U.S. patent application number 12/826109 was filed with the patent office on 2010-12-30 for transducer driver for measuring a parameter of the muscularskeletal system.
This patent application is currently assigned to OrthoSensor. Invention is credited to Andrew Kelly, Marc Stein.
Application Number | 20100331685 12/826109 |
Document ID | / |
Family ID | 43379281 |
Filed Date | 2010-12-30 |
United States Patent
Application |
20100331685 |
Kind Code |
A1 |
Stein; Marc ; et
al. |
December 30, 2010 |
TRANSDUCER DRIVER FOR MEASURING A PARAMETER OF THE MUSCULARSKELETAL
SYSTEM
Abstract
A measurement system for capturing a transit time, phase, or
frequency of energy waves propagating through a propagation medium
is disclosed. The measurement system comprises two different
closed-loop feedback paths. The first path includes a transducer
driver (726), a transducer (704), a propagation structure (702), a
transducer (706), and a zero-crossing receiver (740). The
transducer driver (726) efficiently drives the transducer (704) and
comprises a digital driver (106), a level shifter (112), and a
matching network (114). A second path includes a transducer driver
(1126), a transducer (1104), a propagation medium (1102), a
reflecting surface (1106), and an edge-detect receiver (1140).
Energy waves in the propagating medium (1102) are reflected at
least once. The edge-detect receiver (1140) detects a wave front of
an energy wave. Each positive closed-loop path maintains the
emission, propagation, and detection of energy waves in the
propagation medium.
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.: |
12/826109 |
Filed: |
June 29, 2010 |
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Application
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Filing Date |
Patent Number |
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61221916 |
Jun 30, 2009 |
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61221761 |
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Current U.S.
Class: |
600/438 |
Current CPC
Class: |
A61B 8/15 20130101; A61B
5/6878 20130101; A61B 5/7239 20130101; A61B 5/6846 20130101; A61B
5/4528 20130101; A61B 5/4509 20130101 |
Class at
Publication: |
600/438 |
International
Class: |
A61B 8/00 20060101
A61B008/00 |
Claims
1. A transducer driver circuit in a positive closed-loop path that
generates time and frequency specific energy waves and pulses to
measure a parameter of the muscular-skeletal system.
2. The driver circuit of claim 1 further comprising a level shifter
to raise or lower voltage levels of output pulses to voltage levels
required to efficiently drive an energy emitting resonator or
transducer given the characteristics of the resonator or
transducer.
3. The driver circuit of claim 2 further comprising an impedance
matching network to translate a digital output pulse into a
required wave shape for efficiently and compactly driving the
transducer.
4. The driver circuit of claim 3 further comprising control logic
to generate drive signals according to the transducer
characteristics and operational modes to achieve highly accurate
control, timing, and duration of the generated energy waves and
pulses.
5. The driver circuit of claim 4 where the driver circuit drives
more than one transducer.
6. The driver circuit of claim 4 where the impedance matching
network comprises a pi network.
7. The driver circuit of claim 4 where the driver circuit controls
a duration of stimulation of the transducer.
8. The driver circuit of claim 4 further including a sensor in the
positive closed-loop comprising: a first transducer; a propagation
medium where the first transducer is coupled to the propagation
medium at a first location; and a second transducer coupled to the
propagation medium at a second location where the propagation
medium is affected by the parameter of the muscular-skeletal system
being measured and where there is a known relationship between the
parameter being measured and one of transit time, phase, and
frequency of energy waves propagating through the medium.
9. The driver circuit of claim 4 further including a sensor in the
positive closed-loop comprising: a transducer; a propagation medium
where the transducer is coupled to the propagation medium at a
first location; and a reflecting surface coupled to the propagation
medium at a second location where the propagation medium is
affected by the parameter of the muscular-skeletal system being
measured and where there is a known relationship between the
parameter being measured and one of transit time, phase, and
frequency of energy waves propagating through the medium.
10. The driver circuit of claim 1 where the transducer driver
circuit maintains positive closed loop feedback operating in at
least one of continuous wave mode, pulse-loop mode, and pulse
echo-mode.
11. A sensor comprising: a first transducer; a propagation medium
where the first transducer is coupled to the propagation medium at
a first location; and a second transducer coupled to the
propagation medium at a second location where the series and
parallel resonance of the first transducer does not overlap the
series and parallel resonance of the second transducer.
12. The sensor of claim 11 where the series and parallel resonance
of the first transducer is less than the series and parallel
resonance of the second transducer.
13. The sensor of claim 11 where the series and parallel resonance
of the first transducer is greater than the series and parallel
resonance of the second transducer.
14. The sensor of claim 11 where the propagation medium is a
compressible waveguide to contain, propagate, and direct energy
waves.
15. The sensor of claim 11 where the first transducer emits
ultrasonic energy waves into the propagation medium at the first
location.
16. A sensor system comprising: a transducer driver coupled in
positive closed-loop feedback comprising: a digital driver having
an input and an output; a level shifter having an input coupled to
the input of the digital driver and an output; and a matching
network having an input coupled to an output of the level shifter
and an output.
17. The sensor system of claim 16 further including: a sensor in
the positive closed-loop feedback comprising; a transducer having a
terminal coupled to the output of the matching network; and a
compressible propagation medium where the transducer couples to the
medium at a first location and where the transducer is enabled to
emit ultrasonic energy waves into the propagation medium.
18. The sensor system of claim 17 further including a reflecting
surface at a second location of the propagation medium.
19. The sensor system of claim 17 further including a second
transducer coupled to a second location of the propagation medium
where the second transducer includes a terminal coupled to the
input of the digital driver.
20. The sensor system of claim 17 further including: a control
logic circuit having an input and an output coupled to the input of
the digital driver; and an amplifier having an input coupled to the
output of the level shifter and an output coupled to the input of
the matching network where the sensor system measures one of
transit time, phase, and frequency of the ultrasonic energy waves
propagating through the propagation medium.
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 hereby incorporated herein by reference in
their entirety.
FIELD
[0002] The present invention pertains generally to measurement of
physical parameters, and particularly to, but not exclusively, to
control and driver circuitry for generating energy waves or
pulses.
BACKGROUND
[0003] Sensors are used to provide information to a device or
system. The sensor information can be critical to device operation
or provide additional data on the system or an external
environment. For example, a temperature sensor is commonly used to
monitor the operating temperature of components. The temperature
sensor can be used to monitor average operating temperatures and
instantaneous operating extremes. Sensor data can be used to
understand how device functions or performs in different working
environments, users, and environmental factors. Sensors can trigger
an action such as turning off the system or modifying operation of
the system in response to a measured parameter.
[0004] In general, cost typically increases with the measurement
precision of the sensor. Cost can limit the use of highly accurate
sensors in price sensitive applications. Furthermore, there is
substantial need for low power sensing that can be used in systems
that are battery operated. Ideally, the sensing technology used in
low-power applications will not greatly affect battery life.
Moreover, a high percentage of battery-operated devices are
portable devices comprising a small volume and low weight. Device
portability can place further size and weight constraints on the
sensor technology used. Thus, form factor, power dissipation, cost,
and measurement accuracy are important criteria that are evaluated
when selecting a sensor for a specific application.
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 a block diagram of a transducer driver in
accordance with one embodiment;
[0007] FIG. 2 is a block diagram of the integrated transducer
driver coupled to drive a transducer of a sensing assembly in
accordance with one embodiment;
[0008] FIG. 3 is an exemplary propagation tuned oscillator (PTO)
incorporating the integrated transducer driver to maintain positive
closed-loop feedback in accordance with one embodiment;
[0009] FIG. 4 is a set of graphs of frequency characteristics of a
transducer driven by the integrated transducer driver for
non-optimized and optimized configurations in accordance with one
embodiment;
[0010] FIG. 5 is an illustration of a plot of non-overlapping
resonant frequencies of paired transducers in accordance with an
exemplary embodiment;
[0011] FIG. 6 is a sensor interface diagram incorporating the
transducer driver in a continuous wave multiplexing arrangement for
maintaining positive closed-loop feedback in accordance with one
embodiment;
[0012] FIG. 7 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver for operation
in continuous wave mode;
[0013] FIG. 8 is a sensor interface diagram incorporating the
transducer driver in a pulse multiplexing arrangement for
maintaining positive closed-loop feedback in accordance with one
embodiment;
[0014] FIG. 9 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver for operation
in pulse mode in accordance with one embodiment;
[0015] FIG. 10 is a sensor interface diagram incorporating the
transducer driver in a pulse-echo multiplexing arrangement for
maintaining positive closed-loop feedback in accordance with one
embodiment;
[0016] FIG. 11 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver for operation
in pulse echo mode;
[0017] FIG. 12 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.
DETAILED DESCRIPTION
[0018] Embodiments of the invention are broadly directed to
measurement of physical parameters, and more particularly, to
control and driver circuitry for generating energy waves or
pulses.
[0019] 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.
[0020] 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.
[0021] 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).
[0022] 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.
[0023] FIG. 1 illustrates a low power consumption integrated
transducer driver circuit 100 in accordance with an exemplary
embodiment. In a first embodiment, driver circuit 100 efficiently
drives a transducer to generate time and frequency specific energy
waves and pulses. It includes digital logic to generate drive
signals according to the transducer characteristics and operational
modes to achieve highly accurate control, timing, and duration of
the generated energy waves and pulses. In one arrangement, the
output driver is coupled to an ultrasonic sensing assembly to
efficiently generate continuous ultrasonic waves or ultrasonic
pulses that propagate through a propagation medium. The driver
circuit includes a level shifter 112 to raise or lower voltage
levels of output pulses to voltage levels required to efficiently
drive an energy emitting resonator or transducer given the
characteristics of the resonator or transducer, the frequency and
duration of the output waves, and the shape of the output pulse. It
includes an impedance matching network 114 to translate the digital
output pulse into a required wave shape for efficiently and
compactly driving the transducer. This configuration provides the
benefit for battery or temporarily powered sensing systems to drive
the energy emitting resonators or transducers with much less power
consumption than a Digital to Analog Converter (DAC) based
design.
[0024] In a second embodiment, the driver circuit 100 is
incorporated within a propagation tuned oscillator (PTO) to
maintain positive closed-loop feedback. The PTO can operate in
continuous wave mode, pulse-loop mode, pulse-echo mode, or
controlled combination thereof. The driver circuit 100 is
electrically integrated with the PTO by multiplexing input and
output circuitry, including off-board components of an impedance
matching network, to achieve ultra low-power and small compact
size. In this arrangement, off-board energy emitting resonators or
transducers are operated at optimum frequencies and drive voltages
and currents to achieve optimal performance at a minimum level of
power consumption. The drive circuit 100 can singly drive multiple
energy emitting resonators or transducers to achieve this level of
performance; that is, only one driver circuit can be shared.
Appropriate duty cycles and multiplexing timing for optimum
frequencies of the energy emitting resonators or transducers are
selected to conserve both power and space without compromising
performance. This enables, but is not limited to, the design and
construction of compact measurement modules or devices with
thickness on the order of a few millimeters.
[0025] In one embodiment, low power consumption transducer driver
circuit 100 comprises control logic 108, a digital driver 106,
level shifter 112, an amplifier 116, and matching network 114. The
driver circuit 100 can be implemented in discrete analog
components, digital components, an application integrated circuit,
or a combination thereof. In a low power application, transducer
driver circuit 100 is integrated with other circuitry of the
propagation tuned oscillator. Briefly, the transducer driver
circuit 100 accurately controls emissions of energy waves or
pulses, and parameters thereof, including, but not limited to,
transit time, phase, or frequency of the energy waves or pulses. A
brief description of the method of operation is as follows.
[0026] An input 102 receives a signal to emit an energy wave. Input
102 couples to control logic 108. Control logic 108 controls the
timing and frequency of stimulation of an energy transducer 110. A
digital pulse 104 from digital control logic 108 is provided to an
input of driver 106. In an energy pulse mode, digital control logic
108 also controls the duration of the stimulation. One or more
pulses from an output 118 of driver 106 is coupled to level
shifting circuitry 112. Level shifting circuitry 112 adjusts the
output voltage of driver 106 to efficiently drive energy transducer
110. One or more level shifted pulses are provided at an output 120
of level shifter 112 to amplifier 116. Amplifier 116 amplifies the
signal at output 120 which is provided to an input of matching
network 114. Matching network 114 matches the electrical
characteristics of the energy transducer 110. Output signal 122
from the matching network 114 drive energy transducer 110. Matching
network 114 converts the output pulse from amplifier 116 to the
required wave shape, frequency and phase. Energy waves 124 are
emitted by energy transducer 110 into the medium.
[0027] As discussed above, the electronic components are
operatively coupled together as blocks of integrated circuits. As
will be shown ahead, this integrated arrangement performs its
specific functions efficiently with a minimum number of components.
This is because the circuit components are partitioned between
structures within an integrated circuit and discrete components, as
well as innovative partitioning of analog and digital functions, to
achieve the required performance with a minimum number of
components and minimum power consumption.
[0028] Briefly, an input of digital driver 106 is driven by digital
control logic 108, which ultimately controls the timing and
frequency of the resulting output signal 122. As will be shown
ahead, the output signal 122 drives an energy transducer 110 to
output an energy wave or energy pulse. The drive circuit 100 is
optimally configured to generate the output signal 122 according to
the transducer characteristics (e.g., frequency, stiffness, Q,
ringing, inductance, ringing, decay, feedback) and in certain cases
the operating mode (e.g., continuous, pulse-loop, and pulse echo).
For example, in pulse-loop mode, digital control logic 108 also
controls the duration of the transducer 110 stimulation. Level
shifter 112 adjusts the output voltage of driver output 106 to
efficiently drive energy transducer 110. More specifically, the
level shifter 112 raises or lowers voltage levels of output pulses
to the voltages required to efficiently drive the energy emitting
resonator or transducer 110 given the characteristics of the
resonator or transducer 110, the frequency and duration of the
output waves, and the shape of the output pulse. Matching network
114 matches the electrical characteristics of the energy transducer
110 and converts the output pulse 122 to the required wave shape,
frequency and phase. The generated digital output waveform 122 or
pulse may have a moderately sharp leading edge.
[0029] With regard to the integrated transducer driver 100,
efficient use of power and conservation of charge is required for
ultra low power operation. Energy emitting resonators or
transducers 110 can be stimulated with a sine wave or other form of
continuous wave to efficiently emit energy waves of the required
frequency, phase, and duration. Partitioning circuit components
between structures within the integrated circuit and discrete
components enhances design flexibility and minimize power
consumption without compromising performance. Therefore, the driver
circuit 100 and matched network 114 together efficiently convert
the input pulse 104 to an energy wave 124 of the required
frequency, phase, and duration; which is, specific to operation of
transducer 110.
[0030] The output of the driver amplifier 116 is coupled with the
impedance matching network 114, such as, but not limited to, a pi
network. This pi network can include a discrete inductor or
inductors and a discrete capacitor or capacitors to translate the
digital output pulse into the required wave shape efficiently and
compactly. In one arrangement, the phase and time delay through the
pi network are constant. The pi network may also include resistance
as well as the discrete inductance and capacitance components. The
resistance element is primarily parasitic resistances within the
integrated components and interconnects and is included in the
analysis and design of the pi network to assure matching the
electrical drive requirements of the energy emitting device.
[0031] Driving the energy emitting transducer 110 through the
impedance matching network 114 achieves a waveform 122 that is
input to the energy emitting resonator or transducer 110. This
drives the energy emitting resonators or transducers 110
efficiently and with much less power consumption than a Digital to
Analog Converter (DAC) based design. The integration of miniature,
surface mountable, inductors and capacitors enables highly compact
driver circuit and minimizes the total number of electronic
components. In a hybrid approach, off-chip and return to on-chip,
may have size penalty but can be integrated to save power and
reduce design complexity.
[0032] FIG. 2 illustrates a block diagram of the transducer driver
circuit 100 coupled to a sensing assembly 200 in accordance with an
exemplary embodiment. The sensing assembly 200 comprises a
transmitter transducer 202, an energy propagating medium 204, and a
receiver transducer 206. Alternatively, the sensing assembly can
comprise a single transducer, a propagating medium, and a
reflecting surface. Energy waves or pulses are emitted by the
single transducer into the medium, propagate in the medium, are
reflected by the reflecting surface, and the reflected energy wave
received by the single transducer. This provides the benefit of
lower cost due to the use of the single transducer. As will be
explained ahead in further detail, the sensing assembly 200 in one
embodiment is part of a sensory device that assesses loading, in
particular, the externally applied forces 208 on the sensing
assembly 200. In one embodiment, forces 208 are applied in a
direction corresponding to energy wave propagation in the
propagating structure or medium 204 such that propagating structure
204 is changed dimensionally. The transducer driver circuit 100
drives the transmitter transducer 202 of the sensing assembly 200
to produce energy waves 210 that are directed into the energy
propagating medium 204. The time for an energy wave to propagate
from transducer 202 to transducer 206 is a transit time 214.
Changes in the energy propagating medium 204 due to the externally
applied forces 208 change the frequency, phase, and transit time of
energy waves 210. A controller (not shown), as will be explained
below, operatively coupled to the receiver transducer 206 monitors
an output signal 212 for these characteristic changes to assess
parameters of interest (e.g., force, direction, displacement, etc.)
related to the loading.
[0033] Measurement methods that rely on such propagation of energy
waves or pulses of energy waves are required to achieve highly
accurate and controlled emissions of energy waves or pulses.
Accordingly, the transducer driver 100, controlled in part by
control logic 108, is an efficient device for achieving highly
accurate control of timing and duration of the energy waves 210
(and pulses when in pulse mode or pulse echo mode). The transducer
driver 100 including matched network 122 translates the input
digital pulses 104 into analog waveforms 122 with the required
timing, duration, frequency, and phase to drive the transmitter
transducer 202 to generate the energy waves 210. These functions
are performed efficiently with a minimum of components due to
partitioning of circuit components between structures within the
integrated circuit and discrete components, as well as innovative
partitioning of analog and digital functions. This enables, but is
not limited to, the design and construction of compact measurement
modules or devices with thickness on the order of a few
millimeters. In addition to accurate control of the timing and
duration of energy waves or pulses, partitioning functions between
analog and digital circuitry enhances design flexibility and
facilitates minimizing total size and power consumption of the
circuitry driving energy emitting resonators or transducers 202
without sacrificing functionality or performance.
[0034] There are a wide range of applications for compact
measurement modules or devices having ultra low power circuitry
that enables the design and construction of highly performing
measurement modules or devices that can be tailored to fit a wide
range of nonmedical and medical applications. Applications for
highly compact measurement modules or devices 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 nonmedical 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.
[0035] FIG. 3 is an exemplary propagation tuned oscillator (PTO)
incorporating the transducer driver 100 to maintain positive
closed-loop feedback in accordance with one embodiment. The PTO is
provided to maintain positive closed-loop feedback of energy waves
in the energy propagating structures of the sensing assembly 200. A
positive feedback closed-loop circuit causes the oscillator to tune
the resonant frequency of the energy waves in accordance with
physical changes in the one or more energy propagating structures;
hence the term, propagation tuned oscillator. The physical changes
occur from compression or length changes resulting from externally
applied forces or pressure. The physical changes in the energy
propagating structures change in direct proportion to the external
applied forces and can be precisely evaluated to measure the
applied forces.
[0036] The sensing assembly 302 comprises a first transducer 304, a
second transducer 308, and a waveguide 306 (energy propagating
structure). In one embodiment, waveguide 306 is a compressible
medium that contains, directs, and propagates energy waves coupled
thereto. The sensing assembly 302 is affixed to load bearing or
contacting surfaces 310. External forces applied to the contacting
surfaces 310 compress the waveguide 306 and change the length of
the waveguide 306. This also results in the transducers 304 and 308
being moved a similar distance closer together. This change in
distance affects the transmit time 322 of energy waves 324
transmitted and received between transducers 304 and 308. The PTO 4
in response to these physical changes alters the oscillation
frequency of the ultrasound waves 2 to achieve resonance. This is
accomplished by way of the PTO 312 in conjunction with the
transducer driver 100, the mode control 316 (e.g., continuous,
pulse-loop, and pulse-echo), and sensor interface 318.
[0037] Notably, changes in the waveguide 306 (energy propagating
structure or structures) alter the propagation properties of the
medium of propagation (e.g. transmit time 322). Due to the
closed-loop operation shown, the PTO 312 changes the resonant
frequency of the oscillator and accordingly the frequency of
oscillation of the closed loop circuit. In particular, the PTO 312
adjusts the oscillation frequency to be an integer number of waves.
The digital counter 314 in conjunction with electronic components
counts the number of waves to determine the corresponding change in
the length of the waveguide 306. 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.
[0038] The operation of the sensing system is described in more
detail hereafter. The frequency of ultrasound waves 324 emitted by
ultrasound resonator or transducer 304 is controlled by propagation
tuned oscillator 312. The detecting ultrasound resonator or
transducer 308 can be either a separate ultrasound resonator or
transducer or the emitting resonator or transducer 304 itself
depending on the selected mode of propagation. In the example where
a single transducer is used, a reflecting surface reflects a
propagated energy wave in waveguide 306 back to transducer 304
where it is detected by transducer 304 in a receiving mode. In
either sensor example, propagation tuned oscillator enable the
measurement of the transit time, frequency, or phase of energy
waves through the medium.
[0039] The transit time 322 of ultrasound waves 324 through the
waveguide determines the period of oscillation of propagation tuned
oscillator 312. A change in external forces or conditions upon
surfaces 310 affect the propagation characteristics of waveguide
306 and alter transit time 322. In one embodiment, the number of
wavelengths of ultrasound waves 324 is held constant by propagation
tuned oscillator 312. The constraint of having an integer number of
wavelengths forces the frequency of oscillation of propagation
tuned oscillator 312 to change. The resulting changes in frequency
are captured with digital counter 314 as a measurement of changes
in external forces or conditions applied to surfaces 310.
[0040] The closed loop measurement of the PTO enables high
sensitivity and high signal-to-noise ratio closed-loop (time-based)
measurements that are largely insensitive to most sources of error
that may influence voltage or current driven sensing methods and
devices. The resulting changes in the frequency of operation 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.
[0041] 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.
[0042] FIG. 4 is an example set of two graphs of frequency
characteristics of an ultrasound piezoelectric transducer driven by
the integrated transducer driver for two different configurations
of adhesive and interfacing materials in accordance with an
exemplary embodiment. The plots illustrate changes in the levels of
standing wave ratio (SWR) and the efficiency of conversion of
electrical signals to ultrasound output for a piezoelectric
resonator or transducer with changes in the selection of adhesive
and interfacing materials. The upper trace of values 401 in the top
plot 400 illustrates the minimum level of SWR, 402 the lower trace
403 in the top plot 400 illustrates the minimum conversion loss 404
achieved with one selection of adhesive and interfacing materials.
The equivalent electrical circuit of the associated transducer is
identified in table 405.
[0043] The upper trace 411 of values in the bottom plot 410
illustrates the minimum value of SWR 412 and the lower trace 413
illustrates the minimum conversion loss 414 with a second selection
of adhesive and interfacing materials, where required. The
equivalent electrical circuit of the associated transducer is
identified in table 415. In these plots, the combination of `loss`
and `SWR` is an indication of the conversion efficiency of the
ultrasound transducers at and around their resonant frequencies.
The standing wave ratio is an indication of how much electrical
energy is being reflected back into the driver circuitry from the
interface with the transducer. The conversion loss is the loss of
the unreflected electrical energy into ultrasound energy. The
combination of the standing wave ratio with conversion loss is an
indication of the total conversion efficiency of electrical energy
into ultrasound energy for a given electrical driver circuit,
matching network, and ultrasound resonator or transducer. The two
plots indicate the sensitivity of standing wave ratio and
conversion loss, and thus the level of the conversion efficiency,
to differences in the structure and composition of different
interfaces between the electrical circuitry and the ultrasound
transducers. The optimal selection of adhesive and interfacing
materials, where required, depends on many factors including, but
not limited to, the composition, structure, and dimensions of the
electronic substrate, piezoelectric components, and waveguides.
[0044] FIG. 5 is an illustration of a plot of non-overlapping
resonant frequencies of paired transducers in accordance with an
exemplary embodiment. In a non-limiting example, the
characteristics of transducer A correspond to transducer 304 driven
by the transducer driver 100. The characteristics of transducer B
correspond to transducer 308 of sensing assemblage 302. Operation
too close to their resonant frequencies results in substantial
changes in phase, but limits shifts in frequency with changes in
propagation through the waveguide or propagation medium. One
approach to avoiding operation where the frequency of operation of
an embodiment of a propagation tuned oscillator is bound this way
is to select transducers with different resonant frequencies. The
two transducers may be selected such that their respective series
and parallel resonant frequencies do not overlap. That is, that
both resonant frequencies of one transducer must be higher than
either resonant frequency of the other transducer. This approach
has the benefit of substantial, monotonic shifts in operating
frequency of the present embodiment of a propagation tuned
oscillator with changes in the transit time of energy or ultrasound
waves within the waveguide or propagation medium with minimal
signal processing, electrical components, and power consumption
[0045] Measurement of the changes in the physical length of
individual ultrasound waveguides may be made in several modes. Each
assemblage of one or two ultrasound resonators or transducers
combined with an ultrasound waveguide may 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. The resolution of these measurements can be
further enhanced by advanced processing of the measurement data to
enable optimization of the trade-offs between measurement
resolution versus length of the waveguide, frequency of the
ultrasound waves, and the bandwidth of the sensing and data capture
operations, thus achieving an optimal operating point for a sensing
module or device.
[0046] FIG. 6 is a sensor interface diagram incorporating the
transducer driver 100 in a continuous wave multiplexing arrangement
for maintaining positive closed-loop feedback in accordance with
one embodiment. The positive closed-loop feedback is illustrated by
the bold line path. Initially, multiplexer (mux) 602 receives as
input a clock signal 604, which is passed to the transducer driver
606 to produce the drive line signal 608. Analog multiplexer (mux)
610 receives drive line signal 608, which is passed to the
transmitter transducer 612 to generate energy waves 614. Transducer
612 is located at a first location of an energy propagating medium.
The emitted energy waves 614 propagate through the energy
propagating medium. Receiver transducer 616 is located at a second
location of the energy propagating medium. Receiver transducer 616
captures the energy waves 614, which are fed to analog mux 620 and
passed to the zero-crossing receiver 624. The captured energy waves
by transducer 616 are indicated by electrical waves 618 provided to
mux 620. Zero-crossing receiver 624 outputs a pulse corresponding
to each zero crossing detected from captured electrical waves 618.
The zero crossings are counted and used to determine changes in the
phase and frequency of the energy waves propagating through the
energy propagating medium. In a non-limiting example, a parameter
such as applied force is measured by relating the measured phase
and frequency to a known relationship between the parameter (e.g.
force) and the material properties of the energy propagating
medium. In general, pulse sequence 622 corresponds to the detected
signal frequency. The transducer driver 606 and the zero-crossing
receiver 624 are in a feedback path of the propagation tuned
oscillator. The pulse sequence 622 is coupled through mux 602 in a
positive closed-loop feedback path. The pulse sequence 622 disables
the clock signal 604 such that the path providing pulse sequence
622 is coupled to transducer driver 606 to continue emission of
energy waves into the energy propagating medium and the path of
clock signal 604 to driver 606 is disabled.
[0047] FIG. 7 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver 100 for
operation in continuous wave mode. In particular, with respect to
FIG. 3, it illustrates closed loop measurement of the transit time
322 of ultrasound waves 324 within the waveguide 306 by the
operation of the propagation tuned oscillator 312. This example is
for operation in continuous wave mode. The system can also be
operated in pulse mode and a pulse-echo mode. Pulse mode and pulsed
echo-mode use a pulsed energy wave. Pulse-echo mode uses reflection
to direct an energy wave within the energy propagation medium.
Briefly, the digital logic circuit 746 digitizes the frequency of
operation of the propagation tuned oscillator.
[0048] In continuous wave mode of operation a sensor comprising
transducer 704, propagating structure 702, and transducer 706 is
used to measure the parameter. In general, the parameter to be
measured affects the properties of the propagating medium. For
example, an external force or condition 712 is applied to
propagating structure 702 that changes the length of the waveguide
in a path of a propagating energy wave. A change in length
corresponds to a change in transit time 708 of the propagating
wave. Similarly, the length of propagating structure 702
corresponds to the applied force 712. A length reduction
corresponds to a higher force being applied to the propagating
structure 702. Conversely, a length increase corresponds to a
lowering of the applied force 712 to the propagating structure 702.
The length of propagating structure 702 is measured and is
converted to force by way of a known length to force
relationship.
[0049] Transducer 704 is an emitting device in continuous wave
mode. The sensor for measuring a parameter comprises transducer 704
coupled to propagating structure 702 at a first location. A
transducer 706 is coupled to propagating structure 702 at a second
location. Transducer 706 is a receiving transducer for capturing
propagating energy waves. In one embodiment, the captured
propagated energy waves are electrical sine waves 734 that are
output by transducer 706.
[0050] A measurement sequence is initiated when control circuitry
718 closes switch 720 coupling oscillator output 724 of oscillator
722 to the input of transducer driver 726. One or more pulses
provided to transducer driver 726 initiates an action to propagate
energy waves 710 having simple or complex waveforms through energy
propagating structure or medium 702. Transducer driver 726
comprises a digital driver 728 and matching network 730. In one
embodiment, transducer driver 726 transforms the oscillator output
of oscillator 722 into sine waves of electrical waves 732 having
the same repetition rate as oscillator output 724 and sufficient
amplitude to excite transducer 704.
[0051] Emitting transducer 704 converts the sine waves 732 into
energy waves 710 of the same frequency and emits them at the first
location into energy propagating structure or medium 702. The
energy waves 710 propagate through energy propagating structure or
medium 702. Upon reaching transducer 706 at the second location,
energy waves 710 are captured, sensed, or detected. The captured
energy waves are converted by transducer 706 into sine waves 734
that are electrical waves having the same frequency.
[0052] Amplifier 736 comprises a pre-amplifier 738 and zero-cross
receiver 740. Amplifier 736 converts the sine waves 734 into
digital pulses 742 of sufficient duration to sustain the behavior
of the closed loop circuit. Control circuitry 718 responds to
digital pulses 742 from amplifier 736 by opening switch 720 and
closing switch 744. Opening switch 720 decouples oscillator output
724 from the input of transducer driver 726. Closing switch 744
creates a closed loop circuit coupling the output of amplifier 736
to the input of transducer driver 726 and sustaining the emission,
propagation, and detection of energy waves through energy
propagating structure or medium 702.
[0053] An equilibrium state is attained by maintaining unity gain
around this closed loop circuit wherein sine waves 732 input into
transducer 704 and sine waves 734 output by transducer 706 are in
phase with a small but constant offset. Transducer 706 as disclosed
above, outputs the sine waves 734 upon detecting energy waves
propagating to the second location. In the equilibrium state, an
integer number of energy waves 710 propagate through energy
propagating structure or medium 702.
[0054] Movement or changes in the physical properties of energy
propagating structure or medium 702 change a transit time 708 of
energy waves 710. The transit time 708 comprises the time for an
energy wave to propagate from the first location to the second
location of propagating structure 702. Thus, the change in the
physical property of propagating structure 702 results in a
corresponding time period change of the energy waves 710 within
energy propagating structure or medium 702. These changes in the
time period of the energy waves 710 alter the equilibrium point of
the closed loop circuit and frequency of operation of the closed
loop circuit. The closed loop circuit adjusts such that sine waves
732 and 734 correspond to the new equilibrium point. The frequency
of energy waves 710 and changes to the frequency correlate to
changes in the physical attributes of energy propagating structure
or medium 702.
[0055] The physical changes may be imposed on energy propagating
structure 702 by external forces or conditions 712 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. Translation of the operating frequency into
digital binary numbers facilitates communication, additional
processing, storage, and display of information about the level and
changes in physical parameters of interest. Similarly, the
frequency of energy waves 710 during the operation of the closed
loop circuit, and changes in this frequency, may be used to measure
movement or changes in physical attributes of energy propagating
structure or medium 702.
[0056] Prior to measurement of the frequency or operation of the
propagation tuned oscillator, control logic 718 loads the loop
count into digital counter 750 that is stored in count register
748. The first digital pulses 742 initiates closed loop operation
within the propagation tuned oscillator and signals control circuit
718 to start measurement operations. At the start of closed loop
operation, control logic 718 enables digital counter 750 and
digital timer 752. In one embodiment, digital counter 750
decrements its value on the rising edge of each digital pulse
output by zero-cross receiver 740. Digital timer 752 increments its
value on each rising edge of clock pulses 756. When the number of
digital pulses 742 has decremented, the value within digital
counter 750 to zero a stop signal is output from digital counter
750. The stop signal disables digital timer 752 and triggers
control circuit 718 to output a load command to data register 754.
Data register 754 loads a binary number from digital timer 752 that
is equal to the period of the energy waves or pulses times the
value in counter 748 divided by clock period 756. With a constant
clock period 756, the value in data register 754 is directly
proportional to the aggregate period of the 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 748.
[0057] FIG. 8 is a sensor interface diagram incorporating the
transducer driver 100 in a pulse multiplexing arrangement for
maintaining positive closed-loop feedback in accordance with one
embodiment. In one embodiment, the circuitry other than the sensor
is integrated on an application specific integrated circuit (ASIC).
The positive closed-loop feedback is illustrated by the bold line
path. Initially, mux 802 is enabled to couple one or more digital
pulses 804 to the transducer driver 806. Transducer driver 806
generates a pulse sequence 808 corresponding to digital pulses 804.
Analog mux 810 is enabled to couple pulse sequence 808 to the
transmitter transducer 812. Transducer 812 is coupled to a medium
at a first location. Transducer 812 responds to pulse sequence 808
and generates corresponding energy pulses 814 that are emitted into
the medium at the first location. The energy pulses 814 propagate
through the medium. A receiver transducer 816 is located at a
second location on the medium. Receiver transducer 816 captures the
energy pulses 814 and generates a corresponding signal of
electrical pulses 818. Transducer 816 is coupled to a mux 820. Mux
820 is enabled to couple to zero-cross receiver 824. Electrical
pulses 818 from transducer 816 are coupled to zero-cross receiver
824. Zero-cross receiver 824 counts zero crossings of electrical
pulses 818 to determine changes in phase and frequency of the
energy pulses responsive to an applied force, as previously
explained. Zero-cross receiver 824 outputs a pulse sequence 822
corresponding to the detected signal frequency. Pulse sequence 822
is coupled to mux 802. Mux 802 is decoupled from coupling digital
pulses 804 to driver 806 upon detection of pulses 822. Conversely,
mux 802 is enabled to couple pulses 822 to driver 806 upon
detection of pulses 822 thereby creating a positive closed-loop
feedback path. Thus, in pulse mode, transducer driver 806 and
zero-cross receiver 824 is part of the closed-loop feedback path
that continues emission of energy pulses into the medium at the
first location and detection at the second location to measure a
transit time and changes in transit time of pulses through the
medium.
[0058] FIG. 9 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver 100 for
operation in pulse mode. In particular, with respect to FIG. 3, it
illustrates closed loop measurement of the transit time 322 of
ultrasound waves 324 within the waveguide 306 by the operation of
the propagation tuned oscillator 312. This example is for operation
in pulse mode. The system can also be operated in continuous wave
mode and a pulse-echo mode. Continuous wave mode uses a continuous
wave signal. Pulse-echo mode uses reflection to direct an energy
wave within the energy propagation medium. Briefly, the digital
logic circuit 746 digitizes the frequency of operation of the
propagation tuned oscillator.
[0059] In pulse mode of operation, a sensor comprising transducer
704, propagating structure 702, and transducer 706 is used to
measure the parameter. In general, the parameter to be measured
affects the properties of the propagating medium. For example, an
external force or condition 712 is applied to propagating structure
702 that changes the length of the waveguide in a path of a
propagating energy wave. A change in length corresponds to a change
in transit time 708 of the propagating wave. The length of
propagating structure 702 is measured and is converted to force by
way of a known length to force relationship. One benefit of pulse
mode operation is the use of a high magnitude pulsed energy wave.
In one embodiment, the magnitude of the energy wave decays as it
propagates through the medium. The use of a high magnitude pulse is
a power efficient method to produce a detectable signal if the
energy wave has to traverse a substantial distance or is subject to
a reduction in magnitude as it propagated due to the medium.
[0060] A measurement sequence is initiated when control circuitry
718 closes switch 720 coupling oscillator output 724 of oscillator
722 to the input of transducer driver 726. One or more pulses
provided to transducer driver 726 initiates an action to propagate
energy waves 710 having simple or complex waveforms through energy
propagating structure or medium 702. Transducer driver 726
comprises a digital driver 728 and matching network 730. In one
embodiment, transducer driver 726 transforms the oscillator output
of oscillator 722 into analog pulses of electrical waves 932 having
the same repetition rate as oscillator output 724 and sufficient
amplitude to excite transducer 704.
[0061] Emitting transducer 704 converts the analog pulses 932 into
energy waves 710 of the same frequency and emits them at a first
location into energy propagating structure or medium 702. The
energy waves 710 propagate through energy propagating structure or
medium 702. Upon reaching transducer 706 at the second location,
energy waves 710 are captured, sensed, or detected. The captured
energy waves are converted by transducer 706 into analog pulses 934
that are electrical waves having the same frequency.
[0062] Amplifier 736 comprises a pre-amplifier 738 and zero-cross
receiver 740. Amplifier 736 converts the analog pulses 934 into
digital pulses 742 of sufficient duration to sustain the behavior
of the closed loop circuit. Control circuitry 718 responds to
digital pulses 742 from amplifier 736 by opening switch 720 and
closing switch 744. Opening switch 720 decouples oscillator output
724 from the input of transducer driver 726. Closing switch 744
creates a closed loop circuit coupling the output of amplifier 736
to the input of transducer driver 726 and sustaining the emission,
propagation, and detection of energy waves through energy
propagating structure or medium 702.
[0063] An equilibrium state is attained by maintaining unity gain
around this closed loop circuit wherein pulses 932 input into
transducer 704 and pulses 934 output by transducer 706 are in phase
with a small but constant offset. Transducer 706 as disclosed
above, outputs the pulses 934 upon detecting energy waves
propagating to the second location. In the equilibrium state, an
integer number of energy waves 710 propagate through energy
propagating structure or medium 702.
[0064] Movement or changes in the physical properties of energy
propagating structure or medium 702 change a transit time 708 of
energy waves 710. The transit time 708 comprises the time for an
energy wave to propagate from the first location to the second
location of propagating structure 702. Thus, the change in the
physical property of propagating structure 702 results in a
corresponding time period change of the energy waves 710 within
energy propagating structure or medium 702. These changes in the
time period of the energy waves 710 alter the equilibrium point of
the closed loop circuit and frequency of operation of the closed
loop circuit. The closed loop circuit adjusts such that pulses 932
and 934 correspond to the new equilibrium point. The frequency of
energy waves 710 and changes to the frequency correlate to changes
in the physical attributes of energy propagating structure or
medium 702.
[0065] The physical changes may be imposed on energy propagating
structure 702 by external forces or conditions 712 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. Translation of the operating frequency into
digital binary numbers facilitates communication, additional
processing, storage, and display of information about the level and
changes in physical parameters of interest as disclosed in more
detail hereinabove. Similarly, the frequency of energy waves 710
during the operation of the closed loop circuit, and changes in
this frequency, may be used to measure movement or changes in
physical attributes of energy propagating structure or medium
702.
[0066] Briefly referring back to FIG. 5 an exemplary plot of
non-overlapping resonant frequencies of paired transducers was
shown. One approach to avoiding operation where the frequency of
operation of a propagation tuned oscillator is bound this way is to
select transducers with different resonant frequencies. The two
transducers are selected such that their respective series and
parallel resonant frequencies do not overlap. That is, that both
resonant frequencies of one transducer are higher than either
resonant frequency of the other transducer.
[0067] FIG. 10 is a sensor interface diagram incorporating the
transducer driver 100 in a pulse-echo multiplexing arrangement for
maintaining positive closed-loop feedback in accordance with one
embodiment. The positive closed-loop feedback is illustrated by the
bold line path. Initially, multiplexer (mux) 1002 receives as input
a digital pulse 1004, which is passed to the transducer driver 1006
to produce the pulse sequence 1008. Analog multiplexer (mux) 1010
receives pulse sequence 1008, which is passed to the transducer
1012 to generate energy pulses 1014. Energy pulses 1014 are emitted
into a first location of a medium and propagate through the medium.
In the pulse-echo example, energy pulses 1014 are reflected off a
surface 1016 at a second location of the medium, for example, the
end of a waveguide or reflector, and echoed back to the transducer
1012. The transducer 1012 proceeds to then capture the reflected
pulse echo. In pulsed echo mode, the transducer 1012 performs as
both a transmitter and a receiver. As disclosed above, transducer
1012 toggles back and forth between emitting and receiving energy
waves. Transducer 1012 captures the reflected echo pulses, which
are coupled to analog mux 1010 and directed to the edge-detect
receiver 1022. The captured reflected echo pulses is indicated by
electrical waves 1018. Edge-detect receiver 1022 locks on pulse
edges corresponding to the wave front of a propagated energy wave
to determine changes in phase and frequency of the energy pulses
1014 responsive to an applied force, as previously explained. Among
other parameters, it generates a pulse sequence 1018 corresponding
to the detected signal frequency. The pulse sequence 1018 is
coupled to mux 1002 and directed to driver 1006 to initiate one or
more energy waves being emitted into the medium by transducer 1012.
Pulse 1004 is decoupled from being provided to driver 1006. Thus, a
positive closed loop feedback including transducer driver 1006 is
formed that repeatably emits energy waves into the medium until mux
1002 prevents a signal from being provided to driver 1006. The
edge-detect receiver 1022 is coupled to a second location of the
medium and is in the feedback path. The edge-detect receiver 1002
initiates a pulsed energy wave being provided at the first location
of the medium upon detecting a wave front at the second location
when the feedback path is closed.
[0068] FIG. 11 is an exemplary block diagram of a propagation tuned
oscillator (PTO) incorporating the transducer driver 100 for
operation in pulse echo mode. In particular, with respect to FIG.
3, it illustrates closed loop measurement of the transit time 322
of ultrasound waves 324 within the waveguide 306 by the operation
of the propagation tuned oscillator 312. This example is for
operation in a pulse echo mode. The system can also be operated in
pulse mode and a continuous wave mode. Pulse mode does not use a
reflected signal. Continuous wave mode uses a continuous signal.
Briefly, the digital logic circuit 1146 digitizes the frequency of
operation of the propagation tuned oscillator.
[0069] In pulse-echo mode of operation a sensor comprising
transducer 1104, propagating structure 1102, and reflecting surface
1106 is used to measure the parameter. In general, the parameter to
be measured affects the properties of the propagating medium. For
example, an external force or condition 1112 is applied to
propagating structure 1102 that changes the length of the waveguide
in a path of a propagating energy wave. A change in length
corresponds to a change in transit time of the propagating wave.
Similarly, the length of propagating structure 1102 corresponds to
the applied force 1112. A length reduction corresponds to a higher
force being applied to the propagating structure 1102. Conversely,
a length increase corresponds to a lowering of the applied force
1112 to the propagating structure 1102. The length of propagating
structure 1102 is measured and is converted to force by way of a
known length to force relationship.
[0070] Transducer 1104 is both an emitting device and a receiving
device in pulse-echo mode. The sensor for measuring a parameter
comprises transducer 1104 coupled to propagating structure 1102 at
a first location. A reflecting surface is coupled to propagating
structure 1102 at a second location. Transducer 1104 has two modes
of operation comprising an emitting mode and receiving mode.
Transducer 1104 emits an energy wave into the propagating structure
1102 at the first location in the emitting mode. The energy wave
propagates to a second location and is reflected by reflecting
surface 1106. The reflected energy wave is reflected towards the
first location and transducer 1104 subsequently generates a signal
in the receiving mode corresponding to the reflected energy
wave.
[0071] A measurement sequence in pulse echo mode is initiated when
control circuitry 1118 closes switch 1120 coupling digital output
1124 of oscillator 1122 to the input of transducer driver 1126. One
or more pulses provided to transducer driver 1126 starts a process
to emit one or more energy waves 1110 having simple or complex
waveforms into energy propagating structure or medium 1102.
Transducer driver 1126 comprises a digital driver 1128 and matching
network 1130. In one embodiment, transducer driver 1126 transforms
the digital output of oscillator 1122 into pulses of electrical
waves 1132 having the same repetition rate as digital output 1124
and sufficient amplitude to excite transducer 1104.
[0072] Transducer 1104 converts the pulses of electrical waves 1132
into pulses of energy waves 1110 of the same repetition rate and
emits them into energy propagating structure or medium 1102. The
pulses of energy waves 1110 propagate through energy propagating
structure or medium 1102 as shown by arrow 1114 towards reflecting
surface 1106. Upon reaching reflecting surface 1106, energy waves
1110 are reflected by reflecting surface 1106. Reflected energy
waves propagate towards transducer 1104 as shown by arrow 1116. The
reflected energy waves are detected by transducer 1104 and
converted into pulses of electrical waves 1134 having the same
repetition rate.
[0073] Amplifier 1136 comprises a pre-amplifier 1138 and
edge-detect receiver 1140. Amplifier 1136 converts the pulses of
electrical waves 1134 into digital pulses 1142 of sufficient
duration to sustain the pulse behavior of the closed loop circuit.
Control circuitry 1118 responds to digital output pulses 1142 from
amplifier 1136 by opening switch 1120 and closing switch 1144.
Opening switch 1120 decouples oscillator output 1124 from the input
of transducer driver 1126. Closing switch 1144 creates a closed
loop circuit coupling the output of amplifier 1136 to the input of
transducer driver 1126 and sustaining the emission, propagation,
and detection of energy pulses through energy propagating structure
or medium 1102.
[0074] An equilibrium state is attained by maintaining unity gain
around this closed loop circuit wherein electrical waves 1132 input
into transducer 1104 and electrical waves 1134 output by transducer
1104 are in phase with a small but constant offset. Transducer 1104
as disclosed above, outputs the electrical waves 1134 upon
detecting reflected energy waves reflected from reflecting surface
1106. In the equilibrium state, an integer number of pulses of
energy waves 1110 propagate through energy propagating structure or
medium 1102.
[0075] Movement or changes in the physical properties of energy
propagating structure or medium 1102 change a transit time 1108 of
energy waves 1110. The transit time 1108 comprises the time for an
energy wave to propagate from the first location to the second
location of propagating structure 1102 and the time for the
reflected energy wave to propagate from the second location to the
first location of propagating structure 1102. Thus, the change in
the physical property of propagating structure 1102 results in a
corresponding time period change of the energy waves 1110 within
energy propagating structure or medium 1102. These changes in the
time period of the repetition rate of the energy pulses 1110 alter
the equilibrium point of the closed loop circuit and repetition
rate of operation of the closed loop circuit. The closed loop
circuit adjusts such that electrical waves 1132 and 1134 correspond
to the new equilibrium point. The repetition rate of energy waves
1110 and changes to the repetition rate correlate to changes in the
physical attributes of energy propagating structure or medium
1102.
[0076] The physical changes may be imposed on energy propagating
structure 1102 by external forces or conditions 1112 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. Translation of the operating
frequency into digital binary numbers facilitates communication,
additional processing, storage, and display of information about
the level and changes in physical parameters of interest.
Similarly, the frequency of energy waves 1110 during the operation
of the closed loop circuit, and changes in this frequency, may be
used to measure movement or changes in physical attributes of
energy propagating structure or medium 1102.
[0077] Prior to measurement of the frequency or operation of the
propagation tuned oscillator, control logic 1118 loads the loop
count into digital counter 1150 that is stored in count register
1148. The first digital pulses 1142 initiates closed loop operation
within the propagation tuned oscillator and signals control circuit
1118 to start measurement operations. At the start of closed loop
operation, control logic 1118 enables digital counter 1150 and
digital timer 1152. In one embodiment, digital counter 1150
decrements its value on the rising edge of each digital pulse
output by edge-detect receiver 1140. Digital timer 1152 increments
its value on each rising edge of clock pulses 1156. When the number
of digital pulses 1142 has decremented, the value within digital
counter 1150 to zero a stop signal is output from digital counter
1150. The stop signal disables digital timer 1152 and triggers
control circuit 1118 to output a load command to data register
1154. Data register 1154 loads a binary number from digital timer
1152 that is equal to the period of the energy waves or pulses
times the value in counter 1148 divided by clock period 1156. With
a constant clock period 1156, the value in data register 1154 is
directly proportional to the aggregate period of the 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 1148.
[0078] FIG. 12 is an illustration of a sensor 1200 placed in
contact between a femur 1202 and a tibia 1208 for measuring a
parameter in accordance with an exemplary embodiment. In general, a
sensor 1200 is placed in contact with or in proximity to the
muscular-skeletal system to measure a parameter. In a non-limiting
example, sensor 1200 can be operated in continuous wave mode, pulse
mode, and pulse echo-mode to measure a parameter of a joint or an
artificial joint. Embodiments of sensor 1200 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. Sensor 1200 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.
[0079] In at least one exemplary embodiment, an energy pulse is
directed within one or more waveguides in sensor 1200 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.
[0080] Sensor 1200 can be size constrained by form factor
requirements of fitting within a region the muscular-skeletal
system or a component such as a tool, equipment, or artificial
joint. In a non-limiting example, sensor 1200 is used to measure
load and balance of an installed artificial knee joint. A knee
prosthesis comprises a femoral prosthetic component 1204, an
insert, and a tibial prosthetic component 1206. A distal end of
femur 1202 is prepared and receives femoral prosthetic component
1204. Femoral prosthetic component 1204 typically has two condyle
surfaces that mimic a natural femur. As shown, femoral prosthetic
component 1204 has single condyle surface being coupled to femur
1202. Femoral prosthetic component 1204 is typically made of a
metal or metal alloy.
[0081] A proximal end of femur 1208 is prepared to receive tibial
prosthetic component 1206. Tibial prosthetic component 1206 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 1206 also retains the insert in a fixed
position with respect to femur 1208. The insert is fitted between
femoral prosthetic component 1204 and tibial prosthetic component
1206. The insert has at least one bearing surface that is in
contact with at least condyle surface of femoral prosthetic
component 1204. 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.
[0082] In a knee joint replacement process, the surgeon affixes
femoral prosthetic component 1204 to the femur 1202 and tibial
prosthetic component 1206 to femur 1208. The tibial prosthetic
component 1206 can include a tray or plate affixed to the
planarized proximal end of the femur 1208. Sensor 1200 is placed
between a condyle surface of femoral prosthetic component 1204 and
a major surface of tibial prosthetic component 1206. The condyle
surface contacts a major surface of sensor 1200. The major surface
of sensor 1200 approximates a surface of the insert. Tibial
prosthetic component 1206 can include a cavity or tray on the major
surface that receives and retains sensor 1200 during a measurement
process. Tibial prosthetic component 1206 and sensor 1200 has a
combined thickness that represents a combined thickness of tibial
prosthetic component 1206 and a final (or chronic) insert of the
knee joint.
[0083] In one embodiment, two sensors 1200 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
1206. One or two sensors 1200 may be inserted between femoral
prosthetic component 1204 and tibial prosthetic component 1206.
Each sensor is independent and each measures a respective condyle
of femur 1202. 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 of the system. The shared electronics can
multiplex between each sensor module to take measurements when
appropriate. Measurements taken by sensor 1200 aid the surgeon in
modifying the absolute loading on each condyle and the balance
between condyles. Although shown for a knee implant, sensor 1200
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 1200 can also be adapted to orthopedic tools
to provide measurements.
[0084] The prosthesis incorporating sensor 1200 emulates the
function of a natural knee joint. Sensor 1200 can measure loads or
other parameters at various points throughout the range of motion.
Data from sensor 1200 is transmitted to a receiving station 1210
via wired or wireless communications. In a first embodiment, sensor
1200 is a disposable system. Sensor 1200 can be disposed of after
using sensor 1200 to optimally fit the joint implant. Sensor 1200
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 sensor 1200 for reuse. In a third embodiment, sensor
1200 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 1200 can be a
permanent component of the replacement joint. Sensor 1200 can be
used to provide both short term and long term post-operative data
on the implanted joint. In a fifth embodiment, sensor 1200 can be
coupled to the muscular-skeletal system. In all of the embodiments,
receiving station 1210 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 1210 can record and provide accounting information of
sensor 1200 to an appropriate authority.
[0085] In an intra-operative example, sensor 1200 can measure
forces (Fx, Fy, Fz) with corresponding locations and torques (e.g.
Tx, Ty, and Tz) on the femoral prosthetic component 1204 and the
tibial prosthetic component 1206. The measured force and torque
data is transmitted to receiving station 1210 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.
[0086] As mentioned previously, sensor 1200 can be used for other
joint surgeries; it is not limited to knee replacement implant or
implants. Moreover, sensor 1200 is not limited to trial
measurements. Sensor 1200 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 1200 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, sensor 1200 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 1200 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.
[0087] The present invention is applicable to a wide range of
medical and nonmedical applications including, but not limited to,
frequency compensation; control of, or alarms for, physical
systems; or monitoring or measuring physical parameters of
interest. The level of accuracy and repeatability attainable in a
highly compact sensing module or device may be applicable to many
medical applications monitoring or measuring physiological
parameters throughout the human body including, not limited to,
bone density, movement, viscosity, and pressure of various fluids,
localized temperature, etc. with applications in the vascular,
lymph, respiratory, digestive system, muscles, bones, and joints,
other soft tissue areas, and interstitial fluids.
[0088] 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.
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