Showing papers on "Transducer published in 1978"

The design of efficient broad-band piezoelectric transducers

Abstract: A design method for acoustic thin disk transducers with high efficiency, broad bandwidth, and good impulse response is presented. This method is based on the use of quarter-wave matching layers between the piezoelectric material and the acoustic load. As is made evident using the transmission line model of Krimholtz, Leedom, and Matthaei, the finite thickness of the piezoelectric material must be taken into account in the matching layer design. Criteria for optimum broad-band transducer designs with a given piezoelectric material are developed which show the importance of a high electromechanical coupling coefficient. A method for obtaining Gaussian shaped passbands, necessary for optimum impulse response, is also shown. Several transducers have been built to illustrate this design approach with excellent agreement between theory and experiment. One such transducer has 3.2 dB round trip insertion loss and one octave bandwidth.

Wear plate for piezoelectric ultrasonic transducer arrays

Abstract: A linear transducer array for 90° or other wide angle sector scans is covered by a body contacting wear plate made of a material such as filled silicone rubber or polyurethane epoxy in which the longitudinal sound velocity is equal to or less than that in the body and in which the acoustic impedance for longitudinal sound waves is approximately equal to that of the body. Refraction, if it occurs, enhances the field of view without reducing the transmission of acoustic energy. The wear plate provides mechanical support for a fragile front surface matched array.

Front surface matched piezoelectric ultrasonic transducer array with wide field of view

Abstract: An ultrasonic transducer array with high sensitivity, for use in water tanks and with human subjects in steered beam imagers to make wide angle sector scans, has narrow transducer elements and one or more quarter-wavelength impedance matching layers on the front surface of each element. The matching layers as well as the piezoelectric ceramic are completely cut thorugh and guide acoustic energy incident at any angle to the ceramic. A continuous covering or wear plate is attached to the matching layers and a continuous damping material can cover the backs of the elements.

New system for recording ambulatory blood pressure in man.

Abstract: A new perfusion and transducer unit for ambulatory blood-pressure recording is described, followed by reports of both the laboratory evaluation of the unit and experience with its clinical use. The major change from earlier systems is the perfusion system, now based on an electrically driven ‘delta’ pump. Pressure is measured by a semiconductor strain-gauge pressure transducer. Laboratory evaluation has shown that the transducer with associated tubing and cannulae has a satisfactory frequency response, considerably better than that of the recording system normally used. Both quantitatively and qualitatively there was a very close correspondence between signals obtained from the entire Oxford system (including recording and replay) and signals obtained directly by means of a catheter-tip transducer. Small, but consistent, signal drifts attributable to battery behaviour are described. The system appears remarkably insensitive to temperature variations within the range of expected ambient temperatures. Delta pump performance is satisfactory, producing essentially constant perfusion rates. Clinically, the system has been used for the recording of ambulatory blood pressures in 110 patients for periods up to 72 h with satisfactory results. Reliability appears good, with minimal artefacts atributable to the equipment. This transducer and perfusion system appears to be fully satisfactory and considerably more reliable than the earlier designs.

Water wave energy transducer

Abstract: A water wave energy transducer for converting the motion of a water wave into a controlled mechanical movement such as rotational motion suitable for actuating an electrical generator The transducer comprises a float member floatingly moored in a water body having waves and/or tidal movement, such as a seashore A power gear is rotatably mounted in a swing block on the float with a power shaft extending from the power gear to laterally spaced drive bevel gears mounted for rotation with the power gear These drive bevel gears are coupled to a transmission on the float comprising one-way drive clutches transmitting rotational energy to the drive shaft of a generator or the like to provide rotational energy on both up and down movement of the float A rack is pivotally anchored in the water body, extends up through the float and is slideable with respect to the power gear of the swing block, so that movement of the float with respect to the rack will provide rotation of the power gear

An improved shear wave transducer

Abstract: A new type of shear wave transducer has been developed at Applied Research Laboratories, The University of Texas at Austin (ARL:UT), as part of a program to measure the acoustic parameters of marine sediments. The transducers consist of a ceramic bender element which can be immersed in the medium and has favorable characteristics for the study of the acoustic parameters of unconsolidated sediments.

Observations of the propagation of very short ultrasonic pulses and their reflection by small targets

Abstract: The field of a circular ultrasonic transducer emitting a single‐cycle pulse into water has been observed using a specially constructed small (150 μm) wide‐band receiving probe and a compact stroboscopic schlieren system. The theoretically predicted plane‐wave and diffracted edge‐wave components of the field have been resolved. Good agreement with the theory for a pistonlike source is obtained, except in a region less than 1.5 transducer radii from the transducer. The output of the transducer used in the transmit–receive mode to detect small targets has been measured and the results are in accord with a time‐domain principle of reciprocity between transmission and reception. Implications of the results for field plotting and for the location and characterization of small targets are considered.

Photoacoustics on a microscopic scale

Abstract: We have modified a transmission acoustic microscope by replacing the input lens with an optical counterpart. The input to this system comes from a mode‐locked and Q‐switched Nd : YAG laser at 1.06 μm. Acoustic signals arising from thermoelastic coupling are generated in metallic films at frequencies determined by the modulation envelope of the optical beam. The output acoustic lens and transducer responsive to sound waves at 840 MHz detect the acoustic energy which comes from the heated volume (∼2‐μm diameter) near the focal region. The sample is mechanically scanned through the focal point in a raster pattern to record the photoacoustic images. We suggest this as a method for collecting new information on microscopic structures.

Interaction of magnetostatic waves with a current

Abstract: It is shown that the interaction of magnetostatic waves with a current can be characterized by a coupling constant analogous to, but much greater than, the piezoelectric coupling constant. The theory is applied both to surface and forward‐traveling volume magnetostatic waves, and the problems of excitation, reflection, and absorption by a single microstrip and by a narrow‐band interdigital transducer are treated. It is found that the coupling constant is close to 0.5 for any reciprocal wave, and is greater for any nonreciprocal wave, when the transducer is in contact with the magnetic medium. These values are too large to allow effective signal processing, since the emitted waves react strongly on the transducer; narrow‐band transducers must be lifted above the surface so as to weaken the coupling.

The Design of Efficient Broad-Band Piezoelectric Transducers

Abstract: Absrruct-A design method for acoustic thin disk transducers with high efficiency, broad bandwidth, and good impulse response is presented. This method is based on the use of quarter-wave matching layers between the piezoelectric material and the acoustic load. As is made evident using the transmission line model of Krimholtz, Leedom, and Matthaei, the finite thickness of the piezoelectric material must be taken into account in the matching layer design. Criteria for optimum broad-band transducer designs with a given piezoelectric material are developed which show the importance of a high electromechanical coupling coefficient. A method for obtaining Gaussian shaped passbands, necessary for optimum impulse response, is also shown. Several transducers have been built to illustrate this design approach with excellent agreement between theory and experiment. One such transducer has 3.2 dB round trip insertion loss and one octave bandwidth.

Volume flow measurement system

Abstract: An apparatus and method for direct measurement of the volume flow of fluids through a tube, using an interferometric transit time technique is disclosed. First and second transducers for producing and receiving waves which are capable of being modified by the flow of the fluid in the conduit are positioned so that the conduit is fully and evenly illuminated by the waves. The transducers are located with respect to the conduit so that there will be a component of fluid flow along the axis of the illuminating wave beam. Means are provided to first activate one transducer to transmit waves while the other is in a receive mode and thereafter to place the second transducer in a transmit mode while the first is switched to its receive mode. The received waves are converted to corresponding electric signals by the corresponding transducers, and these signals are periodically sampled and stored for comparison. The result of this comparison is an electric signal which is proportional to fluid flow and is to a high degree independent of flow profile, conduit geometry, and alignment of the conduit within the probe. The device is particularly useful in measuring the flow of blood through a vessel.

Electronic tachometer and combined brushless motor commutation and tachometer system

Abstract: An electronic tachometer utilizes a transducer, typically an optical encoder disc, connected to a movable mechanical element. The transducer produces a pair of triangular waves of fixed relative phase, each having slopes proportional to the velocity of the mechanical element. The triangular waves are differentiated and the resultant signals are sampled by gating pulses derived from the triangular waves themselves. The samples are combined to produce an output signal having a magnitude proportional to element speed and a polarity indicative of direction. In a combined system in which the transducer is attached to the shaft of a brushless motor, another output of the same transducer is used for commutation control of the motor stator windings. This arrangement is particularly useful in a velocity servo system, in which the tachometer output is compared with a signal indicating desired motor velocity. The comparator output is used to modify the commutation control so as to produce the desired motor velocity. Position encoding also may be accomplished using the same transducer.

Telemetering system for operating room and the like

Abstract: A system for telemetering data from a patient to a monitor permitting direct connection of patient's sensors and transducers to the monitor and permitting telemetering by radio or wire without requiring changes in transducer or monitor design or adjustment or calibration. A telemetering system which presents to the monitor variable resistances identical to the varying resistances produced by the transducers at the patient. A temperature transmission channel wherein a thermistor resistance is digitized for transmission, with the digital data being utilized to generate a resistance at the receiver corresponding to the thermistor resistance. A pressure transmission system providing for transmission of waveform and peak and trough values of the waveform, with the waveform being reconstituted at the receiver and converted to a varying resistance for connection to the monitor, simulating the original pressure transducer resistance.

Method and apparatus for providing dynamic focussing and beam steering in an ultrasonic apparatus

Abstract: An acoustic lens having nonuniform cross sectional thickness is disposed in the path of an ultrasonic energy search beam traveling from a transducer probe to an object to be examined. In an alternative embodiment the lens has at least one contoured surface. As the lens undergoes motion in a plane substantially normal to the direction of the search beam, the search beam exhibits a varying focal zone depth and beam path for providing real time ultrasonic scanning of the examined object.

Digital method and apparatus for rotating an information storage disc

Abstract: Method and apparatus for rotating an information storage disc about its central axis at a prescribed angular velocity that varies according to the radial position of an optical transducer for recording information thereon, whereby a uniformly high density of information can be recorded over the entire disc. The apparatus includes a register for storing a digital measure of the radius of the current track being recorded by the transducer, along with velocity signal circuitry for producing a disc velocity signal having a frequency inversely proportional to the measure of radius, and a spindle motor servo, responsive to the disc velocity signal, for controlling the angular velocity of the information disc, accordingly. The velocity signal circuitry includes a crystal oscillator, a counter for counting the clock pulses produced by the oscillator, and a digital word magnitude comparator for generating a reset pulse to reset the counter to an initial zero count every time it determines that the count is equal to the digital measure of radius. The disc velocity signal is then derived by frequency dividing the successive reset pulses.

Thin film inductive transducer

Abstract: This thin film inductive transducer comprises a yoke structure consisting of a pole tip region which joins a back region. To maximize resolution during reading of magnetic transitions from a moving magnetic recording medium, the pole tip region is of preselected constant relatively narrow width, and composed of magnetic layers having edges which extend in a direction normal to the medium for a distance D from an air bearing surface ABS to the back region and having a small thickness at least adjacent the ABS. To minimize the effects of spurious signals from adjacent tracks on the medium, distance D is at least 5/d, where d is the recording density on the medium; however, to maximize transducer efficiency, distance D is not increased significantly above 5/d. To oppose saturation of the yoke structure with applied current and enhance the efficiency of the transducer during recording, the cross-sectional area of the yoke structure is increased in the back region by progressively increasing its width rearward of the pole tip region and concurrently increasing the thickness of said magnetic layers at least about 60%.

Linearized digital thermometer

Abstract: A digital thermometer uses a microprocessor computer containing stored information relating to the response characteristics of a transducer to supply a measurement of temperature. The transducer is preferably a thermistor whose resistance varies in a predetermined and nonlinear relation to its temperature. The microprocessor computer includes a read-only memory which has been preprogrammed with piece-wise linearized information approximating the nonlinear relation of resistance and temperature of the thermistor. A current source develops a voltage across the thermistor which is related to the temperature of the thermistor. The voltage across the thermistor is converted into a digital signal, and the digital signal is related to the piece-wise linearized information stored. The temperature equivalent is calculated from a first order algebraic equation determined by the relationship of the digital signal to the stored information.

Electromechanical transducer-coupled mechanical structure with negative capacitance compensation circuit

Abstract: Arrangements are disclosed for substantially reducing the effect of the inherent transducer capacitance in a transducer-coupled electromechanical system which is subject to vibrational movement. Electrical circuitry is coupled across the transducer output to provide a negative capacitance having a magnitude substantially the same as that of the inherent transducer capacitance, thereby substantially nullifying the inherent transducer capacitance and enabling improved damping (including low-noise damping) to be achieved.

Low and constant pressure transducer probe for ultrasonic diagnostic system

Abstract: A diagnostic ultrasound real time B-scanner system has an improved probe assembly for fluid coupling a movable axis transducer to a patient's body. Pressure is maintained both low and constant by means of a passive pressure compensation apparatus. The probe includes apparatus containing the transducer and a fluid medium and including a compliant subject contacting bag. Pressure exerted by the bag on a subject is a function of (1) the pressure exerted on the fluid medium and (2) the orientation of the probe, due to the shifting weight of the fluid. The passive pressure compensator apparatus includes a gravity actuated apparatus for varying the pressure on the fluid medium as a function of the spatial orientation of the probe. This pressure variation compensates for the weight of the fluid medium and stabilizes the coupling pressure on the surface of the patient's body.

Polymeric piezoelectric transducer with thermoformed protuberances

Abstract: The invention relates to devices using transducer elements comprising a film of piezoelectric polymer arranged between electrodes. The transducer element in accordance with the present invention is in the form of a thermoformed protuberance. These devices are used for detecting and generating elastic compression waves, for infrared radiation, and for storing electrical energy.

Platform for magnetic transducers having dust diverter means

Abstract: A fly off transducer platform or carrier according to the invention comprises a platform for supporting at least one transducer for reading and writing from and onto a data carrier such as a magnetic disc which is driven past the transducer in a given direction and sense. The platform has on its face adjacent the data carrier at least one air gap carried by a skid whose major dimension is parallel to the said given direction. The front face of the said skid, with reference to the said sense of movement of the data carrier, forms a diverter blade to force any unwanted contaminant material to at least one side of the said skid and thus prevents this material from collecting at the air gap.

Driving circuit for piezo-electric multimorph transducer

Abstract: A piezo-electric transducer, such as, a bi-morph leaf, comprised of a pair of piezo-electric elements which are oppositely poled in opposite directions and interposed between inner and outer electrodes with each element being bonded to the other at the respective inner electrodes, is provided with a drive circuit applying a drive voltage across the outer electrodes, one of which is desirably grounded, for deflecting the transducer, and which clamps the voltage at the bonded together inner electrodes to a relatively small maximum value at least in response to a polarity of the drive voltage opposed to the direction in which one of the piezo-electric elements is poled so as to avoid substantial depolarization of at least that one element. The foregoing arrangement is particularly desirable in an apparatus in which a magnetic head is moved along a track on a magnetic tape or other record medium for reproducing information signals recorded in such track which the bi-morph leaf supports the head for deflecting the latter in a direction transverse to that along the track in response to the drive voltage.

Automatic head tracking system

Abstract: In an apparatus for reproducing video or other information signals recorded in a track on a magnetic tape or other record medium; a magnetic head or transducer is moved along the track for reproducing the information signals recorded therein while a bi-morph leaf which supports the head receives an electrical drive signal for deflecting the head in a direction transverse to that along the track. A deflection signal is generated in correspondence to the deflection of the head from a rest position by a circuit which includes a strain gauge fixed on the bi-morph leaf. A control circuit for controlling the deflection of the head includes an oscillator providing a dither oscillation signal which, on application to the bi-morph leaf, causes transverse oscillation of the head about a null position, an envelope detector detecting the envelope of the reproduced output of the head, a multiplier for synchronously demodulating the detected envelope by means of the deflection signal so as to obtain a tracking error signal accurately representative of the deviation of the null position of the head from the center of the track, and an adder adding the tracking error signal to the dither oscillation signal so as to provide therefrom the electrical drive signal and by which the null position of the oscillated head is aligned with the center of the track.

Ultrasonic transducer fabricated as an integral park of a monolithic integrated circuit

Abstract: An array of electrostatic transducers is fabricated on a monolithic integrated circuit chip having provision for detection, amplification, and signal processing of received echoes. The transducer is multilayered with the form of a parallel plate capacitor, and is made by laterally etching an insulating layer through a small hole in the overlying layer to create a void region, then depositing a sealing layer to seal the etch holes. The upper metallic layers cover the transducer array and other monolithic circuitry and are etched to be interconnections for the various components.

Sonic ranging systems to eliminate errors due to variations in the sound velocity in the medium

Abstract: An improved sound ranging system increases the precision of range measurement by automatically correcting for any variation in the velocity of sound in the medium. The automatic correction for the sound velocity utilizes a small sound reflecting target located at a precise fixed distance from the transducer surface. A digital circuit, including a microcomputer, improves the measurement accuracy of the system. The invention includes a time delay and sensitivity control in one of the two time measurement circuits employed in the system to prevent "ghost" signals caused by multiple round-trip target reflections from introducing errors in the range measurements.

Adjustable ultrasonic level measurement device

Abstract: An ulrasonic liquid level measurement device is used to measure the depth of a flowing liquid in a channel using an ultrasonic transducer that is positioned out of contact with the liquid and above and directed toward the channel. An ultrasonic burst is directed toward the channel and the reflected echo from the surface of the liquid is returned and sensed by the transducer. The transit time of ultrasonic transmission and echo return is indicative of the liquid level. An adjustable discriminator is provided to specify a maximum liquid level in the channel and a minimum liquid level, which, typically is the floor of the channel. The maximum and minimum levels are adjustable to accomodate variable channel configurations and transducer mounting arrangements. Automatic adjustment is provided to compensate for different cable lengths which may be used to connect the ultrasonic transducer to the transducer driver and receiving section. Temperature compensation is provided to compensate for changes in ultrasonic transmission propogation through ambient air with temperature, and time variable gain amplification is provided to compensate for geometric spreading of reflected ultrasonic energy echo pulses and for air path absorption.

System for rotating an information storage disc at a variable angular velocity to recover information therefrom at a prescribed constant rate

Abstract: Method and apparatus for recovering information at a substantially constant rate from a rotatable information storage disc. The information is stored on the disc in a plurality of substantially circular and concentrically arranged information tracks, with a substantially uniform recording density, and it is recovered by controllably rotating the disc, relative to a transducer, at an angular velocity substantially inversely proportional to the radius of the corresponding track. The apparatus includes a coarse speed control potentiometer for producing a measure of the radius of the particular information track from which information is being recovered, and fine speed control means for comparing the relative phase angles of a periodic signal in the recovered information and a periodic reference signal and for producing a fine speed control signal proportional to the phase difference. The measure of radius and the fine speed control signal are summed together and coupled to a voltage-controlled oscillator to produce a composite speed control signal, which is coupled to a servo to rotate the disc at a corresponding angular velocity.

Phase insensitive acoustoelectric transducer

Abstract: Conventional ultrasonic transducers transform acoustic waves into electrical signals preserving phase and amplitude information. When the acoustic wavelength is significantly smaller than the transducer diameter, severe phase modulation of the electrical signal can occur. This results in anomalous attenuation measurements, background noise in nondestructive evaluation, and in general complicates data interpretation. This article describes and evaluates a phase-insensitive transducer based on the acoustoelectric effect. Theory of operation of the acoustoelectric transducer (AET) is discussed, and some optimization procedures outlined for its use. Directivity data for the AET are contrasted with a conventional piezoelectric transducer. In addition, transmission scanning data of phantom flaws in metal plates are presented for both transducers and demonstrate a significant improvement in resolution with the AET.

Object indicator for moving vehicles

Abstract: A system for locating and determining the distance to an object with respect to a movable vehicle is provided which utilizes at least three transducers wherein at least two of the three transducers operates either as a receiver transducer, in which case the remaining transducer operates as a transmitter transducer, or two of the three transducers operate as transmitter transducers in which case the remaining transducer operates as a receiver transducer with the system also including means for sequentially operating the three transducers for sending and receiving reflected ultrasonic signals to simultaneously determine both the location and distance of persons or objects with respect to the transducers.