers and elastic energy
propagating structure or structures, biasing spring or springs or
other form of elastic members, an accelerometer, antennas and
electronic circuitry that processes measurement data as well as
controls all operations of ultrasound generation, propagation, and
detection and wireless communications. The electronics assemblage
also supports testability and calibration features that assure the
quality, accuracy, and reliability of the completed wireless
sensing module or device.
[0134] In general, measurement of the changes in the physical
length of individual waveguides can be made in several modes. Each
assemblage of one or two ultrasound resonators or transducers
combined with a waveguide can be controlled to operate in six
different modes. This includes two wave shape modes: continuous
wave or pulsed waves, and three propagation modes: reflectance,
unidirectional, and bi-directional propagation of the ultrasound
wave. In all modes of operation the changes in transit time within
the ultrasound waveguides change the operating frequency of the
propagation tuned oscillator 4 or oscillators. These changes in the
frequency of oscillation of the propagation tuned oscillator or
oscillators can be measured rapidly and with high resolution. This
achieves the required measurement accuracy and precision thus
enabling the capture of changes in the physical parameters of
interest and enabling analysis of the dynamic and static behavior
of the physical system or body.
[0135] The level of accuracy and resolution achieved by the
integration of energy transducers and an energy propagating
structure or structures coupled with the electronic components of
the propagation tuned oscillator enables the construction of, but
is not limited to, compact ultra low power modules or devices for
monitoring or measuring the parameters of interest. The flexibility
to construct sensing modules or devices over a wide range of sizes
enables sensing modules to be tailored to fit a wide range of
applications such that the sensing module or device may be engaged
with, or placed, attached, or affixed to, on, or within a body,
instrument, appliance, vehicle, equipment, or other physical system
and monitor or collect data on physical parameters of interest
without disturbing the operation of the body, instrument,
appliance, vehicle, equipment, or physical system.
[0136] FIG. 11 is a cross-sectional view of a layout architecture
of the sensing module 200 in accordance with an exemplary
embodiment. The blocks are operatively coupled within the
encapsulated enclosure of the sensing module 200 and together form
an encapsulated force sensor 1100. It comprises a top steel plate
1104 coupled to a lower printed circuit board (PCB) 1118 by way of
spring retainer 1106, disc spring 1108, and spring post 1114. The
force sensor 1100 is biased with springs or other means of elastic
support to accurately maintain a required distance between the load
bearing or contact surfaces such as top cover 1102 and to minimize
hysteresis due to material properties of waveguide 1110.
[0137] The encapsulating force sensor 1100 supports and protects
the specialized mechanical and electronic components from external
physical, mechanical, chemical, and electrical, and electromagnetic
intrusion that might compromise sensing or communication operations
of the module or device. The encapsulating force sensor 1100 also
supports internal mechanical and electronic components and
minimizes adverse physical, mechanical, electrical, and ultrasonic
interactions that might compromise sensing or communication
operations of the module or device. Top cover 1102 and unitary main
body 1157 form the encapsulating enclosure. Unitary main body 1157
is a metal, plastic, or polymer body having sufficient strength and
rigidity to withstand forces, pressures, and loads of the
muscular-skeletal system. In particular, the sidewalls or bottom
surface do not deform under normal operating conditions. For
example, the unitary main body 1157 can be formed of polycarbonate
or other biocompatible material. Moreover, unitary main body 1157
can be molded in a manufacturing process that allows detailed
features to be repeatably and reliably manufactured.
[0138] The physical layout architecture of sensor 1100 has the one
or more sensing assemblages overlying the electronic circuitry. A
force, pressure, or load is applied to a surface of sensor 1100.
The surface of sensor 1100 corresponds to top steel plate 1104.
Steel plate 1104 moves in response to a force, pressure, or load.
The steel plate 1104 can support the movement while maintaining a
seal with unitary main body 1157 that isolates an interior of the
enclosure. In general, a sensing assemblage is coupled between
steel plate 1104 and a substrate 1130. Substrate 1130 is a rigid
non-moveable substrate that is supported by the sidewalls of
unitary main body 1157. A periphery of substrate 1130 is in contact
with and supported by a support feature 1128 formed in the
sidewalls of unitary main body 1157. Substrate 1130 does not flex
under loading. The sensing assemblage translates a displacement due
to the force, pressure, or load applied to steel plate 1104 to a
signal. The signal is processed by electronic circuitry in the
enclosure to generate data corresponding to the force, pressure, or
load value. As shown, the sensing assemblage comprises upper piezo
1112, waveguide 1110, and lower piezo 1124. Upper piezo 1112 and
lower piezo 1124 are ultrasonic piezo-electric transducers.
[0139] Electronic circuitry to power, control, interface, operate,
measure, and send sensor data is interconnected together on a
printed circuit board (PCB) 1118. One or more cups 1120 are formed
in unitary main body 1157. In one embodiment, the components
mounted on PCB 1118 reside within cups 1120. One or more structures
1126 support and fix the position of the PCB 1118. The components
on PCB 1118 are suspended in the cups 1120 and do not have contact
with unitary main body 1157 thereby preventing interconnect stress
that could result in long-term reliability issues. The PCB 1118 is
mechanically isolated from substrate 1130. Thus, any force,
pressure, or loading on substrate 1130 is not applied to PCB 1118.
Flexible interconnect is used to connect from the electronic
circuitry on PCB 1118 to upper piezo 1112 and lower piezo 1124.
[0140] In one embodiment, more than one sensing assemblage couples
to predetermined locations of the steel plate 1104. Each sensing
assemblage can measure a parameter applied to steel plate 1104. In
combination, the sensing assemblages can determine a location or
region where the parameter is applied to the surface. For example,
the magnitude and position of the loading on the contacting surface
of sensing module 200 applied by femur 102 and tibia 108 to sensing
module 200 can be measured and displayed as shown in FIG. 2. In a
non-limiting example, three sensing assemblages can be spaced on a
periphery of steel plate 1104. In the example, each sensing
assemblage will measure a force applied to steel plate 1104. The
location of the applied force is closest to the sensing assemblage
detecting the highest force magnitude. Conversely, the sensing
assemblage detecting the weakest force magnitude is farthest from
the applied force. The measured force magnitudes in combination
with the predetermined locations where the sensing assemblages
couple to steel plate 1104 can be used to determine a location
where the parameter is applied.
[0141] The housing electrically insulates the internal electronic,
sensing, and communication components. The encapsulating force
sensor 1100 eliminates parasitic paths that might conduct
ultrasonic energy and compromise excitation and detection of
ultrasound waves within the sensing assemblages during sensing
operations. A temporary bi-directional electrical interconnect
assures a high level of electrical observation and controllability
of the electronic assembly within the encapsulating force sensor
1100. The temporary interconnect also provides a high level of
electrical observation of the sensing subsystem, including the
transducers, waveguides, and mechanical spring or elastic
assembly.
[0142] Ultrasound waveguide 1110 is coupled to the top cover 1102.
A force applied to the top cover 1102 compresses waveguide 1110.
Lower piezo 1124 and upper piezo 1112 are piezo-electric
transducers respectively coupled to waveguide 1110 at a first and
second location. Waveguide 1110 is a compressible propagation
medium for ultrasonic energy waves. The transducers emit energy
waves and detect propagated energy waves in waveguide 1110.
Electronic circuitry is coupled to lower piezo 1124 and upper piezo
1112 to measure transit time, frequency, or phase of the propagated
energy waves. The transit time, frequency, or phase of energy waves
propagating between the first and second locations of waveguide
1110 can be precisely measured and therefore the length of the
ultrasound waveguide 1110. The length of waveguide 1110 is
calculated by a known function relating material properties of the
waveguide 1110 to the parameter being measured. In the example, a
force, pressure, or load is calculated from the measured length of
waveguide 1110.
[0143] The encapsulated force sensor 1100 can accurately and
repeatably measure one pound changes in load with changes in length
of a waveguide comprising 2.5 microns. The maximum change in the
present implementation is specified at less than 5.0 microns. This
assures that the size of the sensing module 200 throughout all
measurements remains within the required dimension (e.g., distance)
of the insert between the load bearing surfaces of the prosthetic
components.
[0144] An exemplary level of control of the compression or
displacement of the waveguides 1110 with changes in load, force,
pressure, or displacement is achieved by positioning the spring or
springs 1108 or other means of elastic support, including the
waveguides 1110 themselves, between the load bearing contact
surfaces to minimize any tendency of the load bearing contact
surfaces to cantilever. Cantilevering can compromise the accuracy
of the inclination of the load bearing contact surface whenever
load, force, pressure, or displacement is applied to any point near
a periphery of the load bearing contact surfaces. In one
embodiment, springs 1108 are disc springs. The spring 1108 is held
in a predetermined location by spring post 1114 and spring retainer
1104.
[0145] The walls of the unitary main body 1157 include a small gap
to enable the steel plate 1104 to move. The hermetic seal is also
flexible to allow the steel plate 1104 of the force sensor 1104 to
slide up and down, like a piston, for distances on the order of a
hundred microns without compromising integrity of the seal. The
hermetic seal completes manufacturing, sterilization, and packaging
processes without compromising ability to meet regulatory
requirements for hermeticity. The level of hermeticity is
sufficient to assure functionality and biocompatibility over the
lifetime of the device. Implant devices with total implant time
less than 24 hours may have less stringent regulatory requirements
for hermeticity. Unbiased electrical circuitry is less susceptible
to damage from moisture. The electronics in one embodiment are only
powered during actual usage. In another embodiment, the
encapsulated force sensor 1100 employs low duty cycles to serve as
a measurement-on-demand device to efficiently perform at low total
operating time when the electronics are powered on.
[0146] The encapsulating force sensor 1100 has a compact size
permitting it to fit for example within a trial insert, final
insert, prosthetic component, tool, equipment, or implant structure
to measure the level and incidence of the load on subsequent
implanted prosthetic devices. It can be constructed using standard
components and manufacturing processes. Manufacturing carriers or
fixtures can be designed to emulate the final encapsulating
enclosure of the sensing module 200. Calibration data can be
obtained during the manufacturing processing thus enabling capture
of accurate calibration data. These calibration parameters can be
stored within the memory circuits integrated into the electronics
assemblage of the sensing module 200. Testability and calibration
further assures the quality and reliability of the encapsulated
enclosure.
[0147] Examples of a wide range of potential medical applications
can include, but are not limited to, implantable devices, modules
within implantable devices, intra-operative implants or modules
within intra-operative implants or trial inserts, modules within
inserted or ingested devices, modules within wearable devices,
modules within handheld devices, modules within instruments,
appliances, equipment, or accessories of all of these, or
disposables within implants, trial inserts, inserted or ingested
devices, wearable devices, handheld devices, instruments,
appliances, equipment, or accessories to these devices,
instruments, appliances, or equipment.
[0148] FIG. 12 is a simplified cross-sectional view of an
embodiment of the load sensing platform 121 in accordance with an
exemplary embodiment. The load sensing platform 121 is placed,
engaged, attached, or affixed to or within a physical system with a
portion of the system contacting the load bearing or contacting
surfaces of the load sensing platform 121. As disclosed in FIG. 1
the load sensing platform 121 can be used intra-operatively to
measure parameters of the muscular-skeletal system during joint
replacement surgery. In the example, the load bearing platform 121
is placed in a joint of the muscular-skeletal system to measure
force, pressure, or load and the location where the force,
pressure, or load is applied. The lower load bearing surface 8
contacts the tibial component 106 of the artificial knee. The upper
load bearing surface 8 contacts the femoral component 104 of the
artificial knee. Not shown are the muscles, ligaments, and tendons
of the muscular-skeletal system that apply a compressive force,
pressure, or load on the surfaces 8 of the load sensing platform
121. The load sensing platform 121 has a form factor that allows
integration in tools, equipment, and implants. The load sensing
platform 121 is bio-compatible and can be placed in an implant or
attached to the muscular-skeletal system to provide long term
monitoring capability of natural structures or artificial
components.
[0149] A compact sensing platform is miniaturized to be placed on
or within a body, instrument, appliance, vehicle, equipment, or
other physical system without disturbing the operation of the body,
instrument, appliance, vehicle, equipment, or physical system. This
facilitates contacting the sources of load, force, pressure,
displacement, density, viscosity, or localized temperature to be
measured. The non-limiting example of load sensing platform 121 can
include circuitry disclosed in FIG. 5. Two or more springs or other
means of elastic support 315 support the load bearing or contacting
surfaces 8. One or more assemblages each comprised of one or two
ultrasound resonators or transducers are coupled between load
bearing surfaces 8.
[0150] As shown, a single sensing assemblage 1 is centrally located
in load sensing platform 121. Sensing assemblage 1 is a stack
comprising the upper transducer 6, the lower transducer 5, and the
waveguide 3. In one embodiment, the waveguide 3 is cylindrical in
shape having a first end and a second end. Transducers 5 and 6
respectively overlie the first and second ends of waveguide 3. An
interface material can be used to attach and enhance acoustical
coupling between a transducer and waveguide. The stack is
positioned in contact with, attached, or coupled to the load
bearing or contacting surfaces 8. Electrical interconnect such as a
flex interconnect couples to terminals of transducers 5 and 6. The
flex interconnect (not shown) electrically connects transducers 5
and 6 to electronic circuitry 307 of the sensing module 200.
[0151] The upper load bearing surface 8 is a surface of an upper
substrate 702. An interior surface of the upper substrate 702
couples to transducer 6. Similarly, the lower load bearing surface
8 is a surface of a lower substrate 704. An interior surface of the
lower substrate couples to the transducer 5. A load, force, or
pressure applied across load bearing surfaces 8 can compress or
lengthen waveguide 3. This arrangement facilitates translating
changes in the parameter or parameters of interest into changes in
the length or compression of the waveguide or waveguides 3 and
converting these changes in the length or compression of the
waveguide 3 or waveguides into electrical signals by way of
transducers 5 or 6 thus enabling sensing assemblage 1 to sense
changes in the physical parameters of interest with minimal
disturbance to the operation of the external body, instrument,
appliance, vehicle, equipment, or physical system. To achieve the
required level of miniaturization, the length of the ultrasound
waveguides 3 is on the order of 10 millimeters in length. The
measurable resolution of compression or displacement of waveguide
is on the order of sub-microns.
[0152] One or more springs 315 or other means of elastic support,
support the load bearing or contacting surfaces 8. The one or more
springs control a compression of load sensing platform 121. For
example, waveguide 3 can comprise a polymer material suitable for
energy wave propagation. In one embodiment, the polymer material
changes dimension when a parameter to be measured is applied to
waveguide 3. A relationship is known between the polymer material
and a measured dimension. Changes in dimension are measured and the
parameter calculated by way of the known relationship. The polymer
material can exhibit mechanical hysteresis whereby the material
in-elastically responds to changes in the applied parameter. In the
example, the length of waveguide 3 responds to the force, pressure,
or load applied across contacting surfaces 8. Moreover, the polymer
material may not rebound in a timely fashion as the force, pressure
or load changes. Springs 315 aid in the transition as waveguide 3
responds to different levels of compression. Springs 315 bring the
load sensing platform 121 to an accurate and repeatable quiescent
state or condition. Springs further prevent the cantilevering of
load bearing surfaces 8 that can reduce an accuracy of measurement.
Cantilevering becomes more prevalent as forces, pressures, and
loads are applied towards the periphery of a contact area of load
bearing surfaces 8.
[0153] In one embodiment, the springs 315 that support load bearing
surfaces 8 are disc springs or a wave springs. Disc springs are
capable of maintaining waveguide 3 at a precise length. The
compression of the waveguide 3 is very accurate over the
measurement range. The compression of the disc springs can be
monotonic over the range of applied levels of force, pressure, or
load. In one embodiment, the surfaces of the disc springs are
polished to assure smooth compression with changes in force applied
to contact surfaces 8. A further benefit of the disk springs is
that they eliminate or minimize cantilevering of the load
supporting substrate that can compromise the accuracy due to the
inclination of load bearing surfaces 8. In the illustration, two
springs 315 are shown that are located on the periphery of load
sensing platform 121. Although not shown, other springs 315 may
reside in the load sensing platform 121 at other predetermined
locations. Typically, the contact area where the parameter is
applied to load bearing surfaces 8 is within an area bounded by
springs 315.
[0154] In one embodiment, a substrate 706 is resides between upper
substrate 702 and lower substrate 704. Sensing assemblage 1 couples
through an opening in substrate 706 to couple to the interior
surfaces of substrates 702 and 704 to measure a force, pressure, or
load applied across load bearing surfaces 8. In the example,
substrate 702 moves as a force, pressure, or load is applied while
substrate 704 remains in a fixed position. Thus, a force, pressure,
or load applied to contacting surface 8 changes a distance between
substrates 702 and 704 and therefore the length of waveguide 3.
Substrates 704 and 706 are planar to one another separated by a
predetermined spacing. Substrates 704 and 706 remain in the fixed
relation to one another under loading.
[0155] Springs 315 are placed between an upper surface of substrate
706 and the interior surface of substrate 702. As disclosed in the
example, springs 315 are disc springs. The disc springs are concave
in shape. The disc spring is formed having a centrally located
circular opening. The surface of springs 315 proximally located to
the circular opening contacts the upper surface of substrate 706.
The surface of springs 315 proximally located to the outer edge of
springs 315 contacts the interior surface of substrate 702. A force
applied across the load bearing surface 8 of load sensing platform
121 will compress springs 315 and waveguide 3. The amount of
compression of waveguide 3 over a measurable range can be very
small but will provide precision accuracy of the parameter. For
example, waveguide 3 may be compressed less than a millimeter for a
force measurement ranging from 5 to 100 lbs. In the example, the
length of waveguide 3 is precisely measured using acoustic energy
wave propagation. The measured length is then converted to the
force, pressure, or load. The springs 315 support movement of the
waveguide 3 upon a change in force, pressure, or loading. For
example, springs 315 repeatably return the load sensing platform
121 to a precise quiescent state upon releasing an applied force.
The characteristics of springs 315 are known over the measurement
range of load sensing platform 121. The calculated measured value
of the parameter can include compensation due to springs 315.
[0156] Spring 315 are in a fixed location in load sensing platform
121. The disc springs are located on the periphery of the load
sensing platform 121. Spring posts 708 and spring retainers 710 are
used to align and fix springs 315 in each predetermined location.
Spring post 708 aligns substrate 702 to substrate 706. Spring post
708 and spring retainer 710 aligns to corresponding openings in
substrate 706. In one embodiment, a cap of post 708 fits into a
corresponding cavity of the interior surface of substrate 702.
Spring retainer 710 is a sleeve that overlies post 708. Post 708
and spring retainer 710 couples through a corresponding opening in
substrate 706. Spring retainer 710 has a lip that overlies and
contacts the upper surface of substrate 706. The spring post 708
and spring retainer 710 couple through the opening in the disc
spring. The edge of the opening rests against the edge of the lip
of retainer 710 thereby retaining and holding spring 315 in the
predetermined location. Spring 315 can move vertically allowing
waveguide 3 to change length due to the parameter being applied to
contact surfaces 8.
[0157] In one embodiment, load sensing platform 121 can locate a
position where the parameter is applied on a load bearing surface.
Locating the position can be achieved by using more than one
sensing assemblages 1. In one embodiment, three sensing assemblages
1 couple to load bearing or contacting surface 8 at three
predetermined locations. The parameter is measured by each sensing
assemblages 1. The magnitudes of each measurement and the
differences between measurements of the sensing assemblages 1 are
compared. For example, the location of the applied parameter is
closer to the sensing assemblage that generates the highest
reading. Conversely, the location of the applied parameter will be
furthest from the sensing assemblage that generates the lowest
reading. The exact location can be determined by comparison of the
measured values of each sensing assemblage in conjunction with
knowledge of the predetermined locations where each assemblage
contacts load bearing or contacting surface 8.
[0158] FIG. 14 is an exemplary block diagram schematic of a compact
low-power energy source 1400 integrated into an exemplary
electronic assembly of the sensing module 200 in accordance with
one embodiment. The schematic illustrates one embodiment of the
capacitive energy storage 1400 having an induction coupling to an
external power source 1402 to transfer energy to a super capacitor
or capacitor as an energy storage device that provides operating
power for sensing module 200. The compact low-power energy source
1400 can comprise an induction coil 1404, a rectifier 1406, a
regulator 1408, a capacitive energy storage device 1410, a power
management circuit 1412, and operational circuitry 1414. The latter
circuits can be analog or discrete components, assembled in part or
whole with other electronic circuitry, custom designed as an ASIC,
or any combination thereof. In one embodiment, the operational
circuitry can include circuitry to operate and produce measurement
data from sensing assemblages, demodulation circuitry for a
wireless receive path, communication circuitry, and secure encoding
circuitry.
[0159] The external energy source 1402 can be coupled to a battery
or batteries or an alternating current power supply. For example,
external energy source 1402 can be an external hand-held device
with its own battery that wirelessly transfers charge from the
battery of the hand-held device to the energy source 1400 of the
sensing device. The surgeon or technician can hold the hand-held
device in close proximity to the sensing device prior to or during
orthopedic surgery to provide sufficient charge to operate the
device during the procedure. The sensing device as a long-term
implant can be charged by the patient at his or her own convenience
to initiate a measurement process that provides information on the
implant status. In other embodiments, the sensing module 200 being
powered by charge from external energy source 1402 can communicate
a signal to indicate a recharging operation is necessary, for
example, when in the proximity of a charging device.
[0160] External energy source 1402 can be coupled wirelessly to
capacitive energy storage device 1410 through electromagnetic
induction coil or coils 1404, rectifier 1406 and regulator 1408.
The charging operation is controlled by power management circuitry
1412. During operation of operating circuitry 1414, power is
transferred from capacitive energy storage device 1410 by power
management circuitry 1412 that includes, but is not limited to,
efficient step-up and step-down voltage converter circuitry that
conserves operating power of circuit blocks at the minimum voltage
levels that support the required level of performance. Clock
frequencies are also optimized for performance, power, and size to
assure digital circuit blocks operate at the optimum clock rates
that support the required level of performance. Circuit components
are partitioned among integrated circuits and discrete components
to minimize power consumption without compromising performance.
Partitioning functions between digital and analog circuit also
enhances design flexibility and facilitates minimizing power
consumption without sacrificing functionality or performance.
[0161] A method of powering and operation of the sensing module is
disclosed below. The method can be practiced with more or less than
the number of steps shown and is not limited to the order shown. To
describe the method, reference will be made to the components of
other figures described hereinabove although it is understood that
the method can be implemented in any other manner using other
suitable components. The sensing module 200 described in FIG. 5
including capacitive energy storage capability and highly
efficient, low power operating performance can be used to
illustrate the operating principles of the method. The method is
initiated when the external power source 1402 begins transmitting
power within range of the induction coil or coils 1404 of the
sensing module 200. In a second step, the induction coils 1404 are
coupled to the electromagnetic waves such that the electromagnetic
waves are sensed. The induction coil or coils 1404 are energized by
the power transmissions from external power source 1402. In a third
step, the coupled electromagnetic waves create an AC power signal
in induction coil or coils 1404. In a fourth step, the rectifier
1406 rectifies the AC power signal to produce a rectified power
signal. In one embodiment, a voltage level across induction coil or
coils 1404 rises to a level that a rectified signal is generated by
full-wave rectifier 1406. In a fifth step, the rectified power
signal is used to charge or provide energy to the capacitive energy
storage device 1410, which holds the charge. In a non-limiting
example, the energy storage device 1410 is a super capacitor or
capacitor having a small form factor with enough storage capability
to power the sensing module 200 for a predetermined period of time.
For example, a total knee reconstruction operation takes
approximately one to two hours. Capacitive energy storage device
1410 would store sufficient charge to power the sensing module 200
to provide measurements for this length of time. Integrating most
of the circuitry on one or two low-power ASICs greatly reduces
power consumption of the system making this possible. In a sixth
step, the voltage regulator 1408 ensures that the capacitive energy
storage device 1410 is charged to, and maintains a voltage level
that is greater than the required operating voltage of the sensing
module 200. In a seventh step, the power management circuitry 1412
monitors the level of charge on capacitive energy storage device
1410 to determine if the voltage exceeds a threshold. The threshold
can correspond to a shunt threshold established by the regulator
1408. The operating electronics circuitry 1414 is enabled when it
is determined in that an adequate level of charge has been stored
to power the sensing module 200 for at least the predetermined time
period.
[0162] In an eighth step, the power management circuitry 1412
disconnects the energy storage device 1410 from the charging
circuitry (1404, 1406, and 1408) when the coupling with external
power source 1402 is removed or terminated. Power management
circuitry 1412 continues to monitor the level of charge on
capacitive energy storage device 1410. The power management
circuitry 1412 powers down the sensing module 200 including the
operational circuitry 1414 when the charge or voltage level falls
below a predetermined threshold. The power management circuitry
1412 subsequently discharges remaining charge on the energy storage
device 1410 to prevent unreliable, intermittent, or erratic
operation of the operational circuitry 1414.
[0163] Under nominal conditions, a charge time from zero charge to
fully charged is approximately 3 minutes. In one embodiment, the
maximum charge time is specified to be no greater than 7 minutes.
The charging time of a capacitor powered system is a major
improvement over the two hours or more required to fully charge a
battery from zero charge regardless of battery capacity. The
capacitive energy storage device 1410 can include capacitors with
solid dielectrics that have longer lifetimes than batteries, can be
left uncharged, and will not degrade regardless of length of time
at a zero charge. In one arrangement, the wireless charging
operation can be performed by electromagnetic induction before
removal of any sterile packaging. The capacitive energy storage
device 1410 is applicable for powering chronic active implantable
devices where data collection is discrete point-of-time
measurements rather than continuous, fulltime data collection and
storage.
[0164] The compact low-power energy source can be used as a backup
power source for sensing module 200 should the primary power source
be terminated. A method performed by the compact low-power energy
source as a backup power source is disclosed below. The method can
be practiced with more or less than the number of steps shown and
is not limited to the order shown. To describe the method,
reference will be made to the components of FIGS. 1, 5 and 14,
although it is understood that the method can be implemented in any
other manner using other suitable components. The medical sensing
device 100 described in FIG. 1 including capacitive energy storage
capability and highly efficient, low power operating performance
can be used to illustrate the operating principles of method as a
back-up power source. Broadly stated, the method is directed to
charging the sensing insert device 100 by way of a wired connection
instead of wireless induction charging.
[0165] In a first step, the induction coil 1404 is electrically
decoupled. In a second step, the rectifier 1406 and the regulator
1408 are disabled. At this juncture, the method enters a state
where capacitive energy storage device 1410 is decoupled from the
wireless charging circuits; that is, the power transmission
components inductor 1404, rectifier 1406, and regulator 1408 are
disabled. As one example, an electrical switching operation
disengages the connection upon the power management circuitry 1412
detecting a direct line charge on the capacitive energy storage
device 1410. In another arrangement, the power management circuitry
1412 further checks whether the induction coils are energized at
the time of the applied line charge, thereby indicating that the
energy is being delivered via a wired connection instead, since no
induction activity by an external power source 1402 is
detected.
[0166] In a second step, the wired energy source starts and charges
capacitive energy storage device 1410. The wired energy source
maintains capacitive energy storage device 1410 at full charge
under normal operating conditions through direct electrical
coupling. Power management circuitry 1412 monitors the level of
charge on capacitive energy storage device 1410. If at a third
step, power from wired energy source is interrupted, power
management circuitry 1412 isolates the capacitive energy storage
device 1410 from the wired energy source. As one example, a power
interruption occurs when an individual manually disconnects the
wired power source from the sensing module 200. This could also
occur in response to an energy spike or power drop in the wired
energy source. As another example, a power interruption could occur
upon the power management circuitry 1412 detecting the presence of
an external power source 1402 attempting to charge the sensing
module 200 and thereby competing with the wired energy source.
[0167] In a fourth step, the power management circuitry 1412 can
commence to supply the energy stored on the capacitive energy
storage device 1410 to operating circuitry 1414 and associated
electronics for normal operation. In a fifth step, power management
circuitry 1412 monitors the level of charge on capacitive energy
storage device 1410. In a sixth step, the power management
circuitry 1412 will allow the continued supply of energy to the
operating circuitry 1414 as long as the voltage on capacitor 1410
exceeds a voltage threshold. In a seventh step, the power
management circuitry 1412 powers down the electronic assembly when
the charge or voltage level falls below the predetermined charge of
voltage threshold. The threshold is chosen to provide sufficient
time to power down the operational circuitry 1414 in an orderly
fashion.
[0168] If the wired energy source is restored, power management
circuitry 1412 resumes the direct connection of power between the
wired energy source and operational circuitry 1414. Power
management circuitry 1412 also resumes the coupling of power
between the wired energy source and capacitive energy storage
device 1410 and resumes maintaining it at full charge.
[0169] A method is disclosed for wireless modulation telemetry in
accordance with one embodiment. The method can be practiced with
more or less than the number of steps shown and is not limited to
the order shown. To describe the method, reference will be made to
the components of FIGS. 1, 5 and 14, although it is understood that
the method can be implemented in any other manner using other
suitable components.
[0170] In a first step, the external wireless energy source 125
acquires input data. As one example, the user can manually enter
the input data via a touchscreen or a user interface menu on the
external wireless energy source 125. In another arrangement, the
input data in response to a user directive can be communicatively
uploaded to the external wireless energy source 125, for example,
by USB or via a wi-fi connection. The input data can be information
such as a serial number, a registration code, biasing parameters
(e.g., spring constants, load balancing), updated parameters,
version control information, security code information, data log
tags, operational control information, or any other data. More
specifically, data and instructions to be transmitted to the
sensing insert device 100 is input into a data input port 128 of
external wireless energy source 125.
[0171] As one example, referring back briefly to FIG. 1, the
receiver station 110 can query a serial number from the sensing
insert device 100 for updating medical records and inventory.
Sensing insert device 100 includes the sensing module 200. As
another example, the external wireless energy source 125 can
download an operation code for adjusting a bias level of one of the
springs in the sensing assemblies 303, or establishing an operating
mode (e.g., standby, debug, flash). Following the acquisition of
input data, the external wireless energy source 125 can be placed
in the proximity of the load insert sensing device 100. At this
point, operation of an external charging device or wireless energy
source 1402 is initiated and contact is established with insert
sensing device 100.
[0172] In a second step, the external wireless energy source 125
proceeds with secure encoding of the input data. As one example,
the external wireless energy source 125 by way of a processor
embeds cyclic redundancy check (CRC) bits into a data communication
packet representing the input data. The CRC is computed and
included in the transmission of each data packet. The cyclic
redundancy check is based on an algorithm that computes a checksum
for a data stream or packets of any length. These checksums can be
used to detect interference or accidental alteration of data during
transmission. Cyclic redundancy checks are good at detecting errors
caused by electrical or electromagnetic noise and therefore enable
robust protection against improper processing of corrupted data
encoded in energy streams having communication of instructions and
data as a secondary function.
[0173] In a third step, the external wireless energy source 125
modulates the input data onto a TX (transmit) power signal. For
instance, the modulation circuit 127 modulates the power signal as
a carrier signal and conveys the input data by adjusting at least
one of an amplitude, phase, or frequency of the power signal. In
the case of wireless energy transfer by resonant induction, the
external wireless energy source 125 can modulate the resonant
frequency over a small bandwidth to convey the input data in a
power efficient manner. In yet another arrangement, timing
intervals between energy emissions can be used to convey input
data. In a fourth step, the external wireless energy source 125
transmits the TX power signal to the sensing insert device 100.
[0174] In a fifth step, the sensing insert device 100 senses the
electromagnetic energy waves on the induction coils. In a sixth
step, a RX power signal is generated from the received
electromagnetic waves. This RX power signal comprises a power
signal to provide charge to power to the sensing insert device 100
and a communication signal. As previously discussed, the compact
low-power energy source 1400 by way of the induction coils 1404,
rectifier 1406, and regulator 1408 sense and convert
electromagnetic waves to a rectified voltage signal that is then
used to charge a super capacitor or capacitor. In one
configuration, the external wireless energy source 125 and the
compact low-power energy source 1400 employ resonant inductive
coupling to provide power efficient transmission over short
distances (e.g., less than 20 cm). As an example, the inductors
(coils) in conjunction with closely spaced capacitor plates are
tuned to a mutual resonant frequency to minimize power loss. The
external wireless energy source 125 modulates the power signal
around the resonant frequency to transmit power efficiently while
simultaneously conveying the communication signal.
[0175] In a seventh step, the sensing insert device 100 demodulates
the communication signal from the RX power signal. The demodulation
extracts the information or data from the modulated carrier wave.
The demodulation circuit can be in one of the rectifier 1406,
regulator 1408, power management circuitry 1412, or operational
circuitry 1412. In an eight step, the sensing insert device 100
securely decodes and validates the information or data. In one
embodiment, a cyclic redundancy check checksum is performed to
verify the data was not corrupted or received incorrectly. The data
is forwarded to control and processing circuitry 307. In the
example, electronic circuitry 307 is on an ASIC integrated circuit
with the communication blocks to perform the demodulation, CRC,
encoding/decoding, and data validation. As an example, the
circuitry can include envelope detectors, phase detectors,
oscillators, multipliers, adders, filters, and logic operators.
[0176] The sensing insert device 100 can then proceed to use the
decoded down-link data, for example, to control at least one
operation, as shown in a ninth step. As an example, the control
operation can place the sensing insert device 100 in a particular
operation mode, such as, stand-by or low-power. As another example,
the control operation can download a serial number to a local
memory on the sensing insert device 100. The serial number can
later be transmitted upon request to a communicatively coupled
receiver station 110.
[0177] Methods are disclosed in FIGS. 15 and 16 for power
conservation in accordance with one or more embodiments. The
methods can be practiced with more or less than the number of steps
shown and is not limited to the order shown. To describe the
method, reference will be made to the components of FIGS. 1, 5 and
14, although it is understood that the method can be implemented in
any other manner using other suitable components. In general, a
sensing module 200 is coupled to the muscular-skeletal system. The
sensing module 200 is used intra-operatively to measure one or more
parameters of the muscular-skeletal system to aid in the
installation of prosthetic components. In the example disclosed
above, the sensing module 200 is placed in a trial insert that
dimensionally is substantially equal to the dimensions of a final
insert. The trial insert is used in conjunction with other final or
permanent prosthetic components to determine fit, function, and
allowing modification to fine tune the installation before the
final insert is inserted. Similarly, one or more of the final
prosthetic components can include sensing module 200. The disclosed
example has the sensing module 200 in the final insert. The sensing
modules 200 in the final prosthetic components can measure
different parameters than the trial insert. For example, pain,
infection, joint kinematics, and bearing surface wear are
post-operative parameters of interest.
[0178] In both the intra-operative and post-operative examples, the
sensing module 200 has a form factor that is dimensionally smaller
than a prosthetic component. In one embodiment, wired connections
for power and communication are not used. In an intra-operative
environment, wired connections can get in way of the procedure and
limit surgical access. Internal implanted prosthetics such as knee,
hip, spine, shoulder, and other joint implants cannot be wired
unless terminals protrude through the skin. This is typically not
desirable nor an effective long-term solution. The sensing module
200 can incorporate a battery as a temporary power source. As
disclosed above, the battery poses the logistical problems of shelf
life, installation, charging, and biological hazard. An alternative
solution to a battery is using a super or ultra capacitor to power
the sensing module 200. The capacitor has the benefits of form
factor, long life, and fast charging time in a solid-state
device.
[0179] The one limitation of a capacitor is the tradeoff of form
factor and charge storage. A super or ultra capacitor having a form
factor equal to or smaller than a watch battery or other small
battery will typically have less energy capability than the
battery. In an intra-operative procedure, such as a total knee
reconstruction, the sensing module 200 has to deliver precision
measurements throughout the surgery. A typical implant operation
can last from one hour to several hours. Similarly, the sensing
module 200 in a final prosthetic component would need to last a
sufficient time to run through one or more measurements of one or
more parameters. In both intra-operative and post-operative
measurements, the measured parameter data would be sent wirelessly
to the surgeon, patient, or healthcare provider. The measured data
can be sent in real-time for display or delayed to be reviewed or
analyzed at an appropriate time. In general, powering the sensing
module 200 with a capacitor would not be a viable solution using
off the shelf electronic components or sensors. A capacitor meeting
the form factor requirements would not store sufficient charge to
sustain device operation for a required operational period of
time.
[0180] Sensing module 200 comprises a compact low-power energy
source 1400 that includes the capacitor 1410 that powers the device
during a measurement process. The capacitor 1410 is able to sustain
operation of sensing module 200 by incorporating power management
circuitry 1412 having one or more power conservation modes and an
application specific integrated circuit (ASIC). The circuitry of
sensing module 200 comprises operational circuitry 1414, charging
circuitry, and power management circuitry 1412. The operational
circuitry 1414 operates one or more sensing assemblages, controls
measurement sequences, processes sensing assemblage data, and
transmits information. The power management circuitry 1412
operatively couples to circuitry of compact low-power energy source
1400 and operational circuitry 1414 to controllably manage power
efficiency of the system thereby enabling the use of the capacitor
1410 to power sensing module 200 for intra-operative and
post-operative muscular-skeletal parameter measurements.
[0181] In one embodiment, the circuitry of sensing module 200
comprises at least one ASIC. The ASIC comprises the majority of the
electronic system. The ASIC is architected to operate at low power
and provide functionality to perform sensor measurements. In
particular, the ASIC includes power management circuitry 1412,
operational circuitry 1414, portions of compact low-energy source
1400, and can include wireless communication circuitry. The ASIC
comprises complementary metallic oxide semiconductor (CMOS)
circuitry that is low voltage and low leakage. The voltage
operation is typically 5 volts or less. Voltage operation of analog
circuitry can be higher. Digital circuitry can be operated at lower
voltages such as 1-3 volts to further reduce power consumption. The
ASIC provides a benefit of reduced form factor and low-power
operation.
[0182] The ASIC is further configured in a block architecture. In
particular, the operational circuitry 1414 is partitioned in a
manner whereby functional blocks can be controlled by the power
management circuitry 1412. A partitioned block, typically performs
a function that is independent or not reliant on other blocks being
operated and thereby can be turned on or off dependent on need to
minimize power consumption. In particular, the power management
circuitry 1412 can disable or delay operation of one or more
functional blocks to reduce power consumption. In one embodiment,
the power management circuitry 1412 makes these decisions based on
monitoring the charge or voltage on the capacitor. The amount of
charge or voltage can be used to determine when a block is enabled.
Partitioning circuit components between structures within the
integrated circuit and discrete components enhances design
flexibility and minimizes power consumption without compromising
performance. Partitioning functions between analog and digital
circuitry also enhances design flexibility and facilitate
minimizing power consumption without sacrificing functionality or
performance.
[0183] Referring to FIG. 15, in a step 1502, a highly efficient
step-up or step-down voltage converter is implemented in the
compact low-power energy source 1400. The step-up or step-down
voltage converter circuitry enables essentially "lossless"
translation of voltage levels. Further conservation of charge is
achieved through selection of operating voltages and frequencies
that meet device performance specifications. In a step 1504,
reduction in power dissipation is achieved by operating circuitry
at minimum frequencies and voltage. The clocking circuitry can be a
significant source of power dissipation. Clock drivers can be
optimized to efficiently drive a predetermined load. A clock tree
or distributed clocking network can be used. The clock tree
distribution is optimized in conjunction with the clock drivers to
minimize delay and maintain timing at and between distributed nodes
providing clock signals. In a step 1506, the clocked circuitry and
the clock frequencies are optimized for power and sized to assure
digital circuit blocks are each operated at the optimum clock
frequency to achieve required performance with minimum power
consumption.
[0184] Referring to FIG. 16, further exemplary embodiments to
reduce power consumption of sensing module 200 that allow a
capacitor power source are disclosed. The power management
circuitry 1412 places the sensing module 200 in one or more power
conservation modes depending on a current power status as disclosed
below. In general, the ASIC can have multiple input and output
channels. Each channel can have a dedicated function. For example,
input channels can be used to couple to multiple sensors to measure
different parameters of the muscular-skeletal system such as
temperature, load, or pH. In a step 1602, the input-output channels
are operated such that a single output channel or a single input
channel is enabled at any point in time. Thus, the inputs or
outputs are enabled sequentially or in sequence and are not
operated in parallel to improve power efficiency. In a step 1604, a
single input circuit and a single output circuit is used. This
eliminates parallel input or output operation. The single input and
single output circuit are multiplexed to the input-output channels.
Typically, measurements of the muscular-skeletal system are not
time constrained allowing sequential operation of the input-outputs
to reduce peak power consumption. Furthermore, integrating only the
single input circuit and the single output driver reduces the
surface area of the integrated circuit as well as the amount of
active circuitry thereby minimizing parasitic leakage paths.
[0185] In a step 1606, the architected design of the ASIC includes
matching such that the input-output channels matches the input and
output requirements of external signals. In the example, specific
knowledge of the component characteristics is required to provide
the match. In one embodiment, impedance matching produces an
efficient energy transfer into and out of the ASIC thereby
conserving power. For example, power efficient matching networks
are used for coupling to telemetry, sensors, or transducers. The
matching is accomplished with appropriate design of the outputs,
drivers, and control circuitry within the ASIC that couple to
off-board components and devices. In a step 1608, off-board sensors
and transducers are also operated at optimum frequencies and drive
voltages and currents to achieve the required performance of the
wireless module or device at the minimum level of power
consumption. Similarly, in a step 1610, operation of all circuit
blocks, charging circuitry, and telemetry circuitry are each
optimized for minimum total power consumption to achieve required
performance levels. This includes, but is not limited to, timing of
off and on states. This is coordinated to minimize power drain by
optimizing timing and duty cycles of all individual circuit blocks
including power drain when powered off plus power consumption to
restart each circuit block versus standby power consumption of the
separate circuit blocks.
[0186] The integration of design methods for ultra low power
consumption achieves outstanding performance with minimum power
drain. This enables highly performing wireless modules or devices
powered by a capacitive energy storage device including, but not
limited to, ultracapacitors, ultra capacitors, super-caps, super
capacitors, or other capacitors. Furthermore, the power management
circuitry 1412 can operate in one or more power conservations
modes. In a first power conservation mode, the power management
circuitry 1412 can turn off, disable, decouple, or disconnect
circuitry not being used to conserve power. In a second power
conservation mode, the power management circuitry 1412 decouples or
turns off the compact low-power energy source 1400 thereby
operating on power from capacitor 1410 when power management
circuitry 1410 detects that wireless energy source 1402 cannot
adequately provide energy or the wireless connection is unstable.
In a third power conservation mode, the power management circuitry
1412 reduces a frequency of operation of one or more blocks in the
ASIC to reduce operating power. In a fourth power conservation
mode, the power management circuitry 1412 disables clock drivers of
a clock tree coupled to circuitry not being used. In a fifth power
conservation mode, the power management circuitry 1412 can place
the operational circuitry in a sleep mode when the circuit is idle
for a predetermined time. In a sixth power conservation mode, the
power management circuitry 1412 allows parameter measurements to be
taken and stored in memory. This can occur when the capacitor 1410
falls below a predetermined threshold. The parameter measurement
data is delayed until to an appropriate time to conserve power. In
a seventh power conservation mode, only a single input or single
output of the ASIC is operated at any time. Finally, an orderly
shutdown occurs to preserve parameter measurement data when the
power management circuitry 1412 detects that the capacitor falls
below a predetermined threshold. In general, the sensing module 200
can be powered by the capacitor 1410 as a result of the power
conservation modes and power optimization thereby taking
measurements for the duration of a total knee reconstruction.
Benefits of the use of capacitors as a power source instead of, or
in conjunction with, other power sources or rechargeable
technologies include, but are not limited to, enabling a high level
of miniaturization, solid state with no chemistries, almost
infinite storage lifetime, storage with zero charge, quick charge
times, and wireless charging.
[0187] While the present invention has been described with
reference to particular embodiments, those skilled in the art will
recognize that many changes may be made thereto without departing
from the spirit and scope of the present invention. Each of these
embodiments and obvious variations thereof is contemplated as
falling within the spirit and scope of the invention.
* * * * *