US20100331685A1 - Transducer driver for measuring a parameter of the muscularskeletal system - Google Patents

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• 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
• 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
• 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.
• 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
• 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:
• FIG. 1 is a block diagram of a transducer driver in accordance with one embodiment;
• 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;
• 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;
• 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;
• FIG. 5 is an illustration of a plot of non-overlapping resonant frequencies of paired transducers in accordance with an exemplary embodiment;
• 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;
• FIG. 7 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the transducer driver for operation in continuous wave mode;
• 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;
• 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;
• 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;
• FIG. 11 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the transducer driver for operation in pulse echo mode;
• 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
• 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.
• 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.
• 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.
• 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).
• 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.
• FIG. 1 illustrates a low power consumption integratedtransducer driver circuit100 in accordance with an exemplary embodiment. In a first embodiment,driver circuit100 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 alevel shifter112 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 animpedance matching network114 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.
• In a second embodiment, thedriver circuit100 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. Thedriver circuit100 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. Thedrive circuit100 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.
• In one embodiment, low power consumptiontransducer driver circuit100 comprisescontrol logic108, adigital driver106,level shifter112, anamplifier116, andmatching network114. Thedriver circuit100 can be implemented in discrete analog components, digital components, an application integrated circuit, or a combination thereof. In a low power application,transducer driver circuit100 is integrated with other circuitry of the propagation tuned oscillator. Briefly, thetransducer driver circuit100 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.
• Aninput102 receives a signal to emit an energy wave.Input102 couples to controllogic108.Control logic108 controls the timing and frequency of stimulation of anenergy transducer110. Adigital pulse104 fromdigital control logic108 is provided to an input ofdriver106. In an energy pulse mode,digital control logic108 also controls the duration of the stimulation. One or more pulses from anoutput118 ofdriver106 is coupled tolevel shifting circuitry112.Level shifting circuitry112 adjusts the output voltage ofdriver106 to efficiently driveenergy transducer110. One or more level shifted pulses are provided at anoutput120 oflevel shifter112 toamplifier116.Amplifier116 amplifies the signal atoutput120 which is provided to an input of matchingnetwork114.Matching network114 matches the electrical characteristics of theenergy transducer110.Output signal122 from thematching network114drive energy transducer110.Matching network114 converts the output pulse fromamplifier116 to the required wave shape, frequency and phase. Energy waves124 are emitted byenergy transducer110 into the medium.
• 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.
• Briefly, an input ofdigital driver106 is driven bydigital control logic108, which ultimately controls the timing and frequency of the resultingoutput signal122. As will be shown ahead, theoutput signal122 drives anenergy transducer110 to output an energy wave or energy pulse. Thedrive circuit100 is optimally configured to generate theoutput signal122 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 logic108 also controls the duration of thetransducer110 stimulation.Level shifter112 adjusts the output voltage ofdriver output106 to efficiently driveenergy transducer110. More specifically, thelevel shifter112 raises or lowers voltage levels of output pulses to the voltages required to efficiently drive the energy emitting resonator ortransducer110 given the characteristics of the resonator ortransducer110, the frequency and duration of the output waves, and the shape of the output pulse.Matching network114 matches the electrical characteristics of theenergy transducer110 and converts theoutput pulse122 to the required wave shape, frequency and phase. The generateddigital output waveform122 or pulse may have a moderately sharp leading edge.
• With regard to the integratedtransducer driver100, efficient use of power and conservation of charge is required for ultra low power operation. Energy emitting resonators ortransducers110 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, thedriver circuit100 and matchednetwork114 together efficiently convert theinput pulse104 to anenergy wave124 of the required frequency, phase, and duration; which is, specific to operation oftransducer110.
• The output of thedriver amplifier116 is coupled with theimpedance matching network114, 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.
• Driving theenergy emitting transducer110 through theimpedance matching network114 achieves awaveform122 that is input to the energy emitting resonator ortransducer110. This drives the energy emitting resonators ortransducers110 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.
• FIG. 2 illustrates a block diagram of thetransducer driver circuit100 coupled to asensing assembly200 in accordance with an exemplary embodiment. Thesensing assembly200 comprises atransmitter transducer202, anenergy propagating medium204, and areceiver transducer206. 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, thesensing assembly200 in one embodiment is part of a sensory device that assesses loading, in particular, the externally appliedforces208 on thesensing assembly200. In one embodiment,forces208 are applied in a direction corresponding to energy wave propagation in the propagating structure or medium204 such that propagatingstructure204 is changed dimensionally. Thetransducer driver circuit100 drives thetransmitter transducer202 of thesensing assembly200 to produceenergy waves210 that are directed into theenergy propagating medium204. The time for an energy wave to propagate fromtransducer202 totransducer206 is atransit time214. Changes in theenergy propagating medium204 due to the externally appliedforces208 change the frequency, phase, and transit time of energy waves210. A controller (not shown), as will be explained below, operatively coupled to thereceiver transducer206 monitors anoutput signal212 for these characteristic changes to assess parameters of interest (e.g., force, direction, displacement, etc.) related to the loading.
• 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, thetransducer driver100, controlled in part bycontrol logic108, is an efficient device for achieving highly accurate control of timing and duration of the energy waves210 (and pulses when in pulse mode or pulse echo mode). Thetransducer driver100 including matchednetwork122 translates the inputdigital pulses104 intoanalog waveforms122 with the required timing, duration, frequency, and phase to drive thetransmitter transducer202 to generate the energy waves210. 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 ortransducers202 without sacrificing functionality or performance.
• 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.
• FIG. 3 is an exemplary propagation tuned oscillator (PTO) incorporating thetransducer driver100 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 thesensing assembly200. 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.
• Thesensing assembly302 comprises afirst transducer304, asecond transducer308, and a waveguide306 (energy propagating structure). In one embodiment,waveguide306 is a compressible medium that contains, directs, and propagates energy waves coupled thereto. Thesensing assembly302 is affixed to load bearing or contactingsurfaces310. External forces applied to the contactingsurfaces310 compress thewaveguide306 and change the length of thewaveguide306. This also results in thetransducers304 and308 being moved a similar distance closer together. This change in distance affects the transmittime322 ofenergy waves324 transmitted and received betweentransducers304 and308. The PTO4 in response to these physical changes alters the oscillation frequency of the ultrasound waves2 to achieve resonance. This is accomplished by way of thePTO312 in conjunction with thetransducer driver100, the mode control316 (e.g., continuous, pulse-loop, and pulse-echo), andsensor interface318.
• Notably, changes in the waveguide306 (energy propagating structure or structures) alter the propagation properties of the medium of propagation (e.g. transmit time322). Due to the closed-loop operation shown, thePTO312 changes the resonant frequency of the oscillator and accordingly the frequency of oscillation of the closed loop circuit. In particular, thePTO312 adjusts the oscillation frequency to be an integer number of waves. Thedigital counter314 in conjunction with electronic components counts the number of waves to determine the corresponding change in the length of thewaveguide306. 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.
• The operation of the sensing system is described in more detail hereafter. The frequency of ultrasound waves324 emitted by ultrasound resonator ortransducer304 is controlled by propagation tunedoscillator312. The detecting ultrasound resonator ortransducer308 can be either a separate ultrasound resonator or transducer or the emitting resonator ortransducer304 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 inwaveguide306 back totransducer304 where it is detected bytransducer304 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.
• Thetransit time322 of ultrasound waves324 through the waveguide determines the period of oscillation of propagation tunedoscillator312. A change in external forces or conditions uponsurfaces310 affect the propagation characteristics ofwaveguide306 and altertransit time322. In one embodiment, the number of wavelengths of ultrasound waves324 is held constant by propagation tunedoscillator312. The constraint of having an integer number of wavelengths forces the frequency of oscillation of propagation tunedoscillator312 to change. The resulting changes in frequency are captured withdigital counter314 as a measurement of changes in external forces or conditions applied tosurfaces310.
• 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.
• 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.
• 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 ofvalues401 in thetop plot400 illustrates the minimum level of SWR,402 thelower trace403 in thetop plot400 illustrates theminimum conversion loss404 achieved with one selection of adhesive and interfacing materials. The equivalent electrical circuit of the associated transducer is identified in table405.
• Theupper trace411 of values in thebottom plot410 illustrates the minimum value ofSWR412 and thelower trace413 illustrates the minimum conversion loss414 with a second selection of adhesive and interfacing materials, where required. The equivalent electrical circuit of the associated transducer is identified in table415. 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.
• 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 transducer304 driven by thetransducer driver100. The characteristics of transducer B correspond to transducer308 ofsensing assemblage302. 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
• 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.
• FIG. 6 is a sensor interface diagram incorporating thetransducer driver100 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 aclock signal604, which is passed to thetransducer driver606 to produce thedrive line signal608. Analog multiplexer (mux)610 receivesdrive line signal608, which is passed to thetransmitter transducer612 to generateenergy waves614.Transducer612 is located at a first location of an energy propagating medium. The emittedenergy waves614 propagate through the energy propagating medium.Receiver transducer616 is located at a second location of the energy propagating medium.Receiver transducer616 captures the energy waves614, which are fed toanalog mux620 and passed to the zero-crossingreceiver624. The captured energy waves bytransducer616 are indicated byelectrical waves618 provided to mux620. Zero-crossingreceiver624 outputs a pulse corresponding to each zero crossing detected from capturedelectrical waves618. 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 sequence622 corresponds to the detected signal frequency. Thetransducer driver606 and the zero-crossingreceiver624 are in a feedback path of the propagation tuned oscillator. Thepulse sequence622 is coupled throughmux602 in a positive closed-loop feedback path. Thepulse sequence622 disables theclock signal604 such that the path providingpulse sequence622 is coupled totransducer driver606 to continue emission of energy waves into the energy propagating medium and the path ofclock signal604 todriver606 is disabled.
• FIG. 7 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating thetransducer driver100 for operation in continuous wave mode. In particular, with respect toFIG. 3, it illustrates closed loop measurement of thetransit time322 of ultrasound waves324 within thewaveguide306 by the operation of the propagation tunedoscillator312. 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 circuit746 digitizes the frequency of operation of the propagation tuned oscillator.
• In continuous wave mode of operation asensor comprising transducer704, propagatingstructure702, andtransducer706 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 orcondition712 is applied to propagatingstructure702 that changes the length of the waveguide in a path of a propagating energy wave. A change in length corresponds to a change intransit time708 of the propagating wave. Similarly, the length of propagatingstructure702 corresponds to the appliedforce712. A length reduction corresponds to a higher force being applied to the propagatingstructure702. Conversely, a length increase corresponds to a lowering of the appliedforce712 to the propagatingstructure702. The length of propagatingstructure702 is measured and is converted to force by way of a known length to force relationship.
• Transducer704 is an emitting device in continuous wave mode. The sensor for measuring a parameter comprisestransducer704 coupled to propagatingstructure702 at a first location. Atransducer706 is coupled to propagatingstructure702 at a second location.Transducer706 is a receiving transducer for capturing propagating energy waves. In one embodiment, the captured propagated energy waves areelectrical sine waves734 that are output bytransducer706.
• A measurement sequence is initiated whencontrol circuitry718 closes switch720coupling oscillator output724 ofoscillator722 to the input oftransducer driver726. One or more pulses provided totransducer driver726 initiates an action to propagateenergy waves710 having simple or complex waveforms through energy propagating structure ormedium702.Transducer driver726 comprises adigital driver728 andmatching network730. In one embodiment,transducer driver726 transforms the oscillator output ofoscillator722 into sine waves ofelectrical waves732 having the same repetition rate asoscillator output724 and sufficient amplitude to excitetransducer704.
• Emittingtransducer704 converts thesine waves732 intoenergy waves710 of the same frequency and emits them at the first location into energy propagating structure ormedium702. The energy waves710 propagate through energy propagating structure ormedium702. Upon reachingtransducer706 at the second location,energy waves710 are captured, sensed, or detected. The captured energy waves are converted bytransducer706 intosine waves734 that are electrical waves having the same frequency.
• Amplifier736 comprises apre-amplifier738 and zero-cross receiver740.Amplifier736 converts thesine waves734 intodigital pulses742 of sufficient duration to sustain the behavior of the closed loop circuit.Control circuitry718 responds todigital pulses742 fromamplifier736 by openingswitch720 andclosing switch744.Opening switch720 decouplesoscillator output724 from the input oftransducer driver726.Closing switch744 creates a closed loop circuit coupling the output ofamplifier736 to the input oftransducer driver726 and sustaining the emission, propagation, and detection of energy waves through energy propagating structure ormedium702.
• An equilibrium state is attained by maintaining unity gain around this closed loop circuit whereinsine waves732 input intotransducer704 andsine waves734 output bytransducer706 are in phase with a small but constant offset.Transducer706 as disclosed above, outputs thesine waves734 upon detecting energy waves propagating to the second location. In the equilibrium state, an integer number ofenergy waves710 propagate through energy propagating structure ormedium702.
• Movement or changes in the physical properties of energy propagating structure or medium702 change atransit time708 of energy waves710. Thetransit time708 comprises the time for an energy wave to propagate from the first location to the second location of propagatingstructure702. Thus, the change in the physical property of propagatingstructure702 results in a corresponding time period change of the energy waves710 within energy propagating structure ormedium702. These changes in the time period of the energy waves710 alter the equilibrium point of the closed loop circuit and frequency of operation of the closed loop circuit. The closed loop circuit adjusts such thatsine waves732 and734 correspond to the new equilibrium point. The frequency ofenergy waves710 and changes to the frequency correlate to changes in the physical attributes of energy propagating structure ormedium702.
• The physical changes may be imposed onenergy propagating structure702 by external forces orconditions712 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 ofenergy waves710 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 ormedium702.
• Prior to measurement of the frequency or operation of the propagation tuned oscillator,control logic718 loads the loop count intodigital counter750 that is stored incount register748. The firstdigital pulses742 initiates closed loop operation within the propagation tuned oscillator and signals controlcircuit718 to start measurement operations. At the start of closed loop operation,control logic718 enablesdigital counter750 anddigital timer752. In one embodiment,digital counter750 decrements its value on the rising edge of each digital pulse output by zero-cross receiver740.Digital timer752 increments its value on each rising edge ofclock pulses756. When the number ofdigital pulses742 has decremented, the value withindigital counter750 to zero a stop signal is output fromdigital counter750. The stop signal disablesdigital timer752 and triggers controlcircuit718 to output a load command to data register754. Data register754 loads a binary number fromdigital timer752 that is equal to the period of the energy waves or pulses times the value incounter748 divided byclock period756. With aconstant clock period756, the value in data register754 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 thecount register748.
• FIG. 8 is a sensor interface diagram incorporating thetransducer driver100 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,mux802 is enabled to couple one or moredigital pulses804 to thetransducer driver806.Transducer driver806 generates apulse sequence808 corresponding todigital pulses804.Analog mux810 is enabled to couplepulse sequence808 to thetransmitter transducer812.Transducer812 is coupled to a medium at a first location.Transducer812 responds topulse sequence808 and generates correspondingenergy pulses814 that are emitted into the medium at the first location. Theenergy pulses814 propagate through the medium. Areceiver transducer816 is located at a second location on the medium.Receiver transducer816 captures theenergy pulses814 and generates a corresponding signal ofelectrical pulses818.Transducer816 is coupled to amux820.Mux820 is enabled to couple to zero-cross receiver824.Electrical pulses818 fromtransducer816 are coupled to zero-cross receiver824. Zero-cross receiver824 counts zero crossings ofelectrical pulses818 to determine changes in phase and frequency of the energy pulses responsive to an applied force, as previously explained. Zero-cross receiver824 outputs apulse sequence822 corresponding to the detected signal frequency.Pulse sequence822 is coupled tomux802.Mux802 is decoupled from couplingdigital pulses804 todriver806 upon detection ofpulses822. Conversely,mux802 is enabled to couplepulses822 todriver806 upon detection ofpulses822 thereby creating a positive closed-loop feedback path. Thus, in pulse mode,transducer driver806 and zero-cross receiver824 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.
• FIG. 9 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating thetransducer driver100 for operation in pulse mode. In particular, with respect toFIG. 3, it illustrates closed loop measurement of thetransit time322 of ultrasound waves324 within thewaveguide306 by the operation of the propagation tunedoscillator312. 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 circuit746 digitizes the frequency of operation of the propagation tuned oscillator.
• In pulse mode of operation, asensor comprising transducer704, propagatingstructure702, andtransducer706 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 orcondition712 is applied to propagatingstructure702 that changes the length of the waveguide in a path of a propagating energy wave. A change in length corresponds to a change intransit time708 of the propagating wave. The length of propagatingstructure702 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.
• A measurement sequence is initiated whencontrol circuitry718 closes switch720coupling oscillator output724 ofoscillator722 to the input oftransducer driver726. One or more pulses provided totransducer driver726 initiates an action to propagateenergy waves710 having simple or complex waveforms through energy propagating structure ormedium702.Transducer driver726 comprises adigital driver728 andmatching network730. In one embodiment,transducer driver726 transforms the oscillator output ofoscillator722 into analog pulses ofelectrical waves932 having the same repetition rate asoscillator output724 and sufficient amplitude to excitetransducer704.
• Emittingtransducer704 converts theanalog pulses932 intoenergy waves710 of the same frequency and emits them at a first location into energy propagating structure ormedium702. The energy waves710 propagate through energy propagating structure ormedium702. Upon reachingtransducer706 at the second location,energy waves710 are captured, sensed, or detected. The captured energy waves are converted bytransducer706 intoanalog pulses934 that are electrical waves having the same frequency.
• Amplifier736 comprises apre-amplifier738 and zero-cross receiver740.Amplifier736 converts theanalog pulses934 intodigital pulses742 of sufficient duration to sustain the behavior of the closed loop circuit.Control circuitry718 responds todigital pulses742 fromamplifier736 by openingswitch720 andclosing switch744.Opening switch720 decouplesoscillator output724 from the input oftransducer driver726.Closing switch744 creates a closed loop circuit coupling the output ofamplifier736 to the input oftransducer driver726 and sustaining the emission, propagation, and detection of energy waves through energy propagating structure ormedium702.
• An equilibrium state is attained by maintaining unity gain around this closed loop circuit whereinpulses932 input intotransducer704 andpulses934 output bytransducer706 are in phase with a small but constant offset.Transducer706 as disclosed above, outputs thepulses934 upon detecting energy waves propagating to the second location. In the equilibrium state, an integer number ofenergy waves710 propagate through energy propagating structure ormedium702.
• Movement or changes in the physical properties of energy propagating structure or medium702 change atransit time708 of energy waves710. Thetransit time708 comprises the time for an energy wave to propagate from the first location to the second location of propagatingstructure702. Thus, the change in the physical property of propagatingstructure702 results in a corresponding time period change of the energy waves710 within energy propagating structure ormedium702. These changes in the time period of the energy waves710 alter the equilibrium point of the closed loop circuit and frequency of operation of the closed loop circuit. The closed loop circuit adjusts such thatpulses932 and934 correspond to the new equilibrium point. The frequency ofenergy waves710 and changes to the frequency correlate to changes in the physical attributes of energy propagating structure ormedium702.
• The physical changes may be imposed onenergy propagating structure702 by external forces orconditions712 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 ofenergy waves710 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 ormedium702.
• Briefly referring back toFIG. 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.
• FIG. 10 is a sensor interface diagram incorporating thetransducer driver100 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 adigital pulse1004, which is passed to thetransducer driver1006 to produce thepulse sequence1008. Analog multiplexer (mux)1010 receivespulse sequence1008, which is passed to thetransducer1012 to generateenergy pulses1014.Energy pulses1014 are emitted into a first location of a medium and propagate through the medium. In the pulse-echo example,energy pulses1014 are reflected off asurface1016 at a second location of the medium, for example, the end of a waveguide or reflector, and echoed back to thetransducer1012. Thetransducer1012 proceeds to then capture the reflected pulse echo. In pulsed echo mode, thetransducer1012 performs as both a transmitter and a receiver. As disclosed above,transducer1012 toggles back and forth between emitting and receiving energy waves.Transducer1012 captures the reflected echo pulses, which are coupled toanalog mux1010 and directed to the edge-detectreceiver1022. The captured reflected echo pulses is indicated byelectrical waves1018. Edge-detectreceiver1022 locks on pulse edges corresponding to the wave front of a propagated energy wave to determine changes in phase and frequency of theenergy pulses1014 responsive to an applied force, as previously explained. Among other parameters, it generates apulse sequence1018 corresponding to the detected signal frequency. Thepulse sequence1018 is coupled tomux1002 and directed todriver1006 to initiate one or more energy waves being emitted into the medium bytransducer1012.Pulse1004 is decoupled from being provided todriver1006. Thus, a positive closed loop feedback includingtransducer driver1006 is formed that repeatably emits energy waves into the medium untilmux1002 prevents a signal from being provided todriver1006. The edge-detectreceiver1022 is coupled to a second location of the medium and is in the feedback path. The edge-detectreceiver1002 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.
• FIG. 11 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating thetransducer driver100 for operation in pulse echo mode. In particular, with respect toFIG. 3, it illustrates closed loop measurement of thetransit time322 of ultrasound waves324 within thewaveguide306 by the operation of the propagation tunedoscillator312. 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 circuit1146 digitizes the frequency of operation of the propagation tuned oscillator.
• In pulse-echo mode of operation asensor comprising transducer1104, propagatingstructure1102, and reflectingsurface1106 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 orcondition1112 is applied to propagatingstructure1102 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 propagatingstructure1102 corresponds to the appliedforce1112. A length reduction corresponds to a higher force being applied to the propagatingstructure1102. Conversely, a length increase corresponds to a lowering of the appliedforce1112 to the propagatingstructure1102. The length of propagatingstructure1102 is measured and is converted to force by way of a known length to force relationship.
• Transducer1104 is both an emitting device and a receiving device in pulse-echo mode. The sensor for measuring a parameter comprisestransducer1104 coupled to propagatingstructure1102 at a first location. A reflecting surface is coupled to propagatingstructure1102 at a second location.Transducer1104 has two modes of operation comprising an emitting mode and receiving mode.Transducer1104 emits an energy wave into the propagatingstructure1102 at the first location in the emitting mode. The energy wave propagates to a second location and is reflected by reflectingsurface1106. The reflected energy wave is reflected towards the first location andtransducer1104 subsequently generates a signal in the receiving mode corresponding to the reflected energy wave.
• A measurement sequence in pulse echo mode is initiated whencontrol circuitry1118 closes switch1120 coupling digital output1124 ofoscillator1122 to the input oftransducer driver1126. One or more pulses provided totransducer driver1126 starts a process to emit one ormore energy waves1110 having simple or complex waveforms into energy propagating structure or medium1102.Transducer driver1126 comprises adigital driver1128 andmatching network1130. In one embodiment,transducer driver1126 transforms the digital output ofoscillator1122 into pulses ofelectrical waves1132 having the same repetition rate as digital output1124 and sufficient amplitude to excitetransducer1104.
• Transducer1104 converts the pulses ofelectrical waves1132 into pulses ofenergy waves1110 of the same repetition rate and emits them into energy propagating structure or medium1102. The pulses ofenergy waves1110 propagate through energy propagating structure or medium1102 as shown byarrow1114 towards reflectingsurface1106. Upon reaching reflectingsurface1106,energy waves1110 are reflected by reflectingsurface1106. Reflected energy waves propagate towardstransducer1104 as shown byarrow1116. The reflected energy waves are detected bytransducer1104 and converted into pulses ofelectrical waves1134 having the same repetition rate.
• Amplifier1136 comprises apre-amplifier1138 and edge-detectreceiver1140.Amplifier1136 converts the pulses ofelectrical waves1134 intodigital pulses1142 of sufficient duration to sustain the pulse behavior of the closed loop circuit.Control circuitry1118 responds todigital output pulses1142 fromamplifier1136 by openingswitch1120 andclosing switch1144.Opening switch1120 decouples oscillator output1124 from the input oftransducer driver1126.Closing switch1144 creates a closed loop circuit coupling the output ofamplifier1136 to the input oftransducer driver1126 and sustaining the emission, propagation, and detection of energy pulses through energy propagating structure or medium1102.
• An equilibrium state is attained by maintaining unity gain around this closed loop circuit whereinelectrical waves1132 input intotransducer1104 andelectrical waves1134 output bytransducer1104 are in phase with a small but constant offset.Transducer1104 as disclosed above, outputs theelectrical waves1134 upon detecting reflected energy waves reflected from reflectingsurface1106. In the equilibrium state, an integer number of pulses ofenergy waves1110 propagate through energy propagating structure or medium1102.
• Movement or changes in the physical properties of energy propagating structure or medium1102 change atransit time1108 ofenergy waves1110. Thetransit time1108 comprises the time for an energy wave to propagate from the first location to the second location of propagatingstructure1102 and the time for the reflected energy wave to propagate from the second location to the first location of propagatingstructure1102. Thus, the change in the physical property of propagatingstructure1102 results in a corresponding time period change of theenergy waves1110 within energy propagating structure or medium1102. These changes in the time period of the repetition rate of theenergy pulses1110 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 thatelectrical waves1132 and1134 correspond to the new equilibrium point. The repetition rate ofenergy waves1110 and changes to the repetition rate correlate to changes in the physical attributes of energy propagating structure or medium1102.
• The physical changes may be imposed onenergy propagating structure1102 by external forces orconditions1112 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 ofenergy waves1110 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 medium1102.
• Prior to measurement of the frequency or operation of the propagation tuned oscillator,control logic1118 loads the loop count intodigital counter1150 that is stored incount register1148. The firstdigital pulses1142 initiates closed loop operation within the propagation tuned oscillator and signalscontrol circuit1118 to start measurement operations. At the start of closed loop operation,control logic1118 enablesdigital counter1150 anddigital timer1152. In one embodiment,digital counter1150 decrements its value on the rising edge of each digital pulse output by edge-detectreceiver1140.Digital timer1152 increments its value on each rising edge ofclock pulses1156. When the number ofdigital pulses1142 has decremented, the value withindigital counter1150 to zero a stop signal is output fromdigital counter1150. The stop signal disablesdigital timer1152 and triggerscontrol circuit1118 to output a load command todata register1154. Data register1154 loads a binary number fromdigital timer1152 that is equal to the period of the energy waves or pulses times the value incounter1148 divided byclock period1156. With aconstant clock period1156, the value in data register1154 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 thecount register1148.
• FIG. 12 is an illustration of asensor1200 placed in contact between afemur1202 and atibia1208 for measuring a parameter in accordance with an exemplary embodiment. In general, asensor1200 is placed in contact with or in proximity to the muscular-skeletal system to measure a parameter. In a non-limiting example,sensor1200 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 ofsensor1200 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.Sensor1200 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.
• In at least one exemplary embodiment, an energy pulse is directed within one or more waveguides insensor1200 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.
• Sensor1200 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,sensor1200 is used to measure load and balance of an installed artificial knee joint. A knee prosthesis comprises afemoral prosthetic component1204, an insert, and atibial prosthetic component1206. A distal end offemur1202 is prepared and receivesfemoral prosthetic component1204.Femoral prosthetic component1204 typically has two condyle surfaces that mimic a natural femur. As shown,femoral prosthetic component1204 has single condyle surface being coupled tofemur1202.Femoral prosthetic component1204 is typically made of a metal or metal alloy.
• A proximal end offemur1208 is prepared to receive tibialprosthetic component1206.Tibial prosthetic component1206 is a support structure that is fastened to the proximal end of the tibia and is usually made of a metal or metal alloy. Thetibial prosthetic component1206 also retains the insert in a fixed position with respect tofemur1208. The insert is fitted between femoralprosthetic component1204 and tibialprosthetic component1206. The insert has at least one bearing surface that is in contact with at least condyle surface offemoral prosthetic component1204. 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.
• In a knee joint replacement process, the surgeon affixesfemoral prosthetic component1204 to thefemur1202 and tibialprosthetic component1206 tofemur1208. Thetibial prosthetic component1206 can include a tray or plate affixed to the planarized proximal end of thefemur1208.Sensor1200 is placed between a condyle surface offemoral prosthetic component1204 and a major surface of tibialprosthetic component1206. The condyle surface contacts a major surface ofsensor1200. The major surface ofsensor1200 approximates a surface of the insert.Tibial prosthetic component1206 can include a cavity or tray on the major surface that receives and retainssensor1200 during a measurement process.Tibial prosthetic component1206 andsensor1200 has a combined thickness that represents a combined thickness of tibialprosthetic component1206 and a final (or chronic) insert of the knee joint.
• In one embodiment, twosensors1200 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 bytibial component1206. One or twosensors1200 may be inserted between femoralprosthetic component1204 and tibialprosthetic component1206. Each sensor is independent and each measures a respective condyle offemur1202. 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 bysensor1200 aid the surgeon in modifying the absolute loading on each condyle and the balance between condyles. Although shown for a knee implant,sensor1200 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,sensor1200 can also be adapted to orthopedic tools to provide measurements.
• Theprosthesis incorporating sensor1200 emulates the function of a natural knee joint.Sensor1200 can measure loads or other parameters at various points throughout the range of motion. Data fromsensor1200 is transmitted to a receivingstation1210 via wired or wireless communications. In a first embodiment,sensor1200 is a disposable system.Sensor1200 can be disposed of after usingsensor1200 to optimally fit the joint implant.Sensor1200 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 sterilizesensor1200 for reuse. In a third embodiment,sensor1200 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,sensor1200 can be a permanent component of the replacement joint.Sensor1200 can be used to provide both short term and long term post-operative data on the implanted joint. In a fifth embodiment,sensor1200 can be coupled to the muscular-skeletal system. In all of the embodiments, receivingstation1210 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 station1210 can record and provide accounting information ofsensor1200 to an appropriate authority.
• In an intra-operative example,sensor1200 can measure forces (Fx, Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on thefemoral prosthetic component1204 and thetibial prosthetic component1206. The measured force and torque data is transmitted to receivingstation1210 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.
• As mentioned previously,sensor1200 can be used for other joint surgeries; it is not limited to knee replacement implant or implants. Moreover,sensor1200 is not limited to trial measurements.Sensor1200 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 aproblem using sensor1200 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,sensor1200 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.Sensor1200 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.
• 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.
• 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.

Claims (20)

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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 4 where the driver circuit drives more than one transducer.

6. The driver circuit ofclaim 4 where the impedance matching network comprises a pi network.

7. The driver circuit ofclaim 4 where the driver circuit controls a duration of stimulation of the transducer.

8. The driver circuit ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 11 where the propagation medium is a compressible waveguide to contain, propagate, and direct energy waves.

15. The sensor ofclaim 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 ofclaim 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 ofclaim 17 further including a reflecting surface at a second location of the propagation medium.

19. The sensor system ofclaim 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 ofclaim 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.

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