JP2001145194A - Ultrasonic wave generator and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To bond a matching means to a case housing a vibrating means, without using adhesives in an ultrasonic wave generator. SOLUTION: A matching means 20 is formed with porous ceramics, and in order to bond the means 20 to a metallic case 21, a plurality of bonding means is provided. The first bonding means 33 is silver solder, the second bonding means 34 is titanium, and the third bonding means is silver solder. Accordingly, the difference between the coefficients of expansion of the metallic case 21 and the ceramics constituting the matching means 20 can be relieved by the titanium, having intermediate coefficient of expansion between the coefficients of expansion of the case 21 and ceramics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave generator used for a flow rate measuring device for measuring a gas flow rate using an ultrasonic wave, a distance measuring device for measuring a distance to an object, and a method for manufacturing the same. It is.

[0002]

2. Description of the Related Art FIG. 7 is a sectional view showing the structure of a conventional ultrasonic generator. 1 is a vibration means, 2 is a case, 3 is a matching means, 4 is a resin filled in the case, 5 and 6 are electrodes, and 7 is a space. The vibration means 1 and the case 2 are adhered using an epoxy adhesive. The case 2 and the matching means 3 are similarly connected using an epoxy adhesive. The resin 4 has a purpose of fixing the case 2 and the vibration means 1 and the electrodes 5 and 6, and a purpose of a sound damping material for preventing the vibration of the vibration means 1 from propagating to the surface opposite to the matching means 3. The vibration means 1 vibrates at about 500 kHz, and the vibration is transmitted to the case 2 via an epoxy-based adhesive, and further transmitted to the matching means 3 via an epoxy-based adhesive. The vibration of the matching means 3 propagates as a sound wave to the gas existing in the space 7.

The role of the matching means 3 is to efficiently propagate the vibration of the vibration means 1 to the gas. The acoustic impedance Z defined by the sound velocity C and the density ρ of a substance as (Equation 1) is

[0004]

(Equation 1)

There is a great difference between the vibration means 1 and gas. Acoustic impedance Z ₁ is 30 × 10 ⁶ of the vibration means 1 (kg / m
^{In 2} s), the acoustic impedance Z ₂ of a gas, for example, air is 4.28 × 10 ² (kg / m ² s). The acoustic impedance of the vibration means 1 is substantially equal to that of the metal. As described above, reflection occurs in the propagation of sound (vibration) on the boundary surfaces having different acoustic impedances, and as a result, the intensity of transmitted sound decreases. However, sound reflection can be reduced by inserting a substance having another acoustic impedance between two substances having different acoustic impedances.

It is generally known that sound reflection can be eliminated by inserting a substance having an acoustic impedance Z ₃ that satisfies the relationship of Equation 2 between the vibration means 1 and the space 7.

[0007]

(Equation 2)

The value of Z ₃ is 0.11 × 10 ⁶ (kg / m ² s)
Becomes A substance that satisfies this acoustic impedance is required to be a solid substance having a low density and a low sound velocity.

Therefore, as shown in FIG. 8, the aligning means 3 applies a small hollow glass 8 to an epoxy resin adhesive 9.
The density is reduced by using a material that has been hardened in step (1). Since the hollow glass 8 needs to be sufficiently smaller than the wavelength of the sound transmitted through the matching means 3, a glass having a size of 100 μm or less is used. The acoustic impedance of the matching means 3 thus obtained is about 1.2 × 10 ⁶ (kg / m ² s).

Further, the intensity of the sound transmitted through the matching means 3 to the gas also depends on the length of the matching means 3. FIG.
Except for the epoxy adhesive and the case 2 for simplicity, the vibration means 1, the matching means 3 and the gas (air) 3
The sound wave 8 from the vibration means 1 is divided into a transmitted wave 9 and a wave 10 reflected at the interface between the matching means 3 and the gas. Reflected wave 10
Is reflected at the boundary surface between the matching means 3 and the vibration means 1, and in this case, the wave 11 is inverted in phase. A part of this wave becomes the wave 12 transmitted at the interface between the matching means 3 and the gas. Since the wave 12 and the wave 9 are synthesized, the transmittance T of the sound intensity radiated to the gas is represented by (Equation 3).

[0011]

(Equation 3)

Where Z ₁ is the acoustic impedance of the vibrating means, Z ₂ is the acoustic impedance of the matching means, Z ₃ is the acoustic impedance of the gas, L is the distance of the matching layer, and k ₂ is given by (Equation 4).

[0013]

(Equation 4)

Here, f is the frequency of vibration, and C ₂ is the matching means 3
Is the speed of sound.

When the distance L at which the transmittance T of Equation 3 is maximized is obtained, L = λ / 4.

When a hollow glass is used as the matching means 3, its sound speed is 2000 m / s, and the sound frequency is 50 m / s.
In the case of 0 kHz, the wavelength λ is 4 mm. Therefore, the optimum length of the alignment means is 1 mm.

FIG. 10 shows a state in which the above-mentioned ultrasonic wave generating means 13 is arranged in a pipe 14 which is a gas flow path. If the ultrasonic generator 13 breaks, gas leaks to the outside of the tube 14, so it is difficult to select a material that is easily broken such as ceramic or resin for the case material of the ultrasonic generator 13. Therefore, a metal such as stainless steel or iron is used for the case.

[0018]

However, in the conventional ultrasonic generator 13, an epoxy resin is used for bonding the alignment means 3 and the case 2. Further, an adhesive 9 made of an epoxy resin is used to solidify the hollow glass 8 constituting the alignment means 3. The gas whose flow rate is to be measured may contain moisture, and in such a case, the moisture may swell in the epoxy resin. In this case, the acoustic impedance of the matching unit 3 changes, and the original purpose of the matching unit 3, such as efficient sound emission, is hindered, which may hinder accurate measurement. Further, the gas whose flow rate is to be measured may contain sulfur.
In such a case, there is a concern that the matching means 3 constituting the ultrasonic generator 13 and the epoxy resin used for bonding the matching means 3 and the case 2 are corroded by sulfur.
When the alignment means 3 is corroded and the adhesive strength changes, the alignment means 3
Therefore, efficient sound emission, which is the original purpose of the device, is hindered, which hinders accurate measurement.

[0019]

SUMMARY OF THE INVENTION An ultrasonic generator according to the present invention has been made in order to solve the above-mentioned problems. First, the matching means is made of a fine hollow ceramic. The alignment means is joined to the metal case by brazing. Since a brazing material is a metal alloy, the matching means can be joined to the metal case without using an epoxy-based adhesive as in the related art. In order to reduce the difference in expansion coefficient between the ceramic and the metal case, which is a problem during brazing, a plurality of joining means are provided at the brazed portion.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention comprises a vibrating means and a matching means for efficiently transmitting the vibration of the vibrating means to a gas, wherein the matching means is a ceramic having a hollow structure. And since the ceramic has a hollow structure, its density is light, and its acoustic impedance can be set to almost the middle value between the acoustic impedance of the vibrating means and the acoustic impedance of gas, whereby the vibration of the vibrating means is applied to the gas. It can be propagated efficiently. Further, a part of the metal case and the alignment means are joined by brazing. The brazing is configured to have a plurality of joining means to reduce a difference in the degree of expansion between the alignment means and the metal case.

The plurality of bonding means use silver brazing as the first bonding means, titanium whose expansion degree due to temperature is smaller than that of the metal case and is larger than the matching means as the second bonding means, and silver brazing as the third bonding means. Thereby, the difference in the degree of expansion between the alignment means and the metal case can be reduced.

Further, the plurality of bonding means are constituted by using silver brazing as the first bonding means, titanium as the second bonding means, silver brazing as the third bonding means, ceramic as the fourth bonding means, and glass as the fifth bonding means. By doing so, since the degree of expansion of the matching means and the fourth joining means is the same, it is possible to securely join the matching means using a plurality of minute hollow ceramics without causing cracks to the matching means having low mechanical strength. Can be.

Further, the plurality of joining means are constituted by using powder joining means in which silver solder and titanium are powdered and mixed, fourth joining means made of ceramic, and fifth joining means made of glass. A plurality of joining means can be easily provided, the workability is improved, and the joining strength between the metal case and the alignment means is appropriately weakened, so that the distortion of the metal case can be eliminated.

Further, the plurality of joining means are configured to use a base layer obtained by mixing and sintering silver braze, titanium, and ceramic into powder, and a fifth joining means made of glass, and a boundary between the fifth joining means and the fifth joining means. By exposing the ceramic to the surface of the base layer and joining the matching means, the portion of the ceramic exposed to the surface of the base layer and the glass as the fifth joining means are joined, and The alignment means can be joined.

Further, by aligning a plurality of minute hollow ceramics and glass into a metal case containing the vibrating means via a plurality of joining means, and raising the temperature in this state, The joining of the plurality of joining means and the matching means and the step of solidifying the matching means can be performed simultaneously.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an external view of an ultrasonic generator according to Embodiment 1 of the present invention. 20 is a matching means, 21 is a main body constituting a metal case, 22 is a lid constituting a metal case, 3
2 is a plurality of joining means, 23 is a vibration means, 24 is a conductive rubber, 25 and 26 are electrodes, and 27 is a gas. A glass 29 is sealed between the electrode 25 and the lid 22 so that the electrode 25
And the lid 22 are electrically insulated. The vibrating means 23 is housed in a metal case, and the main body 21 and the vibrating means 23 are adhered with an epoxy-based adhesive 28. This layer of adhesive 28 is very thin, a few microns thick.
This layer forms a capacitor between the main body 21 and the vibrating means 23, but its capacity is small because the layer is thin.
3 is larger than the capacitance of the capacitor.

An AC voltage of about 5 V is applied between the electrodes 25 and 26. The electrode 26 is connected to the lid 22, and the lid 22 is welded to the main body 21. Thereby, the voltage applied to the electrode 26 is applied to the adhesive 28 via the lid 22 and the main body 21. The other electrode 25 is electrically connected to the vibration means 23 via the conductive rubber 24. Therefore, the voltage applied between the electrodes 25 and 26 is applied to the vibration means 23 and the adhesive 28.
The vibration means 23 and the adhesive 28 can be regarded as a capacitor electrically, and both are connected in series. Since the capacity of the vibration means 23 is smaller, the combined capacity when both are connected in series is , Almost the capacity of the vibration means 23.

The resonance frequency of the vibration means 23 is approximately 500
kHz, so that 500kHz
By applying an alternating voltage of
Vibrates at kHz. This vibration propagates to the main body 21 and causes it to vibrate, and the vibration of the main body 21 propagates to the matching means 20 to vibrate it. The role of the matching means 20 is to efficiently propagate the vibration of the vibration means 23 to the gas 27 as described in the related art. The conductive rubber 24 prevents the vibration of the vibrating means 23 from being transmitted to the lid 22 so that the energy of the vibration can be efficiently transmitted to the matching means 20.
It also plays a role as a vibration damping material so that it is transmitted to the vehicle.

Since the vibration means 23 and the conductive rubber 24 are housed in a metal case, no gas enters the metal case. Therefore, even if an epoxy-based adhesive is used for the vibration means 23 and the main body 21, it does not swell with moisture contained in the gas or corrode with sulfur. By using a metal case and sealing glass between the electrode 25 and the lid 22,
It is possible to reliably prevent gas from entering the metal case.

FIG. 2 shows the structure of the matching means 20. 30 is a hollow ceramic 30 and 31 is glass. Since the hollow ceramic 30 has a high melting point, it is mixed with glass 31 having a melting point of about 1000 ° C., and the temperature is raised to about 1000 ° C. to melt the glass 31 and then cooled.
The hollow ceramic 30 is solidified with glass 31. Assuming that the sound speed of the matching means 20 made by such a method is about 2 km / sec and a vibration of 500 kHz is propagated,
The wavelength of the vibration is 4 mm. By making the size of the hollow ceramic 30 sufficiently small with respect to this wavelength, the effect of the hollow portion on the propagation of vibration can be neglected. Therefore, the size of the hollow ceramic 30 is selected to be less than 1/10 of the wavelength. Since it is a hollow ceramic, its density is light (Expression 1) and its acoustic impedance is 1.5 to 2 (unit is 10 ⁶ k)
g / (scc · m ² )). Thereby, the vibration of the vibration means 23 can be efficiently transmitted to the gas 27.

Brazing is used for joining the aligning means 20 and the main body 21 shown in FIG. Stainless steel is used for the main body 21, and a plurality of hollow ceramics 3 constituting the matching means 20 are formed.
The degree of expansion is significantly different from 0. Therefore, matching means 2
Even if the 0 and the main body 21 are directly brazed, a stress is applied to the joint due to the difference in the degree of expansion, and the alignment means 20 comes off. Therefore, the present invention uses a plurality of joining means 32 to reduce the degree of expansion. Specifically, as shown in FIG. 3, the plurality of joining means 32 use a silver brazing foil as the first joining means 33, a titanium foil as the second joining means 34, and a silver brazing foil as the third joining means 35. 2
0 linear expansion coefficient at ℃ stainless is 14.7K ^-1, titanium 8.6K ^-1, ceramics are 2~6K ^-1. Since the linear expansion coefficient of stainless steel is significantly different from that of ceramic, even if direct joining is attempted, the stress is increased and the stainless steel is separated. The stress can be reduced by interposing titanium having an expansion coefficient between the ceramic and the stainless steel, which has an intermediate value between the two. The main body 21 and the matching means 20 are joined by combining the stainless steel and the titanium foil via the silver brazing foil and combining the titanium foil with oxygen contained in the ceramic.

As described above, since the matching means 20 uses the fine hollow ceramic 30, the mechanical strength is not strong.
For this reason, there is a method shown in FIG. In FIG. 4, reference numeral 36 denotes a ceramic plate as a fourth joining means, and 37 denotes glass as a fifth joining means.

Since the fourth joining means 36 is formed of a ceramic plate, the mechanical strength is higher than that of the matching means 20 using the minute hollow ceramic 30. Ceramic plate 36
And the matching means 20 have almost the same degree of expansion, so that little stress is applied to the matching means 20. The joining between the ceramic plate 36 and the alignment means 20 is performed by glass.

The first joining means, the second joining means, and the third joining means are powdered, mixed and processed into a paste, applied to a metal case, and the ceramic plate 36 is mounted thereon. There is a way to put. The ultrasonic generator of FIG.
The joining means, the second joining means, and the third joining means are powdered and mixed to form a paste-like powder joining means 38, which is applied on a metal case, and a ceramic plate 36 is placed thereon.
FIG. 2 is a configuration diagram showing a state where the components are mounted, heated, and joined. By adjusting the amount of titanium or silver braze powdered in this way, the joining strength can be somewhat adjusted. For example, if the weight ratio between titanium and silver solder is 1: 3
When it is set to 0, the bonding strength can be reduced as compared with the configuration using the titanium foil, and the stress generated due to the difference in the expansion coefficient can be reduced.
The distortion of the stainless steel constituting 1 can be eliminated.

FIG. 6 shows another embodiment of the present invention.
This is a base layer obtained by mixing and sintering a silver solder as a joining means, a titanium as a second joining means, a silver solder as a third joining means, and a ceramic as a fourth joining means. The ceramic is exposed on the base layer surface by polishing or the like. The base layer 39 and the matching means 20 are the fifth
The structure which joins using glass which is a joining means is shown.

Since ceramic is used as powder, when mixed with silver solder and sintered, the ceramic powder is covered with silver solder. By polishing this, a ceramic portion can be exposed on the surface. The ceramic portion and the glass which is the fifth bonding means are bonded, and the glass and the aligning means 20 are further bonded.
Are joined, the main body 21 and the alignment means 20 are joined.

As described above, the aligning means 20 employs a method in which a plurality of minute hollow ceramics 30 and glass 31 are mixed and formed, and the temperature is raised to melt and solidify the glass 31. Therefore, before the glass 31 is melted and hardened, the glass 31 is placed on the plurality of joining means 32 before being formed in the metal case and sintered, whereby the plurality of joining means 32 and the alignment
And the step of solidifying the alignment means 20 can be performed at the same time, and the steps can be shortened.

[0039]

As described above, according to the present invention, the matching means provided between the gas and the vibrating means is made of hollow ceramic, so that glass can be used to solidify them. Therefore, the problem of swelling of water into the epoxy adhesive which occurred when the matching means was formed of hollow glass as in the prior art and an epoxy adhesive was used to solidify them can be solved. By radiating stable ultrasonic waves in the gas, the effect of realizing an ultrasonic flowmeter that accurately measures the flow rate of the gas can be obtained.

Further, by using a plurality of joining means for joining the hollow ceramic matching means and the metal case containing the vibrating means, it is possible to join the metal case and the matching means depending on the degree of expansion. The problem of swelling of water into the epoxy-based adhesive, which occurred when an epoxy-based adhesive was used to join the alignment means and the metal case as in the past, was solved. The same effects as those described above can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of an ultrasonic generator according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of a matching unit of the ultrasonic generator.

FIG. 3 is an enlarged cross-sectional view showing a structure of a joining portion between a matching unit and a metal case of the ultrasonic generator.

FIG. 4 is an enlarged cross-sectional view showing a structure of a joining portion between a matching unit and a metal case of the ultrasonic generator.

FIG. 5 is an enlarged cross-sectional view showing a structure of a joining portion between a matching means and a metal case of the ultrasonic generator.

FIG. 6 is an enlarged cross-sectional view showing a structure of a joining portion between a matching unit and a metal case of the ultrasonic generator.

FIG. 7 is a sectional view showing the structure of a conventional ultrasonic generator.

FIG. 8 is a cross-sectional view showing the structure of a conventional matching means.

FIG. 9 is a conceptual diagram for explaining sounds propagating in different media.

FIG. 10 is a configuration diagram showing an ultrasonic sensor provided in a pipe through which gas flows.

[Explanation of symbols]

 REFERENCE SIGNS LIST 20 matching means 21 main body (metal case) 22 lid (metal case) 23 vibrating means 27 gas 30 hollow ceramic 32 plural bonding means 33 silver brazing foil (first bonding means) 34 titanium foil (second bonding means) 35 silver Brazing foil (third joining means) 36 ceramic plate (fourth joining means) 37 glass (fifth joining means) 38 powder joining means 39 base layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Biao Nagai 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. F-term (reference) 2F035 DA05 5D019 AA14 AA18 AA22 BB12 EE04 FF01 GG01 GG12 5J083 AA02 AC40 AD04 CA17 CA20 CA50 CB08

Claims (6)

[Claims] 1. A vibrating means, a matching means for efficiently transmitting vibration of said vibrating means to a gas, a metal case accommodating said vibrating means, and brazing said matching means and a part of said metal case. A plurality of joining means for joining, wherein the matching means uses a plurality of minute hollow ceramics, and the plurality of joining means alleviates a difference in expansion degree between the matching means and the metal case. Ultrasonic generator. 2. The ultrasonic generator according to claim 1, wherein the plurality of joining means are constituted by using silver brazing as first joining means, titanium as second joining means, and silver brazing as third joining means. 3. A plurality of joining means using silver brazing as the first joining means, titanium as the second joining means, silver brazing as the third joining means, ceramic as the fourth joining means, and glass as the fifth joining means. The ultrasonic generator according to claim 1, wherein 4. A method according to claim 1, wherein said plurality of joining means comprises powder joining means in which silver solder and titanium are powdered and mixed, fourth joining means made of ceramic, and fifth joining means made of glass. The ultrasonic generator according to claim 1. 5. A plurality of joining means, comprising: a base layer obtained by mixing and sintering powdery silver solder, titanium and ceramic;
And a fifth joining means made of glass.
2. The ultrasonic generator according to claim 1, wherein the ceramic is exposed on the surface of the base layer which is a boundary with the joining means, and the matching means is joined. 6. A method in which a plurality of minute hollow ceramics and glass are mixed with each other through a plurality of joining means, and a temperature is increased in this state. A method of manufacturing an ultrasonic generator, comprising simultaneously joining a plurality of joining means and the matching means and hardening the matching means.