U.S. patent application number 12/748029 was filed with the patent office on 2010-12-30 for sensing device and method for an orthopedic joint.
This patent application is currently assigned to OrthoSensor. Invention is credited to Marc T. Stein.
Application Number | 20100331733 12/748029 |
Document ID | / |
Family ID | 43379281 |
Filed Date | 2010-12-30 |
United States Patent
Application |
20100331733 |
Kind Code |
A1 |
Stein; Marc T. |
December 30, 2010 |
SENSING DEVICE AND METHOD FOR AN ORTHOPEDIC JOINT
Abstract
One embodiment is directed to a sensor for measuring a skeletal
system. A signal path of the system comprises an amplifier (612), a
sensor element, and an amplifier (620). The sensor element
comprises a transducer (4), a waveguide (5), and a transducer (30).
An external condition is applied to the sensor element. For
example, the sensor element is placed in an artificial orthopedic
joint to measure loading of the joint. Pulsed energy waves are
emitted by the transducer (4) into the waveguide (5). The
transducer (30) receives each pulsed energy wave after it
propagates through the waveguide (5). The transit time of each
pulsed energy wave corresponds to the external condition applied to
the sensor. The transducer (30) outputs a signal corresponding to
each pulsed energy wave. A detection circuit edge detects the
signal and outputs a pulse to the transducer (4) to generate a new
pulse energy wave.
Inventors: |
Stein; Marc T.; (Chandler,
AZ) |
Correspondence
Address: |
Orthosensor, Inc.
1560 Sawgrass Corporate Pkwy, 4th Floor
Sunrise
FL
33323
US
|
Assignee: |
OrthoSensor
Sunrise
FL
|
Family ID: |
43379281 |
Appl. No.: |
12/748029 |
Filed: |
March 26, 2010 |
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Application
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Patent Number |
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61221761 |
Jun 30, 2009 |
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61221767 |
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Current U.S.
Class: |
600/587 |
Current CPC
Class: |
A61B 5/7239 20130101;
A61B 8/15 20130101; A61B 5/4528 20130101; A61B 5/6878 20130101;
A61B 5/6846 20130101; A61B 5/4509 20130101 |
Class at
Publication: |
600/587 |
International
Class: |
A61B 5/103 20060101
A61B005/103 |
Claims
1. A pulsed-loop mode measurement system comprising: one or more
sensing assemblies; a pulsed system; one or more load surfaces; and
electronic circuitry, where the pulsed system maintains positive
closed-loop feedback of pulsed energy waves in one or more energy
propagating structures of the sensing assembly and where the system
measures parameters of the muscular-skeletal system.
2. The system of claim 1, where the pulsed system modulates a time
period of pulsed energy waves as a function of changes in distance
or velocity through a medium of the one or more energy propagating
structures, or a combination of changes in distance and velocity,
caused by changes in the one or more energy propagating
structures.
3. The system of claim 1, further comprising a pulse shaper to
dampen a wave shape for optimal transmission and reception in
accordance with a matched network.
4. The system of claim 1, further comprising a digital block for
digitizing the frequency of operation of the pulsed system.
5. The system of claim 1 where the pulsed system is configured to
operate wireless in pulsed-loop mode according to one or more
operational criteria, such as, but not limited to, power level,
applied force level, standby mode, application context,
temperature, or other parameter level.
6. The system of claim 5, where the system operates to measure
changes in propagation time due to changes in the length of one or
more waveguides coupled to the one or more load surfaces such that
the physical length change under load are in proportion to the
applied force.
7. A sensor module comprising one or more sensors for sensing a
muscular-skeletal system each sensor comprising: a first
transducer; a waveguide having a first surface and a second surface
where the first transducer couples to the first surface of the
waveguide; and a second transducer coupled to the second surface of
the waveguide where pulsed energy waves propagate through the
waveguide and where a transit time of a pulsed energy wave through
the wave guide corresponds to one or more measured parameters of
the muscular-skeletal system.
8. The sensor module of claim 7 where a change in length of the
waveguide results in a corresponding change in the transit time of
the pulsed energy wave and where the transit time or a change in
transit time in conjunction with material properties of the
waveguide corresponds to the one or more measured parameters.
9. The sensor module of claim 7 where each pulsed energy wave is
detected after propagating through the waveguide, where a pulse is
generated when each pulsed energy wave is detected, and where the
pulse is coupled to the first transducer.
10. The sensor module of claim 9 further including: a first
amplifier having an input and an output coupled to an input of the
first transducer; and a second amplifier having an input coupled to
an output of the second transducer and an output coupled to the
input of the first amplifier.
11. The sensor module of claim 7 where the waveguide comprises a
polymer material.
12. The sensor module of claim 7 where the sensor module further
includes: a first load bearing surface having an external surface
and an internal surface; a second load bearing surface having an
external surface and an internal surface where a stack is formed
comprising: the first transducer coupled to the internal surface of
the first load bearing surface; the waveguide; and the second
transducer where the second transducer is coupled to the internal
surface of the second load bearing surface.
13. The sensor of module of claim 12 where the sensor module is
coupled between an orthopedic joint to measure at least one of
pressure, weight, strain, wear, vibration, viscosity, density,
temperature, or distance.
14. The sensor module of claim 12 further including at least one
biasing spring coupled between the internal surface of the first
and second load bearing surfaces.
15. A sensor comprising: a first amplifier having an input and an
output; a first transducer having a terminal coupled to the output
of the first amplifier; a second transducer; an energy wave
propagation medium coupled between the first and second transducer;
and a second amplifier having an input coupled to a terminal of the
second transducer and an output coupled to the input of the first
amplifier where the sensor measures parameters of the
muscular-skeletal system.
16. The sensor of claim 15 where one or more pulsed energy waves
are provided to the input of the first amplifier to initiate
sensing.
17. The sensor of claim 16 where positive close loop feedback is
applied after the sensor is initiated where a time period of energy
waves are substantially equal when conditions on the sensor remain
constant.
18. The sensor of claim 17 where a leading edge of a pulse provided
to the first transducer is in phase but with a constant offset to
the leading edge of a pulse output by the second transducer when
conditions on the sensor remain constant.
19. The sensor of claim 18 where a transit time of an energy wave
propagating through the medium corresponds to a parameter being
measured and where a change in the medium due to the parameter
being measured produces a corresponding change in the transit
time.
20. The sensor of claim 19 where the transit time of energy waves
propagating through the medium corresponds to one of pressure,
weight, strain, wear, vibration, density, temperature, or
distance.
21. The sensor of claim 10 where an integer number of energy waves
couple through the medium under an equilibrium condition.
22. The sensor of claim 15 where the first amplifier comprises: a
digital driver having an input corresponding to the input of the
first amplifier and an output; and a matching network having an
input coupled to the output of the digital driver and an output
corresponding to the output of the first amplifier.
23. The sensor of claim 15 where the second amplifier comprises: a
preamplifier having an input corresponding to the input of the
second amplifier and an output; and an edge-detect receiver having
an input coupled to the output of the preamplifier and an output
corresponding to the output of the second amplifier.
24. The sensor of claim 15 further including: a pulse circuit
having an output for providing pulses of energy waves; a first
switch having a first terminal coupled to the output of the pulse
circuit and a second terminal coupled to the input of the first
amplifier where the first switch is closed to initiate the sensor
and where the first switch is closed when an energy wave is
detected at the output of the second amplifier; and a second switch
having a first terminal coupled to the output of the second
amplifier and a second terminal coupled to the input of the first
amplifier where the first switch is open when the first switch is
closed and where the second switch is closed when the first switch
is open thereby forming a closed loop system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S.
provisional patent applications Nos. 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 incorporated herein by reference in its
entirety.
FIELD
[0002] The disclosure relates in general to orthopedics, and
particularly though not exclusively, is related to measuring a
parameter of a mammalian muscular-skeletal system.
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 as
information from simulations, mechanical prototypes, and long-term
patient joint replacement data 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] Exemplary embodiments will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0006] FIG. 1 is an illustration of a sensor placed in contact
between a femur and a tibia for measuring a parameter in accordance
with an exemplary embodiment;
[0007] FIG. 2 is a simplified cross-sectional view of a sensing
module (or assemblage) in accordance with an exemplary
embodiment;
[0008] FIG. 3 is an exemplary assemblage for illustrating
reflectance and unidirectional modes of operation;
[0009] FIG. 4 is an exemplary assemblage that illustrates
propagation of ultrasound waves within a waveguide in the
bi-directional mode of operation of this assemblage;
[0010] FIG. 5 is an exemplary cross-sectional view of a sensor
element to illustrate changes in the propagation of ultrasound
waves with changes in the length of a waveguide;
[0011] FIG. 6 is an exemplary block diagram of a measurement system
in accordance with an exemplary embodiment; and
[0012] FIG. 7 is measurement system operating in a pulsed mode with
digital output according to one embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0013] The following description of exemplary embodiment(s) is
merely illustrative in nature and is in no way intended to limit
the invention, its application, or uses.
[0014] 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 the enabling description where
appropriate. For example specific computer code may not be listed
for achieving each of the steps discussed, however one of ordinary
skill would be able, without undo experimentation, to write such
code given the enabling disclosure herein. Such code is intended to
fall within the scope of at least one exemplary embodiment.
[0015] Additionally, the sizes of structures used in exemplary
embodiments are not limited by any discussion herein (e.g., the
sizes of structures can be macro (centimeter, meter, and larger
sizes), micro (micrometer), and nanometer size and smaller).
[0016] Notice that similar reference numerals and letters refer to
similar items in the following figures, and thus once an item is
defined in one figure, it may not be discussed or further defined
in the following figures.
[0017] In all of the examples illustrated and discussed herein, any
specific values, should be interpreted to be illustrative only and
non-limiting. Thus, other examples of the exemplary embodiments
could have different values.
[0018] FIG. 1 is an illustration of a sensor 100 placed in contact
between a femur 102 and a tibia 108 for measuring a parameter in
accordance with an exemplary embodiment. In general, sensor 100 is
placed in or in proximity to the skeletal system. In a non-limiting
example, sensor 100 is placed within an artificial joint coupled to
two or more bones of a skeletal system that move in relation to one
another. Embodiments of sensor 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 replacement implant is within predetermined
ranges that maximize patient function and the working life of the
joint prosthesis and minimize rework, thus enabling joint implants
to become more consistent from surgeon to surgeon. A further issue
is that there is little or no implant data generated from the
implant surgery, post-operatively, and long term. Sensor 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.
[0019] In at least one exemplary embodiment, an energy pulse is
directed within one or more waveguides in sensor 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. In one embodiment, the polymer waveguide can be
compressed and has little or no hysteresis in the system. A transit
time of an energy pulse through a medium is related to the material
properties of the medium. 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.
[0020] Sensor 100 can be size constrained by form factor
requirements of fitting within a region of a joint of the skeletal
system. In a non-limiting example, sensor 100 is used as an aid to
adjust and balance a replacement knee joint. A knee prosthesis
comprises a femoral prosthetic component 104, an insert, and a
tibial prosthetic component 106. A distal end of femur 102 is
prepared and receives femoral prosthetic component 104. Femoral
prosthetic component 104 typically has two condyle surfaces that
mimic a natural femur. As shown, femoral prosthetic component 104
has single condyle surface being coupled to femur 100. Femoral
prosthetic component 104 is typically made of a metal or metal
alloy.
[0021] 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 place fixed in
position with respect to tibia 108. The insert is fitted between
femoral prosthetic component 104 and tibial prosthetic component
106. The insert has at least one bearing surface that is in contact
with at least condyle surface of femoral prosthetic component 104.
The condyle surface can move in relation to the bearing surface of
the insert such that the lower leg can rotate under load. The
insert is typically made of a high wear plastic material that
minimizes friction.
[0022] In a knee joint replacement process, the surgeon affixes
femoral prosthetic component 104 to the femur 102 and tibial
prosthetic component 106 to tibia 108. The tibial prosthetic
component 106 can include a tray or plate affixed to the planarized
proximal end of the tibia 108. Sensor 100 is placed between a
condyle surface of femoral prosthetic component 104 and a major
surface of tibial prosthetic component 106. The condyle surface
contacts a major surface of sensor 100. The major surface of sensor
100 approximates a surface of the insert. Tibial prosthetic
component 106 can include a cavity or tray on the major surface
that receives and retains sensor 100 during a measurement process.
Tibial prosthetic component 106 and sensor 100 has a combined
thickness that represents a combined thickness of tibial prosthetic
component 106 and a final (or chronic) insert of the knee
joint.
[0023] In one embodiment, two sensors 100 are fitted into two
separate cavities, the cavities are within a trial insert (that may
also be referred to as the tibial insert, rather than the tibial
component itself) that is held in position by tibial component 106.
One or two sensors 100 may be inserted between femoral prosthetic
component 104 and tibial prosthetic component 106. Each sensor is
independent and each measures a respective condyle of femur 102.
Separate sensors also accommodate a situation where a single
condyle is repaired and only a single sensor is used.
Alternatively, the electronics can be shared between two sensors to
lower cost and complexity the circuitry of which will be disclosed
in more detail hereinbelow. The shared electronics can multiplex
between each sensor module to take measurements when appropriate.
Measurements taken by sensor 100 aid the surgeon in modifying the
absolute loading on each condyle and the balance between condyles.
Although shown for a knee implant, sensor 100 can be used to
measure other orthopedic joints such as the spine, hip, shoulder,
elbow, ankle, wrist, interphalangeal joint, metatarsophalangeal
joint, metacarpophalangeal joints, and others. Alternatively,
sensor 100 can be adapted to orthopedic tools to provide
measurements.
[0024] The prosthesis incorporating sensor 100 emulates the
function of a natural knee joint. Sensor 100 can measure loads or
other parameters at various points throughout the range of motion.
Data from sensor 100 is transmitted to a receiving station 110 via
wired or wireless communications. In a first embodiment, sensor 100
is a disposable system. After using sensor 100 to optimally fit the
joint implant, it can be disposed of after the operation is
completed. Sensor 100 is a low cost disposable system that reduces
capital expenditures, maintenance, and accounting when compared to
other measurement systems. In a second embodiment, a methodology
can be put in place to clean and sterilize sensor 100 for reuse. In
a third embodiment, sensor 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, sensor 100 can be a permanent component of the
replacement joint. Sensor 100 can be used to provide both short
term and long term post-operative data on the implanted joint. 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. Receiving
station 110 can record and provide accounting information of sensor
100 to an appropriate authority.
[0025] In an intra-operative example, sensor 100 can measure forces
(Fx, Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty,
and Tz) on the femoral prosthetic component 104 and the tibial
prosthetic component 106. The measured force and torque data is
transmitted to receiving station 110 to provide real-time
visualization for assisting the surgeon in identifying any
adjustments needed to achieve optimal joint pressure and balancing.
The data has substantial value in determining ranges of load and
alignment tolerances required to minimize rework and maximize
patient function and longevity of the joint.
[0026] As mentioned previously, sensor 100 can be used for other
joint surgeries; it is not limited to knee replacement implant or
implants. Moreover, sensor 100 is not limited to trial
measurements. Sensor 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 sensor 100 can reduce catastrophic failure of the
joint that a patient is unaware of. 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, sensor 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. Sensor 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.
[0027] FIG. 2 is a simplified cross-sectional view of a sensing
module 101 (or assemblage in accordance with an exemplary
embodiment. The sensing module (or assemblage) is an
electro-mechanical assembly comprising electrical components and
mechanical components that when configured and operated in
accordance with a sensing mode performs as a positive feedback
closed-loop measurement system. The measurement system can
precisely measure applied forces, such as loading, on the
electro-mechanical assembly.
[0028] In one embodiment, the electrical components can include
ultrasound resonators or transducers, ultrasound waveguides, and
signal processing electronics, but are not limited to these. The
mechanical components can include biasing springs 32, spring
retainers and posts, and load platforms 6, but are not limited to
these. The electrical components and mechanical components can be
inter-assembled (or integrated) onto a printed circuit board 36 to
operate as a coherent ultrasonic measurement system within sensing
module 101 and according to the sensing mode. As will be explained
hereinbelow in more detail, the signal processing electronics
incorporate edge detect circuitry that detects an edge of a signal
after it has propagated through waveguide 5. The detection
initiates the generation of a new pulse by an ultrasound resonator
or transducer that is coupled to waveguide 5 for propagation
therethrough. A change in transit time of a pulse through waveguide
5 is measured and correlates to a change in material property of
waveguide 5.
[0029] Sensing module 101 comprises one or more assemblages 3 each
comprised one or more ultrasound resonators. As illustrated,
waveguide 5 is coupled between transducers 4 and 30 and affixed to
load bearing or contacting surfaces 6. In one exemplary embodiment,
an ultrasound signal is coupled for propagation through waveguide
5. The sensing module 101 is placed, attached to, or affixed to, or
within a body, instrument, or other physical system 7 having a
member or members 8 in contact with the load bearing or contacting
surfaces 6 of the sensing module 101. This arrangement facilitates
translating the parameters of interest into changes in the length
or compression or extension of the waveguide or waveguides 5 within
the sensing module or device 100 and converting these changes in
length into electrical signals. This facilitates capturing data,
measuring parameters of interest and digitizing that data, and then
subsequently communicating that data through antenna 34 to external
equipment with minimal disturbance to the operation of the body,
instrument, appliance, vehicle, equipment, or physical system 7 for
a wide range of applications.
[0030] The sensing module 101 supports three modes of operation of
pulse propagation and measurement: reflectance, unidirectional, and
bi-directional. These modes can be used as appropriate for each
individual application. In unidirectional and bi-directional modes,
a chosen ultrasound resonator or transducer is controlled to emit
pulses of ultrasound waves into the ultrasound waveguide and one or
more other ultrasound resonators or transducers are controlled to
detect the propagation of the pulses of ultrasound waves at a
specified location or locations within the ultrasound waveguide. In
reflectance or pulse-echo mode, a single ultrasound or transducer
emits pulses of ultrasound waves into waveguide 5 and subsequently
detects pulses of echo waves after reflection from a selected
feature or termination of the waveguide. In pulse-echo mode, echoes
of the pulses can be detected by controlling the actions of the
emitting ultrasound resonator or transducer to alternate between
emitting and detecting modes of operation. Pulse and pulse-echo
modes of operation may require operation with more than one pulsed
energy wave propagating within the waveguide at equilibrium.
[0031] Many parameters of interest within physical systems or
bodies can be measured by evaluating changes in the transit time of
energy pulses. The frequency, as defined by the reciprocal of the
average period of a continuous or discontinuous signal, and type of
the energy pulse is determined by factors such as distance of
measurement, medium in which the signal travels, accuracy required
by the measurement, precision required by the measurement, form
factor of that will function with the system, power constraints,
and cost. In the non-limiting example, pulses of ultrasound energy
provide accurate markers for measuring transit time of the pulses
within waveguide 5. In general, an ultrasonic signal is an acoustic
signal having a frequency above the human hearing range (e.g.
>20 KHz) including frequencies well into the megahertz range. In
one embodiment, a change in transit time of an ultrasonic energy
pulse corresponds to a difference in the physical dimension of the
waveguide from a previous state. For example, a force or pressure
applied across the knee joint compresses wave guide 5 to a new
length and changes the transit time of the energy pulse When
integrated as a sensing module and inserted or coupled to a
physical system or body, these changes are directly correlated to
the physical changes on the system or body and can be readily
measured as a pressure or a force.
[0032] FIG. 3 is an exemplary assemblage 200 for illustrating
reflectance and unidirectional modes of operation. It comprises one
or more transducers 202, 204, and 206, one or more waveguides 214,
and one or more optional reflecting surfaces 216. The assemblage
200 illustrates propagation of ultrasound waves 218 within the
waveguide 214 in the reflectance and unidirectional modes of
operation. Either ultrasound resonator or transducer 202 and 204 in
combination with interfacing material or materials 208 and 210, if
required, can be selected to emit ultrasound waves 218 into the
waveguide 214.
[0033] In unidirectional mode, either of the ultrasound resonators
or transducers for example 202 can be enabled to emit ultrasound
waves 218 into the waveguide 214. The non-emitting ultrasound
resonator or transducer 204 is enabled to detect the ultrasound
waves 218 emitted by the ultrasound resonator or transducer
202.
[0034] In reflectance mode, the ultrasound waves 218 are detected
by the emitting ultrasound resonator or transducer 202 after
reflecting from a surface, interface, or body at the opposite end
of the waveguide 214. In this mode, either of the ultrasound
resonators or transducers 202 or 204 can be selected to emit and
detect ultrasound waves. Additional reflection features 216 can be
added within the waveguide structure to reflect ultrasound waves.
This can support operation in a combination of unidirectional and
reflectance modes. In this mode of operation, one of the ultrasound
resonators, for example resonator 202 is controlled to emit
ultrasound waves 218 into the waveguide 214. Another ultrasound
resonator or transducer 206 is controlled to detect the ultrasound
waves 218 emitted by the emitting ultrasound resonator 202 (or
transducer) subsequent to their reflection by reflecting feature
216.
[0035] FIG. 4 is an exemplary assemblage 300 that illustrates
propagation of ultrasound waves 310 within the waveguide 306 in the
bi-directional mode of operation of this assemblage. In this mode,
the selection of the roles of the two individual ultrasound
resonators (302, 304) or transducers affixed to interfacing
material 320 and 322, if required, are periodically reversed. In
the bi-directional mode the transit time of ultrasound waves
propagating in either direction within the waveguide 306 can be
measured. This can enable adjustment for Doppler effects in
applications where the sensing module 308 is operating while in
motion 316. 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 316. An advantage is provided in situations
wherein the body, instrument, appliance, vehicle, equipment, or
other physical system 314, 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 312 of the body, instrument,
appliance, vehicle, equipment, or other physical system being
measured to be in motion 316 during sensing of load, force,
pressure, or displacement. Other adjustments to the measurement for
physical changes to system 314 are contemplated and can be
compensated for in a similar fashion. For example, temperature of
system 314 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.
[0036] The use of waveguide 306 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.
[0037] 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.
[0038] 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.
[0039] FIG. 5 is an exemplary cross-sectional view of a sensor
element 400 to illustrate changes in the propagation of ultrasound
waves 414 with changes in the length of a waveguide 406. In
general, 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 408 compresses waveguide 406 thereby
changing the length of waveguide 406. Sensing circuitry (not shown)
measures propagation characteristics of ultrasonic signals in the
waveguide 406 to determine the change in the length of the
waveguide 406. 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.
[0040] As illustrated, external force 408 compresses waveguide 406
and pushes the transducers 402 and 404 closer to one another by a
distance 410. This changes the length of waveguide 406 by distance
412 of the waveguide propagation path between transducers 402 and
404. Depending on the operating mode, the sensing circuitry
measures the change in length of the waveguide 406 by analyzing
characteristics of the propagation of ultrasound waves within the
waveguide.
[0041] One interpretation of FIG. 5 illustrates waves emitting from
transducer 402 at one end of waveguide 406 and propagating to
transducer 404 at the other end of the waveguide 406. The
interpretation includes the effect of movement of waveguide 406 and
thus the velocity of waves propagating within waveguide 406
(without changing shape or width of individual waves) and therefore
the transit time between transducers 402 and 404 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.
[0042] 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.
[0043] 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.
[0044] FIG. 6 is an exemplary block diagram 500 of a positive
feedback closed-loop measurement system in accordance with one
embodiment. The measurement system comprises components of the
sensing module 101 shown in FIG. 2. The measurement system includes
a sensing assemblage 502 and a pulsed system 504 that detects
energy waves 506 in one or more waveguides 5 of the sensing
assembly 502. A pulse 520 is generated in response to the detection
of energy waves 506 to initiate a propagation of a new pulse in
waveguide 5.
[0045] The sensing assembly 502 comprises transducer 4, transducer
30, and a waveguide 5 (or energy propagating structure). In a
non-limiting example, sensing assemblage 502 is affixed to load
bearing or contacting surfaces 508. External forces applied to the
contacting surfaces 508 compress the waveguide 5 and change the
length of the waveguide 5. The transducers 4 and 30 will also be
moved closer together. The change in distance affects the transmit
time 510 of energy waves 506 transmitted and received between
transducers 4 and 30. The pulsed system 504 in response to these
physical changes will detect each energy wave sooner (e.g. shorter
transit time) and initiate the propagation of new pulses associated
with the shorter transit time. As will be explained below, this is
accomplished by way of pulse system 504 in conjunction with the
pulse circuit 512, the mode control 514, and the edge detect
circuit 516.
[0046] Notably, changes in the waveguide 5 (energy propagating
structure or structures) alter the propagation properties of the
medium of propagation (e.g. transmit time 510). A pulsed 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 pulse
is provided to transducer 4 coupled to a first surface of waveguide
5. Transducer 4 generates a pulsed energy wave 506 coupled into
waveguide 5. In a non-limiting example, transducer 4 is a
piezo-electric device capable of transmitting and receiving
acoustic signals in the ultrasonic frequency range.
[0047] Transducer 30 is coupled to a second surface of waveguide 5
to receive the propagated pulsed signal and generates a
corresponding electrical signal. The electrical signal output by
transducer 30 is coupled to edge detect circuit 516. In at least
one exemplary embodiment, edge detect circuit 516 detects a leading
edge of the electrical signal output by transducer 30 (e.g. the
propagated energy wave 506 through waveguide 5). The detection of
the propagated pulsed signal occurs earlier (due to the
length/distance reduction of waveguide 5) than a signal prior to
external forces 508 being applied to sensing assemblage 502. Pulse
circuit 512 generates a new pulse in response to detection of the
propagated pulsed signal by edge detect circuit 516. The new pulse
is provided to transducer 4 to initiate a new pulsed sequence.
Thus, each pulsed sequence is an individual event of pulse
propagation, pulse detection and subsequent pulse generation that
initiates the next pulse sequence.
[0048] The transit time 510 of the propagated pulse corresponds to
the time from the detection of one propagated pulse to the next
propagated pulse. There is delay associated with each circuit
described above. Typically, the total delay of the circuitry is
significantly less than the propagation time of a pulsed signal
through waveguide 5. Also, 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 508 occur relatively slowly in relation to the pulsed signal
propagation time such as in a physiologic or mechanical system. The
digital counter 518 in conjunction with electronic components
counts the number of propagated pulses to determine a corresponding
change in the length of the waveguide 5. 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.
[0049] In at least one exemplary embodiment, pulsed system 504 in
conjunction with one or more sensing assemblages 502 are used to
take measurements on a muscular-skeletal system. In a non-limiting
example, sensing assemblage 502 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. The measurements can be made in extension
and in flexion. Assemblage 502 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 502 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.
[0050] One method of operation holds the number of pulsed energy
waves propagating through waveguide 5 as a constant integer number.
A time period of a pulsed energy wave corresponds to the time
between the leading pulse edges of adjacent pulsed energy waves. A
stable time period is one in which the time period changes very
little over a number of pulsed energy waves. This occurs when
conditions that affect sensing assemblage 502 stay consistent or
constant. Holding the number of pulsed energy waves propagating
through waveguide 5 to an integer number is a constraint that
forces a change in the time between pulses when the length of
waveguide 5 changes. The resulting change in time period of each
pulsed energy wave corresponds to a change in aggregate pulse
periods that is captured using digital counter 518 as a measurement
of changes in external forces or conditions 508.
[0051] A further method of operation according to one embodiment is
described hereinbelow for pulsed energy wave 506 propagating from
transducer 4 and received by transducer 30. In at least one
exemplary embodiment, pulsed energy wave 506 is an ultrasonic
energy wave. Transducers 4 and 30 are piezo-electric resonator
transducers. Although not described, wave propagation can occur in
the opposite direction being initiated by transducer 30 and
received by transducer 4. Furthermore, detecting ultrasound
resonator transducer 30 can be a separate ultrasound resonator as
shown or transducer 4 can be used solely depending on the selected
mode of propagation (e.g. reflective sensing). Changes in external
forces or conditions 508 affect the propagation characteristics of
waveguide 5 and alter transit time 510. As mentioned previously,
pulsed system 504 holds constant an integer number of pulsed energy
waves 506 propagating through waveguide 5 (e.g. an integer number
of pulsed energy wave time periods) thereby controlling the
repetition rate. As noted above, once pulsed system 504 stabilizes,
the digital counter 518 digitizes the repetition rate of pulsed
energy waves, for example, by way of edge-detection, as will be
explained hereinbelow in more detail.
[0052] In an alternate embodiment, the repetition rate of pulsed
energy waves 506 emitted by transducer 4 can be controlled by pulse
circuit 512. The operation remains similar where the parameter to
be measured corresponds to the measurement of the transit time 510
of pulsed energy waves 506 within waveguide 5. It should be noted
that an individual ultrasonic pulse can comprise one or more energy
waves with a damping wave shape as shown. The pulsed energy wave
shape is determined by the electrical and mechanical parameters of
pulse circuit 512, interface material or materials, where required,
and ultrasound resonator or transducer 4. 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 520. The mode of the propagation of the pulsed
energy waves 506 through waveguide 5 is controlled by mode control
circuitry 514 (e.g., reflectance or uni-directional). The detecting
ultrasound resonator or transducer may either be a separate
ultrasound resonator or transducer 30 or the emitting resonator or
transducer 4 depending on the selected mode of propagation
(reflectance or unidirectional).
[0053] 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 pulses within
a waveguide of known length can be achieved by modulating the
repetition rate of the ultrasound pulses 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.
[0054] 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.
[0055] Measurement by pulsed system 504 and sensing assemblage 502
enables high sensitivity and signal-to-noise ratio as 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.
[0056] FIG. 7 is a measurement system operating in pulsed mode with
digital output according to one embodiment. In particular, with
respect to FIG. 6, it illustrates positive feedback closed-loop
measurement of the transit time 510 of pulsed energy waves 506
within the waveguide 5 by the operation of pulsed system 504. A
pulsed mode is one of the modes of operation of the system. In
pulsed mode, a pulsed energy wave is provided by emitting
transducer 4, propagated through waveguide 5 (e.g. propagating
structure). Briefly, the digital logic circuit 675 digitizes the
frequency of operation of the pulsed system 504.
[0057] Referring to FIG. 2, in pulse mode of operation, the sensing
module 101 measures a time of flight (TOF) between when a pulsed
energy wave is transmitted by transducer 4 and received at
transducer 30. The time of flight determines the length of the
waveguide propagating path, and accordingly indicates the change in
length of the waveguide 5. In another arrangement, differential
time of flight measurements can be used to determine the change in
length of the waveguide 5. A pulse can comprise one or more waves.
The waves may have equal amplitude and frequency (square wave
pulse) or they may have different amplitudes, for example, damped
or decaying amplitude (trapezoidal pulse) or some other complex
waveform. The pulsed system detects an edge of each pulse
propagating through the waveguide and holds the delay between the
leading edge of each pulse constant under stable operating
conditions.
[0058] A pulse method facilitates separation of ultrasound
frequency, damping waveform shape, and repetition rate of pulses of
ultrasound waves. Separating ultrasound frequency, damping waveform
shape, and repetition rate enables operation of ultrasound
transducers at or near resonance to achieve higher levels of
conversion efficiency and power output thus achieving efficient
conversion of ultrasound energy. Likewise, separating frequency and
repetition rate enables control of damping factors within pulses of
ultrasound waves by selecting frequencies at some distance from the
resonance points of the ultrasound transducers. This may enable,
but is not limited to, lower power operation for ultra-low power
devices.
[0059] In a non-limiting example, a pulse mode operation is
initiated with control circuitry 606 closing switch 604, which
couples an output of pulse circuit 608 to an input of amplifier
612. Pulse circuit 608 initializes the circuit by sending one or
more pulses to amplifier 612. Amplifier 612 provides analog pulses
614 to an input of transducer 4. Amplifier 612 having digital
driver 642 and matching network 644 transforms the digital output
(e.g. square wave) of pulse circuit 610 into shaped or analog
pulses 614 that are modified for emitting transducer 4. The
repetition rate of pulses 614 is equal to the pulse rate at output
610 of pulse circuit 612. Amplifier 612 drives transducer 4 with
sufficient power to generate energy waves 616. In at least one
exemplary embodiment, transducer 4 converts the pulsed electrical
waves into pulsed energy waves 616 having the same repetition rate
and emits them into energy propagating structure or waveguide 5. In
a non-limiting example, energy waves 616 are ultrasound waves.
[0060] In general, ultrasound transducers naturally resonate at a
predetermined frequency. Providing a square wave to the input of
emitting transducer 4 could yield undesirable results. Digital
driver 642 of amplifier 612 drives matching network 644. Matching
network 644 is optimized to match an input impedance of emitting
transducer 4 for efficient power transfer. In at least one
exemplary embodiment, digital driver 642, matching network 644,
solely, or in combination shapes or filters pulses provided to the
input of amplifier 612. The waveform is modified from a square wave
to analog pulse 614 to minimize ringing and to aid in the
generation of a damped waveform by emitting transducer 4. In one
embodiment, the pulsed energy wave emitted into waveguide 5 can
ring with a damped envelope that affects signal detection which
will be disclosed in more detail below.
[0061] The one or more pulsed energy waves 616 propagate through
energy propagating structure or medium 5 and are detected by
detecting transducer 30. Detecting transducer 30 converts the
pulsed energy waves 616 into pulses 618 of electrical waves having
the same repetition rate. The signal output of detecting transducer
30 may need amplification. Amplifier 620 comprises pre-amplifier
622 and edge-detect receiver 624. Pre-amplifier 622 receives and
amplifies analog pulses 618 from transducer 30. Edge-detect
receiver 624 detects an edge of each arriving pulse corresponding
to each propagated pulsed energy wave 616 through waveguide 5. As
mentioned previously, each pulsed energy wave can be a ringing
damped waveform. In at least one exemplary embodiment, edge-detect
receiver 624 detects a leading edge of each arriving pulse 618.
Edge-detect receiver 624 can have a threshold such that signals
below the threshold cannot be detected. Edge-detect receiver 624
can include a sample and hold that prevents triggering on
subsequent edges of a ringing damped signal. The sample and hold
can be designed to "hold" for a period of time where the damped
signal will fall below the threshold but less than the shortest
edge to edge time period between adjacent pulses under all
operating conditions. Amplifier 620 generates a digital pulse 626
triggered off of each leading edge of each propagated pulsed energy
wave 616 detected by transducer 30. Each digital pulse 626 is of
sufficient length to sustain the pulse behavior of the closed loop
circuit as it is coupled back to amplifier 612 through switch
628.
[0062] Control circuitry 606 responds to the initial digital output
pulses 626 from amplifier 620 by closing switch 628 and opening
switch 604. Closing switch 628 creates a positive feedback closed
loop circuit coupling a pulse generated by amplifier 620 to the
input of amplifier 612 and sustaining a sequence of pulsed energy
wave emission into wave guide 5, propagation of the pulsed energy
wave 616 through waveguide 5, detection of the pulsed energy wave
after traveling through waveguide 5, and generation of the next
digital pulse.
[0063] In one embodiment, the delay of amplifier 620 and 612 is
small in comparison to the propagation time of a pulsed energy wave
through waveguide 5. In an equilibrium state, an integer number of
pulses of energy waves 616 in waveguide 5 have equal time periods
and transit times when propagating through energy propagating
structure waveguide 5. For example, three pulsed energy waves
propagate through waveguide 5. As one energy pulse wave exists
waveguide 5, a new energy pulse wave is emitted into waveguide 5 as
electronic circuitry comprised of amplifier 620 and 612, having
little or no delay, maintain equilibrium. Movement or changes in
the physical properties of the energy propagating structure or
waveguide 5 change the transit time 630 of energy waves 616. This
disrupts the equilibrium thereby changing when a pulsed energy wave
is detected by edge-detect receiver 624. A transit time is reduced
should external forces 632 compress waveguide 5 in the direction of
propagation of energy waves 616. Conversely, the transit time is
increased should external forces 632 result in waveguide 5
expanding in length. The change in transit time delivers digital
pulses 626 earlier or later than previous pulses thereby producing
an adjustment to the delivery of analog pulses 618 and 614 to a new
equilibrium point. The new equilibrium point will correspond to a
different transit time, e.g. different repetition rate with the
same integer number of pulses.
[0064] As previously disclosed, the repetition rate of energy waves
616 during operation of the closed loop circuit, and changes in
this repetition rate, can be used to measure changes in the
movement or changes in the physical attributes of energy
propagating structure or medium 5. The changes can be imposed on
the energy propagating structure or medium 5 by external forces or
conditions 632 thus translating the levels and changes of the
parameter or parameters of interest into signals that may be
digitized for subsequent processing, storage, and display. Thus,
the repetition rate of pulses of energy waves 616 during the
operation of the closed loop circuit, and changes in this
repetition rate, can be used to measure movement or changes in
physical attributes of energy propagating structure or medium
5.
[0065] The changes in physical attributes of energy propagating
structure or medium 5 by external forces or conditions 632
translates the levels and translates the parameter or parameters of
interest into a time period difference of adjacent pulses or a
difference accumulated or averaged over multiple time periods. The
time period of transit time 630 corresponds to a frequency for the
time period measured. The time period can be digitized for
subsequent transmission, processing, storage, and display.
Translation of the time period into digital binary numbers
facilitates communication, additional processing, storage, and
display of information about the level and changes in physical
parameters of interest. Prior to measurement of the frequency of
operation of the pulse sequence generation circuitry, control logic
606 loads the loop count into digital counter 638 that is stored in
digital register 640.
[0066] Digital logic circuit 675 is described in more detail
hereinbelow. As previously mentioned, a first pulse from digital
pulses 610 initiates a parameter measurement or sensing of
waveguide 5. In at least one exemplary embodiment, sensing does not
occur until initial equilibrium has been established. Control
circuit 606 detects digital pulses 626 from amplifier 620 (closing
switch 628 and opening switch 604) to establish equilibrium and
start measurement operations. In an extended configuration of
pulse-loop mode, a digital block is coupled to the pulsed-loop mode
measurement system for digitizing the frequency of operation.
Translation of the time period of pulsed energy waves into digital
binary numbers facilitates communication, additional processing,
storage, and display of information about the level and changes in
physical parameters of interest. During this process, control
circuit 606 enables digital counter 638 and digital timer 634.
Digital counter 638 decrements its value on the rising edge of each
digital pulse 626 output by amplifier 620. Digital timer 634
increments its value on each rising edge of pulses from clock
output 610. A clock such as a crystal oscillator is used to clock
digital logic circuit 675 and as a reference in which to gauge time
periods of pulsed energy waves. Alternatively, pulse circuit 608
can be a reference clock. When the number of digital pulses 626 has
decremented the value within digital counter 638 to zero a stop
signal is output from digital counter 638. The stop signal disables
digital timer 634 and triggers control logic 606 to output a load
command to data register 636. Data register 636 loads a binary
number from digital timer 634 that is equal to the period of the
energy waves or pulses times the value originally loaded into
counter 638 divided by a clock period corresponding to oscillator
output 610. With a constant clock period, the value in data
register 636 is directly proportional to the aggregate period of
the pulsed energy waves or pulses accumulated during the
measurement operation. Duration of the measurement operation and
the resolution of measurements may be adjusted by increasing or
decreasing the value preset in the count register 640.
[0067] This method of operation further enables setting the level
of precision or resolution of the captured data by using long cycle
counts to optimize trade-offs between measurement resolution versus
pulse repetition rate, ultrasound frequency, and damping waveform
shape, as well as the bandwidth of the sensing and the speed of the
data processing operations to achieve an optimal operating point
for a sensing module or device that matches the operating
conditions of the system containing, or subject to, the parameter
or parameters of interest.
[0068] In at least one exemplary embodiment, the sensor system
includes the system as a wireless module that operates according to
one or more criteria such as, but not limited to, power level,
applied force level, standby mode, application context,
temperature, or other parameter level. Pulse shaping can also be
applied to increase reception quality depending on the operational
criteria. The wireless sensing module comprises the pulsed
measurement system, one or more sensing assemblies, one or more
load surfaces, an accelerometer, electronic circuitry, a
transceiver, and an energy supply. The wireless sensing module
measures a parameter such as force/pressure and transmits the
measurement data to a secondary system for further processing and
display. The electronic circuitry in conjunction with the sensing
assemblies accurately measures physical displacements of the load
surfaces on the order of a few microns or less along various
physical dimensions. The sensing assembly physically changes in
response to an applied force, such as an applied load. Electronic
circuitry operating in a positive feedback closed-loop circuit
configuration precisely measures changes in propagation time due to
changes in the length of the waveguides; physical length changes
which occur in direct proportion to the applied force.
[0069] In a non-limiting example, an ultrasound signal is used in
the measurement system. For illustration purposes the measurement
system measures a load, pressure, or force. The system has two
surfaces to which the measured parameter (e.g. load, pressure,
force) can be applied. In one embodiment, one of the surfaces is in
a fixed position and the measured parameter is applied to the
remaining surface. Alternatively, the measured parameter can be
applied across both surfaces. In one embodiment, the system will
measure within a range of 3-60 pounds.
[0070] The sensing element comprises two piezoelectric transducers
and a medium. One or more sensing elements can be used. The sensing
element is placed between the surfaces of the measurement system.
In one embodiment, the waveguide comprises a polymer such as
urethane or polyethylene. In a non-limiting example, the polymer
can be stretched or compressed when subjected to the parameter
under measurement and has little or no hysteresis in the system. In
general, the waveguide efficiently contains and directs an
ultrasonic pulsed energy wave such that a measurement of either the
transit time of the pulsed energy wave to propagate through the
waveguide or time period of the pulsed energy wave can be taken.
The waveguide can be cylindrically shaped having a first end and a
second end of the cylinder. The piezoelectric transducers are
attached at the first and second ends of the waveguide to emit and
receive ultrasonic pulsed energy waves. The transducers are
attached to be acoustically coupled the waveguide and can have an
intermediate material layer to aid in improving the transfer of the
ultrasonic pulsed energy wave.
[0071] In the non-limiting example, the waveguide in a relaxed
state is a cylinder or column 47 millimeters long which can
accommodate one or more ultrasonic pulsed energy waves. The length
of the waveguide corresponds to the thickness of the sensor and is
thus an indication that a very small form factor sensor can be
built using this methodology. In one embodiment, the waveguide is
placed in a compressed state in the sensor module. In the
non-limiting example, the waveguide is subjected to a force or
pressure that changes the dimensions of the cylinder. More
specifically, an applied force or pressure on the surfaces of the
system modifies the length of the waveguide. In one embodiment, the
waveguide is compressed from the 47 millimeter relaxed state to a
thickness of approximately 39 millimeters. The 39 millimeter
compressed state corresponds to the state where no load is applied
to the surfaces of the sensor module.
[0072] In the non-limiting example, the emitting piezoelectric
transducer has a different resonant frequency than the receiving
piezoelectric transducer. The emitting piezoelectric transducer has
a resonance frequency of approximately 8 megahertz. It has a
diameter of approximately 3.3 millimeters and is approximately 0.23
millimeters thick. The receiving piezoelectric transducer has a
resonance frequency of approximately 10-13 megahertz. It has a
diameter of 4 millimeters and is approximately 0.17 millimeters. In
one embodiment, the waveguide has a diameter greater than or equal
to the diameter of the largest piezoelectric transducer. In the
example, the waveguide would have a diameter greater than or equal
to 4 millimeters.
[0073] The sensing module can very accurately measure transit time
or a time period of the pulsed energy wave as disclosed
hereinabove. In at least one exemplary embodiment, a single pulsed
energy wave can be used to take a measurement thereby minimizing
energy usage. Alternatively, more than one measurement can be taken
sequentially, periodically, or randomly depending on the
application requirements. The measured transit time or time period
corresponds to the length of the medium or waveguide. The transit
time or time period is correlated to a force or pressure required
to compress the waveguide by the measured amount. Preliminary
measurements indicate that the sensing module can detect changes in
the length of the waveguide on the order of submicrons. Thus, the
sensing module can measure the force or changes in force with high
precision.
[0074] Upon reviewing the aforementioned embodiments, it would be
evident to an artisan with ordinary skill in the art that said
embodiments can be modified, reduced, or enhanced without departing
from the scope and spirit of the claims described below. As an
example:
[0075] Changing repetition rate or wave composition of complex
waveforms to measure time delays.
[0076] Changing repetition rate of acoustical, sonic, or light,
ultraviolet, infrared, RF or other electromagnetic waves, pulses,
or echoes of pulses to measure changes in the parameter or
parameters of interest.
[0077] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
* * * * *