Ultrasonic transducer and ultrasonic flow meter

Abstract

The invention provides an ultrasonic transducer (10) and an ultrasonic flow meter capable of transmitting and receiving ultrasonic waves without exposing a piezoelectric element to a fluid to be measured. An ultrasonic transducer (10) is provided with: a substrate (11) having a back surface (11b) exposed to a fluid to be measured, and a surface (11a) on the opposite side from the back surface (11b); and a piezoelectric element (12) that is mounted on the front surface (11a) and transmits and receives ultrasonic waves via the rear surface (11b).

Description

Technical Field

[0001] This disclosure relates to an ultrasonic transducer and an ultrasonic flow meter. Background Technology

[0002] Patent document 1 discloses an ultrasonic transducer capable of transmitting and receiving ultrasonic waves.

[0003] [Existing Technical Documents]

[0004] [Patent Literature]

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-16934 Summary of the Invention

[0006] [The problem the invention aims to solve]

[0007] The ultrasonic transducer disclosed in Patent Document 1 includes a piezoelectric element. The piezoelectric element vibrates its vibrating surface when a voltage is applied, thereby transmitting and receiving ultrasonic waves. That is, in the ultrasonic transducer disclosed in Patent Document 1, the vibrating surface is always exposed to the measuring gas environment during use.

[0008] Therefore, when using the ultrasonic transducer disclosed in Patent Document 1 to measure the flow rate or velocity of the fluid being measured (hereinafter referred to as "fluid measurement"), the vibrating surface of the piezoelectric element will always be exposed to the fluid being measured. Consequently, foreign matter such as dust or dirt can easily adhere to the vibrating surface of the piezoelectric element, or scratches can easily occur. 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.

[0009] This disclosure was made to solve the problems described above, and aims to provide an ultrasonic transducer that can transmit and receive ultrasonic waves without exposing the piezoelectric element to the fluid being measured.

[0010] [Technical means to solve the problem]

[0011] The ultrasonic transducer disclosed herein includes: a substrate having one side exposed to the fluid being measured and another side located opposite to the one side; and a piezoelectric element mounted on the other side for transmitting and receiving ultrasonic waves via the one side.

[0012] [The effects of the invention]

[0013] According to this disclosure, it is possible to transmit and receive ultrasonic waves without exposing the piezoelectric element to the fluid being measured. Attached Figure Description

[0014] Figure 1 This is a longitudinal cross-sectional view of the ultrasonic transducer according to Embodiment 1.

[0015] Figure 2 This is a longitudinal cross-sectional view of the ultrasonic transducer in Embodiment 2.

[0016] Explanation of icon numbers

[0017] 10, 20: Ultrasonic transducers

[0018] 11: Substrate

[0019] 11a: Surface

[0020] 11b: Back

[0021] 12: Piezoelectric elements

[0022] 13: Matrix

[0023] 13a: Cavity

[0024] 14: Piezoelectric thin film

[0025] 15: Sound Matching Layer Detailed Implementation

[0026] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0027] Implementation method 1.

[0028] use Figure 1 To illustrate the ultrasonic transducer 10 of Embodiment 1. Figure 1 This is a longitudinal cross-sectional view of the ultrasonic transducer 10 according to Embodiment 1.

[0029] Figure 1 The ultrasonic transducer 10 of Embodiment 1 shown is envisioned for application, for example, to an ultrasonic flow meter (illustration omitted). The ultrasonic flow meter includes a pair of ultrasonic transducers 10, which transmit and receive ultrasonic waves between each other, thereby enabling fluid measurement. Furthermore, the fluid being measured by the ultrasonic flow meter is, for example, a gas such as coal gas or a fluid such as water.

[0030] Furthermore, the pair of ultrasonic transducers 10 included in the ultrasonic flow meter have the same structure and function. Therefore, in Figure 1 The diagram is illustrated using one of the ultrasonic transducers 10 and another ultrasonic transducer 10 as examples. Figure 1 The arrow T shown indicates the direction in which the other ultrasonic transducer 10 is configured relative to one of the ultrasonic transducers 10. That is, the fluid being measured flows relative to one of the ultrasonic transducers 10 on the side where the arrow T is shown.

[0031] like Figure 1As shown, the ultrasonic transducer 10 of Embodiment 1 includes a substrate 11 and a piezoelectric element 12.

[0032] The substrate 11 has a surface 11a and a back surface 11b. The surface 11a and the back surface 11b are surfaces located on opposite sides of each other in the thickness direction of the substrate 11. Moreover, the surface 11a is the other surface and is the mounting surface for mounting the piezoelectric element 12 to the substrate 11. The back surface 11b is one of the surfaces that is always exposed to the fluid being measured in the environment in which the ultrasonic transducer 10 is used.

[0033] The piezoelectric element 12 is configured, for example, as a piezoelectric micromachined ultrasonic transducer (PMUT). The piezoelectric element 12 consists of a piezoelectric thin film 14 formed of a piezoelectric material formed on a substrate 13 made of silicon or the like. Ultrasonic waves are transmitted and received by vibrating the piezoelectric thin film 14 in a drum-like shape. Furthermore, the piezoelectric material is a material that converts stress into electricity and vice versa. This type of piezoelectric element 12 is manufactured, for example, using semiconductor manufacturing technology.

[0034] The piezoelectric element 12 is disposed on the surface 11a of the substrate 11. That is, the piezoelectric element 12 will not be exposed to the fluid being measured in the operating environment of the ultrasonic transducer 10. The piezoelectric element 12 has a substrate 13 and a piezoelectric film 14. In addition, the piezoelectric film 14 constitutes a vibrating diaphragm.

[0035] The bottom end of the substrate 13 is provided on the surface 11a of the substrate 11. The substrate 13 is formed, for example, in a cylindrical shape. Therefore, the substrate 13 has a cavity 13a inside. The cavity 13a opens at the front end of the substrate 13. In addition, the substrate 13 is not limited to a cylindrical shape as long as it has a cavity 13a opening at the front end. Moreover, the cavity 13a is formed, for example, by silicon etching technology used in semiconductor manufacturing processes.

[0036] A piezoelectric film 14 is disposed at the front end of the substrate 13. The outer periphery of the piezoelectric film 14 is mounted on the inner peripheral surface of the substrate 13. Therefore, the piezoelectric film 14 is in contact with the void portion 13a of the substrate 13, thereby easily generating greater vibration. The surface of the piezoelectric film 14 located on the opposite side of the surface in contact with the void portion 13a becomes the vibration surface. Furthermore, the piezoelectric film 14 is electrically connected to a circuit provided on the surface 11a of the substrate 11.

[0037] For example, when a voltage is applied to displace (vibrate) the piezoelectric film 14 toward the side opposite to the cavity 13a (outside the substrate 13), the piezoelectric element 12 transmits ultrasonic waves through the vibration of the piezoelectric film 14. Conversely, when a voltage is applied to displace (vibrate) the piezoelectric film 14 toward the cavity 13a side (inside the substrate 13), the piezoelectric element 12 receives ultrasonic waves through the vibration of the piezoelectric film 14. Furthermore, the piezoelectric element 12 intermittently transmits ultrasonic waves and receives ultrasonic waves during periods when it is not transmitting them. Additionally, the magnitude of the applied voltage can be fixed or variable.

[0038] In the case where the piezoelectric film 14 vibrates to transmit ultrasonic waves, the ultrasonic waves propagate from the vibrating piezoelectric film 14 through the substrate 13 to the substrate 11, and then are transmitted from the back surface 11b of the substrate 11 through the measured fluid to another ultrasonic transducer 10. On the other hand, when the piezoelectric film 14 vibrates to receive ultrasonic waves, the ultrasonic waves from the other ultrasonic transducer 10 are input to the back surface 11b of the substrate 11 through the measured fluid, and then received from the substrate 11 through the vibrating piezoelectric film 14 via the substrate 13.

[0039] Furthermore, the acoustic impedance values ​​in the substrate 11 and the substrate 13 are set as close as possible to each other. Therefore, the propagation of ultrasonic waves from the substrate 13 to the substrate 11 and from the substrate 11 to the substrate 13 is carried out efficiently.

[0040] The ultrasonic transducer 10 of Embodiment 1 includes: a substrate 11 having a back surface 11b exposed to the fluid being measured and a surface 11a located on the opposite side of the back surface 11b; and a piezoelectric element 12 mounted on the surface 11a, which transmits and receives ultrasonic waves via the back surface 11b. Therefore, the ultrasonic transducer 10 of Embodiment 1 can transmit and receive ultrasonic waves without exposing the piezoelectric element 12 to the fluid being measured.

[0041] In the ultrasonic transducer 10 of Embodiment 1, the piezoelectric element 12 includes: a substrate 13, the bottom end of which is mounted on the surface 11a of a substrate 11 and has a cavity 13a therein; and a piezoelectric thin film 14, which is disposed at the front end of the substrate 13 and is in contact with the cavity 13a therein. Therefore, the ultrasonic transducer 10 of Embodiment 1 can increase the vibration amplitude of the piezoelectric thin film 14, thereby increasing the adjustment range of the frequency band in the ultrasonic wave.

[0042] In Embodiment 1, the ultrasonic transducer 10 uses a piezoelectric thin film 14 as the vibrating diaphragm. Therefore, the ultrasonic transducer 10 of Embodiment 1 can easily manufacture the piezoelectric element 12 using semiconductor manufacturing technology.

[0043] The ultrasonic flow meter of Embodiment 1 is an ultrasonic flow meter that measures the fluid by transmitting and receiving ultrasonic waves between two ultrasonic transducers 10. 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 surface 11a located on the opposite side of the back surface 11b; and a piezoelectric element 12 mounted on the surface 11a, which transmits and receives ultrasonic waves between the transducer 10 and the other ultrasonic transducer via the surface 11a. Therefore, the ultrasonic flow meter of Embodiment 1 can transmit and receive ultrasonic waves without exposing the piezoelectric element 12 to the fluid being measured.

[0044] Implementation method 2.

[0045] use Figure 2 To illustrate the ultrasonic transducer 20 of embodiment 2. Figure 2 This is a longitudinal sectional view of the ultrasonic transducer 20 according to Embodiment 2. Furthermore, for structures that have the same function as those described in Embodiment 1, the same reference numerals are used and their descriptions are omitted.

[0046] like Figure 2 As shown, the ultrasonic transducer 20 in Embodiment 2 is... Figure 1 An acoustic matching layer 15 is added to the structure of the ultrasonic transducer 10 of Embodiment 1 shown.

[0047] An acoustic matching layer 15 is disposed on the back surface 11b of the substrate 11. That is, the acoustic matching layer 15 is disposed on both the transmitting and receiving surfaces of the ultrasonic waves in the ultrasonic transducer 20. There is a difference in acoustic impedance between the ultrasonic transducer 20 and the fluid being measured. This difference causes the ultrasonic waves to be reflected by the fluid being measured, preventing them from effectively propagating to the other ultrasonic transducer 20. Therefore, the acoustic matching layer 15 serves to minimize the difference between the acoustic impedance of the ultrasonic transducer 20 and the acoustic impedance of the fluid being measured. Thus, the acoustic matching layer 15 can minimize the reflection of ultrasonic waves relative to the fluid being measured.

[0048] Ideally, the acoustic impedance of the material forming the acoustic matching layer 15 is adjusted so that the value obtained by multiplying the piezoelectric element 12 by the measured fluid is the square root. Moreover, the acoustic matching layer 15 is formed, for example, from a material composed of a thermosetting resin such as epoxy resin and spherical glass beads for creating an air layer therein.

[0049] Ideally, the mounting area (mounting area) of the acoustic matching layer 15 facing the back surface 11b is larger than the mounting area (encapsulation area) of the piezoelectric element 12 facing the surface 11a. In this case, all piezoelectric elements 12 mounted on the surface 11a are disposed inside the acoustic matching layer 15 mounted on the back surface 11b. Furthermore, ideally, the shape of the acoustic matching layer 15 is the same as or circular as the shape of the piezoelectric element 12.

[0050] As described above, the ultrasonic transducer 20 of Embodiment 2 includes an acoustic matching layer 15 disposed on the back surface 11b of the substrate 11. Therefore, the ultrasonic transducer 20 of Embodiment 2 can minimize the reflection of ultrasonic waves relative to the measured fluid, thereby enabling the ultrasonic waves to propagate efficiently.

[0051] In the ultrasonic transducer 20 of Embodiment 2, the acoustic matching layer 15 comprises a thermosetting resin and glass beads. Therefore, the ultrasonic transducer 20 can reduce the difference between the acoustic impedance of the ultrasonic transducer 20 and the acoustic impedance of the fluid being measured with a simple structure.

[0052] The mounting area of ​​the acoustic matching layer 15 facing the back surface 11b is larger than the mounting area of ​​the piezoelectric element 12 facing the surface 11a. All the piezoelectric elements 12 mounted on the surface 11a are arranged inside the acoustic matching layer 15 mounted on the back surface 11b. Therefore, the ultrasonic transducer 20 of Embodiment 2 can ensure that the transmitted and received ultrasonic waves always pass through the acoustic matching layer 15.

[0053] Furthermore, within the scope of this disclosure, various embodiments can be freely combined, or any constituent elements in each embodiment can be modified, or any constituent elements in each embodiment can be omitted.

Claims

1. An ultrasonic transducer, characterized in that... include: The substrate has one side exposed to the fluid being measured, and another side located on the opposite side of said one side; as well as A piezoelectric element is mounted on the other side to transmit and receive ultrasonic waves via one of the sides.

2. The ultrasonic transducer according to claim 1, characterized in that, The piezoelectric element has: The base, with its bottom end mounted on the other side, and having a cavity therein; and A vibrating diaphragm is disposed at the front end of the substrate and is in contact with the cavity portion.

3. The ultrasonic transducer according to claim 2, characterized in that, The vibrating diaphragm is a piezoelectric thin film formed from a piezoelectric material.

4. The ultrasonic transducer according to any one of claims 1 to 3, characterized in that... include: An acoustic matching layer is disposed on one of the surfaces.

5. The ultrasonic transducer according to claim 4, characterized in that, The acoustic matching layer comprises thermosetting resin and glass beads.

6. The ultrasonic transducer according to claim 4, characterized in that, The mounting area of ​​the acoustic matching layer facing one side is larger than the mounting area of ​​the piezoelectric element facing the other side. The piezoelectric element, which is mounted on the other side, is disposed inside the acoustic matching layer, which is mounted on one of the sides.

7. An ultrasonic flow meter that measures a fluid by transmitting and receiving ultrasonic waves between two ultrasonic transducers, characterized in that... At least one of the two ultrasonic transducers includes: A substrate having one side facing another ultrasonic transducer and another side located on the opposite side of said one side; and A piezoelectric element is mounted on the other side to transmit and receive ultrasonic waves via one of the sides between the piezoelectric element and the other ultrasonic transducer.

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