JP2019176291A - Ultrasonic transducer - Google Patents

Abstract

To provide an ultrasonic transducer with excellent characteristics and reliability.SOLUTION: The ultrasonic transducer with excellent reliability and improved ultrasonic irradiation characteristics is achieved, in which the electrical connection reliability between an acoustic matching layer 1 and a piezoelectric vibrator 2 is ensured by connecting and fixing the acoustic matching layer 1 containing the conductive component to the piezoelectric vibrator 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic transducer for use in a flow rate measuring device that measures the flow rate of gas using ultrasonic waves and a distance measuring device that measures the distance to an object, and in particular, the acoustic impedance of a piezoelectric vibrator and The present invention relates to an acoustic matching layer that matches the acoustic impedance of a fluid to be measured, and further relates to an ultrasonic transducer using the acoustic matching layer.

  In recent years, an ultrasonic flowmeter that measures the time during which an ultrasonic wave propagates through a flow rate measuring unit and measures the flow rate by measuring the moving speed of a fluid is being used in a gas meter or the like. In such an ultrasonic flowmeter, accuracy is required, and in order to improve the accuracy, in an ultrasonic transducer that transmits ultrasonic waves to a gas or receives ultrasonic waves that have propagated through the gas, The acoustic impedance of the configured acoustic matching layer is important.

  The acoustic impedance Z is defined by the sound speed C and the density ρ in the substance as shown in Expression (1).

Z = ρ × C (1)
The acoustic impedance differs greatly between a solid, which is a piezoelectric vibrator, which is a vibration means, and a gas, which is an ultrasonic radiation medium. For example, the acoustic impedance (Z0) of a piezoelectric ceramic such as PZT (lead zirconate titanate) which is a general piezoelectric vibrator is about 30 × 10 6 kg / m ² / s. Further, the acoustic impedance (Z3) of a gas that is a radiation medium, for example, air, is about 400 kg / m ² / s.

  On such boundary surfaces with different acoustic impedances, reflection occurs in the propagation of the sound wave, and the intensity of the sound wave transmitted through the radiation medium becomes weak. As a method for solving this problem, the acoustic impedance Z0 and Z3 of the piezoelectric vibrator, which is the vibration means, and the gas, which is the ultrasonic radiation medium, have an acoustic impedance having a relationship of Equation (2) between the two. In general, a method of increasing the intensity of sound wave transmission by reducing the reflection of sound by inserting a substance having the above is known. This material is the acoustic matching layer.

Z = (Z0 × Z3) (1/2) (2)
The optimum value when the acoustic impedance satisfying this condition is matched is about 11 × 10 4 kg / m ² / s. An acoustic matching layer that satisfies this acoustic impedance is required to be solid and have a low density, and it is necessary that the acoustic matching layer does not break even when an ultrasonic transducer is used.

  Actually, in order to operate the ultrasonic transducer, it is necessary to apply a voltage to the piezoelectric vibrator. Usually, an electrical matching is often obtained by fixing an acoustic matching layer on a metal casing containing a piezoelectric vibrator and applying a voltage to a surface facing the metal casing and the metal casing ( For example, see Patent Document 1).

Japanese Patent No. 4771370

The material that can be used for the acoustic matching layer of an ultrasonic transducer is low acoustic density, so it is an acoustic matching consisting of a silica-based ceramic material or a mixture of a hollow sphere such as a glass balloon and a bonding material such as epoxy resin. The layers are known.

  Then, an adhesive is applied to the surface of the acoustic matching layer created by the above method by printing to form an adhesive layer, and the surface of the acoustic matching layer is bonded to the surface of the piezoelectric vibrator or the inner wall surface. When bonded to the surface of the metal case, the adhesive is not completely buried in the concave portion of the acoustic matching layer, and the adhesive is bonded while leaving a minute gap. Due to the presence of bubbles, there was a problem that the adhesive strength between the surface of the acoustic matching layer material and the surface of the piezoelectric vibrator or the case was not sufficiently exhibited.

  In Patent Document 1, a metal case is improved including electrical bonding without introducing a metal case between the acoustic matching layer and the piezoelectric vibrator. Specifically, the acoustic matching layer is directly joined to the piezoelectric vibrator by covering the surface portion excluding the side wall surface of the acoustic matching layer with a conductive film baked with a highly conductive material such as Ag, so that the piezoelectric vibrator is bonded. This ensures electrical bonding from the acoustic matching layer side.

  However, there are three problems with this joining method. First, since the acoustic matching layer and the conductive film have different densities, the acoustic impedance is partially increased by the high-density layer made of the conductive film, and the sensitivity characteristic of the acoustic matching layer is lowered. The second point is that the Ag material used as the conductive film is limited in terms of reliability and use from the viewpoint of corrosiveness to the gas species (for example, city gas) applied to the flow rate measurement. Third, it is considered desirable to avoid the formation of such a conductive film from the viewpoint of cost reduction.

  The present invention solves the above-described conventional problems, and an object thereof is to provide an acoustic matching layer that exhibits excellent characteristics and excellent reliability, and an ultrasonic transducer using the matching layer. .

  In order to solve the above-described conventional problems, the ultrasonic transducer according to the present invention includes an acoustic matching layer containing a conductive component and a piezoelectric vibrator to which the acoustic matching layer is fixed. The acoustic matching layer applies a material in which conductive powder is mixed in an acoustic matching layer disposed on the piezoelectric vibrator side. As a result, the density of the acoustic matching layer does not change in the stacking direction with the piezoelectric vibrator, so the acoustic matching layer can be configured without changing the acoustic impedance, and the connection stability with the piezoelectric vibrator is ensured. can do. By such means, the ultrasonic vibration of the acoustic matching layer can be maximized.

  According to the ultrasonic transducer of the present invention, an appropriate acoustic impedance and connection stabilization can be achieved, and an ultrasonic transducer with higher sensitivity and higher reliability than conventional ones can be obtained.

(A) Sectional view showing the ultrasonic transducer of the first embodiment (b) Plan view (A)-(c) The figure explaining the manufacturing method of this Embodiment 1

  The outlines of the acoustic matching layer, the ultrasonic transducer and the ultrasonic flowmeter of the present invention are as follows.

  An ultrasonic transducer according to a first aspect of the present invention comprises an acoustic matching layer containing a conductive component and a piezoelectric vibrator to which the acoustic matching layer is fixed. The acoustic matching layer and the piezoelectric vibrator are directly joined to each other. By doing so, the joining reliability of the ultrasonic transducer can be ensured.

According to a second aspect of the present invention, in the first aspect of the invention, the acoustic impedance of the acoustic matching layer is smaller than that of the piezoelectric vibrator, and the density is 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. The ultrasonic irradiation surface can be sufficiently vibrated while ensuring the bonding reliability.

According to a third aspect of the present invention, in the first or second aspect of the invention, the second acoustic matching layer having a density of 0.2 g / cm ³ or less is laminated on the acoustic wave irradiation surface of the acoustic matching layer, thereby ultrasonic irradiation. By maximizing the vibration on the surface, it is possible to obtain an ultrasonic transducer with improved characteristics and reliability.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the acoustic matching layer and the piezoelectric vibrator are mechanically fixed. It can be a transducer.

Hereinafter, embodiments of an acoustic matching layer and an ultrasonic transducer according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the form of this invention.
(Embodiment 1)
Hereinafter, an example of the ultrasonic transducer of this embodiment will be described in detail.

[Ultrasonic transducer]
FIG. 1 is a cross-sectional view illustrating an example of the ultrasonic transducer 111 of the present disclosure. The ultrasonic transducer 111 includes a laminate 11, a laminate fixing jig 4 and a terminal 5.

  The laminate 11 includes an acoustic matching layer 1 and a piezoelectric vibrator 2. The acoustic matching layer 1 is in direct contact with the piezoelectric vibrator 2 without passing through other layers. The piezoelectric vibrator 2 is made of piezoelectric ceramics and is polarized in the thickness direction. The piezoelectric vibrator 2 has electrodes on the upper and lower surfaces in the thickness direction. The upper surface electrode is electrically connected to the acoustic matching layer 1, and ultrasonic vibration is generated by applying a voltage between the lower surface electrodes. Is generated.

  Further, by forming the acoustic matching layer 3 on the acoustic matching layer 1, it is possible to further improve the characteristics.

  The acoustic matching layer 1 or the acoustic matching layer 3 formed on the acoustic matching layer 1 is for transmitting an ultrasonic wave to a fluid or receiving an ultrasonic wave propagating through the fluid, and is excited by a driving AC voltage. The mechanical vibration of the piezoelectric vibrator 2 is efficiently emitted as an ultrasonic wave to an external medium, and the reached ultrasonic wave has a role of being efficiently converted into a voltage.

Examples of a material suitable for the acoustic matching layer 1 in the present invention include a resin mixed with a conductive component. Examples of the resin mixed with the conductive component include glassy carbon, epoxy resin containing carbon powder, hard acrylic resin, hard urethane resin, PEEK resin, PPS resin, POM resin, and ABS resin. The density is preferably 0.5 g / cm ³ to 2.0 g / cm ³ . When the acoustic matching layer 1 is used as a single layer, a material having a low density is suitable for gas measurement. When the acoustic matching layer 1 is laminated with an acoustic matching layer 3 described later, a high-density material is suitable. Note that the optimum density is around 1.3 g / cm ³ and shows high characteristics when laminated.

  A material suitable for the acoustic matching layer 3 is a hard resin foam made of a foamed resin having a closed pore structure and having a structure including a plurality of holes and adjacent wall portions.

Examples of the hard resin foam include a hard acrylic foam, a hard PVC foam, a hard polypropylene foam, a hard polymethacrylimide foam, and a hard urethane foam. For example, Sekisui Plastics Co., Ltd. as a hard acrylic foam. As an example, Daicel-Evonik's Lohacell is sold. The density condition is preferably 0.2 g / cm ³ .

  When the acoustic matching layer 3 is made of a hard resin foam, it is excellent in improving the characteristics of the ultrasonic transducer for gas.

  The acoustic matching layer 3 desirably has a thickness of approximately ¼ of the wavelength λ of the sound wave propagating through the acoustic matching layer 3. Thereby, the sound wave reflected between the two main surfaces of the acoustic matching layer 3 and incident on the acoustic matching layer 1 is weakened by a phase shift of 1/2. Therefore, the intensity of the sound wave incident on the acoustic matching layer 1 with a delay due to unnecessary reflection can be reduced, and the influence of the reflected wave can be suppressed.

  The ultrasonic transducer of this embodiment can be manufactured, for example, according to the following procedure. First, as shown in FIG. 2A, an acoustic matching layer 1, an acoustic matching layer 3, and a piezoelectric vibrator 2 are prepared. The acoustic matching layer 1 and the acoustic matching layer 3 are previously polished with a wrapping film and processed so as to have a desired surface roughness and thickness. The acoustic matching layer 3 and the acoustic matching layer 1 are bonded with an adhesive, and the bonded body is placed on the piezoelectric vibrator 2 to obtain a laminate 11.

  Next, as shown in FIG. 2 (b), the L-shaped laminated fixing jig 4 is disposed oppositely, and the laminated body 11 is placed on the bottom thereof, and then, as shown in FIG. The tip of the laminated fixing jig 4 is bent and mechanically fixed. Thereby, electrical connection between the acoustic matching layer 1 and the piezoelectric vibrator 2 is ensured. Finally, the terminal 5 is connected to the acoustic matching layer 1 and the piezoelectric vibrator 2 to complete the ultrasonic transducer. In addition, as the fixing method of the laminated body 11, in this Embodiment, the caulking by two L-shaped metal fittings was used, However, An appropriate method, such as fixing with a volt | bolt and a nut, can be used. Further, not only partial fixation, but also the entire circumference of the laminate 11 may be mechanically fixed.

(Example)
Hereinafter, the result of having produced the ultrasonic transducer of the embodiment and examining the characteristics will be described.

1. Sample Preparation [Example (A)]
(A) Processing of acoustic matching layer As the acoustic matching layer 1, conductive carbon (glassy carbon: manufactured by Tokai Carbon) was used. This material has a density of 1.5 g / cm ³ .

The thickness of the acoustic matching layer was adjusted to 800 μm using a wrapping film sheet (grain size 60 μm, 3M). This sample was processed into a circular shape having a diameter of 10.8 mm.
(B) Fixing of acoustic matching layer and piezoelectric vibrator The acoustic matching layer 1 and the piezoelectric vibrator 2 were superposed, and fixed with a laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transmitter / Receiver A terminal 5 was attached to an acoustic matching layer 1 and a piezoelectric vibrator 2 that were superposed by a laminated fixture 4.

[Example (B)]
(A) Processing of first acoustic matching layer As the acoustic matching layer 1, conductive carbon (glassy carbon: manufactured by Tokai Carbon) was used. This material has a density of 1.5 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of the acoustic matching layer to the case and the piezoelectric vibrator The acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the acoustic matching layer 1. It fixed with the laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

[Example (C)]
(A) Processing of first acoustic matching layer As the acoustic matching layer 1, conductive PEEK (PEEK430-AE3: manufactured by Toray) was used. This material has a density of 1.3 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of the acoustic matching layer to the case and the piezoelectric vibrator The acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the acoustic matching layer 1. It fixed with the laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

[Example (D)]
(A) Processing of first acoustic matching layer As the acoustic matching layer 1, conductive PPS (PEEK230-AE3: manufactured by Toray) was used. This material has a density of 1.4 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of the acoustic matching layer to the case and the piezoelectric vibrator The acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the acoustic matching layer 1. It fixed with the laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

[Example (E)]
(A) Processing of first acoustic matching layer As the acoustic matching layer 1, conductive POM (POM131-AE3: manufactured by Toray) was used. This material has a density of 1.4 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of the acoustic matching layer to the case and the piezoelectric vibrator The acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the acoustic matching layer 1. It fixed with the laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

[Example (F)]
(A) Processing of first acoustic matching layer As the acoustic matching layer 1, conductive ABS (ABS610-AE1: manufactured by Toray) was used. This material has a density of 1.3 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of the acoustic matching layer to the case and the piezoelectric vibrator The acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the acoustic matching layer 1. It fixed with the laminated fixing jig 4 by caulking.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

[Comparative Example (G)]
(A) Processing of the first acoustic matching layer PEEK (PEEK NC: manufactured by Toray) was used as the acoustic matching layer 1. This material has a density of 1.3 g / cm ³ . As the acoustic matching layer 3, polymethacrylimide ROHACELL (R) (density 0.07 g / cm ³ ) was used as a hard plastic foam.

The thickness of the acoustic matching layer 1 and the acoustic matching layer 3 was adjusted to 800 μm using a wrapping film sheet (particle size 60 μm, 3M). These were processed into a circular shape with a diameter of 10.8 mm. (B) Joining of acoustic matching layer to case and piezoelectric vibrator The conductive paste Ag was applied to one side of the acoustic matching layer 1 to form an electrode surface. Further, the acoustic matching layer 3 is fixed on the acoustic matching layer 1 with an adhesive, and the piezoelectric vibrator 2 is overlaid on the side of the acoustic matching layer 1 on which the conductive paste is applied, and the caulking laminated fixing jig 4 is attached. Fixed.
(C) Formation of Ultrasonic Transceiver A terminal 5 was attached to an acoustic matching layer 3 fixed to the upper part of the acoustic matching layer 1 and a piezoelectric vibrator 2 stacked on the lower part with a laminated fixing jig 4.

2. Evaluation of characteristics The sensitivity of the fabricated ultrasonic transducer was measured. In the measurement method, a pair of produced ultrasonic transducers were made to face each other, one was used as a transmitter, and the other was used as a receiver, and ultrasonic waves were transmitted and received.

In addition, a thermal shock test was performed as a method for confirming the reliability of bonding, and evaluation was performed by measuring sensitivity characteristics before and after the injection. In addition, about the conditions of a thermal shock test, -40 degreeC 30 minutes, 80 degreeC3
0 minutes was set as 1 cycle, and it was confirmed by carrying out 1000 cycles. Table 1 summarizes these values and the characteristics of the acoustic matching layer 26.

  In addition, as for the sensitivity, the relative value with respect to the comparative example, and as for the reliability, “Δ” is written in the sample similar to the comparative example, and “x” is written in the low sample. “◎” and “◯” are marked on samples superior to the comparative examples.

3. Consideration of results As shown in Table 1, by providing conductivity to the acoustic matching layer, electrical connection can be easily performed without using a case, and a highly sensitive ultrasonic transducer can be obtained. . In the prior art, it is considered that the connection reliability of the conductive paste is low.

The acoustic matching layer is required to have a highly elastic property in order to ensure propagation performance without attenuating sound waves. As a material of the acoustic matching layer 1 exhibiting such material properties, an engineering plastic is preferable among the resin materials. Moreover, when laminating | stacking the hard plastic foam and the acoustic matching layer 1, the tendency for density 1.3g / cm < ³ > vicinity is confirmed from the simulation by acoustic impedance.

  Conventional technology G, which has selected materials from this point of view, has established sensitivity characteristics, but when it is put into a thermal shock test, the adhesive strength between the engineering plastic and the conductive adhesive is reduced, so electrical connection is ensured. It is difficult to establish reliability.

  On the other hand, by providing conductivity to the acoustic matching layer 1 itself, it is not necessary to consider the bonding at the interface between the matching layer material and the conductive adhesive, which has occurred in the past, and it is possible to satisfy both characteristics and reliability at the same time. . Moreover, the electrical connection can be stabilized without using a case, and an ultrasonic transducer that satisfies the sensitivity characteristics can be obtained.

  The laminate and the ultrasonic transducer of the present disclosure are preferably used for flow meters for measuring various fluids. Further, the present invention is suitably used for various devices having sonar performance, such as a detection device that detects a target object and a distance measuring device that measures a distance to the target object.

DESCRIPTION OF SYMBOLS 1 Acoustic matching layer 2 Piezoelectric vibrator 3 Acoustic matching layer 4 Lamination fixing jig 5 Terminal 11 Laminated body 111 Ultrasonic transducer

Claims (4)

An ultrasonic transducer comprising an acoustic matching layer containing a conductive component and a piezoelectric vibrator to which the acoustic matching layer is fixed. The ultrasonic transducer according to claim 1, wherein an acoustic impedance of the acoustic matching layer is smaller than that of the piezoelectric vibrator, and a density is 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. The ultrasonic transducer according to claim 1, wherein a second acoustic matching layer having a density of 0.2 g / cm ³ or less is laminated on a sound wave irradiation surface of the acoustic matching layer. The ultrasonic transducer according to any one of claims 1 to 3, wherein the acoustic matching layer and the piezoelectric vibrator are mechanically fixed.