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Showing papers on "Transducer published in 1989"


Patent
13 Apr 1989
TL;DR: An electrosurgical angioplasty catheter with ultrasonic enhancement is described in this paper, which comprises an elongated, flexible plastic tubular body having located at its distal tip an electrode structure for effecting rf cutting along with a transducer for ultrasonically driving the cutting electrodes and the support thereof.
Abstract: An electrosurgical angioplasty catheter with ultrasonic enhancement is described. It comprises an elongated, flexible plastic tubular body having located at its distal tip an electrode structure for effecting rf cutting along with a transducer for ultrasonically driving the rf cutting electrodes and the support thereof. The electronics module for driving the cutting electrodes and the ultrasonic transducer also includes means for receiving echo signals picked up by the transducer whereby Doppler flow readings and ultrasound imaging of the blood vessel being worked upon can be obtained.

508 citations


Patent
22 Jun 1989
TL;DR: In this paper, a transducer assembly for visualization and treatment of transcutaneous and intraoperative sites includes in combination a visualization transducers and a treatment transducers, each of which are movable with both linear and rotary degrees of freedom.
Abstract: A transducer assembly for visualization and treatment of transcutaneous and intraoperative sites includes in combination a visualization transducer and a treatment transducer, each of which are movable with both linear and rotary degrees of freedom. Movement of each transducer is by various motor and geared drive arrangements wherein certain degrees of freedom for one transducer are separate and independent from the degrees of freedom for the other transducer. At least one degree of freedom for each transducer is common and the transducers are moved concurrently. One arrangement of the transducer combination is for prostate treatment and includes a specific shape and configuration for anatomical considerations and a control unit which is operable external to the patient to control both transducers and a reflective scanner which are inserted into the patient as part of the ultrasound probe.

267 citations


Patent
20 Nov 1989
TL;DR: In this paper, the authors present an apparatus that allows the three-dimensional reconstruction of anatomic structures through the acquisition of two-dimensional echographic images produced by real-time processing of signals reflected and/or scattered by said structures when these are hit by a beam of ultrasound generated, according to a predetermined scanning plane, by a piezoelectric transducer contained within an Echographic probe.
Abstract: An apparatus that allows the three-dimensional reconstruction of anatomic structures through the acquisition of two-dimensional echographic images produced by the real-time processing of signals reflected and/or scattered by said structures when these are hit by a beam of ultrasound generated, according to a predetermined scanning plane, by a piezoelectric transducer contained within an echographic probe. According to the invention, the scanning plane, in which the sector-scan transducer emits the beam of ultrasound, rotates through an angle of 180°, with intermediate angular increments having a predetermined amplitude and frequency, around the longitudinal axis of the probe, while the latter remains fixed relative to the examined anatomic structure, there being provided means for the actuation and the control of the rotation of the scanning plane. The rotation of the scanning plane with respect to the probe may be obtained either mechanically by means of a motor that rotates the transducer through a predetermined angle, said motor being also arranged to provide the scanning motion to the transducer itself, or electronically by using a transducer constituted by a matrix or array of piezoelectric elements and by selecting a vector of said elements rotating around the longitudinal axis of the probe.

206 citations


Patent
21 Apr 1989
TL;DR: In this article, a hyperthermia treatment apparatus combining a generator of a focused ultrasonic beam comprising a main high frequency electric wave emitter and a main piezoelectric transducer whose active surface is focusing was presented.
Abstract: A hyperthermia treatment apparatus combining a generator of a focused ultrasonic beam comprising a main high frequency electric wave emitter and a main piezoelectric transducer whose active surface is focusing, with an echography device comprising an auxiliary high frequency electric pulse generator associated with an auxiliary piezoelectric transducer and means for causing the zone to be treated to be swept by the ultrasonic examination beam generated by said auxiliary transducer; and with switching and adjustment means for causing, during a main treatment and checking operating mode, emission of said focused beam by said main transducer energized by said main emitter during periodic time intervals separated by shorter time intervals during which the emission of the examination beam and the formation of echographic images are effected.

202 citations


Journal ArticleDOI
TL;DR: In this article, the basic characteristics and progress in transducer properties of different types of piezoelectric ceramics are reviewed and application of these materials in practical ultrasonic transducers is also reported.
Abstract: The author reviews the basic characteristics and progress in transducer properties of the different types of piezoelectric ceramics. The application of these materials in practical ultrasonic transducers is also reported.

186 citations


Patent
04 Oct 1989
TL;DR: In this paper, the frequency response of the ultrasonic transducers used in the measurement is removed from the signal received when measuring the material, which yields a frequency response which is indicative of the material alone.
Abstract: In the field of non-destructive evaluation of materials, conventional ultrasonic measurement techniques are limited to materials having a thickness which is relatively large compared to the wavelength of the ultrasonic signal used. The present technique enables the accurate ultrasonic non-destructive measurement of materials which are relatively small compared to the wavelength of the ultrasonic signal used. Ultrasonic signals received from a thin material are processed in the frequency-domain either directly or by use of a Fast Fourier Transform. Specifically, the frequency response of the ultrasonic transducers used in the measurement is removed from the frequency response of the signal received when measuring the material. This yields a frequency response which is indicative of the material alone. Then, the measured frequency response of the material is evaluated to determine unknown parameters of the material. For instance, the phase of the measured signal is determined over a predetermined frequency range (usually the bandwidth of the transducers), and the phase is used to determine the speed of ultrasonic waves travelling in the material for frequencies within the predetermined range. Likewise, the magnitude of the measured signal is determined over the predetermined frequency range, and the magnitude is used to determine the attenuation of ultrasonic waves travelling in the material for frequencies within the predetermined range.

185 citations


PatentDOI
TL;DR: Apparatus for use in cannulation of blood vessels includes a hollow needle having a sharpened end for penetrating tissue, a trocar including a transducer mounted on one end for positioning within the hollow needle for transmitting and receiving ultrasonic waves through thesharpened end of the needle.

174 citations


Patent
10 Jan 1989
TL;DR: In this article, a method and apparatus for alerting the operator of a vehicle as to the distance from the rear of the vehicle to a structure such as a loading dock to which the vehicle is being backed through the utilization of sonar ranging and means for converting a detected range into an audible call out.
Abstract: A method and apparatus is provided for alerting the operator of a vehicle as to the distance from the rear of the vehicle to a structure such as a loading dock to which the vehicle is being backed through the utilization of sonar ranging and means for converting a detected range into an audible call out of the distance from the back of the vehicle to the structure to which the vehicle is being backed. In one embodiment the talking unit is activated upon the placing of the vehicle in reverse gear. When used on trucks, the transducer is removably mountable to the rear of the truck, with a transmission line lead to the cab of the truck. In the preferred embodiment, a 50 kH 2 transducer is utilized to project a fan beam of radiation from the back of the vehicle so that not only is the closest projecting object in the path of the beam detected and the distance thereto annunciated, any pedestrians or persons having a height commensurate with that of the mounted transducer will cause the range to that person to be annunciated, thereby providing an alarm indication to the driver. In a further embodiment, the transducer is protected from the elements and is either open to the elements only during backing, or is cleaned such that road grime and other hydrocarbons do not contaminate the transducer surface except at such limited times as when the vehicle is in reverse. The audiblization of the distance between the back of the truck and the structure to which it is backed may be provided at a predetermined rate, or may be predicated on a predetermined range change or, may be called out only at preset distances.

167 citations


Patent
01 Feb 1989
TL;DR: In this article, a sensing system including a sensing device with cooperating electrical components which move relative to each other in response to a sensed environmental parameter to yield a reactance signal, which is transmitted to a remotely located processor having an oscillator for receiving the transmitted signal and generating a transduced signal whose value corresponds to the value of the environmental parameter.
Abstract: A sensing system including a sensing device (1) with cooperating electrical components (40, 41) which move relative to each other in response to a sensed environmental parameter to yield a reactance signal, which is transmitted to a remotely located processor having an oscillator for receiving the transmitted signal and generating a transduced signal whose value corresponds to the value of the environmental parameter.

161 citations


PatentDOI
TL;DR: In this paper, an ultrasound densitometer for measuring the physical properties and integrity of a member in vivo includes a transmit transducer from which acoustic signals are transmitted, and a receive transducers which receives the acoustic signals after they have been transmitted through the member and/or a material with known acoustic properties.
Abstract: An ultrasound densitometer for measuring the physical properties and integrity of a member in vivo includes a transmit transducer from which acoustic signals are transmitted, and a receive transducer which receives the acoustic signals after they have been transmitted through the member and/or a material with known acoustic properties. The densitometer allows the physical properties of a member to be measured without having to determine the distance between the transducers. The densitometer is able to measure the physical properties and integrity of the member from the transit time of acoustic signals through the member and/or by determining the absolute attenuation of at least one specific frequency component of acoustic signals transmitted through the member.

153 citations


Patent
10 Oct 1989
TL;DR: A magnetoresistive read transducer has passive end regions separated by a central active region in which an MR layer is formed which extends over substantially only the central active regions and in which a hard magnetic layer is created in each end region as mentioned in this paper.
Abstract: A magnetoresistive (MR) read transducer having passive end regions separated by a central active region in which an MR layer is formed which extends over substantially only the central active region and in which a hard magnetic layer is formed in each end region. The hard magnetic layers form an abutting junction having electrical and magnetic continuity with the MR layer to produce a longitudinal bias in the MR sensor. The transducer is produced by a method in which the same stencil defines the extent of both the MR layer and the hard magnetic layers so that the abutting junctions are formed easily and reliably.

Patent
05 Dec 1989
TL;DR: An ultrasound transducer for use with an ultrasound brain lesioning system includes an acoustic focusing lens, an acoustic coupling medium disposed between the focusing lens and the transducers, and a pressurized fluid contacting the rear surface of transducers to maintain a spaced relation between transducers and focusing lenses as discussed by the authors.
Abstract: An ultrasound transducer for use with an ultrasound brain lesioning system includes an acoustic focusing lens, a piezoelectric transducer plate disposed in spaced relation with the focusing lens, an acoustic coupling medium disposed between the focusing lens and the transducer, and a pressurized fluid contacting the rear surface of the transducer to maintain a spaced relation between the transducer plate and the back surface of the lens. An electrical excitation signal is supplied to the transducer to promote production of an ultrasonic signal by the transducer.

Patent
17 Feb 1989
TL;DR: In this article, a transducer (100) is used for receiving an acoustic signal, an analog-to-digital converter (108), which changes the output of transducers into a series of digital pulses representing the incoming acoustic signal.
Abstract: Contained within a single housing (120), is a transducer (100) for receiving an acoustic signal, an analog-to-digital converter (108), which changes the output of transducer (100) into a series of digital pulses representing the incoming acoustic signal. The output of the system may be in serial form. This serial output (114) is transmitted (116) to a remote receiver (122) by wires, light, optical fibers, or as radio waves. The receiver's (122) output (124) is applied to a digital system (130), which processes or reconstructs the acoustic signal. The system may include a digital signal processor (300) within the housing (120) for processing the signal (110) prior to transmission. The analog to digital converter may be a delta-sigma oversampling type, or a sub-ranging floating point type, or use adaptive differential pulse code modulation. Power may be derived remotely by transmission over the signal medium.

Journal ArticleDOI
TL;DR: In this paper, an axially symmetric Bessel function pattern is polarized into a piezoelectric ceramic element and the resulting circular disk transducer has the usual full-plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the bessel function J0 (r), both in amplitude and in phase.
Abstract: We report experimental results from a first‐of‐a‐kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is ‘‘polarized into’’ a piezoelectric ceramic element. The resulting circular‐disk transducer has the usual full‐plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1‐in.‐diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss‐Hermite model. Bessel transducers are of particular interest in attempts to achieve ‘‘diffractionless’’ beams.

Journal ArticleDOI
TL;DR: In this paper, the effect of backing layers, electrode configuration, transducer surface area and tuning circuits on insertion loss and pulse-echo response of polyvinylidene fluoride (PVDF) transducers is investigated.

Patent
13 Jun 1989
TL;DR: In this article, an ultrasonic imaging apparatus consisting of a transducer, an A/D converter for converting the gain-controlled signals to digital signals, and a delay/addition circuit for delaying the digital signals and adding them to output a received signal.
Abstract: An ultrasonic imaging apparatus comprises an ultrasonic transducer for outputting ultrasonic beams and converting echo waves of the ultrasonic beams to a B-mode echo signal corresponding to a B-mode for obtaining a tomographic image and a D-mode echo signal corresponding to a D-mode for obtaining Doppler data, a transmitter circuit for driving the transducer for generating the ultrasonic beams for scanning a subject, a receiver circuit including a gain control circuit for controlling the gain of the B-mode and D-mode echo signals output from the ultrasonic transducer so that the level of the B-mode echo signal is made to equal to that of the D-mode echo signal and for outputting gain-controlled echo signals, and A/D converter for converting the gain-controlled signals to digital signals, and a delay/addition circuit for delaying the digital signals and adding them to output a received signal, a B-mode processor circuit for producing a B-mode image signal from the received signal, a D-mode processor circuit for producing Doppler data from the received signal, and a display for displaying the B-mode image signal and D-mode data.

Patent
08 Feb 1989
TL;DR: In this paper, the authors present an approach for digital calibration of plug-in transducers and the like, which comprises means for digitally storing error-correcting tables in a physical location which is associated with the transducer, and a means for interpreting those tables.
Abstract: The present invention is for digital calibration of plug-in transducers and the like. The invention comprises means for digitally storing error-correcting tables in a physical location which is associated with the transducer, and a means for interpreting those tables.

Patent
15 Feb 1989
TL;DR: In this article, a shear mode piezoelectric transducer for an ink jet system described in the specification is described, where the plate is polarized parallel to the plane of the plate and in directions extending away from the center of the pressure chamber with which the transducers are used.
Abstract: In the shear mode piezoelectric transducer for an ink jet system described in the specification, a piezoelectric plate (17) is polarized parallel to the plane of the plate and in directions extending away from the center of the pressure chamber with which the transducer is used, and electrodes (20, 21) mounted on opposite surfaces of the plate impose electric fields orthogonal to the direction of polarization. The resulting shear motion of the transducer decreases the volume of the pressure chamber (11), ejecting a drop of ink from an orifice (15) communicating with the pressure chamber. The piezoelectric plate (17) used in the transducer is prepared by imposing electric fields within the plate in the direction parallel to the plane of the plate between electrodes mounted on opposite sides of the plate in the central region of the pressure chamber and electrodes mounted on opposite sides of the plate in the peripheral regions of the pressure chamber.

Patent
13 Jan 1989
TL;DR: In this article, a transducer is used to measure the flow of liquid in a vessel of a patient comprising of red blood cells, and a first moment detector is provided to provide an electrical output representing a characteristic of the flow in the vessel.
Abstract: System for measuring a characteristic of flow of liquid in a vessel of a patient comprising a transducer positioned in a vessel in a patient for supplying ultrasonic energy. The transducer produces a substantially uniform beam which encompasses the vessel. The transducer receives ultrasonic energy back scattered from the red blood cells and provides an electrical output signal. A first moment detector is provided which receives the electrical output from the transducer and provides a first moment signal. Normalization is provided to the output of the first moment detector to provide an electrical output representing a characteristic of the flow of the liquid in the vessel.

PatentDOI
TL;DR: The FLEXBAR as discussed by the authors is a sonar transducer element that is basically a piezoceramic "free-free" flexure bar, but modified so as to radiate as a "monopole" rather than as a 'dipole", and retaining the unique properties of being nodally mounted and dynamically balanced.
Abstract: The FLEXBAR is a sonar transducer element that is basically a piezoceramic "free-free" flexure bar, but modified so as to radiate as a "monopole" rather than as a "dipole", and retaining the unique properties of being nodally mounted and dynamically balanced. One of the important consequences of this simple modification is the fact that the reaction forces on the FLEXBAR mountings and, the concomitant structure-borne vibrations, are virtually eliminated. This property, and related properties, result in unexpected but significant improvement in the performance of low-frequency, high-power, board-band sonar transducer arrays.

PatentDOI
TL;DR: In this article, an electronic noise attenuation system for attenuating a sound wave propagated from a source of noise by generating another sound wave 180° out of phase and having the same sound pressure with the propagated sound wave from electro-mechanic transducer means disposed in a propagation passage of sound waves is presented.
Abstract: An electronic noise attenuation system for attenuating a sound wave propagated from a source of noise by generating another sound wave 180° out of phase and having the same sound pressure with the propagated sound wave from electro-mechanic transducer means disposed in a propagation passage of sound waves. In the electronic noise attenuation system, a drive signal for drive the electro-mechanic transducer means is generated in accordance with output signals respectively output from upstream-side and downstream-side mechano-electric transducer means respectively disposed in the propagation passage with the electro-mechanic transducer means therebetween. Namely, the drive signal is created by performing an operation on a difference signal between the output signal of the upstream mechano-electric transducer means and the drive signal according to a given transfer function. Also, the transfer function is determined in accordance with the difference signal and the output signal of the downstream mechano-electric transducer means.

Journal ArticleDOI
D. R. Kerr1
TL;DR: Analyse, proprietes et conception d'un capteur d'effort ayant une structure mecanique du type plateforme de Stewart as mentioned in this paper, a capteur de effort.
Abstract: Analyse, proprietes et conception d'un capteur d'effort ayant une structure mecanique du type plateforme de Stewart

Patent
Frederick J. Barr1
25 Aug 1989
TL;DR: In this article, a scale factor is applied to the output of a pressure transducer and a particle velocity transducers positioned substantially adjacent one another in the water to reduce coherent noise in a marine reflection prospecting system.
Abstract: A marine seismic reflection prospecting system reduces coherent noise by applying a scale factor to the output of a pressure transducer and a particle velocity transducer positioned substantially adjacent one another in the water. The transducers can be positioned at a point in the water above the bottom and, thereby, eliminate downgoing components of reverberation, or they can be positioned on the water's bottom and, thereby, eliminate both upgoing and downgoing components of the reverberation. The scale factor, which derives from the acoustical impedance of the water or water-bottom material, can be determined both deterministically and statistically. The former involves measuring and comparing the responses of the pressure and velocity transducers to a pressure wave induced in the water. The latter involves comparing the magnitude of the pressure signal autocorrelation to the pressure and velocity signal crosscorrelation at selected lag values or, alternatively, comparing the magnitude of the pressure signal autocorrelation to the velocity signal autocorrelation at selected lag values.

Journal ArticleDOI
K. Suzuki1, K. Higuchi1, H. Tanigawa1
TL;DR: An electric ultrasonic transducer is developed by using a silicon IC process to obtain high sensitivity and the desired frequency responses in air, and should be helpful in the design of phased-array transducers integrated with electronic scanning circuits.
Abstract: An electric ultrasonic transducer is developed by using a silicon IC process. Design considerations are first presented to obtain high sensitivity and the desired frequency responses in air. The measured transmitter sensitivity is 19.1 dB (0 dB=1 mu bar/V) at a point 50 cm away from the devices, when the devices are operated at 150 kHz. The receiving sensitivity is 0.47 mV/Pa in the 10-130-kHz range, with bias voltages as low as 30 V. An electronic sector scanning operation is also achieved by time-sequentially driving seven elements arranged in a linear array on the same chip. The results should be helpful in the design of phased-array transducers integrated with electronic scanning circuits. >

Patent
30 Jan 1989
TL;DR: In this paper, a miniature transducer with an ultrathin tensioned silicon diaphragm is fabricated on glass wafers and sandwiched around a processed semiconductor wafer, where a large number of the miniature transducers are fabricated simultaneously.
Abstract: A miniature transducer having an ultrathin tensioned silicon diaphragm so as to be responsive to extremely small changes in pressure. A silicon wafer is masked to define diaphragm areas, and etched to form a setback or capacitor gap a predefined depth. The mask is removed, and the entire silicon wafer is etched a second time to achieve the desired diaphragm thickness. The first and second etches are carried out independently, and thus the capacitor gap and diaphragm thickness can be independently formed. Mask and metallizing steps are carried out on glass wafers, and sandwiched around the processed semiconductor wafer, whereupon a large number of the miniature transducers are fabricated simultaneously. Unique patterning, etching and metallizing steps carried out on the sandwich structure allow a number of quadrature unit cells to be formed, thereby maximizing the area of the semiconductor and glass structures. By proper selection of materials, the diaphragm is tensioned during the fabrication of the transducer structures.

Patent
06 Jul 1989
TL;DR: In this article, the phase shift between the transmission signal and the reception signal is measured digitally in that the measuring time intervals corresponding to the phase shifts the periods of a signal are counted with a counting frequency which is substantially greater than the frequency of transmission signal.
Abstract: For flow rate measurement by means of ultrasonic waves, on a measuring tube two ultrasonic transducers are arranged spaced apart from each other, one operating as transmitting transducer and the other as receiving transducer. For determining the flow rate the phase shift between the transmission signal and the reception signal is measured digitally in that the measuring time intervals corresponding to the phase shift the periods of a signal are counted with a counting frequency which is substantially greater than the frequency of the transmission signal. The start phase which the counting frequency signal has at the beginning of each counting operation with respect to the measuring time interval is varied from measuring time interval to measuring time interval in a measuring cycle including a plurality of successive measuring time intervals and the counts obtained in the course of the measuring cycle are evaluated to form a measured value with increased measurement resolution.

Journal ArticleDOI
TL;DR: In this article, the fabrication process and properties of a capacitive silicon sensor for the detection of airborne sound are described, which consists of two chips; one chip carries a 150nm-thick silicon nitride membrane of 0.8×0.8 mm2, and the second chip represents a complete back plate including the back electrode and the air gap spacer.
Abstract: The fabrication process and the properties of a capacitive silicon sensor for the detection of airborne sound are described. The device consists of two chips; one chip carries a 150‐nm‐thick silicon nitride membrane of 0.8×0.8 mm2 , and the second chip represents a complete back plate including the back electrode and the air gap spacer. Both chips are produced by means of an orientation‐dependent etching procedure. The overall dimensions of the transducer are 1.7×2×0.6 mm3 . Measurements of the acoustic properties yield sensitivities between −60 and −90 dB re: 1 V/Pa, depending on the tension of the diaphragm. The most sensitive microphones have a frequency response extending up to 2 kHz, while the less sensitive transducers have higher cutoff frequencies.

Patent
Steven J Woodward1
12 Sep 1989
TL;DR: In this paper, an echo profile is enhanced by removing narrow peaks likely to correspond with certain types of spurious echo, and narrow valleys which may represent fragmentation of a wanted echo, which are identified by comparing the profile with a time varying threshold generated derived from a linear regression performed on part of the threshold, various different types of comparison being performed and their results combined prior to selecting the most likely true echo on the basis of the combined results.
Abstract: In acoustic level sensing apparatus, in which pulses of acoustic energy are transmitted by an electrically energized transducer towards a surface to be sensed, and the electrical output from the transducer following the pulse is digitized and analyzed to detect a return echo from the surface, so as to produce a digitized echo profile. The digitzed echo profile is enhanced by removing narrow peaks likely to correspond with certain types of spurious echo, and narrow valleys which may represent fragmentation of a wanted echo. Echoes are identified by comparing the profile with a time varying threshold generated derived from a linear regression performed on part of the threshold, various different types of comparison being performed and their results combined prior to selecting the most likely true echo on the basis of the combined results.

Journal ArticleDOI
TL;DR: In this article, a measurement technique for analyzing the surface velocity patterns of ultrasonic transmitters is presented, based on the angular spectrum method of wave field analysis, with each element in the spatial frequency domain multiplied by the appropriate phase factor.
Abstract: A measurement technique for analyzing the surface velocity patterns of ultrasonic transmitters is presented. The technique is based on the angular spectrum method of wave field analysis. In this approach, acoustic propagation between parallel planar surfaces is modeled using the two‐dimensional (2‐D) Fourier transform of the wave field, with each element in the spatial frequency domain multiplied by the appropriate phase factor. The technique was extended from the basic monochromatic model to the wideband pulsed case. An experimental system was built to measure the acoustic fields from various transducers, including single‐element and multielement phased arrays. Backpropagation results are shown for circular planar, circular focused, and rectangular phase steered transducers. The results demonstrate the ability of the extended angular spectrum method to reconstruct the surface velocity distribution of complex acoustic radiators.

Patent
19 Apr 1989
TL;DR: In this article, a piezoresistive transducer bridge is supplied by a constant current source in one embodiment, and by a voltage of constant amplitude in another embodiment, where voltage to the bridge is reversed on a periodic basis.
Abstract: A reliable indication of temperature-compensated pressure is provided from each of the wheels of a vehicle to an operator within the vehicle. A piezoresistive transducer bridge is supplied by a constant current source in one embodiment, and by a voltage of constant amplitude in another embodiment. Voltage to the bridge is reversed on a periodic basis. The use of constant current enables compensation for temperature-induced drift in transducer bridge output. The use of constant voltage enables compensation for ambient temperature, and provides an absolute, rather than a relative indication of pressure or "flatness" within the tire. Voltage polarity reversal permits compensation of amplifier offset voltage. Energy is transmitted to an from the wheel by means of a tuned circuit which is excited by a primary coil when the vehicle's engine is running. The secondary coil mounted on the wheel may be either short-circuited or selectively opened and closed to alter the operation of the primary coil, thus providing an indication of tire pressure, that indication being detected and processed by suitable microcomputer circuitry which may exist on board the vehicle. Most of the active circuit elements of the invention may be implemented in a single monolithic integrated circuit, which can be attached to a tire valve.