JPH1031491A - Manufacturing method for acoustic lens, and resin acoustic lens of converging type probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely manufacture a resin acoustic lens having a short focal distance, a high measurement precision and a high yield by controlling the reaction rate so as to obtain a specific reaction rate and forming a hardened resin. SOLUTION: A lens main body 11 formed by a resin material is entirely shaped in a column form. The tip section 11a has a cone shape and an inward concaved spherial lens surface 12 is formed at the tip section. When ultrasonic waves are emitted from the tip section of the body 11, a graded index is produced by a lens surface 12 and a focus P is formed. In the acoustic lens, the body 11 is made of a resin (a synthetic resin) having a heat-hardened characteristic (or a radiation hardened characteristic) by adding an additive to a main material. The hardened resin is formed by using the resin specifically having a reaction rate of at least more than 60%, preferably 60 to 95%. Note that the reaction rate of the formed hardened resin is normally obtained by using the measurement conducted by a Fourier transformation type infrared spectroscopic analysis device, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an acoustic lens and a resin acoustic lens for a focusing probe, and more particularly, to a focusing acoustic filter made of a curable resin obtained by adding a curing agent to a main component. The present invention relates to a method of manufacturing a short-focus acoustic lens having a high resolution with a high resolution at a high yield, and a resin acoustic lens suitable for a focusing probe.

[0002]

2. Description of the Related Art A focusing probe used in an ultrasonic flaw detector or the like is provided with a piezoelectric element for generating an ultrasonic wave and an acoustic lens for transmitting the ultrasonic wave and focusing the ultrasonic wave on a focal point. The acoustic lens is provided with a piezoelectric element on its end plane. A spherical lens surface is formed at the tip of the acoustic lens. The ultrasonic wave output from the piezoelectric element passes through the inside of the lens body of the acoustic lens, and is emitted from the lens surface at the tip into water as a propagation medium. When the ultrasonic wave propagates through the acoustic lens and is emitted from the lens surface, the ultrasonic wave is refracted by the lens surface and is focused on the surface of the sample in a point-like manner. The focal length of the focusing acoustic lens is determined based on the refraction angle on the lens surface.

In the focusing probe, designing the focal length has the same meaning as determining the refraction angle on the lens surface of the acoustic lens. Since the refraction angle follows Snell's law, it can be determined from the sound velocity of water as a propagation medium, the sound velocity of a lens material, the lens aperture diameter, and the spherical radius of the lens surface.

[0004] Materials of the focusing acoustic lens for forming the focal point include single crystal sapphire, silicon, aluminum and fused silica glass, and resin (synthetic resin). When the materials of the acoustic lens are arranged in ascending order of the ultrasonic frequency to be used, as described above, the order is single crystal sapphire and silicon, aluminum and fused silica glass, and resin. The reason for using different lens materials according to the frequency of the ultrasonic waves is that there is a difference in attenuation of the ultrasonic waves. Therefore, as a lens material, for example, about 100
At frequencies higher than MHz, for example, single-crystal sapphire having low high-frequency attenuation is frequently used, and at frequencies lower than that, for example, fused quartz is frequently used, and at frequencies lower than about 30 MHz, resins that can be easily handled are frequently used.

Similarly, the focal length of the acoustic lens is about 1 mm for the single crystal sapphire lens type, about 10 mm for the fused silica lens type, and about 20 mm for the resin lens type, from the relation of attenuation of ultrasonic waves.
mm, and more.

[0006] Single crystal sapphire and fused silica glass have a substantially constant sound speed as a material of an acoustic lens. Therefore, despite a very short focal length, the surface of the lens determined from the lens aperture diameter and the lens spherical radius is very small. The refraction angle does not deviate from the design value. On the other hand, in the case of a resin lens,
It has the characteristic that the sound speed changes and the refraction angle changes for each molded product, so that the focal length varies for each molded resin lens. However, since the focal length of the resin lens is relatively long, even if there is variation, there is no practical problem with the conventional resin acoustic lens.

For example, a thermosetting resin is used as a resin material of a conventional resin acoustic lens, and a resin acoustic lens mainly includes a hardener added to a resin component serving as a main component.
It was made by heat treatment.

[0008]

In recent years, as for synthetic resins, fillers (fillers) have been used at higher ratios than in the past in order to achieve high functions, as typified by engineering plastics and sealing materials for semiconductors. Since high-frequency ultrasonic waves are used for filling, the number of parts and materials that have high attenuation and are difficult to obtain good measurement results have increased. Therefore, in order to obtain good measurement results by ultrasonic testing,
The use of relatively low frequency ultrasound has become required. In addition, since components have been reduced in size or thickness, high-resolution acoustic lenses have been required to inspect these components with ultrasonic waves. Accordingly, an acoustic lens made of resin and having a short focal length has been required.

Therefore, based on the above technical requirements, the ultrasonic flaw detector is suitable for a relatively low frequency ultrasonic wave of about 30 MHz or less and has a focusing type having a resin lens having a short focal length. Tentacles have been used.

However, in the case of a conventional resin lens, there is a large variation in the characteristics of each molded product due to the manufacturing process, and therefore the sound speed changes for each molded product. There was a problem that the yield was low. Based on experiments by the inventor, it was concluded that the yield was about 50% when manufactured with an accuracy of ± 2% and a focal length of 15 mm.

A first object of the present invention is to solve the above-mentioned problems, and a method of manufacturing an acoustic lens capable of manufacturing a resin acoustic lens having a relatively short focal length and high measurement accuracy with high yield and high accuracy. Is to provide.

A second object of the present invention is to provide a resin acoustic lens of a focusing probe having a relatively short focal length, a high measurement resolution, and a high production yield.

[0013]

Means for Solving the Problems The first invention (claim 1)
According to the method for manufacturing an acoustic lens according to (1), in order to achieve the first object, an acoustic lens formed of a curable resin obtained by adding a curing agent to a main material and used for a focusing probe is used. This is a method for producing the curable resin by controlling the reaction rate such that the reaction rate of the curable resin is preferably 60 to 95%.

According to a second aspect of the present invention (corresponding to claim 2), in the method of manufacturing an acoustic lens according to the first aspect, the reaction rate of the curable resin is 80% or more.

According to a third aspect of the present invention (corresponding to claim 3), in the method for manufacturing an acoustic lens according to the first aspect, the curable resin is a thermosetting resin, and a heat treatment is performed to control a reaction rate. It is characterized by using.

According to a fourth aspect of the present invention (corresponding to claim 4), in the method for manufacturing an acoustic lens according to the third aspect, the main agent and the curing agent having a weight ratio of substantially 10: 1 are substantially combined. 3
It is characterized by being mixed in a temperature environment of 0 ° C.

According to a fifth aspect of the present invention (corresponding to claim 5), in the acoustic lens manufacturing method according to the third aspect, the main agent and the curing agent having a weight ratio of substantially 10: 1 are substantially combined. 7
Mixing in a temperature environment of 0 ° C., followed by heating at substantially 100 ° C. for about 40 minutes, and thereafter substantially 150 ° C.
It is characterized by heating at a temperature of at least about 60 minutes.

According to a sixth aspect of the present invention (corresponding to claim 6), in the method for manufacturing an acoustic lens according to the first aspect, the curable resin is a radiation curable resin, and the radiation rate is controlled by controlling the reaction rate. Is used.

An acoustic lens according to a seventh aspect of the present invention (corresponding to claim 7) is a resin acoustic lens used for a focusing probe in order to achieve the second object. The acoustic lens is formed by adding a curing agent to a main component, and has a reaction rate of preferably 60 to 95%.

According to an eighth aspect of the present invention (corresponding to claim 8), in the acoustic lens manufacturing method according to the seventh aspect, the accuracy of the focal length is included within an error range of 2 to 8%. It is characterized by the following.

[0021]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the configuration of a typical acoustic lens used for a focusing probe using ultrasonic waves. In this figure,
The lens body 11 is formed of a resin material. Lens body 11
Is a spherical lens surface 1 having a cylindrical shape as a whole, a conical tip 11a, and an inward recess at the tip.
2 are formed. When an ultrasonic wave is emitted from the distal end of the lens body 11, the lens surface 12 provides convergence, and the focal point P is formed. Lens body 1 of acoustic lens
A lower electrode (Au / Cr) 13 is attached to the upper flat surface of 1, and a plate-like piezoelectric element 15 is provided between the lower electrode 13 and the upper electrode (Au / Cr) 14. Upper electrode 1
When a relatively low frequency (approximately 30 MHz or less) electric signal is applied from the frequency signal generation source (not shown) to the lower electrode 4 and the lower electrode 13, the piezoelectric element 15 vibrates, and the same relatively low frequency ultrasonic wave is emitted. Occur. Ultrasonic waves generated by the piezoelectric element 15 propagate through the lens body 11, are refracted by the lens surface 12, and are emitted from the lens surface 12. In the figure, reference numeral 16 denotes a damper member.

In the above acoustic lens, the lens body 11
Is made of a thermosetting (or radiation-curable) resin (synthetic resin) obtained by adding a curing agent to a main component. The curable resin is molded using a resin having a reaction rate of at least 60% or more, preferably 60 to 95%. Here, the “reaction rate” is defined as a ratio of a reaction at the time of mixing the main agent and the curing agent in a resin made by adding the curing agent to the main agent and mixing the main agent and the curing agent as described above, and more specifically In the chemical structure relating to the bonding between the functional group of the base material and the functional group of the curing agent, the meaning is substantially the same as the degree of bonding. The reaction rate has a correspondence with the strength of the curable resin, that is, the degree of curing. Therefore, usually, the reaction rate of the molded curable resin can be obtained, for example, by obtaining the uncured ratio or the cured ratio using measurement by a Fourier transform infrared spectrometer.

By molding the resin acoustic lens so as to satisfy the above conditions for the reaction rate, a resin acoustic lens which is a relatively low frequency ultrasonic wave of about 30 MHz or less and has a relatively short focal length can be obtained. In addition, it can be manufactured at a high yield so that there is little variation in its characteristics and the speed of sound for each molded product is almost constant.

The present inventor has concluded based on experiments that the resin used for the lens body 11 of the resin acoustic lens can suppress the variation in sound speed as the reaction rate of the molded product increases. Was. That is, the reaction rate is at least 6
If it is 0% or more (preferably 60 to 95%), it has been found that a low-frequency ultrasonic wave can be used to obtain a resin acoustic lens having a short focal length and a good production yield. . This will be specifically described with reference to FIGS.

FIG. 2 shows the results of an experiment on the relationship between the reaction rate and the speed of sound of a molded product when a thermosetting resin is used for the lens body 11. According to FIG. 2, the reaction rate is about 60%.
, The sound speed is about 2590 to 2740 m / s, and when the reaction rate is about 80%, the sound speed is about 2620 to 2690 m / s.
/ S, when the reaction rate is about 90%, the sound speed is about 2630-
2680 m / s. That is, it can be seen that as the reaction rate increases, the width of the variation in sound speed decreases. As shown by the dashed line in FIG. 2, when considering the degree of change in which the width of the variation in the speed of sound is reduced, the reaction rate is at least 60%, preferably 60%.
% Is desirably included in the range of 95% to 95%.

Based on the above experimental results, the lens aperture diameter was set to a constant value of, for example, 6.4 mm, the sound speed of the resin acoustic lens was set to 2650 m / s, and the spherical radius of the lens surface 12 was adjusted so that the focal length became 15 mm. FIG. 3 shows the dispersion of the focal length when the probe is set and a low frequency ultrasonic probe of 25 MHz is manufactured. According to FIG. 3, when the reaction rate is about 60%, the focal length is about 14.4-15.
5 mm, the focal length is about 1 when the reaction rate is about 80%.
When the response rate is 4.7 to 15.2 mm and the reaction rate is about 90%, it indicates that the focal length is about 14.8 to 15.1 mm. That is, it can be seen that as the reaction rate increases, the width of the variation in the focal length decreases.

FIG. 4 shows the relationship between the above experimental results and the reaction rate and the accuracy of a probe having a focal length of 15 mm. According to FIG. 4, the reaction rate is about 60.
%, The focal length precision (error) is about 8%, and when the response rate is about 80%, the focal length precision (error) is about 4%.
% And a response rate of about 90%, it indicates that the precision (error) of the focal length is about 2%. That is, it can be seen that the accuracy (error) of the focal length decreases as the reaction rate increases.

According to the above experimental results, when the reaction rate of the thermosetting resin molded as the lens body 11 is controlled so as to be 60 to 90%, the sound speed, the focal length, and the focal length of each molded product are controlled. It is clear that the variation is small in terms of accuracy and the like, and it is clear that a resin acoustic lens that can handle relatively low-frequency ultrasonic waves and has a short focal length can be manufactured with a high yield. According to the change characteristics shown in FIGS. 2 to 4, the reaction rate may be higher than 90%, but as described above, the reaction rate is preferably 60 to 95%.
, More preferably 80% or more.

The beam diameter (d _-6 ) and beam length (L) of the ultrasonic wave near the focal point of the focusing probe are expressed by the following equations (Equation 1) and (Equation 2), respectively. It is known. Here, the beam diameter corresponds to the azimuth resolution, and the beam length corresponds to the depth of focus. In the case of a probe with a long focal length, the depth of focus is large, so even if the sound velocity accuracy of the resin lens is somewhat coarse, it can be within the design value.However, in the case of a probe with a small depth of focus, the accuracy is poor. This will deviate from the design value.

[0031]

## EQU1 ## d- ₆ = 0.71λf / (D / 2)

[0032]

L = (2α / (α ² -1)) f where α
= D ² / (4λf)

In the above equations, λ is the wavelength, D is the aperture diameter, f
Is the focal length.

For reference, FIG. 5 shows a calculation example of the permissible error for each focal length obtained based on the above equation (Equation 2). In the calculation, the frequency of the ultrasonic wave is 25 MHz, and the aperture diameter of the lens surface is 6.4 mm.

Next, an embodiment of a method for manufacturing a resin acoustic lens will be described.

First, an example of manufacturing a lens molded product using a thermosetting resin will be described. First, as a first example, a production method in which, for example, a bisphenol A-based epoxy resin is used and its reaction rate is 60% will be described. The main agent is bisphenol A epoxy resin (product name: Caster 101), and the curing agent is aliphatic amine (product name:
HD). In the main agent and the curing agent, the weight ratio of the main agent and the curing agent is about 10: 1, the curing agent is added to the main agent and mixed, and the temperature environment at the time of mixing is set at about 30 ° C. A molded article having a ratio of substantially 60% can be obtained.

As a second embodiment, a production method in which a bisphenol A-based epoxy resin is used and the reaction rate of which is 80% will be described. Similarly, the main component is a bisphenol A-based epoxy resin, the curing agent is an aliphatic amine, and the weight ratio of the main component to the curing agent is about 10: 1. A curing agent is added to the main agent and mixed, the temperature environment at the time of mixing is set to about 70 ° C., and the mixture is stirred for about 1 minute.
The composition is cured by heating at 0 ° C. for about 40 minutes, and then heat-treated at about 150 ° C. for about 1 hour. Then, a molded article having a reaction rate of substantially 80% can be obtained.

In the manufacturing method according to the second embodiment, the time of the final heat treatment at 150 ° C. is adjusted.
The reaction rate can be varied. For example, when the heat treatment time is 0, that is, when a heat treatment at 150 ° C. is not performed at all, a molded article having a reaction rate of about 63%, when the heat treatment time is about 4 hours, a molded article having a reaction rate of about 85%, and the heat treatment time is 8 hours In this case, a molded product having a reaction rate of about 89% can be obtained. Therefore, in order to give the molded resin acoustic lens a higher reaction rate, the time of the heat treatment at 150 ° C. may be increased.

FIG. 6 shows an example of the relationship between the heat treatment time at 150 ° C. and the variation in the speed of sound.

When assembling as an acoustic lens of a focusing probe, the lower electrode 13, the upper electrode 14, and the piezoelectric element 15 are provided for a lens molded product of a thermosetting resin having the required reaction rate. Together with
A spherical lens surface 12 is formed by pressing a stainless steel ball according to the focal length against the front end of the lens body.

As described above, when manufacturing a short-focus resin lens with high accuracy in an acoustic lens used for a focusing probe, if the reaction rate of the resin is controlled to a desired value, a high value is obtained. The resin acoustic lens of the focusing probe can be manufactured with a high yield.

In the above description, the main ingredient is bisphenol A
Although the aliphatic epoxy resin and the curing agent are aliphatic amines, the above production method can be applied to other main agents and curing agents having similar relationships.

In the above embodiment, heat treatment was used as a method of controlling the reaction rate of the resin used as the acoustic lens. However, in the case of an ultraviolet curable resin such as an acrylic resin, the reaction rate was controlled by controlling the amount of ultraviolet irradiation. By controlling the rate as described above, it is possible to manufacture a focus focusing probe with a high yield. In the case of an acrylic resin, the relationship between the reaction rate and the irradiation amount is, as shown in JP-A-4-341808,
It is known that the reaction rate increases as the irradiation dose increases. Therefore, the irradiation amount of the ultraviolet rays is determined so that a reaction rate corresponding to the required accuracy of sound speed is obtained. Other photo-curable resins, γ-ray curable resins, X-ray curable resins, etc. (generally referred to as “radiation-curable resins”) have similar properties and manufacturing advantages by controlling the reaction rate as described above. Can be manufactured.

In the above embodiment, a spherical lens is used as an acoustic lens, and a point focusing type probe having a focal position within a predetermined minute range has been described as an example. It may be a focusing probe or a line focusing probe using a cylindrical lens.

[0045]

As is apparent from the above description, according to the present invention, when an acoustic lens of a converging ultrasonic probe is made of resin, the reaction rate becomes a desired value in the manufacturing process. With this control, a resin acoustic lens having a short focal length and high measurement accuracy can be manufactured with high yield and high accuracy.

In addition, it is possible to manufacture a resin acoustic lens of a focusing probe having a short focal length, a high measurement resolution, and a high production yield, and has a practicality corresponding to a change tendency of components and materials in recent years. And a resin acoustic lens having a high level can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a typical structure of an acoustic lens of a focusing probe.

FIG. 2 is a characteristic diagram showing an experimental result on a relationship between a reaction rate and a sound speed of a molded product when a thermosetting resin is used for a lens body.

FIG. 3 shows the results of the experiment shown in FIG. 2 when the spherical radius of the lens surface is set with respect to a specific lens aperture diameter, sound velocity, and focal length and a specific low-frequency ultrasonic probe is manufactured. FIG. 11 is a characteristic diagram showing a result of replacement with a relationship between a rate and a focal length.

FIG. 4 shows the results of the experiment shown in FIG.
It is a characteristic view shown as a relation with the accuracy in a 5 mm probe.

FIG. 5 is a table showing a calculation example of an allowable error for each focal length when an ultrasonic frequency is 25 MHz and an aperture diameter of a lens surface is 6.4 mm.

FIG. 6: A curing agent is added to and mixed with a main agent having a weight ratio of 10: 1.
FIG. 4 is a characteristic diagram showing an example of a relationship between a subsequent heat treatment time at 150 ° C. and a variation in sound speed in a case where the composition is heated and cured at about 100 ° C. for about 40 minutes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Lens main body 12 Lens surface 13 Lower electrode 14 Upper electrode 15 Piezoelectric element 16 Damper member

Claims (8)

[Claims] 1. A method of manufacturing an acoustic lens which is formed of a curable resin obtained by adding a curing agent to a main agent and is used for a focusing probe, wherein a reaction rate of the curable resin is 60 to
A method of manufacturing an acoustic lens, wherein the curable resin is molded by controlling the reaction rate so as to be 95%. 2. The method for manufacturing an acoustic lens according to claim 1, wherein the reaction rate of the curable resin is 80% or more. 3. The method of manufacturing an acoustic lens according to claim 1, wherein the curable resin is a thermosetting resin, and a heat treatment is used to control the reaction rate. 4. The method of manufacturing an acoustic lens according to claim 3, wherein the base agent and the curing agent having a weight ratio of substantially 10: 1 are mixed in a temperature environment of substantially 30 ° C. 5. The method according to claim 5, wherein the base material and the curing agent having a weight ratio of substantially 10: 1 are mixed in a temperature environment of substantially 70 ° C.,
4. The method according to claim 3, wherein the heating is performed at substantially 100 [deg.] C. for 40 minutes, and then at substantially 150 [deg.] C. for at least 60 minutes. 6. The method of manufacturing an acoustic lens according to claim 1, wherein said curable resin is a radiation-curable resin, and a radiation treatment is used for controlling said reaction rate. 7. A resin acoustic lens used for a focusing probe, wherein the resin acoustic lens is formed by adding a curing agent to a main component, and has a reaction rate of 60 to 95%. A resin acoustic lens for a focusing probe. 8. A resin acoustic lens for a focusing probe according to claim 7, wherein the accuracy of the focal length is within an error range of 2 to 8%.