# US 5,345,427 A · Ultrasonic transducer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,345,427 A - Document ID: US5345427A - Status: Granted - Kind: A - Application number: 08/037,457 - Filed: 1993-03-26 - Granted: 1994-09-06 - Earliest claimed: 1992-03-31 - Assignees: NGK Insulators, Ltd. - Inventors: Yoshihiko Ishida; Yuji Asai; Makoto Tani - Web page: https://patentgrep.com/patent/US5345427A ## CPC - B06B 1/0644: {using a single piezoelectric element (B06B1/0688 takes precedence)} - B06B: METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, {e.g.} FOR PERFORMING MECHANICAL WORK IN GENERAL (for particular applications, see the relevant subclasses, e.g. B07B1/40, B23Q17/12, B24B31/06; measurement of mechanical vibrations G01H; in direction finding, locating, distance or velocity measuring G01S; {generating seismic energy G01V1/02}; control of mechanical vibrations in general G05D; sound-producing devices, e.g. bells, sirens, whistles G10K, {e.g. methods or devices for transmitting, conducting, or directing sound in general G10K11/00}; generation of electrical oscillations H03B; electromechanical resonators in general H03H; electromechanical transducers {for communication techniques, e.g. microphones, speakers} H04R) ## Abstract A phase-insensitive ultrasonic transducer has a zinc oxide single crystal as a piezoelectric semiconducting acoustoelectric element, providing high sensitivity and operable over a range of wavelengths of the ultrasonic waves. The electrical conductivity of said zinc oxide single crystal may be selected in the range 10.sup.-8 to 10.sup.-2 .OMEGA..sup.-1.cm.sup.-1. The single crystal can have an attenuation rate for ultrasonic waves of 10 MHz of at least 0.8 cm.sup.-1. ## Claims ### Claim 1 An acoustoelectric ultrasonic wave sensing element comprising a zinc oxide single crystal in which ultrasonic waves are transduced into electric voltage accompanied by phonon-charge carrier interaction. ### Claim 2 An ultrasonic transducer comprising a zinc oxide single crystal having a pair of opposite faces to which a pair of electrodes are attached, wherein a thickness d between said opposite faces and an electrical conductivity .sigma. of said crystal satisfy the following: 10.sup.-8 (.OMEGA.cm).sup.-1 21 .sigma.<10.sup.-2 (.OMEGA.cm).sup.-1 and ##EQU6## .epsilon. being the dielectric constant of said zinc oxide single crystal and v being the velocity of sound in said zinc oxide single crystal. ### Claim 3 (depends on 2) The ultrasonic transducer of claim 2, wherein said thickness of said zinc oxide single crystal is in a range of 120 .mu.m<d<120 cm. ### Claim 4 (depends on 2) The ultrasonic transducer of claim 2, wherein the electrical conductivity of said zinc oxide single crystal is in a range of 10.sup.-7 to 10.sup.-4 .OMEGA..sup.-1 cm.sup.-1. ### Claim 5 (depends on 2) The ultrasonic transducer of claim 2, wherein said single crystal has an attenuation rate for ultrasonic waves of 10 MHz of at least 0.8 cm.sup.-1. ### Claim 6 (depends on 2) The ultrasonic transducer of claim 2, wherein said zinc oxide single crystal contains at least one acceptor element and not more than 2 ppm non-acceptor impurity elements. ### Claim 7 (depends on 2) The ultrasonic transducer of claim 2, wherein said zinc oxide single crystal contains at least one donor element and not more than 2 ppm non-donor impurity elements. ### Claim 8 (depends on 2) The ultrasonic transducer of claim 2, wherein said zinc oxide single crystal has a charge carrier mobility greater than 8 cm.sup.2 /volt-second. ### Claim 9 An ultrasonic detection apparatus having an acoustoelectric ultrasonic sensing transducer comprising a zinc oxide single crystal having a pair of opposite faces to which a pair of electrodes are attached, and means for detecting electrical signals induced at said pair of electrodes by ultrasonic waves in said crystal, wherein said electrical signals include signals into which said ultrasonic waves are transduced accompanied by phonon-charge carrier interaction. ### Claim 10 (depends on 9) The ultrasonic detection apparatus of claim 9, wherein the c-axis of said zinc oxide single crystal is parallel to the direction of ultrasonic vibration of the ultrasonic waves sensed by said sensing transducer, and said electrodes are arranged opposite each other in the direction of propagation of said sensed ultrasonic waves in said zinc oxide single crystal. ### Claim 11 (depends on 9) The ultrasonic detection apparatus of claim 9, wherein said detecting means includes a wave filter for removing from said signals frequency signals corresponding to the frequency of said ultrasonic waves. ### Claim 12 An ultrasonic measuring apparatus having an ultrasonic transmitter, means for causing said transmitter to emit ultrasonic waves, an acoustoelectric ultrasonic sensing transducer comprising a zinc oxide single crystal having a pair of opposite faces to which a pair of electrodes are attached, and means for detecting electrical signals induced at said pair of electrodes by ultrasonic waves in said crystal, wherein said electrical signals include signals into which said ultrasonic waves are transduced accompanied by phonon-charge carrier interaction. ### Claim 13 (depends on 12) An ultrasonic measuring apparatus of claim 12 operable in reflection mode, wherein said ultrasonic transmitter and said ultrasonic sensing transducer are housed together in a unitary housing. ### Claim 14 (depends on 12) An ultrasonic measuring apparatus of claim 12, wherein said wave emitted by said ultrasonic transmitter have a predetermined frequency and said detecting means includes a wave filter to remove from said signals a frequency corresponding to said predetermined frequency. ### Claim 15 (depends on 12) An ultrasonic measuring apparatus of claim 12, wherein the c-axis of said zinc oxide single crystal is parallel to the direction of ultrasonic vibration of the ultrasonic waves sensed by said sensing transducer, and said electrodes are arranged opposite each other in the direction of propagation of said sensing ultrasonic waves in said zinc oxide single crystal. ### Claim 16 A method of converting ultrasonic energy into electrical signals wherein a piezoelectric semiconducting zinc oxide single crystal is employed as a transducer in which acoustoelectric energy conversion occurs without photoconduction. ### Claim 17 A method of detection of ultrasonic waves comprising: sensing said waves by means of an ultrasonic sensing transducer comprising a zinc oxide single crystal having a pair of opposite faces to which a pair of electrodes are attached, wherein a thickness d between said opposite faces and an electrical conductivity .sigma. of said crystal satisfy the following: 10.sup.-8 (.OMEGA.cm).sup.-1 <.sigma.<10.sup.-2 (106 cm).sup.-1 and ##EQU7## .epsilon.being the dielectric constant of the zinc oxide single crystal and v being the velocity of sound in the zinc oxide single crystal; and monitoring electrical signals generated between said pair of electrodes. ### Claim 18 (depends on 17) The method of claim 17, wherein the electrical conductivity .sigma. of zinc oxide single crystal satisfies the following: 0.2.pi.f.epsilon..ltoreq..sigma..ltoreq.20.pi.f.epsilon. f being the average ultrasonic wave frequency and .epsilon.being the dielectric constant of the zinc oxide single crystal. ### Claim 19 (depends on 17) The method of claim 17, wherein said thickness d satisfies the following: 1.lambda..ltoreq.d.ltoreq.10.lambda. .lambda. being the average wavelength of the ultrasonic waves in said zinc oxide single crystal. ### Claim 20 (depends on 17) The method of claim 17, wherein the c-axis of said zinc oxide single crystal is parallel to the direction of ultrasonic vibration of the ultrasonic waves sensed by said sensing transducer, and said electrodes are arranged opposite each other in the direction of propagation of said sensed ultrasonic waves in said zinc oxide single crystal.