Ultrasonic sensor

Abstract

To provide an ultrasonic sensor with enhanced sensitivity on the basis of the inventor's new findings regarding the relationship between mass and sensitivity.SOLUTION: An ultrasonic sensor 11 includes a first ultrasonic module 12a that generates ultrasonic waves on the basis of a first ultrasonic vibrator 13a of a first mass, and a second ultrasonic module 12b that is combined with the first ultrasonic module 12a and outputs an electrical signal on the basis of ultrasonic waves received by a second ultrasonic vibrator 13b of a second mass that is lighter than the first mass.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic sensor including an ultrasonic module that outputs an electrical signal based on received ultrasonic waves. [Background technology]

[0002] Generally, as disclosed in Patent Document 1, for example, in an ultrasonic sensor, one ultrasonic vibrator serves as both a transmitting module and a receiving module. Since transmission and reception are achieved with one ultrasonic vibrator, the resonant frequency during transmission and reception is the same. Good sensitivity can be ensured based on the resonance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 62-100100 Summary of the Invention [Problem to be solved by the invention]

[0004] An ultrasonic transducer comprises, for example, a piezoelectric material. The piezoelectric material is formed, for example, from PZT (lead zirconate titanate). To oscillate the ultrasonic transducer, an AC voltage with a frequency that matches the natural frequency is supplied to the piezoelectric material. As is known, the natural frequency of an object can be derived depending on its mass and rigidity. For example, in a bolt-clamped Langevin transducer, a reduction in the oscillation frequency is achieved depending on the weight of the metal block. To date, the relationship between the mass of the piezoelectric material and its sensitivity has not been studied in ultrasonic sensors.

[0005] An object of the present invention is to provide an ultrasonic sensor with improved sensitivity based on the inventor's new findings regarding the relationship between mass and sensitivity. [Means for solving the problem]

[0006] One form of the present invention comprises a first ultrasonic module that generates ultrasonic waves based on a first ultrasonic vibrator of a first mass, and a second ultrasonic module that is combined with the first ultrasonic module and outputs an electrical signal based on the ultrasonic waves received by a second ultrasonic vibrator of a second mass that is lighter than the first mass. [Effects of the Invention]

[0007] As described above, according to the disclosed invention, an ultrasonic sensor with increased sensitivity can be provided based on the inventor's new findings regarding the relationship between mass and sensitivity. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a conceptual diagram illustrating a schematic configuration of an ultrasonic sensor according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a conceptual diagram illustrating a schematic configuration of an ultrasonic sensor. [Figure 3] FIG. 10 is a conceptual diagram illustrating the configuration of an ultrasonic sensor according to a second embodiment of the present invention. [Figure 4] FIG. 1 is a conceptual diagram illustrating a schematic configuration of an ultrasonic sensor. [Figure 5] 1 is a side view schematically illustrating a configuration of a first ultrasonic module (or a second ultrasonic module) according to a specific example. [Figure 6] 6A is a graph showing the relationship between the mass of the piezoelectric element and the amplitude during transmission, and 6B is a graph showing the relationship between the mass of the piezoelectric element and the received voltage. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0010] FIG. 1 shows a schematic configuration of an ultrasonic sensor according to a first embodiment of the present invention. The ultrasonic sensor 11 includes a first ultrasonic module 12a that transmits ultrasonic waves and a second ultrasonic module 12b that is combined with the first ultrasonic module 12a and receives ultrasonic waves. The first ultrasonic module 12a generates ultrasonic waves using a first ultrasonic transducer 13a with a first mass. The second ultrasonic module 12b receives ultrasonic waves using a second ultrasonic transducer 13b with a second mass that is lighter than the first mass. The second ultrasonic module 12b outputs an electrical signal based on the received ultrasonic waves.

[0011] The first ultrasonic vibrator 13a includes a piezoelectric element 14a that ultrasonically vibrates in response to the supply of power, and a weighting mechanism 15a that detachably connects a weight to the piezoelectric element 14a. The piezoelectric element 14a is made of, for example, PZT (lead zirconate titanate). The piezoelectric element 14a is a cylindrical body (or cylinder) of second mass that extends a specific length L in the longitudinal direction. When polarized in the longitudinal direction, electrodes are connected to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are connected to both ends in the diametric direction.

[0012] The weighting mechanism 15a includes, for example, an electromagnet that exerts a magnetic force in response to the supply of power. The electromagnet functions as a weight that is coupled to the piezoelectric body 14a through the action of the magnetic force. The weighting mechanism 15a can establish a first mass of the first ultrasonic transducer 13a in response to the coupling of the weight. As shown in FIG. 2, when the weight is separated in response to the cutting of power, a second mass of the first ultrasonic transducer 13a can be established. In this way, the first ultrasonic transducer 13a can be switched between the first mass and the second mass in response to the supply and cutting of power.

[0013] The first ultrasonic module 12a includes a housing 16 that supports a piezoelectric element 14a. The housing 16 includes a vibration plate 16a coupled to the piezoelectric element 14a and a container 16b that rises from the outer periphery of the vibration plate 16a and surrounds the piezoelectric element 14a. Vibrations of the piezoelectric element 14a are transmitted to the vibration plate 16a. Ultrasonic waves are transmitted from the vibration plate 16a in a predetermined directional direction. The directional direction can be specified by a reference line DR1. The container 16b can be fixed to a specific structure. The movement of the container 16b is constrained by the structure.

[0014] The second ultrasonic vibrator 13b includes a piezoelectric body 14b that ultrasonically vibrates in response to the supply of power, and a weighting mechanism 15b that detachably connects a weight to the piezoelectric body 14b. The piezoelectric body 14b is made of, for example, PZT (lead zirconate titanate). The piezoelectric body 14b is a cylindrical body (or cylinder) of second mass that extends a specific length L in the longitudinal direction. The cylinder is formed to have the same diameter as the cylindrical body of the first ultrasonic vibrator 13a. When polarized in the longitudinal direction, electrodes are connected to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are connected to both ends in the diametric direction.

[0015] The weighting mechanism 15b includes, for example, an electromagnet that exerts a magnetic force in response to the supply of power. As shown in FIG. 2, the electromagnet functions as a weight that is coupled to the piezoelectric body 14b through the action of magnetic force. The weighting mechanism 15b can establish a first mass of the second ultrasonic transducer 13b in response to the coupling of the weight. When the weight is separated in response to the cutting of power, a second mass of the second ultrasonic transducer 13b can be established. In this way, the second ultrasonic transducer 13b can be switched between the first mass and the second mass in response to the supply and cutting of power.

[0016] The second ultrasonic module 12b includes a housing 17 that supports the piezoelectric element 14b. The housing 17 includes a diaphragm 17a that is coupled to the piezoelectric element 14b and a housing 17b that rises from the outer periphery of the diaphragm 17a and surrounds the piezoelectric element 14b. Vibration from the diaphragm 17a is transmitted to the piezoelectric element 14b. Ultrasonic waves act on the diaphragm 17a from a predetermined directional direction. The directional direction can be specified by a reference line DR2. The housing 17b can be fixed to a specific structure. The movement of the housing 17b is constrained by the structure.

[0017] A controller 21 is connected to the first ultrasonic module 12a and the second ultrasonic module 12b. For example, signal lines are used for the connection. The controller 21 includes an oscillator 22 that supplies a drive voltage to the piezoelectric bodies 14a and 14b. An AC voltage of a resonant frequency is applied from the oscillator 22 to the piezoelectric bodies 14a and 14b. The AC voltage is boosted by a step-up transformer 23 and acts on the piezoelectric bodies 14a and 14b. The piezoelectric bodies 14a and 14b oscillate at a resonant frequency in response to the AC voltage. In this way, the piezoelectric bodies 14a and 14b generate ultrasonic waves. A power source 24 is connected to the oscillator 22 to supply the AC voltage.

[0018] Here, the AC voltage applied to the piezoelectric elements 14a and 14b can be set to, for example, less than 4000 V. Setting the AC voltage to less than 4000 V reduces the power consumption of the ultrasonic sensor 11. The step-up transformer 23 can be sufficiently low in performance. If the AC voltage is set to 200 V, the AC voltage can be introduced from an outlet. The step-up transformer 23 can be omitted.

[0019] The controller 21 includes a receiver 25 that receives a received voltage from the piezoelectric elements 14a and 14b. The piezoelectric elements 14a and 14b resonate in response to the received ultrasonic waves. In response to the resonance, the piezoelectric elements 14a and 14b generate a received voltage. The received voltage is amplified and supplied to the receiver 25. Here, the frequency of the AC voltage applied to the piezoelectric elements 14a and 14b is set to be equal to or greater than the natural frequency of the first mass and equal to or less than the natural frequency of the second mass. In this setting, the piezoelectric elements 14a and 14b only need to have characteristics that prevent a decrease in sensitivity over a wide frequency band even when the frequency is far from the resonant frequency. With these characteristics, increased sensitivity can be achieved based on the combination of the first and second masses compared to when an AC voltage at the resonant frequency is applied between the second masses.

[0020] The controller 21 includes a calculation unit 26 that controls the operation of the ultrasonic sensor 11. The calculation unit 26 calculates the time difference between transmission by the first ultrasonic module 12a and reception by the second ultrasonic module 12b. The calculation unit 26 measures, for example, the time from transmission of an ultrasonic wave to reception of the ultrasonic wave. Power is supplied to the calculation unit 26 from the power source 24 when calculating the time difference.

[0021] A controller 21 is connected to the weighting mechanisms 15a and 15b. Signal lines are used for the connection. A switching signal is supplied to the weighting mechanisms 15a and 15b from a calculation unit 26. When ultrasonic waves are transmitted from the first ultrasonic module 12a and received by the second ultrasonic module 12b, the calculation unit 26 couples an electromagnet to the piezoelectric body 14a in the first ultrasonic module 12a to impart a first mass to the first ultrasonic vibrator 13a, and detaches the electromagnet from the piezoelectric body 14b in the second ultrasonic module 12b to impart a second mass to the second ultrasonic vibrator 13b. Conversely, when ultrasonic waves are transmitted from the second ultrasonic module 12b and received by the first ultrasonic module 12a, the calculation unit 26 couples an electromagnet to the piezoelectric body 14b in the second ultrasonic module 12b to impart a first mass to the second ultrasonic vibrator 13b, while detaching the electromagnet from the piezoelectric body 14a in the first ultrasonic module 12a to impart a second mass to the first ultrasonic vibrator 13a.

[0022] Here, the ultrasonic sensor 11 is configured as an ultrasonic flowmeter using a transit time difference method. The first ultrasonic module 12a and the second ultrasonic module 12b are attached to, for example, a pipe 28. A gas flow path 29 is defined in the pipe 28. The gas flows, for example, from upstream 29a to downstream 29b. The diaphragm 16a of the first ultrasonic module 12a and the diaphragm 17a of the second ultrasonic module 12b each face the flow path 29. The housing 16b of the first ultrasonic module 12a and the housing 17b of the second ultrasonic module 12b are each constrained by the pipe 28. The calculation unit 26 calculates the time difference between transmission by the first ultrasonic module 12a and reception by the second ultrasonic module 12b, and then calculates the time difference between transmission by the second ultrasonic module 12b and reception by the first ultrasonic module 12a. The calculation unit 26 measures, for example, the time from transmission of an ultrasonic wave to reception of the ultrasonic wave.

[0023] An acoustic matching layer can be laminated on the surface of the diaphragms 16a and 17a. The acoustic matching layer is made of a material with an acoustic impedance intermediate between that of the diaphragms 16a and 17a and the gas. This can suppress the reflection of ultrasonic waves at the interface with the gas, and reduce the power consumption of the ultrasonic sensor 11.

[0024] Next, the operation of the ultrasonic sensor 11 according to this embodiment will be described. To measure the flow rate, the calculation unit 26 establishes a first mass of the first ultrasonic vibrator 13a in the first ultrasonic module 12a and establishes a second mass of the second ultrasonic vibrator 13b in the second ultrasonic module 12b. A switching signal for coupling the electromagnet is supplied from the calculation unit 26 to the weighting mechanism 15a of the first ultrasonic module 12a. The piezoelectric element 14a of the first ultrasonic module 12a is connected to the oscillator 22 of the controller 21. A switching signal for decoupling the electromagnet is supplied from the calculation unit 26 to the weighting mechanism 15b of the second ultrasonic module 12b. The piezoelectric element 14b of the second ultrasonic module 12b is connected to the receiver 25 of the controller 21.

[0025] The calculation unit 26 instructs the oscillation unit 22 to output an AC voltage of the resonance frequency. In response to the supply of AC voltage, the piezoelectric element 14a of the first ultrasonic oscillator 13a oscillates within a specified time. Ultrasonic waves are transmitted from the vibration plate 16a in the direction of the reference line DR1. The ultrasonic waves cross the flow path 29 along the reference lines DR1 and DR2 and reach the vibration plate 17a. The ultrasonic waves are pushed by the airflow. The piezoelectric element 14b of the second ultrasonic oscillator 13b resonates with the ultrasonic waves. In response to the resonance, a received voltage is output from the piezoelectric element 14b. The received voltage is received by the receiving unit 25. The calculation unit 26 calculates the time from the transmission of the ultrasonic waves to the reception of the ultrasonic waves (hereinafter referred to as the "first time"). The calculated first time is temporarily stored, for example, in a memory.

[0026] Next, the calculation unit 26 establishes a first mass of the second ultrasonic transducer 13b in the second ultrasonic module 12b, and establishes a second mass of the first ultrasonic transducer 13a in the first ultrasonic module 12a. A switching signal for disconnecting the electromagnet is supplied from the calculation unit 26 to the weighting mechanism 15a of the first ultrasonic module 12a. The piezoelectric element 14a of the first ultrasonic module 12a is connected to the receiving unit 25 of the controller 21. A switching signal for connecting the electromagnet is supplied from the calculation unit 26 to the weighting mechanism 15b of the second ultrasonic module 12b. The piezoelectric element 14b of the second ultrasonic module 12b is connected to the oscillator 22 of the controller 21.

[0027] The calculation unit 26 instructs the oscillation unit 22 to output an AC voltage of the resonance frequency. In response to the supply of the AC voltage, the piezoelectric element 14b of the second ultrasonic oscillator 13b oscillates within a specified time. Ultrasonic waves are transmitted from the vibration plate 17a in the direction of the reference line DR2. The ultrasonic waves cross the flow path 29 along the reference lines DR2 and DR1 and reach the vibration plate 16a. The ultrasonic waves travel against the airflow. The piezoelectric element 14a of the first ultrasonic oscillator 13a resonates with the ultrasonic waves. In response to the resonance, a received voltage is output from the piezoelectric element 14a of the first ultrasonic oscillator 13a. The received voltage is received by the receiving unit 25. The calculation unit 26 calculates the time from the transmission of the ultrasonic waves to the reception of the ultrasonic waves (hereinafter referred to as the "second time"). The calculated second time is temporarily stored, for example, in a memory.

[0028] The calculation unit 26 calculates the airflow velocity based on the first time and the second time. Once the airflow velocity is calculated in this manner, the airflow rate can be determined based on the cross-sectional area of ​​the pipe 28. The calculation unit 26 can output numerical data that determines the flow rate.

[0029] The ultrasonic sensor 11 according to this embodiment includes a first ultrasonic module 12a that generates ultrasonic waves based on a first ultrasonic transducer 13a having a first mass, and a second ultrasonic module 12b that is combined with the first ultrasonic module 12a and outputs an electrical signal based on ultrasonic waves received by a second ultrasonic transducer 12b having a second mass that is lighter than the first mass. The inventors discovered that reducing the weight of the second ultrasonic transducer 13b reduces the inertial force of the second ultrasonic transducer 13b. The amplitude of the ultrasonic waves generated by the second ultrasonic transducer 13b increases in response to the reduced inertial force. This increases the voltage generated by the second ultrasonic transducer 13b when receiving ultrasonic waves. The reception sensitivity of the second ultrasonic module 13b can be improved.

[0030] Similarly, the ultrasonic sensor 11 according to this embodiment generates ultrasonic waves based on the second ultrasonic transducer 13b having a first mass, and can output an electrical signal based on the ultrasonic waves received by the first ultrasonic transducer 12a having a second mass lighter than the first mass. Here, the inertial force of the first ultrasonic transducer 13a is reduced by reducing the weight of the first ultrasonic transducer 13a. The amplitude of the ultrasonic waves in the first ultrasonic transducer 13a increases in response to the reduced inertial force. In this way, the voltage generated in the first ultrasonic transducer 13a when receiving ultrasonic waves can be increased. The reception sensitivity of the first ultrasonic module 13a can be improved.

[0031] The first ultrasonic module 12a according to this embodiment includes a piezoelectric element 14a having a second mass and vibrating ultrasonically in response to the supply of power, and a weighting mechanism 15a that detachably couples a weight to the piezoelectric element 14a and applies a first mass in response to the weight coupling. Because the piezoelectric element 14a has the same shape as the piezoelectric element 14b of the second ultrasonic module 12b, their resonant frequencies can be matched. Although the coupling of the weight causes a shift in the resonant frequency of the first ultrasonic transducer 13a, the mass of the weight is set within a range that increases the voltage generated by the second ultrasonic transducer 13b compared to the piezoelectric elements 14a and 14b of the same shape, regardless of the shift in resonant frequency. This allows the reception sensitivity to be increased, overcoming the effect of the shift in resonant frequency.

[0032] In this embodiment, the roles of transmission and reception are interchanged between the first ultrasonic module 12a and the second ultrasonic module 12b. The second ultrasonic module 12b according to this embodiment includes a piezoelectric element 14b having a second mass and vibrating ultrasonically in response to the supply of power, and a weighting mechanism 15b that detachably couples a weight to the piezoelectric element 14b and applies a first mass in response to the coupling of the weight. As described above, although the coupling of the weight causes a shift in the resonant frequency of the second ultrasonic transducer 13b, the mass of the weight is set within a range that increases the voltage generated by the first ultrasonic transducer 13a compared to the piezoelectric elements 14a and 14b of the same shape, regardless of the shift in resonant frequency. This allows the reception sensitivity to be increased, overcoming the effect of the shift in resonant frequency.

[0033] FIG. 3 shows a schematic configuration of an ultrasonic sensor according to a second embodiment of the present invention. The ultrasonic sensor 11a includes a first ultrasonic module 12a that transmits ultrasonic waves and a second ultrasonic module 12b that is combined with the first ultrasonic module 12a and receives ultrasonic waves. The first ultrasonic module 12a generates ultrasonic waves using a first ultrasonic transducer 13a with a first mass. The second ultrasonic module 12b receives ultrasonic waves using a second ultrasonic transducer 13b with a second mass that is lighter than the first mass. The second ultrasonic module 12b outputs an electrical signal based on the received ultrasonic waves.

[0034] The first ultrasonic vibrator 13a includes a first piezoelectric element 31a having a specific length L that vibrates in the longitudinal direction. The first piezoelectric element 31a is formed from, for example, PZT (lead zirconate titanate). The first piezoelectric element 31a is a cylindrical body (or cylinder) of a first diameter that extends in the longitudinal direction. The diameter of the cylinder is perpendicular to the longitudinal direction. When polarized in the longitudinal direction, electrodes are coupled to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are coupled to both ends in the diametric direction.

[0035] The first ultrasonic module 12a includes a housing 16 that supports a first piezoelectric element 31a. The housing 16 includes a vibration plate 16a coupled to the first piezoelectric element 31a and a container 16b that rises from the outer periphery of the vibration plate 16a and surrounds the first piezoelectric element 31a. Vibrations of the first piezoelectric element 31a are transmitted to the vibration plate 16a. Ultrasonic waves are transmitted from the vibration plate 16a in a predetermined directional direction. The directional direction can be specified by a reference line DR1. The container 16b can be fixed to a specific structure. The movement of the container 16b is constrained by the structure.

[0036] The second ultrasonic vibrator 13b includes a second piezoelectric element 31b having a specific length L that vibrates in the longitudinal direction. The second piezoelectric element 31b is lighter than the first piezoelectric element 31a. The second piezoelectric element 31b is formed from, for example, PZT (lead zirconate titanate). The second piezoelectric element 31b is a cylindrical body (or cylinder) extending in the longitudinal direction and having a second diameter. The diameter of the cylinder is perpendicular to the longitudinal direction. The second diameter is set to be smaller than the first diameter. When polarized in the longitudinal direction, electrodes are coupled to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are coupled to both ends in the diametric direction.

[0037] The second ultrasonic module 12b includes a housing 17 that supports the second piezoelectric element 31b. The housing 17 includes a diaphragm 17a coupled to the second piezoelectric element 31b and a housing 17b that rises from the outer periphery of the diaphragm 17a and surrounds the second piezoelectric element 31b. Vibrations from the diaphragm 17a are transmitted to the second piezoelectric element 31b. Ultrasonic waves act on the diaphragm 17a from a predetermined directional direction. The directional direction can be specified by a reference line DR2. The housing 17b can be fixed to a specific structure. The movement of the housing 17b is constrained by the structure.

[0038] A controller 21 is connected to the first ultrasonic module 12a and the second ultrasonic module 12b. For example, signal lines are used for the connection. The controller 21 includes an oscillator 22 that supplies a drive voltage to the first piezoelectric element 31a. An AC voltage of a resonant frequency is applied to the first piezoelectric element 31a from the oscillator 22. The AC voltage is amplified by a step-up transformer 23 and acts on the first piezoelectric element 31a. The first piezoelectric element 31a oscillates at a resonant frequency in response to the AC voltage. In this way, the first piezoelectric element 31a generates ultrasonic waves. A power source 24 is connected to the oscillator 22 to supply the AC voltage.

[0039] Here, the AC voltage applied to the first piezoelectric element 31a can be set to, for example, less than 4000V. By setting the AC voltage to less than 4000V, the power consumption of the ultrasonic sensor 11a can be reduced. The step-up transformer 23 can be sufficiently powered with low performance. If the AC voltage is set to 200V, the AC voltage can be introduced from an outlet. The step-up transformer 23 can be omitted.

[0040] The controller 21 includes a receiver 25 that receives a received voltage from the second piezoelectric element 31b. The second piezoelectric element 31b resonates in response to the received ultrasonic waves. In response to the resonance, the second piezoelectric element 31b generates a received voltage. The received voltage is amplified and supplied to the receiver 25.

[0041] The controller 21 includes a calculation unit 26 that controls the operation of the ultrasonic sensor 11a. The calculation unit 26 calculates the time difference between transmission by the first ultrasonic module 12a and reception by the second ultrasonic module 12b. The calculation unit 26 measures, for example, the time from transmission of ultrasonic waves to reception of the ultrasonic waves. Power is supplied to the calculation unit 26 from the power source 24 when calculating the time difference.

[0042] As shown in Figure 4, the first ultrasonic module 12a further includes a second ultrasonic transducer 13b having a second mass that is lighter than the first mass. The first ultrasonic module 12a can receive ultrasonic waves using the second ultrasonic transducer 13b. As described above, the receiving unit 25 of the controller 21 is connected to the second ultrasonic transducer 13b. A signal line is used for the connection. The receiving unit 25 receives a received voltage from the second piezoelectric element 31b.

[0043] The second ultrasonic vibrator 13b includes a second piezoelectric element 31b having a specific length L that vibrates in the longitudinal direction. The second piezoelectric element 31b is lighter than the first piezoelectric element 31a. The first ultrasonic module 12a and the second ultrasonic module 12b may include the same second piezoelectric element 31b. The second piezoelectric element 31b is formed from, for example, PZT (lead zirconate titanate). The second piezoelectric element 31b is a cylindrical body (or a cylinder) extending in the longitudinal direction and having a second diameter. The diameter of the cylinder is perpendicular to the longitudinal direction. The second diameter is set to be smaller than the first diameter. When polarized in the longitudinal direction, electrodes are connected to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are connected to both ends in the diametric direction.

[0044] The first ultrasonic module 12a includes a positioning mechanism 32 that positions the first ultrasonic transducer 13a on a reference line DR1 that specifies the direction of ultrasonic waves during transmission, and positions the second ultrasonic transducer 13b on the reference line DR1 during reception. The positioning mechanism 32 switches between the first ultrasonic transducer 13a and the second ultrasonic transducer 13b during transmission and reception. In response to the switching, ultrasonic waves are transmitted from the first ultrasonic transducer 13a with a determined directivity during transmission, and are received by the second ultrasonic transducer 13b with a determined directivity during reception.

[0045] The second ultrasonic module 12b further includes a first ultrasonic vibrator 13a having a first mass. The second ultrasonic module 12b can generate ultrasonic waves using the first ultrasonic vibrator 13a. As described above, the oscillator 22 of the controller 21 is connected to the first ultrasonic vibrator 13a. A signal line is used for the connection. The oscillator 22 applies an AC voltage of a resonant frequency to the first piezoelectric element 31a.

[0046] The first ultrasonic vibrator 13a includes a first piezoelectric element 31a having a specific length L that vibrates in the longitudinal direction. The first piezoelectric element 31a is heavier than the second piezoelectric element 31b. The first ultrasonic module 12a and the second ultrasonic module 12b may include the same first piezoelectric element 31a. The first piezoelectric element 31a is formed from, for example, PZT (lead zirconate titanate). The first piezoelectric element 31a is a cylindrical body (or cylinder) extending in the longitudinal direction and having a first diameter. The diameter of the cylinder is perpendicular to the longitudinal direction. The first diameter is set to be larger than the second diameter. When polarized in the longitudinal direction, electrodes are coupled to both ends in the longitudinal direction. When polarized in the diametric direction, electrodes are coupled to both ends in the diametric direction.

[0047] The second ultrasonic module 12b includes a positioning mechanism 33 that positions the first ultrasonic transducer 13a on a reference line DR2 that specifies the direction of ultrasonic waves during transmission, and positions the second ultrasonic transducer 13b on the reference line DR2 during reception. The positioning mechanism 33 switches between the first ultrasonic transducer 13a and the second ultrasonic transducer 13b during transmission and reception. In response to the switching, ultrasonic waves are transmitted from the first ultrasonic transducer 13a with a determined directivity during transmission, and are received by the second ultrasonic transducer 13b with a determined directivity during reception.

[0048] The controller 21 is connected to the positioning mechanisms 32 and 33. Signal lines are used for the connection. A switching signal is supplied to the positioning mechanisms 32 and 33 from the calculation unit 26. When the calculation unit 26 selects the first ultrasonic transducer 13a in the first ultrasonic module 12a, it selects the second ultrasonic transducer 13b in the second ultrasonic module 12b. When the calculation unit 26 selects the second ultrasonic transducer 13b in the first ultrasonic module 12a, it selects the first ultrasonic transducer 13a in the second ultrasonic module 12b.

[0049] Here, the ultrasonic sensor 11a is configured as an ultrasonic flowmeter using a transit time difference method. The first ultrasonic module 12a and the second ultrasonic module 12b are attached to, for example, a pipe 28. A gas flow path 29 is defined in the pipe 28. The gas flows, for example, from upstream 29a to downstream 29b. The diaphragm 16a of the first ultrasonic module 12a and the diaphragm 17a of the second ultrasonic module 12b each face the flow path 29. The housing 16b of the first ultrasonic module 12a and the housing 17b of the second ultrasonic module 12b are each constrained by the pipe 28. The calculation unit 26 calculates the time difference between transmission by the first ultrasonic module 12a and reception by the second ultrasonic module 12b, and then calculates the time difference between transmission by the second ultrasonic module 12b and reception by the first ultrasonic module 12a. The calculation unit 26 measures, for example, the time from transmission of an ultrasonic wave to reception of the ultrasonic wave.

[0050] An acoustic matching layer can be laminated on the surface of the diaphragms 16a and 17a. The acoustic matching layer is made of a material with an acoustic impedance intermediate between that of the diaphragms 16a and 17a and the gas. This can suppress the reflection of ultrasonic waves at the interface with the gas, thereby reducing the power consumption of the ultrasonic sensor 11a.

[0051] Next, the operation of the ultrasonic sensor 11a according to this embodiment will be described. To measure the flow rate, the calculation unit 26 selects the first ultrasonic transducer 13a in the first ultrasonic module 12a and the second ultrasonic transducer 13b in the second ultrasonic module 12b. A switching signal for selecting the first ultrasonic transducer 13a is supplied from the calculation unit 26 to the positioning mechanism 32 of the first ultrasonic module 12a. The first piezoelectric element 31a of the first ultrasonic module 12a is connected to the oscillation unit 22 of the controller 21. A switching signal for selecting the second ultrasonic transducer 13b is supplied from the calculation unit 26 to the positioning mechanism 33 of the second ultrasonic module 12b. The second piezoelectric element 31b of the second ultrasonic module 12b is connected to the receiving unit 25 of the controller 21.

[0052] The calculation unit 26 instructs the oscillator 22 to output an AC voltage of the resonance frequency. In response to the supply of AC voltage, the first piezoelectric element 31a oscillates within a specified time. Ultrasonic waves are transmitted from the vibration plate 16a in the direction of the reference line DR1. The ultrasonic waves cross the flow path 29 along the reference lines DR1 and DR2 and reach the vibration plate 17a. The ultrasonic waves are pushed by the airflow. The second piezoelectric element 31b resonates with the ultrasonic waves. In response to the resonance, a received voltage is output from the second piezoelectric element 31b. The received voltage is received by the receiving unit 25. The calculation unit 26 calculates the time from the transmission of the ultrasonic waves to the reception of the ultrasonic waves (hereinafter referred to as the "first time"). The calculated first time is temporarily stored, for example, in a memory.

[0053] Next, the calculation unit 26 selects the second ultrasonic transducer 13b in the first ultrasonic module 12a and selects the first ultrasonic transducer 13a in the second ultrasonic module 12b. A switching signal for selecting the second ultrasonic transducer 13b is supplied from the calculation unit 26 to the positioning mechanism 32 of the first ultrasonic module 12a. The second piezoelectric element 31b of the first ultrasonic module 12a is connected to the receiving unit 25 of the controller 21. A switching signal for selecting the first ultrasonic transducer 13a is supplied from the calculation unit 26 to the positioning mechanism 33 of the second ultrasonic module 12b. The first piezoelectric element 31a of the second ultrasonic module 12b is connected to the oscillator 22 of the controller 21.

[0054] The calculation unit 26 instructs the oscillator 22 to output an AC voltage of the resonance frequency. In response to the supply of AC voltage, the first piezoelectric element 31a oscillates within a specified time. Ultrasonic waves are transmitted from the vibration plate 17a in the direction of the reference line DR2. The ultrasonic waves cross the flow path 29 along the reference lines DR2 and DR1 and reach the vibration plate 16a. The ultrasonic waves travel against the airflow. The second piezoelectric element 31b resonates with the ultrasonic waves. In response to the resonance, a received voltage is output from the second piezoelectric element 31b. The received voltage is received by the receiving unit 25. The calculation unit 26 calculates the time from the transmission of the ultrasonic waves to the reception of the ultrasonic waves (hereinafter referred to as the "second time"). The calculated second time is temporarily stored, for example, in a memory.

[0055] The calculation unit 26 calculates the airflow velocity based on the first time and the second time. Once the airflow velocity is calculated in this manner, the airflow rate can be determined based on the cross-sectional area of ​​the pipe 28. The calculation unit 26 can output numerical data that determines the flow rate.

[0056] The ultrasonic sensor 11a according to this embodiment includes a first ultrasonic module 12a that generates ultrasonic waves based on a first ultrasonic transducer 13a having a first mass, and a second ultrasonic module 12b that is combined with the first ultrasonic module 12a and outputs an electrical signal based on ultrasonic waves received by a second ultrasonic transducer 12b having a second mass that is lighter than the first mass. The inventors discovered that reducing the weight of the second ultrasonic transducer 13b reduces the inertial force of the second ultrasonic transducer 13b. The amplitude of the ultrasonic waves generated by the second ultrasonic transducer 13b increases in response to the reduced inertial force. This increases the voltage generated by the second ultrasonic transducer 13b when receiving ultrasonic waves. The reception sensitivity of the second ultrasonic module 13b can be improved.

[0057] In this case, the first ultrasonic vibrator 13a includes a first piezoelectric element 31a of a specific length L that vibrates in the longitudinal direction, and the second ultrasonic vibrator 13b includes a second piezoelectric element 31b of a specific length L that vibrates in the longitudinal direction and is lighter than the first piezoelectric element 31a. A long piezoelectric element that vibrates in the longitudinal direction has a resonance frequency that depends on its length. Therefore, if the lengths are the same, the resonance frequencies can match even if the masses are different. In this way, the resonance frequencies of the first ultrasonic vibrator 13a and the second ultrasonic vibrator 13b can be matched. The second piezoelectric element 31b on the receiving side can resonate well with the ultrasonic waves transmitted from the first piezoelectric element 31a. Good sensitivity can be ensured.

[0058] In this embodiment, the first piezoelectric element 31a and the second piezoelectric element 31b are cylindrical or columnar elements that extend in the longitudinal direction and have different diameters in a direction perpendicular to the longitudinal direction. Due to the difference in diameter, the second piezoelectric element 31b can be lighter than the first piezoelectric element 31a. The masses of the first piezoelectric element 31a and the second piezoelectric element 31b can be different while matching the resonant frequencies. Good sensitivity can be ensured.

[0059] In the first ultrasonic module 12a and the second ultrasonic module 12b, the first ultrasonic transducer 13a and the second ultrasonic transducer 13b are arranged in a single housing 16, 17. One ultrasonic module 12a, 12b can be used for both transmission and reception.

[0060] Here, the first ultrasonic module 12a and the second ultrasonic module 12b further include positioning mechanisms 32 and 33 that, during transmission, position the first ultrasonic transducer 13a on reference lines DR1 and DR2 that specify the direction of ultrasonic waves, and that, during reception, position the second ultrasonic transducer 13b on reference lines DR1 and DR2. The positioning mechanisms 32 and 33 switch between the first ultrasonic transducer 13a and the second ultrasonic transducer 13b during transmission and reception. In response to the switching, ultrasonic waves are transmitted from the first ultrasonic transducer 13a with a predetermined directivity during transmission, and are received by the second ultrasonic transducer 13b with a predetermined directivity during reception. In this way, transmission and reception can be effectively achieved with a single ultrasonic module 12a and 12b.

[0061] FIG. 5 schematically illustrates the structure of an ultrasonic module 51 according to one specific example. The ultrasonic module 51 can be used in the first ultrasonic module 12a and the second ultrasonic module 12b. The ultrasonic module 51 includes a first piezoelectric element 31a having a specific length L that vibrates in the longitudinal direction, and a second piezoelectric element 31b that is lighter than the first piezoelectric element 31a and also vibrates in the longitudinal direction. The first piezoelectric element 31a is connected to a positioning mechanism 32 (33). The positioning mechanism 32 (33) includes a driver 52 coupled to the first piezoelectric element 31a and displaced in the longitudinal direction, and a drive source 53 that causes the driver 52 to displace in the longitudinal direction. The driver 52 is positioned at a first position that separates the first piezoelectric element 31a from the diaphragm 16a (17a), as shown in FIG. 5A, and at a second position that couples the first piezoelectric element 31a to the diaphragm 16a (17a), as shown in FIG. 5B. The driving source 53 can be composed of, for example, a threaded shaft fixed to the driver 52 and a nut engaged with the threaded shaft so as to be rotatable about a rotation axis coaxial with the threaded shaft. The driving source 53 restricts the movement of the driver 52. The first piezoelectric element 31a vibrates ultrasonically at a resonance frequency determined according to the specific length L. Ultrasonic waves are emitted from the surface of the vibration plate 16a (17a) in response to the vibration of the first piezoelectric element 31a. An acoustic matching layer, for example, is laminated on the surface of the vibration plate 16a (17a).

[0062] The second piezoelectric element 31b is coupled to the diaphragm 16a (17a). The second piezoelectric element 31b vibrates integrally with the diaphragm 16a (17a). Ultrasonic waves acting on the surface of the diaphragm 16a (17a) cause the second piezoelectric element 31b to resonate at a resonance frequency determined according to the specific length L. A voltage is output from the second piezoelectric element 31b based on the piezoelectric effect. When the driver 52 is positioned at the first position, vibration is transmitted from the diaphragm 16a (17a) only to the second piezoelectric element 31b. During transmission, the ultrasonic module 51 positions the first piezoelectric element 31a on a reference line DR1 (DR2) that specifies the direction of the ultrasonic waves, and during reception, positions the second piezoelectric element 31b on the reference line DR1 (DR2).

[0063] The inventors observed the characteristics of the piezoelectric element when constructing the ultrasonic sensors 11 and 11a. The displacement of the piezoelectric element, i.e., the amplitude of the diaphragms 16a and 17a, was measured during ultrasonic transmission. A laser Doppler displacement meter was used for the measurements. The displacement was averaged at three central points on the diaphragms 16a and 17a. The diameter of the piezoelectric element was kept constant. The mass of the piezoelectric element was changed depending on the length L. A square wave of 200 V was applied to the piezoelectric element. The frequency of the square wave was set to the resonant frequency for each piezoelectric element. As shown in Figure 6A, the heavier the piezoelectric element, the larger the amplitude obtained, even at a constant voltage. The larger the amplitude, the higher the ultrasonic transmission energy. Furthermore, if the length L of the piezoelectric element is kept constant, the resonant frequency can be maintained constant regardless of the diameter.

[0064] Next, the received voltage of the piezoelectric element was measured when receiving ultrasound. An impedance analyzer was used for the measurements. The diameter of the piezoelectric element was kept constant. The mass of the piezoelectric element was changed according to the change in length L. A square wave of 1 [V] was applied to the piezoelectric element. The frequency of the square wave was swept from 1 [Hz] to 100 [kHz]. The maximum voltage value during the sweep was recorded as the received voltage. As shown in Figure 6B, the lighter the piezoelectric element, the larger the received voltage obtained. The higher the received voltage, the higher the ultrasound reception sensitivity can be. [Explanation of symbols]

[0065] 11...Ultrasonic sensor 11a...ultrasonic sensor, 12a...First ultrasonic module 12b...Second ultrasonic module 13a...First ultrasonic vibrator 13b...Second ultrasonic vibrator 14a...Piezoelectric body 14b...Piezoelectric body 15a...Loading mechanism 15b...Loading mechanism 16...(First ultrasonic module) housing 17...Housing (of second ultrasonic module) 31a...first piezoelectric element 31b...second piezoelectric element 32... Positioning mechanism 33... Positioning mechanism DR1...reference line (direction) DR2...reference line (direction) L...(piezoelectric body) length

Claims

1. a first ultrasonic module that generates ultrasonic waves based on a first ultrasonic transducer having a first mass; a second ultrasonic module combined with the first ultrasonic module and configured to output an electrical signal based on the ultrasonic waves received by a second ultrasonic transducer having a second mass lighter than the first mass; An ultrasonic sensor comprising:

2. The first ultrasonic module includes a piezoelectric element having the second mass and vibrating ultrasonically in response to the supply of power, and a weighting mechanism that detachably couples a weight to the piezoelectric element and establishes the first mass in response to the coupling of the weight. The ultrasonic sensor of claim 1 .

3. The second ultrasonic module includes a piezoelectric element having the second mass and vibrating ultrasonically in response to the supply of power, and a weighting mechanism that detachably couples a weight to the piezoelectric element and establishes the first mass in response to the coupling of the weight. The ultrasonic sensor according to claim 2 .

4. The first ultrasonic transducer includes a first piezoelectric element having a specific length that vibrates in a longitudinal direction, The second ultrasonic transducer includes a second piezoelectric element having a specific length that vibrates in a longitudinal direction and is lighter than the first piezoelectric element. The ultrasonic sensor of claim 1 .

5. The first piezoelectric element and the second piezoelectric element are cylindrical or columnar elements that extend in the length direction and have different diameters in a direction perpendicular to the length direction. The ultrasonic sensor according to claim 4 .

6. The first ultrasonic transducer and the second ultrasonic transducer are disposed in a single housing. The ultrasonic sensor of claim 1 .

7. The ultrasonic wave receiving device further includes a positioning mechanism that positions the first ultrasonic transducer on a reference line that specifies the direction of the ultrasonic waves when transmitting, and positions the second ultrasonic transducer on the reference line when receiving. The ultrasonic sensor according to claim 6.

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