# Patent

## Title
Zero-crossing receiver for orthopedic parameter sensing

## Abstract

A sensor system uses positive closed-loop feedback to provide energy waves into a medium. It comprises a transducer (604), a propagating structure (602), and a transducer (606). A parameter is applied to the propagating structure that affects the medium. A sensor is coupled to a propagation tuned oscillator (416) that forms a positive closed-loop feedback path. The propagation tuned oscillator (416) includes a zero-crossing receiver (200) that generates a pulse upon sensing a transition of an energy wave from the propagating structure (602). The zero-crossing receiver (200) is in the feedback path that maintains the emission of energy waves into the propagating structure (602). The zero-crossing receiver (200) comprises a preamplifier (206), a filter (208), an offset adjustment circuit (210), a comparator (212) and a pulse circuit (218). The transit time, phase, or frequency is measured of the propagating energy waves and correlated to the parameter being measured.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of U.S. provisional patent application 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 circuitry for detecting specific features of the energy waves or pulses.
BACKGROUND
The skeletal system of a mammal is subject to variations among species. Further changes can occur due to environmental factors, degradation through use, and aging. An orthopedic joint of the skeletal system typically comprises two or more bones that move in relation to one another. Movement is enabled by muscle tissue and tendons attached to the skeletal system of the joint. Ligaments hold and stabilize the one or more joint bones positionally. Cartilage is a wear surface that prevents bone-to-bone contact, distributes load, and lowers friction.
There has been substantial growth in the repair of the human skeletal system. In general, orthopedic joints have evolved using information from simulations, mechanical prototypes, and patient data that is collected and used to initiate improved designs. Similarly, the tools being used for orthopedic surgery have been refined over the years but have not changed substantially. Thus, the basic procedure for replacement of an orthopedic joint has been standardized to meet the general needs of a wide distribution of the population. Although the tools, procedure, and artificial joint meet a general need, each replacement procedure is subject to significant variation from patient to patient. The correction of these individual variations relies on the skill of the surgeon to adapt and fit the replacement joint using the available tools to the specific circumstance.



BRIEF DESCRIPTION OF THE DRAWINGS
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 an illustration of a sensor placed in contact between a femur and a tibia for measuring a parameter in accordance with an exemplary embodiment;
FIG. 2 is a block diagram of a zero-crossing receiver in accordance with one embodiment;
FIG. 3 illustrates a block diagram of the zero-crossing receiver coupled to a sensing assembly in accordance with an exemplary embodiment;
FIG. 4 is an exemplary propagation tuned oscillator (PTO) incorporating the zero-crossing receiver to maintain positive closed-loop feedback in accordance with one embodiment.
FIG. 5 is a sensor interface diagram incorporating the zero-crossing receiver in a continuous wave multiplexing arrangement for maintaining positive closed-loop feedback in accordance with one embodiment;
FIG. 6 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the zero-crossing receiver for operation in continuous wave mode;
FIG. 7 is a sensor interface diagram incorporating the zero-crossing receiver in a pulse mode multiplexing arrangement for maintaining positive closed-loop feedback in accordance with one embodiment;
FIG. 8 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the zero-crossing receiver for operation in pulse mode in accordance with one embodiment; and
FIG. 9 is an exemplary method for measuring a parameter that corresponds to a transit time of an energy wave propagating through a medium in accordance with the present invention.



DETAILED DESCRIPTION
Embodiments of the invention are broadly directed to measurement of physical parameters, and more particularly, to fast-response circuitry for detecting specific features of the 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 is an illustration of a sensor 100 placed in contact between a femur 102 and a tibia 108 for measuring a parameter in accordance with an exemplary embodiment. In general, a sensor 100 is placed in contact with or in proximity to the muscular-skeletal system to measure a parameter. In a non-limiting example, sensor 100 is used to measure a parameter of a muscular-skeletal system during a procedure such as an installation of an artificial joint. Embodiments of sensor 100 are broadly directed to measurement of physical parameters, and more particularly, to evaluating changes in the transit time of a pulsed energy wave propagating through a medium. In-situ measurements during orthopedic joint implant surgery would be of substantial benefit to verify an implant is in balance and under appropriate loading or tension. In one embodiment, the instrument is similar to and operates familiarly with other instruments currently used by surgeons. This will increase acceptance and reduce the adoption cycle for a new technology. The measurements will allow the surgeon to ensure that the 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 100 can provide implant status data to the orthopedic manufacturers and surgeons. Moreover, data generated by direct measurement of the implanted joint itself would greatly improve the knowledge of implanted joint operation and joint wear thereby leading to improved design and materials.
In at least one exemplary embodiment, an energy pulse is directed within one or more waveguides in sensor 100 by way of pulse mode operations and pulse shaping. The waveguide is a conduit that directs the energy pulse in a predetermined direction. The energy pulse is typically confined within the waveguide. In one embodiment, the waveguide comprises a polymer material. For example, urethane or polyethylene are polymers suitable for forming a waveguide. 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.
Sensor 100 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 100 is used to measure load and balance of an installed artificial knee joint. A knee prosthesis comprises a femoral prosthetic component 104, an insert, and a tibial prosthetic component 106. A distal end of femur 102 is prepared and receives femoral prosthetic component 104. Femoral prosthetic component 104 typically has two condyle surfaces that mimic a natural femur. As shown, femoral prosthetic component 104 has single condyle surface being coupled to femur 100. Femoral prosthetic component 104 is typically made of a metal or metal alloy.
A proximal end of tibia 108 is prepared to receive tibial prosthetic component 106. Tibial prosthetic component 106 is a support structure that is fastened to the proximal end of the tibia and is usually made of a metal or metal alloy. The tibial prosthetic component 106 also retains the insert in a fixed position with respect to tibia 108. The insert is fitted between femoral prosthetic component 104 and tibial prosthetic component 106. The insert has at least one bearing surface that is in contact with at least condyle surface of femoral prosthetic component 104. The condyle surface can move in relation to the bearing surface of the insert such that the lower leg can rotate under load. The insert is typically made of a high wear plastic material that minimizes friction.
In a knee joint replacement process, the surgeon affixes femoral prosthetic component 104 to the femur 102 and tibial prosthetic component 106 to tibia 108. The tibial prosthetic component 106 can include a tray or plate affixed to the planarized proximal end of the tibia 108. Sensor 100 is placed between a condyle surface of femoral prosthetic component 104 and a major surface of tibial prosthetic component 106. The condyle surface contacts a major surface of sensor 100. The major surface of sensor 100 approximates a surface of the insert. Tibial prosthetic component 106 can include a cavity or tray on the major surface that receives and retains sensor 100 during a measurement process. Tibial prosthetic component 106 and sensor 100 has a combined thickness that represents a combined thickness of tibial prosthetic component 106 and a final (or chronic) insert of the knee joint.
In one embodiment, two sensors 100 are fitted into two separate cavities, the cavities are within a trial insert (that may also be referred to as the tibial insert, rather than the tibial component itself) that is held in position by tibial component 106. One or two sensors 100 may be inserted between femoral prosthetic component 104 and tibial prosthetic component 106. Each sensor is independent and each measures a respective condyle of femur 102. Separate sensors also accommodate a situation where a single condyle is repaired and only a single sensor is used. Alternatively, the electronics can be shared between two sensors to lower cost and complexity of the system. The shared electronics can multiplex between each sensor module to take measurements when appropriate. Measurements taken by sensor 100 aid the surgeon in modifying the absolute loading on each condyle and the balance between condyles. Although shown for a knee implant, sensor 100 can be used to measure other orthopedic joints such as the spine, hip, shoulder, elbow, ankle, wrist, interphalangeal joint, metatarsophalangeal joint, metacarpophalangeal joints, and others. Alternatively, sensor 100 can also be adapted to orthopedic tools to provide measurements.
The prosthesis incorporating sensor 100 emulates the function of a natural knee joint. Sensor 100 can measure loads or other parameters at various points throughout the range of motion. Data from sensor 100 is transmitted to a receiving station 110 via wired or wireless communications. In a first embodiment, sensor 100 is a disposable system. Sensor 100 can be disposed of after using sensor 100 to optimally fit the joint implant. Sensor 100 is a low cost disposable system that reduces capital costs, operating costs, facilitates rapid adoption of quantitative measurement, and initiates evidentiary based orthopedic medicine. In a second embodiment, a methodology can be put in place to clean and sterilize sensor 100 for reuse. In a third embodiment, sensor 100 can be incorporated in a tool instead of being a component of the replacement joint. The tool can be disposable or be cleaned and sterilized for reuse. In a fourth embodiment, sensor 100 can be a permanent component of the replacement joint. Sensor 100 can be used to provide both short term and long term post-operative data on the implanted joint. In a fifth embodiment, sensor 100 can be coupled to the muscular-skeletal system. In all of the embodiments, receiving station 110 can include data processing, storage, or display, or combination thereof and provide real time graphical representation of the level and distribution of the load. Receiving station 110 can record and provide accounting information of sensor 100 to an appropriate authority.
In an intra-operative example, sensor 100 can measure forces (Fx, Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on the femoral prosthetic component 104 and the tibial prosthetic component 106. The measured force and torque data is transmitted to receiving station 110 to provide real-time visualization for assisting the surgeon in identifying any adjustments needed to achieve optimal joint pressure and balancing. The data has substantial value in determining ranges of load and alignment tolerances required to minimize rework and maximize patient function and longevity of the joint.
As mentioned previously, sensor 100 can be used for other joint surgeries; it is not limited to knee replacement implant or implants. Moreover, sensor 100 is not limited to trial measurements. Sensor 100 can be incorporated into the final joint system to provide data post-operatively to determine if the implanted joint is functioning correctly. Early determination of a problem using sensor 100 can reduce catastrophic failure of the joint 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 100 can be shaped such that it can be placed or engaged or affixed to or within load bearing surfaces used in many orthopedic applications (or used in any orthopedic application) related to the musculoskeletal system, joints, and tools associated therewith. Sensor 100 can provide information on a combination of one or more performance parameters of interest such as wear, stress, kinematics, kinetics, fixation strength, ligament balance, anatomical fit and balance.
FIG. 2 is a block diagram of a zero-crossing receiver 200 in accordance with one embodiment. In a first embodiment, the zero-crossing receiver 200 is provided to detect transition states of energy waves, such as the transition of each energy wave through a mid-point of a symmetrical or cyclical waveform. This enables capturing of parameters including, but not limited to, transit time, phase, or frequency of the energy waves. The receiver rapidly responds to a signal transition and outputs a digital pulse that is consistent with the energy wave transition characteristics and with minimal delay. The zero-crossing receiver 200 further discriminates between noise and the energy waves of interest, including very low level waves by way of adjustable levels of noise reduction. A noise reduction section 218 comprises a filtering stage and an offset adjustment stage to perform noise suppression accurately over a wide range of amplitudes including low level waves.
In a second embodiment, a zero-crossing receiver is provided to convert an incoming symmetrical, cyclical, or sine wave to a square or rectangular digital pulse sequence with superior performance for very low level input signals. The digital pulse sequence represents pulse timing intervals that are consistent with the energy wave transition times. The zero-crossing receiver is coupled with a sensing assembly to generate the digital pulse sequence responsive to evaluating transitions of the incoming sine wave. This digital pulse sequence conveys timing information related to parameters of interest, such as applied forces, associated with the physical changes in the sensing assembly.
In a third embodiment, the integrated zero-crossing receiver is incorporated within a propagation tuned oscillator (PTO) to maintain positive closed-loop feedback when operating in a continuous wave mode or pulse-loop mode. The integrated edge zero-crossing receiver is electrically integrated with the PTO by multiplexing input and output circuitry to achieve ultra low-power and small compact size. Electrical components of the PTO are integrated with components of the zero-crossing receiver to assure adequate sensitivity to low-level signals.
In one embodiment, low power zero-crossing receiver 200 can be integrated with other circuitry of the propagation tuned oscillator to further improve performance at low signal levels. The zero-crossing receiver 200 comprises a preamplifier 206, a filter 208, an offset adjustment circuitry 210, a comparator 212, and a digital pulse circuit 214. The filter 208 and offset adjustment circuitry 210 constitute a noise reduction section 218 as will be explained ahead. The zero-crossing receiver 200 can be implemented in discrete analog components, digital components or combination thereof. The integrated zero-crossing receiver 200 practices measurement methods that detect the midpoint of energy waves at specified locations, and under specified conditions, to enable capturing parameters including, but not limited to, transit time, phase, or frequency of energy waves. A brief description of the method of operation is as follows.
An incoming energy wave 202 is coupled from an electrical connection, antenna, or transducer to an input 204 of zero-crossing receiver 200. Input 204 of zero-crossing receiver 200 is coupled to pre-amplifier 206 to amplify the incoming energy wave 202. The amplified signal is filtered by filter 208. Filter 208 is coupled to an output of pre-amplifier 206 and an input of offset adjustment circuitry 210. In one configuration, filter 208 is a low-pass filter to remove high frequency components above the incoming energy wave 202 bandwidth. In another arrangement, the filter is a band-pass filter with a pass-band corresponding to the bandwidth of the incoming energy wave 202. It is not however limited to either arrangement. The offset of the filtered amplified wave is adjusted by offset adjustment circuitry 210. An input of comparator 212 is coupled to an output of offset adjustment circuitry 210. Comparator 212 monitors the amplified waveforms and triggers digital pulse circuitry 214 whenever the preset trigger level is detected. Digital pulse circuit 214 has an input coupled to the output of comparator 212 and an output for providing digital pulse 216. The digital pulse 216 can be further coupled to signal processing circuitry, as will be explained ahead.
In a preferred embodiment, 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.
FIG. 3 illustrates a block diagram of the integrated zero-crossing receiver 200 coupled to a sensing assembly 300 in accordance with an exemplary embodiment. The pre-amplifier 206 and the digital pulse circuit 214 are shown for reference and discussion. In one embodiment, sensing assembly 300 comprises a transmitter transducer 302, an energy propagating structure (or medium) 304, and a receiver transducer 306. As will be explained further hereinbelow, the sensing assembly 300 in one embodiment is part of a sensory device that measures a parameter such as force, pressure, or load. In a non-limiting example, an external parameter such as an applied force 308 affects the sensing assembly 200. As shown, applied force 308 modifies propagating structure 304 dimensionally. In general, the sensing assembly 300 conveys one or more parameters of interest such as distance, force weight, strain, pressure, wear, vibration, viscosity, density, direction, and displacement related to a change in energy propagating structure 304. An example is measuring loading applied by a joint of the muscular-skeletal system as disclosed above using sensing assembly 300 between the bones of the joint.
A transducer driver circuit (not shown) drives the transmitter transducer 302 of the sensing assembly 300 to produce energy waves 310 that are directed into the energy propagating structure 304. Changes in the energy propagating medium 304 due to an applied parameter such as applied forces 308 change the frequency, phase, and transit time of energy waves 310 (or pulses). In one embodiment, applied forces 308 affect the length of propagating structure 304 in a direction of a path of propagation of energy waves 310. The zero-crossing receiver 200 is coupled to the receiver transducer 306 to detect zero-crossings of the reproduced energy wave 202. Upon detecting a zero-crossing digital pulse circuit 214 is triggered to output a pulse 216. The timing of the digital pulse 216 conveys the parameters of interest (e.g., distance, force weight, strain, pressure, wear, vibration, viscosity, density, direction, displacement, etc.).
Measurement methods that rely on such propagation of energy waves 310 or pulses of energy waves are required to achieve highly accurate and controlled detection of energy waves or pulses. Moreover, pulses of energy waves may contain multiple energy waves with complex waveforms therein leading to potential ambiguity of detection. In particular, directing energy waves 310 into the energy propagating structure 304 can generate interference patterns caused by nulls and resonances of the waveguide, as well as characteristics of the generated energy waves 310. These interference patterns can multiply excited waveforms that result in distortion of the edges of the original energy wave.
Briefly referring back to FIG. 2, to reliably detect the arrival of a pulse of energy waves, the zero-crossing receiver 200 leverages noise reduction section 218 that incorporates two forms of noise reduction. Frequencies above the operating frequencies for physical measurements of the parameters of interest are attenuated with the filter 208. In addition, the offset level of the incoming waveform is adjusted by the offset adjustment 210 to optimize the voltage level at which the comparator 212 triggers an output pulse. This is more reliable than amplifying the incoming waveform because it does not add additional amplification of noise present on the input. The combination of rapid response to the arrival of incoming symmetrical, cyclical, or sine waves with adjustable levels of noise reduction achieves reliable zero-crossing detection by way of the ultra low power zero-crossing receiver 200 with superior performance for very low level signals.
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. 4 is an exemplary propagation tuned oscillator (PTO) 400 incorporating the zero-crossing receiver 200 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 402. A positive feedback closed-loop circuit causes the PTO 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 an applied parameter to the propagating medium. For example, temperature changes or length changes are different parameters that can modify the propagating medium dimensionally. The length change can result from externally applied forces or pressure. In one embodiment, 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.
The sensing assembly 402 comprises a first transducer 404, a second transducer 406, and a waveguide 408. The waveguide 408 is an energy propagating structure or medium. Waveguide 408 contains and directs the energy wave. The sensing assembly 402 is affixed to load bearing or contacting surfaces 410. In one embodiment, external forces applied to the contacting surfaces 410 compress the waveguide 408 and change the length of the waveguide 408. This pushes the transducers 404 and 406 closer to together. This change in distance affects a transmit time 412 of energy waves 414 transmitted and received between transducers 404 and 406. The PTO 416 in response to these physical changes alters the oscillation frequency of the ultrasound waves 414 to achieve resonance.
Notably, changes in the waveguide 408 (energy propagating structure or structures) alter the propagation properties of the medium of propagation (e.g. transmit time 412). Due to the closed-loop operation shown, the PTO 416 changes the resonant frequency of the oscillator and accordingly the frequency of oscillation of the closed loop circuit. In one embodiment, the PTO 416 adjusts the oscillation frequency to be an integer number of waves. A digital counter 418 in conjunction with electronic components counts the number of waves to determine the corresponding change in the length of the waveguide 408. 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 following is an example of the operation of sensing assembly 402, propagation tuned oscillator 416, and digital counter 418. In the example, the energy waves are acoustic waves at ultrasonic frequencies. The frequency of ultrasound waves 414 is controlled by propagation tuned oscillator 416. The ultrasound waves are emitted by ultrasound resonator or transducer 404 into a first location of waveguide 408. The emitted ultrasound waves by transducer 404 propagate through waveguide 408.
In the illustrated embodiment, a transducer 406 is coupled to waveguide 408 at a second location. Energy waves are emitted by transducer 404 into waveguide 408. Ultrasound waves 414 propagate to the second location and received by transducer 406. In one embodiment, transducer 406 outputs an electrical wave corresponding to ultrasound waves 414. In general, the transit time 412 of ultrasound waves 414 to propagate from the first location to the second location of waveguide 408 determines the period of oscillation of propagation tuned oscillator 416. Alternatively, transducer 404 can be both emit and receive energy waves. A reflecting surface at the second location can be used to direct the energy waves back to transducer 404 to be received. Transducer 404 toggles back and forth between the emitting and receiving modes.
Under quiescent conditions, the length of waveguide 408 does not change. Thus, the frequency of propagation tuned oscillator 416 remains constant. Changes in external forces or conditions 410 affect the propagation characteristics of waveguide 408 and alter transit time 412. In one embodiment, the number of wavelengths of ultrasound waves 414 is held constant by propagation tuned oscillator 416. Holding the number of wavelengths or energy waves constant at an integer number forces the frequency of oscillation of propagation tuned oscillator 416 to change. The resulting changes in frequency are captured with digital counter 418 that corresponds to external forces or conditions 410. In general, there is a known relationship between the parameter being applied to waveguide 408 and the length of waveguide 408. PTO 416 and digital counter 418 provides an accurate measurement of the length of waveguide 408. The known relationship between length and the parameter is then applied to the measurement to convert the measured length to the parameter measurement.
The closed loop measurement of the PTO enables high sensitivity and signal-to-noise ratio, as closed-loop time-based measurements are largely insensitive to most sources of error that may influence voltage or current driven sensing methods and devices. The resulting changes in the 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.
Measurement methods that rely on the propagation of energy waves, or energy waves within energy pulses, may require the detection of a specific point of energy waves at specified locations, or under specified conditions, to enable capturing parameters including, but not limited to, transit time, phase, or frequency of the energy waves. 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. 5 is a sensor interface diagram incorporating the zero-crossing receiver 200 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) 502 receives as input a clock signal 504, which is passed to the transducer driver 506 to produce the drive line signal 508. Analog multiplexer (mux) 510 receives drive line signal 508, which is passed to the transmitter transducer 512 to generate energy waves 514. Transducer 512 is located at a first location of an energy propagating medium. The emitted energy waves 514 propagate through the energy propagating medium. Receiver transducer 516 is located at a second location of the energy propagating medium. Receiver transducer 516 captures the energy waves 514, which are fed to analog mux 520 and passed to the zero-crossing receiver 200. The captured energy waves by transducer 516 are indicated by electrical waves 518 provided to mux 520. Zero-crossing receiver 200 outputs a pulse corresponding to each zero crossing detected from captured electrical waves 518. 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 522 corresponds to the detected signal frequency. The zero-crossing receiver 200 is in a feedback path of the propagation tuned oscillator. The pulse sequence 522 is coupled through mux 502 in a positive closed-loop feedback path. The pulse sequence 522 disables the clock signal 504 such that the path providing pulse sequence 522 is coupled to driver 506 to continue emission of energy waves into the energy propagating medium and the path of clock signal 504 to driver 506 is disabled.
FIG. 6 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the zero-crossing receiver 640 for operation in continuous wave mode. In particular, with respect to FIG. 4, it illustrates closed loop measurement of the transit time 412 of ultrasound waves 414 within the waveguide 408 by the operation of the propagation tuned oscillator 416. 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 646 digitizes the frequency of operation of the propagation tuned oscillator.
In continuous wave mode of operation a sensor comprising transducer 604, propagating structure 602, and transducer 606 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 612 is applied to propagating structure 602 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 608 of the propagating wave. Similarly, the length of propagating structure 602 corresponds to the applied force 612. A length reduction corresponds to a higher force being applied to the propagating structure 602. Conversely, a length increase corresponds to a lowering of the applied force 612 to the propagating structure 602. The length of propagating structure 602 is measured and is converted to force by way of a known length to force relationship.
Transducer 604 is an emitting device in continuous wave mode. The sensor for measuring a parameter comprises transducer 604 coupled to propagating structure 602 at a first location. A transducer 606 is coupled to propagating structure 602 at a second location. Transducer 606 is a receiving transducer for capturing propagating energy waves. In one embodiment, the captured propagated energy waves are electrical sine waves 634 that are output by transducer 606.
A measurement sequence is initiated when control circuitry 618 closes switch 620 coupling oscillator output 624 of oscillator 622 to the input of amplifier 626. One or more pulses provided to amplifier 626 initiates an action to propagate energy waves 610 having simple or complex waveforms through energy propagating structure or medium 602. Amplifier 626 comprises a digital driver 628 and matching network 630. In one embodiment, amplifier 626 transforms the oscillator output of oscillator 622 into sine waves of electrical waves 632 having the same repetition rate as oscillator output 624 and sufficient amplitude to excite transducer 604.
Emitting transducer 604 converts the sine waves 632 into energy waves 610 of the same frequency and emits them at the first location into energy propagating structure or medium 602. The energy waves 610 propagate through energy propagating structure or medium 602. Upon reaching transducer 606 at the second location, energy waves 610 are captured, sensed, or detected. The captured energy waves are converted by transducer 606 into sine waves 634 that are electrical waves having the same frequency.
Amplifier 636 comprises a pre-amplifier 638 and zero-cross receiver 640. Amplifier 636 converts the sine waves 634 into digital pulses 642 of sufficient duration to sustain the behavior of the closed loop circuit. Control circuitry 618 responds to digital pulses 642 from amplifier 636 by opening switch 620 and closing switch 644. Opening switch 620 decouples oscillator output 624 from the input of amplifier 626. Closing switch 644 creates a closed loop circuit coupling the output of amplifier 636 to the input of amplifier 626 and sustaining the emission, propagation, and detection of energy waves through energy propagating structure or medium 602.
An equilibrium state is attained by maintaining unity gain around this closed loop circuit wherein sine waves 632 input into transducer 604 and sine waves 634 output by transducer 606 are in phase with a small but constant offset. Transducer 606 as disclosed above, outputs the sine waves 634 upon detecting energy waves propagating to the second location. In the equilibrium state, an integer number of energy waves 610 propagate through energy propagating structure or medium 602.
Movement or changes in the physical properties of energy propagating structure or medium 602 change a transit time 608 of energy waves 610. The transit time 608 comprises the time for an energy wave to propagate from the first location to the second location of propagating structure 602. Thus, the change in the physical property of propagating structure 602 results in a corresponding time period change of the energy waves 610 within energy propagating structure or medium 602. These changes in the time period of the energy waves 610 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 632 and 634 correspond to the new equilibrium point. The frequency of energy waves 610 and changes to the frequency correlate to changes in the physical attributes of energy propagating structure or medium 602.
The physical changes may be imposed on energy propagating structure 602 by external forces or conditions 612 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 610 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 602.
Prior to measurement of the frequency or operation of the propagation tuned oscillator, control logic 618 loads the loop count into digital counter 650 that is stored in count register 648. The first digital pulses 642 initiates closed loop operation within the propagation tuned oscillator and signals control circuit 618 to start measurement operations. At the start of closed loop operation, control logic 618 enables digital counter 650 and digital timer 652. In one embodiment, digital counter 650 decrements its value on the rising edge of each digital pulse output by edge-detect receiver 640. Digital timer 652 increments its value on each rising edge of clock pulses 656. When the number of digital pulses 642 has decremented, the value within digital counter 650 to zero a stop signal is output from digital counter 650. The stop signal disables digital timer 652 and triggers control circuit 618 to output a load command to data register 654. Data register 654 loads a binary number from digital timer 652 that is equal to the period of the energy waves or pulses times the value in counter 648 divided by clock period 656. With a constant clock period 656, the value in data register 654 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 648.
FIG. 7 is a sensor interface diagram incorporating the integrated zero-crossing receiver 200 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 702 is enabled to couple one or more digital pulses 704 to the transducer driver 706. Transducer driver 705 generates a pulse sequence 708 corresponding to digital pulses 704. Analog mux 710 is enabled to couple pulse sequence 708 to the transmitter transducer 712. Transducer 712 is coupled to a medium at a first location. Transducer 712 responds to pulse sequence 708 and generates corresponding energy pulses 714 that are emitted into the medium at the first location. The energy pulses 714 propagate through the medium. A receiver transducer 716 is located at a second location on the medium. Receiver transducer 716 captures the energy pulses 714 and generates a corresponding signal of electrical pulses 718. Transducer 716 is coupled to a mux 720. Mux 720 is enabled to couple to zero-cross receiver 200. Electrical pulses 718 from transducer 716 are coupled to zero-cross receiver 200. Zero-cross receiver 200 counts zero crossings of electrical pulses 718 to determine changes in phase and frequency of the energy pulses responsive to an applied force, as previously explained. Zero-cross receiver 200 outputs a pulse sequence 722 corresponding to the detected signal frequency. Pulse sequence 722 is coupled to mux 702. Mux 702 is decoupled from coupling digital pulses 704 to driver 706 upon detection of pulses 722. Conversely, mux 702 is enabled to couple pulses 722 to driver 706 upon detection of pulses 722 thereby creating a positive closed-loop feedback path. Thus, in pulse mode, zero-cross receiver 200 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. 8 is an exemplary block diagram of a propagation tuned oscillator (PTO) incorporating the zero-crossing receiver 640 for operation in pulse mode. In particular, with respect to FIG. 4, it illustrates closed loop measurement of the transit time 412 of ultrasound waves 414 within the waveguide 408 by the operation of the propagation tuned oscillator 416. 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 646 digitizes the frequency of operation of the propagation tuned oscillator.
In pulse mode of operation, a sensor comprising transducer 604, propagating structure 602, and transducer 606 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 612 is applied to propagating structure 602 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 608 of the propagating wave. The length of propagating structure 602 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 when control circuitry 618 closes switch 620 coupling oscillator output 624 of oscillator 622 to the input of amplifier 626. One or more pulses provided to amplifier 626 initiates an action to propagate energy waves 610 having simple or complex waveforms through energy propagating structure or medium 602. Amplifier 626 comprises a digital driver 628 and matching network 630. In one embodiment, amplifier 626 transforms the oscillator output of oscillator 622 into analog pulses of electrical waves 832 having the same repetition rate as oscillator output 624 and sufficient amplitude to excite transducer 604.
Emitting transducer 604 converts the analog pulses 832 into energy waves 610 of the same frequency and emits them at a first location into energy propagating structure or medium 602. The energy waves 610 propagate through energy propagating structure or medium 602. Upon reaching transducer 606 at the second location, energy waves 610 are captured, sensed, or detected. The captured energy waves are converted by transducer 606 into analog pulses 834 that are electrical waves having the same frequency.
Amplifier 636 comprises a pre-amplifier 638 and zero-cross receiver 640. Amplifier 636 converts the analog pulses 834 into digital pulses 642 of sufficient duration to sustain the behavior of the closed loop circuit. Control circuitry 618 responds to digital pulses 642 from amplifier 636 by opening switch 620 and closing switch 644. Opening switch 620 decouples oscillator output 624 from the input of amplifier 626. Closing switch 644 creates a closed loop circuit coupling the output of amplifier 636 to the input of amplifier 626 and sustaining the emission, propagation, and detection of energy waves through energy propagating structure or medium 602.
An equilibrium state is attained by maintaining unity gain around this closed loop circuit wherein pulses 832 input into transducer 604 and pulses 834 output by transducer 606 are in phase with a small but constant offset. Transducer 606 as disclosed above, outputs the pulses 834 upon detecting energy waves propagating to the second location. In the equilibrium state, an integer number of energy waves 610 propagate through energy propagating structure or medium 602.
Movement or changes in the physical properties of energy propagating structure or medium 602 change a transit time 608 of energy waves 610. The transit time 608 comprises the time for an energy wave to propagate from the first location to the second location of propagating structure 602. Thus, the change in the physical property of propagating structure 602 results in a corresponding time period change of the energy waves 610 within energy propagating structure or medium 602. These changes in the time period of the energy waves 610 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 832 and 834 correspond to the new equilibrium point. The frequency of energy waves 610 and changes to the frequency correlate to changes in the physical attributes of energy propagating structure or medium 602.
The physical changes may be imposed on energy propagating structure 602 by external forces or conditions 612 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 610 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 602.
FIG. 9 is an exemplary method 900 for measuring a parameter that corresponds to a transit time of an energy wave propagating through a medium in accordance with the present invention. The method can be practiced with more or less than the number of steps shown and is not limited to the order shown. In a step 902, one or more pulsed energy waves are provided to a medium. The energy wave is provided at a first location on the medium. In one embodiment, the energy wave is a continuous wave. Alternatively, a pulsed energy wave can be provided. In general, the energy wave propagation medium is subjected to the parameter to be measured. In a non-limiting example, the parameter is a force or pressure that changes the medium dimensionally. A pulsed energy wave emitted into the medium will propagate through the medium. In one embodiment, the medium is a waveguide that directs the wave propagation. In a step 904, each energy wave is sensed or detected. In continuous wave mode or pulse mode, the energy wave propagates from the first location to a second location on the medium where it is sensed. The second location in pulse mode is different from the first location. Conversely, in a pulse-echo mode, an energy wave is reflected upon propagating to the second location. The reflected wave is sensed or detected upon returning to the first location. Thus, the second location in step 904 corresponds to the first location on the medium in a pulse echo mode application. In a step 906, a positive closed loop feedback is maintained while measuring the parameter. A zero-crossing receiver as disclosed herein is in the feedback path of the closed loop. An energy wave is emitted or provided at the first location of the medium upon sensing or detecting an energy wave that has propagated through the medium thereby continuing the process of energy wave emission, energy wave propagation through the medium, and sensing of the propagated wave at the second location.
In one example an energy wave is an ultrasonic energy wave. Sensing of the energy wave at the second location includes the conversion of the ultrasonic energy wave to a corresponding electrical wave. In the continuous wave mode and the pulse mode, the conversion to the electrical wave is by the second transducer. In a step 908, an electrical wave corresponding to an energy wave at the second location is amplified.
In a step 910, the corresponding electrical wave is filtered. In one embodiment, a low pass filter is used to filter out high frequencies above the energy wave frequency. In a second embodiment, a bandpass filter is used to filter out both high frequencies and low frequencies respectively above and below the energy wave frequency. Filtering prevents reduces noise and allows consistent detection of an energy wave transition.
In a step 912, an adjustment is performed that adds an offset to the corresponding electrical wave. The offset further reduces noise issues by allowing the transition of small signals to be detected. In one embodiment, the signal is offset such that the signal is above the noise floor and thus can be easily sensed and the transition detected and differentiated from noise.
In a step 914, a pulse circuit is triggered when a transition of sufficient magnitude is detected. In a step 916, triggering the pulse circuit generates a pulse. In a step 918, the pulse circuit is triggered when a transition greater than a preset trigger level is detected. The preset trigger level is selected to be greater than the noise to prevent false triggering. The process of triggering is extremely consistent between energy wave to energy wave such that the measured time between pulses would be substantially equal under equilibrium conditions. Furthermore, the pulse to pulse times under equilibrium would be approximately equal (less a small but constant circuit delay) to the transit times of the corresponding energy waves to propagate through the medium. The pulse magnitude and duration of the pulse output by the zero-crossing receiver is sufficient to excite the transducer at the first location to emit an energy wave into the medium.
In a step 922, the positive closed-loop feedback is broken to stop the propagation of pulsed energy waves in the medium. In one embodiment, the pulse generated in step 916 from the sensing of the transition of an energy wave is prevented or decoupled from being provided to the transducer at the first location. Thus, the loop is broken and an energy wave is not emitted into the medium due to the prior detected energy wave at the second location.
In a step 924, one of transit time, phase, or frequency of the energy waves propagating through the medium is measured. As mentioned previously, the parameter being measured affects the medium. In a step 920, a parameter of the muscular-skeletal system is applied to the medium. Examples of the parameter is force, position, or temperature. The change in the medium due to the parameter affects transit time, phase, or frequency. Furthermore, the parameter has a known relationship with the medium. Thus, the measurement of the transit time, phase, or frequency can be related back to the parameter. A conversion is performed to produce an accurate measurement of the parameter using energy wave propagation.
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

1. A sensor comprising:
a non gaseous energy propagating structure, where the energy propagating structure does not include living tissue; and
a zero crossing receiver, where the receiver is configured to detect transition states of energy waves directly propagating through the energy propagating structure in response to a parameter of a muscular-skeletal system.

2. The receiver of claim 1 where the receiver converts an incoming symmetrical, cyclical, or sine energy wave to a square or rectangular digital pulse sequence.

3. The receiver of claim 2 where the receiver discriminates between noise and the energy waves of interest by way of adjustable levels of noise reduction.

4. The receiver of claim 3 where an energy wave is ultrasonic and where the energy wave is converted to a corresponding electrical wave having an equal frequency or repetition rate.

5. The receiver of claim 4 further comprising:
a preamplifier coupled to receive the energy wave;
a filter operatively coupled to the preamplifier to reduce noise in the receiver;
an offset adjustment operatively coupled to the filter to offset the energy wave; a comparator operatively coupled to the offset adjustment; and
a pulse circuit operatively coupled to the comparator where the comparator triggers the pulse circuit when a trigger level is detected and where the pulse circuit outputs a pulse in response to the comparator detecting the trigger level.

6. The receiver of claim 5 where the energy wave is a sine wave.

7. The receiver of claim 5 where the energy wave is a pulsed energy wave.

8. The receiver of claim 5 where the filter is a low-pass filter.

9. The receiver of claim 5 where the filter is a band-pass filter.

10. The receiver of claim 1 where the receiver maintains positive close-loop feedback to continue the emission, propagation, and detection of energy waves in the medium when operating in continuous wave mode or pulse mode.

11. A method of propagating energy waves into a non gaseous energy propagating structure, where the energy propagating structure does not include living tissue, comprising the steps of:
providing energy waves in the energy propagating structure at a first location;
sensing each energy wave after directly propagating to a second location; and
maintaining positive closed-loop feedback with a zero-crossing receiver where an energy wave is provided at the first location after a transition of an energy wave at the second location is detected.

12. The method of claim 11 further including the steps of:
amplifying an electrical wave corresponding to an energy wave at the second location;
filtering the electrical wave corresponding to the energy wave;
adjusting an offset of the electrical wave; and
triggering a pulse circuit when the transition is detected; and generating a pulse.

13. The method of claim 12 further including a step of triggering the pulse circuit when a preset trigger level is detected during the transition.

14. The method of claim 12 further including a step of applying a parameter of the muscular-skeletal system to the energy propagating structure.

15. The method of claim 11 further including a step of breaking the positive closed loop feedback to stop the propagation of pulsed energy waves in the energy propagating structure.

16. The method of claim 11 further including a step of measuring one of transit time, phase, or frequency of energy waves propagating through the energy propagating structure.

17. A system for measuring a parameter comprising:
a sensor coupled to a zero-crossing receiver where the sensor comprises:
a first transducer for emitting an ultrasonic energy wave;
a non gaseous energy propagating structure, where the energy propagating structure does not include living tissue, where the first transducer is coupled to the energy propagating structure at a first location; and
a second transducer for receiving a directly propagated ultrasonic energy wave where the second transducer is coupled to the energy propagating structure at a second location, where the second transducer converts the propagated energy wave to a corresponding electrical wave having an equal frequency or repetition rate; and

the zero-crossing receiver comprising:
a preamplifier coupled to receive the energy wave;
a filter operatively coupled to the preamplifier to reduce noise in the receiver;
an offset adjustment operatively coupled to the filter to offset the energy wave;
a comparator operatively coupled to the offset adjustment; and
a pulsecircuit operatively coupled to the comparator where the comparator triggers the pulse circuit when a trigger level is detected and where the pulse circuit outputs a pulse in response to the comparator detecting the trigger level.

18. The system of claim 17 where the zero-crossing receiver and the sensor are coupled in a positive closed-loop feedback path to maintain emission, propagation, and detection of energy waves in the energy propagating structure.

19. The system of claim 18 where the energy wave is sinusoidal or pulsed.