# US 2009/0260422 A1 · Ultrasonic sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2009/0260422 A1 - Document ID: US20090260422A1 - Status: Published application - Kind: A1 - Application number: 12/385,714 - Filed: 2009-04-16 - Published: 2009-10-22 - Earliest claimed: 2008-04-18 - Assignees: Denso Corporation; Nippon Soken, Inc. - Inventors: Makiko Sugiura; Yasuyuki Okuda; Takaaki Kawai; Takahiko Yoshida; Hisanaga Matsuoka; Toshiki Isogai; Mitsuyasu Matsuura - Web page: https://patentgrep.com/patent/US20090260422A1 ## CPC - G01S 7/52004: {Means for monitoring or calibrating (short-range imaging G01S7/5205)} - G01S 7/52: of systems according to group G01S15/00 - G01S 7/52006: {with provision for compensating the effects of temperature} - G01S 7/521: Constructional features - G01S 15/003: {Bistatic sonar systems; Multistatic sonar systems} - G01S 15/876: {Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector (G01S15/872 takes precedence)} - G01S 15/931: of land vehicles - G01S 2015/939: {vertical stacking of sensors, e.g. to enable obstacle height determination} - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract An ultrasonic sensor includes a transmitting device, a receiving device, and a circuit device. The circuit device determines that the receiving device receives an ultrasonic wave reflected from an object, when an output voltage of the receiving device is equal to or greater than a first threshold. The circuit device includes a humidity detection section configured to detect an ambient humidity of the transmitting and receiving devices and a threshold adjustment section configured to calculate, based on the detected ambient humidity, a sound pressure of the ultrasonic wave that is received by the receiving device after propagating over a round-trip distance between the ultrasonic sensor and the object. The threshold adjustment section reduces the first threshold, when the output voltage corresponding to the calculated sound pressure is less than a second threshold that is greater the first threshold. ## Claims ### Claim 1 An ultrasonic sensor for detecting an object, comprising: a transmitting device for transmitting an ultrasonic wave to the object, the transmitting device including a first piezoelectric element configured to emit the ultrasonic wave, the transmitting device further including a first acoustic matching member though which the emitted ultrasonic wave propagates to an outside; a receiving device for receiving the ultrasonic wave reflected from the object, the receiving device including a second piezoelectric element configured to detect the reflected ultrasonic wave and produce an output voltage corresponding to the detected ultrasonic wave, the receiving device further including a second acoustic matching member though which the reflected ultrasonic wave propagates to the second piezoelectric element; a circuit device for applying a voltage to the first piezoelectric element to cause the first piezoelectric element to emit the ultrasonic wave, the circuit device determining that the receiving device receives the reflected ultrasonic wave when the output voltage of the second piezoelectric element is equal to or greater than a first threshold voltage, wherein the circuit device includes a humidity detection section configured to detect an ambient humidity of the transmitting and receiving devices and a threshold adjustment section configured to calculate, based on the detected ambient humidity, a sound pressure of the ultrasonic wave that is received by the receiving device after propagating over a round-trip distance between the ultrasonic sensor and the object, the threshold adjustment section reducing the first threshold voltage when the output voltage corresponding to the calculated sound pressure is less than a second threshold voltage, and the second threshold voltage being greater the first threshold voltage. ### Claim 2 (depends on 1) The ultrasonic sensor according to claim 1, wherein the threshold adjustment section calculates the sound pressure of the ultrasonic wave from the following three equations, K=1.92×(Go/G×H)1.3×105 . . . (α), where K is a variable, Go is an atmospheric pressure, G is a saturated vapor pressure, and H is the ambient humidity, M=(33+0.2T)F2×10−12+NF/{K/(2πF)+(2πF)/K} . . . (b), where M is an absorption coefficient, T is a temperature, F is a frequency of the ultrasonic wave, and N is a predetermined coefficient, and P=Ae−MR/R . . . (c), where P is the sound pressure, A is a predetermined coefficient, and R is the round-trip distance. ### Claim 3 (depends on 2) The ultrasonic sensor according to claim 2, wherein the humidity detection section applies a first detection voltage of a first frequency to the first piezoelectric element for a predetermined time period to cause the first piezoelectric element to emit the ultrasonic wave of the first frequency, the first frequency being slightly less than the resonance frequency, the humidity detection section calculates a first absorption coefficient from the equation (c) based on the sound pressure, the sound pressure being calculated from an amplitude of the output voltage of the second piezoelectric element that detects the reflected ultrasonic wave of the first frequency, the humidity detection section applies a second detection voltage of a second frequency to the first piezoelectric element for a predetermined time period to cause the first piezoelectric element to emit the ultrasonic wave of the second frequency, the second frequency being slightly greater than the resonance frequency, the humidity detection section calculates a second absorption coefficient from the equation (c) based on the sound pressure, the sound pressure being calculated from the amplitude of the output voltage of the second piezoelectric element that detects the reflected ultrasonic wave of the second frequency, the humidity detection section derives a first equation containing the variable K by substituting the first absorption coefficient into the equation (b) and a second equation containing the variable K by substituting the second absorption coefficient into the equation (b), and the humidity detection section calculates the humidity from the equation (a) and the derived first and second equations. ### Claim 4 (depends on 1) The ultrasonic sensor according to claim 1, wherein the first acoustic matching member is made of resin. ### Claim 5 (depends on 1) The ultrasonic sensor according to claim 1, further comprising: a gel-like absorber configured to protect at least one of the transmitting and receiving devices from an external force, wherein the humidity detection section detects the ambient humidity based on a dielectric constant of the absorber. ### Claim 6 (depends on 1) The ultrasonic sensor according to claim 1, further comprising: a surface acoustic wave element located on a surface of one of the first and second piezoelectric elements, the surface acoustic wave element emitting a surface acoustic wave and receiving the emitted surface acoustic wave, wherein the humidity detection section detects the ambient humidity based on a difference in frequency between the emitted surface acoustic wave and the received surface acoustic wave. ### Claim 7 (depends on 1) The ultrasonic sensor according to claim 1, wherein the first piezoelectric element comprises a plurality of piezoelectric elements stacked together to form a multilayer piezoelectric element. ### Claim 8 (depends on 1) The ultrasonic sensor according to claim 1, wherein the second piezoelectric element is made of piezoelectric zirconate titanate. ### Claim 9 (depends on 1) The ultrasonic sensor according to claim 1, wherein each of the first and second piezoelectric elements is made of polyvinylidene fluoride. ### Claim 10 (depends on 1) The ultrasonic sensor according to claim 1, wherein the receiving device comprises a plurality of receiving devices that are arranged in an array pattern. ### Claim 11 An ultrasonic sensor for detecting an object, comprising: a transmitting device for transmitting an ultrasonic wave to the object, the transmitting device including a first piezoelectric element configured to emit the ultrasonic wave, the transmitting device further including a first acoustic matching member through which the emitted ultrasonic wave propagates to an outside; a receiving device for receiving the ultrasonic wave reflected from the object, the receiving device including a second piezoelectric element configured to detect the reflected ultrasonic wave, the receiving device further including a second acoustic matching member through which the reflected ultrasonic wave propagates to the second piezoelectric element; a circuit device for applying a first voltage of a first frequency to the first piezoelectric element to cause the first piezoelectric element to emit the ultrasonic wave of the first frequency, the circuit device including a resonance frequency detection section configured to detect a resonance frequency of one of the first and second acoustic matching members, wherein the circuit device adjusts the first frequency of the first voltage to the detected resonance frequency. ### Claim 12 (depends on 11) The ultrasonic sensor according to claim 11, wherein the first and second acoustic matching members have the same temperature dependence of Young's modulus. ### Claim 13 (depends on 11) The ultrasonic sensor according to claim 11, wherein the circuit device applies a second voltage of a second frequency to the circuit device for a predetermined time period to cause the first piezoelectric element to emit the ultrasonic wave of the second frequency, the resonance frequency detection section detects the resonance frequency by detecting a reverberation frequency of an output signal of the second piezoelectric element that detects the reflected ultrasonic wave of the second frequency to the second piezoelectric element, and the output signal has the reverberation frequency after completion of propagation of the reflected ultrasonic wave of the second frequency to the second piezoelectric element. ### Claim 14 (depends on 11) The ultrasonic sensor according to claim 11, wherein the circuit device further includes an impedance measurement section configured to measure an impedance of the first piezoelectric element when a frequency of a voltage of the first piezoelectric element changes or an impedance of the second piezoelectric element when a frequency of a voltage of the second piezoelectric element changes, and the resonance frequency detection section detects the resonance frequency by detecting the frequency corresponding to a local minimum value of the measured impedance. ### Claim 15 (depends on 11) The ultrasonic sensor according to claim 11, wherein the circuit device further includes a temperature detection section configured to detect a temperature of the first acoustic matching member, wherein the resonance frequency detection section detects the resonance frequency based on the following equation, Fc=[E/{3×p(1−v)}]1/2/4L, where Fc is the resonance frequency, E is a Young's modulus of the first acoustic matching member, the Young's modulus being dependent on the detected temperature, p is a density of the first acoustic matching member, v is a Poisson ratio of the first acoustic matching member, and L is a length of the first acoustic matching member in a propagation direction of the ultrasonic wave. ### Claim 16 (depends on 15) The ultrasonic sensor according to claim 15, further comprising: a gel-like absorber configured to protect the first acoustic matching member from an external force, wherein the temperature detection section detects the temperature based on a dielectric constant of the absorber. ### Claim 17 (depends on 15) The ultrasonic sensor according to claim 15, further comprising: a surface acoustic wave element located on a surface of the first piezoelectric element, the surface acoustic wave element emitting a surface acoustic wave and receiving the emitted surface acoustic wave, wherein the temperature detection section detects the temperature based on a difference in frequency between the emitted surface acoustic wave and the received surface acoustic wave. ### Claim 18 (depends on 1) The ultrasonic sensor according to claim 1, wherein the circuit device further includes a temperature detection section configured to detect a temperature of the second acoustic matching member, wherein the resonance frequency detection section detects the resonance frequency based on the following equation, Fc=[E/{3×p(1−v)}]1/2/4L, where Fc is the resonance frequency, E is a Young's modulus of the second acoustic matching member, the Young's modulus being dependent on the detected temperature, p is a density of the second acoustic matching member, v is a Poisson ratio of the second acoustic matching member, and L is a length of the second acoustic matching member in a propagation direction of the ultrasonic wave. ### Claim 19 (depends on 18) The ultrasonic sensor according to claim 18, further comprising: a gel-like absorber configured to protect the second acoustic matching member from an external force, wherein the temperature detection section detects the temperature based on a dielectric constant of the absorber. ### Claim 20 (depends on 18) The ultrasonic sensor according to claim 18, further comprising: a surface acoustic wave element located on a surface of the second piezoelectric element, the surface acoustic wave element emitting a surface acoustic wave and receiving the emitted surface acoustic wave, wherein the temperature detection section detects the temperature based on a difference in frequency between the emitted surface acoustic wave and the received surface acoustic wave. ### Claim 21 (depends on 11) The ultrasonic sensor according to claim 11, wherein the first piezoelectric element comprises a plurality of piezoelectric elements stacked together to form a multilayer piezoelectric element. ### Claim 22 (depends on 11) The ultrasonic sensor according to claim 11, wherein the second piezoelectric element is made of piezoelectric zirconate titanate. ### Claim 23 (depends on 11) The ultrasonic sensor according to claim 11, wherein each of the first and second piezoelectric elements is made of polyvinylidene fluoride. ### Claim 24 (depends on 11) The ultrasonic sensor according to claim 11, wherein the receiving device comprises a plurality of receiving devices that are arranged in an array pattern.