JP2005260409A - Ultrasonic oscillator, its fabrication process, and ultrasonic fluid measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance reliability of an ultrasonic oscillator, and to provide a high reliability ultrasonic flowmeter employing it. <P>SOLUTION: Reliability is enhanced by constituting an ultrasonic oscillator 1 of a rectangular-parallelepiped piezoelectric 2, and composing a sound matching layer 3 of a porous ceramic body including organic glass. A high reliability ultrasonic flowmeter 7 is realized using that ultrasonic oscillator 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic fluid measurement device that measures the flow velocity and flow rate of a fluid and an ultrasonic transducer used therefor.

Conventionally, this type of ultrasonic transducer has a configuration as shown in FIG. FIG. 11 shows the appearance of the ultrasonic transducer 101, where 102 is a square columnar piezoelectric body, and 103 is an acoustic matching layer provided on one square surface of the piezoelectric body 102. Electrodes 104 and 105 made of baked silver are provided on the upper and lower surfaces of the piezoelectric body 102. The acoustic matching layer 103 has been used by filling a material with many voids such as a glass balloon or a plastic balloon and bubbles into an epoxy resin and hardening it (for example, see Patent Document 1).
JP 11-215594 A

  In the conventional ultrasonic transducer 101 having such a configuration, since an epoxy resin is used for the acoustic matching layer 103, it swells at a high temperature and high humidity, or has a relatively low softening point. There were issues such as.

  The present invention solves the above-mentioned conventional problems, and an ultrasonic transducer is constituted by an acoustic matching layer made of a filler made of an inorganic material and a ceramic porous body.

  In order to solve the above-described conventional problems, the ultrasonic vibrator of the present invention is configured by an acoustic matching layer made of an inorganic material and a ceramic porous body, and a piezoelectric body. Therefore, since it does not swell even at high temperature and high humidity, and its softening point is relatively high, an ultrasonic vibrator having stable temperature characteristics can be realized in a temperature range that is normally used. Another object of the present invention is to provide a highly reliable ultrasonic flowmeter because the flowmeter is configured using this ultrasonic transducer.

  As described above, according to the present invention, a highly reliable ultrasonic transducer can be realized.

  In the first invention, the ultrasonic vibrator is configured to include a ceramic porous body including a filler made of an inorganic material having a sound speed slower than the sound speed in the gas, and a piezoelectric body. With this configuration, an ultrasonic transducer that does not swell even at high temperature and high humidity and has a relatively high softening point can be realized in a temperature range that is normally used.

  In the second invention, in particular, the porous body of the first invention is made of ceramic. With this configuration, an acoustic matching layer that does not swell even under high temperature and high humidity can be realized.

  In a third invention, the ceramic of the second invention is constituted by a material containing at least one selected from alumina, silica, zirconia, and cordierite and a low-melting glass as a binder. With this configuration, a ceramic porous body having a high porosity can be easily configured.

  4th invention comprised the 1st filler with organic glass. With this configuration, an acoustic matching layer that does not swell even under high temperature and high humidity can be realized.

  5th invention comprised the organic glass of 4th invention with the material containing at least 1 chosen from a silicon oxide, a titanium oxide, a zirconia, and an alumina. With this configuration, an acoustic matching layer that does not swell even under high temperature and high humidity can be realized.

  A sixth invention includes the ultrasonic transducer according to any one of the first to fifth inventions, a fluid measuring unit including a flow channel through which a fluid flows, an upstream portion and a downstream through which the fluid flows. A pair of the ultrasonic transducers opposed to each other, a propagation unit for measuring the propagation time for ultrasonic waves to propagate between the pair of ultrasonic transducers, and a calculation unit for calculating the flow rate. With this configuration, a highly reliable ultrasonic fluid measuring device can be realized.

  7th invention shows the manufacturing method of the ultrasonic transducer | vibrator in any one of 1st-3rd invention, coat | covers a flammable ball with ceramic powder, burns off the said flammable ball after shaping | molding, It was set as the manufacturing method characterized by forming. By this manufacturing method, a ceramic porous body having a high porosity can be easily realized.

8th invention shows the manufacturing method of the ultrasonic transducer | vibrator in any one of 1st-3rd invention, after mixing a surfactant with slurry-like ceramic powder, introduce | transducing a bubble, and after shaping | molding drying The production method is characterized in that the surfactant is burned off and sintered. By this manufacturing method, a ceramic porous body having a high porosity can be realized easily and efficiently.
9th invention shows the manufacturing method of the ultrasonic transducer | vibrator in any one of 1st, 4th and 5th invention, and the inner surface of a ceramic porous body is previously wash | cleaned with an acid or alkali, Then, a solution-form filler And manufacturing by drying. With this manufacturing method, a highly reliable acoustic matching layer could be realized.

  A tenth aspect of the invention shows a method of manufacturing an ultrasonic transducer according to any one of the first, fourth, fifth and ninth aspects of the invention. When a solution-like filler is filled, vibrations such as ultrasonic waves are added. The manufacturing method is characterized in that it is filled while forming. By this manufacturing method, a highly reliable acoustic matching layer could be realized stably.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attaches | subjects the same number in a figure has shown the same thing, Description is abbreviate | omitted.

(Embodiment 1)
FIG. 1 is an external view of an ultrasonic transducer 1 according to Embodiment 1 of the present invention, 2 is a rectangular parallelepiped piezoelectric body, and the height T, width W, and length L are as shown in FIG. Define. An acoustic matching layer 3 is provided on the upper surface of the piezoelectric body 2. Electrodes 4 and 5 made of baked silver were formed on the upper and lower surfaces of the piezoelectric body. FIG. 2 shows the main part of the acoustic matching layer 3. Reference numeral 6 denotes a void portion of the ceramic porous body, which is filled with a filler having a sound velocity that is slower than the sound velocity in the gas. With this configuration, the strength of the ceramic porous body is increased, and the ceramic porous body is not broken when it is polished to an optimum plate thickness as an acoustic matching layer.

  Further, the surface of the acoustic matching layer 3 was also smoothed, and the acoustic characteristics were slightly improved by about 15 [%]. This is considered to be a result of the internal vibration being efficiently transmitted into the gas by including the filler. Moreover, since the speed of sound of the ultrasonic wave in the filler is slower than the speed of sound in the gas, the change in the speed of sound due to the presence or absence of the filler becomes very small, and the acoustic matching layer can be easily designed.

  In addition, the constituent material of the ceramic porous body was made of at least one material selected from alumina, silica, zirconia, and cordierite. By using these materials and low melting point glass, ceramic components such as alumina, silica, zirconia, cordierite, etc. should be sufficiently finely ground to make the aggregate part of the porous body sufficiently thin. I was able to. Further, since the low melting point glass is used, it can be fired at a low temperature, and the sintering of the material constituting the aggregate hardly proceeds, and a low density ceramic porous body can be constituted.

  Since the pores of the ceramic porous body are formed as communication holes, low-density organic glass having a low sound speed can be easily infiltrated into the pores and can be filled. As such an organic glass, an organic glass composed of silicon oxide, titanium oxide, zirconia, alumina or the like is suitable.

  In addition, since the pores of the ceramic porous body are filled with a filler, even if left in high temperature and high humidity, there is no condensation inside the pores. A sonic transducer could be constructed. In addition, since the acoustic matching layer is composed of a ceramic porous body made of an inorganic material, the softening point can be made relatively large, and an ultrasonic transducer having stable temperature characteristics can be realized.

(Embodiment 2)
FIG. 3 shows an ultrasonic flowmeter 7 using a pair of ultrasonic transducers as an example of an ultrasonic fluid measuring apparatus based on the present invention. The pair of ultrasonic transducers 8 and 9 are provided opposite to the upstream side and the downstream side of the flow path 10 through which the fluid flows. A solid arrow 11 indicates the direction in which the fluid flows, and a broken double arrow 12 indicates the direction in which the ultrasonic waves propagate. Further, the angle θ represents the crossing angle between the direction 11 in which the fluid flows and the direction 12 in which the ultrasonic wave propagates.

The measurement principle of the ultrasonic flowmeter as the ultrasonic fluid measuring device having such a configuration will be briefly described. When the flow velocity of the fluid flowing through the flow path 10 is Vf, the ultrasonic wave propagation velocity is Vs, and the distance between the ultrasonic transducers is Ld, the upstream ultrasonic transducer 8 moves to the downstream ultrasonic transducer 9. If the ultrasonic wave propagation time measurement result is Tud,
Tud = {Ld / [Vs + Vf × cos (θ)]}
It becomes.

  Similarly, when the ultrasonic propagation time measurement result from the downstream ultrasonic transducer 9 to the upstream ultrasonic transducer 8 is Tdu, the result is as follows.

Tdu = {Ld / [Vs−Vf × cos (θ)]}
From these,
Tud = Ld / [Vs + Vf × cos (θ)]
Tdu = Ld / [Vs−Vf × cos (θ)]
Therefore,
Vs + Vf × cos (θ) = Ld / Tud
Vs−Vf × cos (θ) = Ld / Tdu
From these, by subtracting both sides of the lower expression from the upper expression, the term of the ultrasonic sound velocity Vs can be eliminated, and the following is obtained.

2 × Vf × cos (θ) = Ld × [{1 / Tud} − {1 / Tdu}]
From this result, since the distance Ld and the crossing angle (θ) between the ultrasonic transducers are known, they can be easily calculated. In this way, the fluid flow velocity Vf is obtained. The flow rate Qm is calculated by multiplying the flow velocity Vf by the cross-sectional area Sr of the flow path 10.

  Similarly, when both sides of the above equation and the lower equation are added, the term of the fluid flow velocity is eliminated, and the following is obtained.

2 × Vs = Ld × [{1 / Tud} + {1 / Tdu}]
From this result, the speed of sound Vs is also obtained, and the temperature of the fluid can also be calculated from this.

  In this way, a highly reliable ultrasonic flow meter could be configured. In addition, an ultrasonic flowmeter having stable characteristics against temperature changes could be realized.

  In this embodiment, the flow rate Qm is calculated by obtaining the flow velocity Vf of the fluid. However, it is not always necessary to obtain the flow rate, and only the flow velocity Vf may be obtained. it can.

(Embodiment 3)
A method for producing the ceramic porous body will be described. An inorganic material such as alumina, silica, zirconia, cordierite, and low-melting glass are sufficiently finely pulverized. The particle size is prepared to be 10 μm or less. More desirably, it is 1 μm or less. The pulverized powder is mixed with polyvinyl alcohol as a binder to form a slurry.

  Next, the slurry is sprayed and pasted onto a resin ball such as acrylic and dried. The sprayed and pasted powder desirably has a thickness of about several μm. The diameter of the resin ball is preferably about 10 to 50 μm. The resin balls sprayed with the mist-like slurry, pasted and dried are compression-molded into a predetermined shape and fired.

  In this firing, the resin ball is carbonized by sufficiently supplying oxygen, and is released from the molded body as carbon dioxide. At this time, the resin balls sequentially escape from the surface of the molded body as carbon dioxide, and later, holes as communication holes remain. If the supply amount of oxygen is insufficient, it results in remaining inside the molded body as a carbide. The pores formed in this way become a ceramic porous body.

  The pore distribution of the ceramic porous body thus prepared is shown in FIG. FIG. 4 shows the pore diameter on the horizontal axis and the relative ratio on the vertical axis. Reference numeral 13 denotes a curve indicating the pore distribution, and a broken line 14 denotes the particle size distribution of the used resin balls. From the figure, the pore distribution 13 shows a considerably broader distribution than the particle size distribution 13 of the resin balls. This is presumably because the shells of the resin balls are united or the shells in contact are connected through the interface. Thus, it can be seen that most of the formed holes are distributed between 50 and 100 μm. It can also be considered as a result that a plurality of holes are combined to form a communication hole.

  Thus, by manufacturing a ceramic porous body, the porous body as a communicating hole can be comprised, and it is thought that it is the structure suitable for introducing organic glass into a void | hole.

(Embodiment 4)
Another method for producing the ceramic porous body will be described.

  An inorganic material such as alumina, silica, zirconia, cordierite, and low-melting glass are sufficiently finely pulverized. The particle size is prepared to be 10 μm or less. More desirably, it is 1 μm or less. A surfactant is mixed with the pulverized powder to form a slurry. Next, gas is introduced into the slurry, the slurry is foamed, and a large number of bubbles are introduced. In this state, after standing and drying, it is fired at the melting temperature of the low-melting glass and solidified to form a ceramic porous body.

  At this time, the film-form surfactant reacts with oxygen at the time of firing, burns out sequentially from the surface of the molded body, and thereafter, pores as communication holes remain. If the supply amount of oxygen is insufficient, it results in remaining inside the molded body as a carbide. The pores formed in this way become a ceramic porous body. As for the pore distribution of the ceramic porous body thus prepared, the same characteristics as the results shown in FIG. 4 were obtained. As a result, holes connected by the communication holes are obtained. Thus, by manufacturing a ceramic porous body, the porous body as a communicating hole can be comprised and the structure which can introduce | transduce organic glass easily into a void | hole is obtained.

(Embodiment 5)
A method for introducing the organic glass into the ceramic porous body will be described.

  An organic glass material such as silicon oxide, titanium oxide, zirconia, or alumina is prepared. This material is diluted with a solvent such as alcohol and mixed with a suitable catalyst.

  Next, the porous ceramic is etched with an acid or alkali solution. By this etching treatment, the inside of the ceramic porous body, that is, the surface inside the pores is partially etched and activated. The organic glass diluted with the solvent was infiltrated into the activated state, reacted with the pores of the ceramic porous body, and the organic glass was impregnated into the pores to form an acoustic matching layer. When the acoustic matching layer of the porous ceramic body with organic glass formed in this way was polished on both sides to achieve the optimum plate thickness, the adhesive strength between the organic glass and the porous ceramic body was significantly improved. I found out.

  That is, in the ceramic porous body in which the organic glass is not formed, a part of the ceramic porous body is chipped during polishing, or when a part of the ceramic porous body is chipped, a part of the ceramic porous body and a part of the organic glass are In some cases, the ceramic porous body was cut off during polishing after the adhesion strength between the organic glass and the ceramic porous body was improved. Further, even if a part of the ceramic porous body is missing, a part of the ceramic porous body and a part of the organic glass are not separated. Thus, the adhesive strength was increased and the workability as an acoustic matching layer was greatly improved.

(Embodiment 6)
A method for introducing the organic glass into the ceramic porous body will be described. Characteristics of the introduced organic glass by oscillating the solution by ultrasonic vibration when introducing organic glass such as silicon oxide, titanium oxide, zirconia, and alumina diluted in a solvent into the porous ceramic body The density was found to be stable.

  That is, when the density of the introduced organic glass is estimated from the porosity and bulk density of the ceramic measured in advance and the weight and bulk density after the introduction of the organic glass, the introduced organic glass is obtained when the solution is swung. The estimated density was 0.3 ± 0.03 [g / cc], but when the solution was not shaken, it was 0.3 ± 0.08 [g / cc]. This is probably because the organic glass in the solution was uniformly diluted and the uniformity of the reaction was improved as a result of the solution being shaken. Thus, an acoustic matching layer having uniform characteristics could be formed by introducing the organic glass while moving the solution.

  As described above, the ultrasonic vibrator, the ultrasonic flowmeter, and the manufacturing method thereof according to the present invention include an ultrasonic fluid measuring device that measures a flow rate and a flow rate of a liquid such as water as well as a gas, and an ultrasonic vibration used in the ultrasonic fluid measuring device. Applicable to children.

The perspective view of the ultrasonic transducer | vibrator in Embodiment 1 of this invention Embodiment 1 of the present invention is an enlarged view of an acoustic matching layer Conceptual diagram of ultrasonic flowmeter in embodiment 2 of the present invention Particle size distribution chart in Example 3 of the present invention A perspective view of a conventional ultrasonic transducer

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic vibrator 2 Piezoelectric body 3 Acoustic matching layer 4, 5 Electrode 7 Ultrasonic flowmeter (fluid measuring device)
8, 9 Ultrasonic vibrator 10 Flow path

Claims (10)

An ultrasonic vibrator comprising a porous body containing a filler having a sound speed slower than that in a gas, and a piezoelectric body. The ultrasonic transducer according to claim 1, wherein the porous body is made of ceramic. The ultrasonic transducer according to claim 2, wherein the ceramic is formed of a material containing at least one selected from alumina, silica, zirconia, and cordierite and a low-melting glass as a binder. The ultrasonic transducer according to claim 1, wherein the filler is made of organic glass. The ultrasonic vibrator according to claim 4, wherein the organic glass is formed of a material containing at least one selected from silicon oxide, titanium oxide, zirconia, and alumina. An ultrasonic fluid measurement device comprising the ultrasonic transducer according to any one of claims 1 to 5, wherein a fluid measurement unit including a flow path through which a fluid flows, and an upstream part through which the fluid flows in the flow path, Ultrasound including a pair of the ultrasonic transducers opposed to the downstream portion, measuring a propagation time during which the ultrasonic waves propagate between the pair of ultrasonic transducers, and calculating a flow velocity or a flow rate Fluid measuring device. It is a manufacturing method of the ultrasonic vibrator in any one of Claims 1-3, Comprising: A ceramic powder is coat | covered to a combustible ball | bowl, and after forming, the said combustible ball | bowl is burned off and it forms by sintering. A method of manufacturing an ultrasonic vibrator. It is a manufacturing method of the ultrasonic vibrator in any one of Claims 1-3, Comprising: Surfactant is mixed with a slurry-like ceramic powder, a bubble is introduce | transduced, and after shaping | molding drying, the said surfactant is used. A method for manufacturing an ultrasonic vibrator, wherein the ultrasonic vibrator is formed by baking and sintering. 6. The method for manufacturing an ultrasonic transducer according to claim 1, wherein the inner surface of the ceramic porous body is previously washed with an acid or alkali, and then filled with a solution-like filler and dried. A method for manufacturing an ultrasonic transducer, characterized by comprising: 10. The method of manufacturing an ultrasonic transducer according to claim 1, wherein the ultrasonic transducer is filled while applying a vibration such as an ultrasonic wave when the solution-like filler is filled. A method of manufacturing an ultrasonic transducer characterized by the above.

Images