Ultrasonic transducer and ultrasonic flow meter

Abstract

To provide an ultrasonic transducer 10 capable of transmitting and receiving ultrasonic waves without exposing a piezoelectric element to fluid being measured.SOLUTION: An ultrasonic transducer 10 comprises: a substrate 11 having a back surface 11b exposed to fluid being measured and a surface 11a located opposite to the back surface 11b; and a piezoelectric element 12 mounted on the surface 11a that transmits and receives ultrasonic waves via the back surface 11b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an ultrasonic transducer and an ultrasonic flow meter. [Background technology]

[0002] Patent Document 1 discloses an ultrasonic transducer that is capable of transmitting and receiving ultrasonic waves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-16934 Summary of the Invention [Problem to be solved by the invention]

[0004] The ultrasonic transducer disclosed in Patent Document 1 includes a piezoelectric element. When a voltage is applied to the piezoelectric element, its vibration surface vibrates, thereby transmitting and receiving ultrasonic waves. That is, in the ultrasonic transducer disclosed in Patent Document 1, the vibration surface is always exposed to the measurement atmosphere in the usage environment.

[0005] Therefore, even when the ultrasonic transducer disclosed in Patent Document 1 is used to measure the flow rate or flow velocity of a fluid to be measured (hereinafter referred to as "fluid measurement"), the vibration surface of the piezoelectric element is constantly exposed to the fluid to be measured. As a result, foreign matter such as dust or dirt adheres to the vibration surface of the piezoelectric element, or the vibration surface is easily scratched. As a result, the ultrasonic transducer disclosed in Patent Document 1 may suffer from a decrease in transmission and reception accuracy, i.e., measurement accuracy.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an ultrasonic transducer that can transmit and receive ultrasonic waves without exposing the piezoelectric element to the fluid to be measured. [Means for solving the problem]

[0007] The ultrasonic transducer according to the present disclosure comprises a substrate having one surface exposed to the fluid to be measured and another surface located opposite the one surface, and a piezoelectric element mounted on the other surface and transmitting and receiving ultrasonic waves via the one surface. [Effects of the Invention]

[0008] According to the present disclosure, ultrasonic waves can be transmitted and received without exposing the piezoelectric element to the fluid to be measured. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a longitudinal sectional view of an ultrasonic transducer according to a first embodiment. [Figure 2] FIG. 10 is a longitudinal sectional view of an ultrasonic transducer according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0011] Embodiment 1 An ultrasonic transducer 10 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a longitudinal sectional view of the ultrasonic transducer 10 according to the first embodiment.

[0012] The ultrasonic transducer 10 according to the first embodiment shown in Fig. 1 is intended to be applied to, for example, an ultrasonic flow meter (not shown). The ultrasonic flow meter includes a pair of ultrasonic transducers 10, and enables fluid measurement by transmitting and receiving ultrasonic waves between the pair of ultrasonic transducers 10. The fluid to be measured by the ultrasonic flow meter is, for example, a gas or other gas, or a fluid such as water.

[0013] Furthermore, the pair of ultrasonic transducers 10 provided in the ultrasonic flowmeter have the same configuration and the same functions. For this reason, one ultrasonic transducer 10 is shown as a representative of the other ultrasonic transducer 10 in Fig. 1. The arrow T in Fig. 1 indicates the direction in which the other ultrasonic transducer 10 is disposed relative to the first ultrasonic transducer 10. In other words, the fluid to be measured flows on the side of the arrow T relative to the first ultrasonic transducer 10.

[0014] As shown in FIG. 1, the ultrasonic transducer 10 according to the first embodiment includes a substrate 11 and a piezoelectric element 12.

[0015] The substrate 11 has a front surface 11a and a back surface 11b. The front surface 11a and the back surface 11b are surfaces located on opposite sides of the substrate 11 in the thickness direction. The front surface 11a is the other surface and is a mounting surface for mounting the piezoelectric element 12 on the substrate 11. The back surface 11b is one surface and is always exposed to the fluid to be measured in the environment in which the ultrasonic transducer 10 is used.

[0016] The piezoelectric element 12 is configured as, for example, a PMUT (Piezoelectric Micromachined Ultrasonic Transducer). The piezoelectric element 12 has a piezoelectric thin film 14 made of a piezoelectric material formed on a base 13 made of silicon or the like, and transmits and receives ultrasonic waves by vibrating the piezoelectric thin film 14 like a drum. Note that the piezoelectric material is a material that converts stress into electricity and also converts electricity into stress. Such a piezoelectric element 12 is manufactured using, for example, semiconductor manufacturing technology.

[0017] The piezoelectric element 12 is provided on the surface 11a of the substrate 11. That is, the piezoelectric element 12 is not exposed to the fluid to be measured in the environment in which the ultrasonic transducer 10 is used. The piezoelectric element 12 has a base 13 and a piezoelectric thin film 14. The piezoelectric thin film 14 forms a vibration membrane.

[0018] The base end of the base 13 is provided on the surface 11a of the substrate 11. The base 13 is formed, for example, in a cylindrical shape. Therefore, the base 13 has a hollow portion 13a therein. The hollow portion 13a opens at the tip of the base 13. Note that the shape of the base 13 is not limited to a cylindrical shape as long as it has the hollow portion 13a that opens at the tip. The hollow portion 13a is formed, for example, by a silicon etching technique used in the semiconductor manufacturing process.

[0019] The piezoelectric thin film 14 is provided at the tip of the substrate 13. The outer periphery of the piezoelectric thin film 14 is attached to the inner periphery of the substrate 13. Therefore, when the piezoelectric thin film 14 comes into contact with the cavity 13a of the substrate 13, it is more likely to generate larger vibrations. The surface of the piezoelectric thin film 14 opposite the surface that comes into contact with the cavity 13a becomes the vibration surface. The piezoelectric thin film 14 is also electrically connected to a circuit provided on the surface 11a of the substrate 11.

[0020] For example, when a voltage is applied to displace (vibrate) the piezoelectric thin film 14 toward the opposite side of the cavity 13a (outside the base 13), the piezoelectric element 12 transmits ultrasonic waves due to the vibration of the piezoelectric thin film 14. On the other hand, when a voltage is applied to displace (vibrate) the piezoelectric thin film 14 toward the cavity 13a (inside the base 13), the piezoelectric element 12 receives ultrasonic waves due to the vibration of the piezoelectric thin film 14. The piezoelectric element 12 then transmits ultrasonic waves intermittently and receives ultrasonic waves while the ultrasonic waves are not being transmitted. The magnitude of the applied voltage may or may not be constant.

[0021] At this time, when the piezoelectric thin film 14 vibrates to transmit an ultrasonic wave, the ultrasonic wave propagates from the vibrating piezoelectric thin film 14 to the substrate 11 via the base 13, and then passes through the fluid to be measured from the back surface 11b of the substrate 11 to be transmitted to the other ultrasonic transducer 10. On the other hand, when the piezoelectric thin film 14 vibrates to receive an ultrasonic wave, the ultrasonic wave from the other ultrasonic transducer 10 passes through the fluid to be measured, is input to the back surface 11b of the substrate 11, and then passes from the substrate 11 via the base 13 to be received by the vibrating piezoelectric thin film 14.

[0022] Furthermore, the acoustic impedance value of the substrate 11 and the acoustic impedance value of the base 13 are set to values ​​that are as close to each other as possible, so that ultrasonic waves are efficiently propagated from the base 13 to the substrate 11, and vice versa.

[0023] As described above, the ultrasonic transducer 10 according to the first embodiment includes the substrate 11 having the back surface 11b exposed to the fluid to be measured and the front surface 11a located on the opposite side to the back surface 11b, and the piezoelectric element 12 mounted on the front surface 11a and transmitting and receiving ultrasonic waves via the back surface 11b. Therefore, the ultrasonic transducer 10 according to the first embodiment can transmit and receive ultrasonic waves without exposing the piezoelectric element 12 to the fluid to be measured.

[0024] In the ultrasonic transducer 10 according to the first embodiment, the piezoelectric element 12 has a base 13 whose base end is mounted on the surface 11a of the substrate 11 and has a cavity 13a therein, and a piezoelectric thin film 14 provided at the tip of the base 13 and in contact with the cavity 13a therein. Therefore, the ultrasonic transducer 10 according to the first embodiment can increase the vibration width of the piezoelectric thin film 14, and therefore can increase the adjustable width of the frequency band of the ultrasonic waves.

[0025] The ultrasonic transducer 10 according to the first embodiment uses a piezoelectric thin film 14 as the vibration membrane. Therefore, the piezoelectric element 12 of the ultrasonic transducer 10 according to the first embodiment can be easily manufactured using semiconductor manufacturing technology.

[0026] The ultrasonic flowmeter according to the first embodiment is an ultrasonic flowmeter that performs fluid measurement of a fluid to be measured by transmitting and receiving ultrasonic waves between two ultrasonic transducers 10, and at least one of the two ultrasonic transducers 10 includes a substrate 11 having a back surface 11b facing the other ultrasonic transducer 10 and a front surface 11a located on the opposite side of the back surface 11b, and a piezoelectric element 12 mounted on the front surface 11a and transmitting and receiving ultrasonic waves via the front surface 11a between the other ultrasonic transducer 10. Therefore, the ultrasonic flowmeter according to the first embodiment can transmit and receive ultrasonic waves without exposing the piezoelectric element 12 to the fluid to be measured.

[0027] Embodiment 2 An ultrasonic transducer 20 according to embodiment 2 will be described with reference to Fig. 2. Fig. 2 is a longitudinal sectional view of the ultrasonic transducer 20 according to embodiment 2. Note that components having the same functions as those described in embodiment 1 above are denoted by the same reference numerals, and description thereof will be omitted.

[0028] As shown in FIG. 2, an ultrasonic transducer 20 according to the second embodiment is obtained by adding an acoustic matching layer 15 to the configuration of the ultrasonic transducer 10 according to the first embodiment shown in FIG.

[0029] The acoustic matching layer 15 is provided on the back surface 11b of the substrate 11. That is, the acoustic matching layer 15 is provided on the ultrasonic wave transmitting and receiving surfaces of the ultrasonic transducer 20. There is a difference in acoustic impedance between the ultrasonic transducer 20 and the fluid to be measured. This difference causes ultrasonic waves to be reflected by the fluid to be measured, preventing the ultrasonic waves from being efficiently transmitted to the other ultrasonic transducer 20. Therefore, the acoustic matching layer 15 serves to adjust the difference between the acoustic impedance of the ultrasonic transducer 20 and the acoustic impedance of the fluid to be measured to be small. Therefore, the acoustic matching layer 15 can minimize the reflection of ultrasonic waves from the fluid to be measured.

[0030] The ideal acoustic impedance of the material forming the acoustic matching layer 15 is preferably adjusted so that the square root of the product of the piezoelectric element 12 and the fluid to be measured is equal to the impedance of the piezoelectric element 12. The acoustic matching layer 15 is formed from a composite material that includes a thermosetting resin such as epoxy resin and spherical glass beads that provide an air layer therein.

[0031] Here, it is desirable that the mounting area (mounting area) of acoustic matching layer 15 on rear surface 11b be larger than the mounting area (mounting area) of piezoelectric element 12 on front surface 11a. In this case, all of piezoelectric element 12 attached to front surface 11a is disposed inside acoustic matching layer 15 attached to rear surface 11b. It is also desirable that the shape of acoustic matching layer 15 be the same as the shape of piezoelectric element 12 or be circular.

[0032] As described above, the ultrasonic transducer 20 according to the second embodiment includes the acoustic matching layer 15 provided on the rear surface 11b of the substrate 11. Therefore, the ultrasonic transducer 20 according to the second embodiment can minimize the reflection of the ultrasonic waves from the fluid to be measured, and can efficiently propagate the ultrasonic waves.

[0033] In the ultrasonic transducer 20 according to the second embodiment, the acoustic matching layer 15 contains a thermosetting resin and glass beads. Therefore, the ultrasonic transducer 20 has a simple configuration and can reduce the difference between the acoustic impedance of the ultrasonic transducer 20 and the acoustic impedance of the fluid to be measured.

[0034] The mounting area of ​​the acoustic matching layer 15 on the rear surface 11b is larger than the mounting area of ​​the piezoelectric elements 12 on the front surface 11a, and all of the piezoelectric elements 12 mounted on the front surface 11a are disposed inside the acoustic matching layer 15 mounted on the rear surface 11b. Therefore, the ultrasonic transducer 20 according to the second embodiment can always allow the transmitted and received ultrasonic waves to pass through the acoustic matching layer 15.

[0035] It should be noted that within the scope of the present disclosure, the embodiments may be freely combined, or any component in each embodiment may be modified, or any component in each embodiment may be omitted. [Explanation of symbols]

[0036] 10,20 Ultrasonic transducer 11 Circuit Board 11a surface 11b Back side 12 Piezoelectric element 13 Base 13a Cavity 14 Piezoelectric thin film 15 Acoustic Synthesis Layer

Claims

1. a substrate having one surface exposed to a fluid to be measured and another surface located on the opposite side to the one surface; a piezoelectric element mounted on the other surface and configured to transmit and receive ultrasonic waves via the one surface.

1. An ultrasonic transducer comprising:

2. The piezoelectric element is a base body having a base end mounted on the other surface and having a cavity therein; a vibration membrane provided at the tip of the base body and in contact with the cavity; 2. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer comprises:

3. The vibration membrane is a piezoelectric thin film formed from a piezoelectric material.

3. The ultrasonic transducer according to claim 2.

4. an acoustic matching layer provided on the one surface; 4. The ultrasonic transducer according to claim 1, wherein the ultrasonic transducer comprises: a first insulating layer;

5. The acoustic matching layer includes a thermosetting resin and glass beads.

5. The ultrasonic transducer according to claim 4.

6. an attachment area of ​​the acoustic matching layer on the one surface is larger than an attachment area of ​​the piezoelectric element on the other surface; The piezoelectric element attached to the other surface is disposed inside the acoustic matching layer attached to the one surface.

5. The ultrasonic transducer according to claim 4.

7. An ultrasonic flowmeter that measures a fluid to be measured by transmitting and receiving ultrasonic waves between two ultrasonic transducers, At least one of the two ultrasonic transducers is a substrate having one surface facing the other ultrasonic transducer and another surface located opposite to the one surface; a piezoelectric element mounted on the other surface and configured to transmit and receive ultrasonic waves between the other ultrasonic transducer and the piezoelectric element via the one surface.

1. An ultrasonic flow meter comprising:

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