JPH0346836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sound wave focusing means used in an ultrasound microscope.

[Conventional technology]

In recent years, it has become possible to generate and detect ultrahigh-frequency sound waves of up to 1 GHz, making it possible to realize sound wavelengths of approximately 1 μm underwater, and as a result, it has become possible to obtain high-resolution sound wave imaging devices. In other words, a concave lens is used to create a focused acoustic beam, achieving a high resolution of 1 μm.

By inserting a sample into the beam and detecting the reflected ultrasonic waves from the sample, the elastic properties of minute regions of the sample can be elucidated, or while the sample is mechanically scanned in two dimensions, the intensity of this signal can be measured. If displayed as a brightness signal on a cathode ray tube, the fine structure of the sample can be enlarged.

FIG. 1 is a diagram showing the main components of the ultrasound microscope. The focusing, transmission and reception of ultrasonic waves is carried out by a spherical lens 1, whose structure consists of optically polishing one side of a material made of cylindrical fused silica or the like, and then placing a piezoelectric thin film (ZnO) 2 on top of it with upper and lower electrodes 3. A pulse 5 generated from a pulse oscillator 4 is applied to the piezoelectric thin film 2 sandwiched in a sandwich structure to generate an ultrasonic wave 6. In addition, a concave hemispherical hole with a diameter of about 0.1 mmφ to 1.0 mmφ is formed at the other end, and a medium (for example, Water) 8 is fulfilled.

Ultrasonic waves 6 generated by the piezoelectric thin film 2 propagate in the cylinder as plane waves. When this plane wave reaches the hemispherical hole, quartz (velocity of sound 6000m/s) and water (velocity of sound
1500 m/s), a refraction effect occurs, and a focused ultrasonic wave 6 can be irradiated onto the surface of the sample 7. Conversely, the ultrasound reflected from the sample 7 is collected and phased by a spherical lens, becomes a plane wave, reaches the piezoelectric thin film 2, and is converted into an RF signal 9 here. This RF signal 9 is received by a receiver 10,
Here, the signal is detected by a diode and converted into a video signal 11, which is used as an input signal for a CRT display 12.

In the apparatus configured in this way, when the sample 7 is two-dimensionally scanned within the x-y plane by the sample stage drive power supply 13, the intensity of reflection from the sample surface as the sample scans changes two-dimensionally. displayed on surface 12.

Generally speaking, a portion of ultrasonic waves is reflected by the surface of an object, but a large portion of the ultrasound waves enters the object, regardless of whether the object is optically transparent or not, and is reflected by the hardness and density inside the object. , it returns as an echo reflecting differences in viscosity and defects. Ultrasonic microscopes can utilize this property to detect aspects inside a sample.

As is clear from the above description, the conventional example uses a positive spherical lens as its focusing principle, which utilizes the sound speed difference between the crystal and the medium. Therefore, it is necessary to form a hemispherical concave hole in the crystal, but S
Because the acoustic attenuation of the medium (usually water) up to the focal point is extremely large, in order to create a lens with a low F number, for example, create a microspherical hole of 0.2 mm, reduce the distance from the lens surface to the focal point, and reduce the sound waves. Attenuation must be avoided. Furthermore, in order to function as a spherical lens, there must be no unevenness of at least 1/10 wavelength of the acoustic wave length. This is for a 1GHz sound wave
It is on the order of 0.1 μm.

[Problem to be solved by the invention]

Conventionally, such lenses are processed using a polishing method, which is an extremely difficult process.
He makes lenses with a diameter of 0.5mm.

The present invention has been made in view of the above points, and its object is to provide a method for efficiently obtaining an acoustic spherical lens having a minute diameter and a mirror surface.

It is well known in the industry that when creating glasses such as quartz glass, or when using natural quartz, crystal, etc., bubbles due to residual gas etc. exist or are generated inside the glass, and how to remove these bubbles. It is widely known that this determines the quality of materials. By the way, for example, when we carefully observed the bubbles in quartz, we found that the bubbles had extremely good sphericity, and their interfaces had mirror surfaces that were impossible to achieve using polishing methods. In fact, a piezoelectric element was attached to the other side of a quartz plate containing air bubbles by carving out the bubbles, resulting in a 1GHz
When we conducted a sound wave focusing experiment, we found that it showed extremely good focusing properties, confirming that it is an excellent spherical lens for focusing high-frequency sound waves. The air bubbles scattered in the quartz plate exist in various spherical shapes ranging from 0.5 mm to 10 μm, so it is possible to create a spherical lens with a micro diameter, specularity, and sphericity that is impossible with polishing methods. You can get it.

As mentioned above, a method for making a spherical lens using air bubbles contained in a lens material has been previously filed (see Japanese Patent Application No. 54-57096 and Japanese Patent Application Laid-open No. 55-149998). This paper proposes a method for making spherical lenses.

[Means for solving problems]

The present invention involves stacking a plurality of plates that serve as lens materials,
By heating this, bubbles generated by minute gases present at the interface between the plates are generated inside the plate, and by turning the stacked plates upside down and reheating, a large number of spherical bubbles are generated. The method is characterized in that an acoustic spherical lens is produced by forming a bubble in a plate of lens material, and cutting and shaping the plate of lens material to expose a desired surface of the bubble.

[Effect]

According to the above method, a large number of bubbles can be generated in the stacked upper and lower plates, and a perfectly spherical bubble of a desired size can be easily selected and used for an acoustic lens. .

〔Example〕

As an example of the previous proposal, a method is also described in which a material that generates gas that is a source of bubbles is actively utilized. As shown in FIG.
15 are stacked as shown in a and heated in a furnace to around the melting point temperature of quartz, the gas present in the contact surface of the quartz gathers at one point in a perfectly spherical shape. When cooled in this state, a perfect spherical hole can be found near the contact with the quartz plate 15, as shown in b. This is used for spherical lenses.

However, if we carefully observe the bubbles generated during the above-mentioned work process, we can see that the number of bubbles is greatest at the contact and boundary surfaces of the quartz plates, as shown in Figure 3. The number of bubbles gradually decreases toward the top. The range is approximately 1 mm to 1.5 mm, although it depends on the heating time.

The quartz plates 14 and 15, in which air bubbles had been formed in the quartz plates in this manner, were introduced into the furnace again and heated. However, at this time, the vertical relationship of the quartz plates was reversed. That is, heating was performed with the quartz plate 15 containing air bubbles placed at the bottom. As a result, it was observed that the bubbles that had been present on the interface started moving again and ascending toward the quartz plate 14 side.

After heating for a predetermined period of time, it is slowly cooled and taken out from the furnace to check the distribution of air bubbles. It was found that it is distributed. This means that by turning the quartz plates 14 and 15 upside down during heating, the number of bubbles formed in the quartz plates can be easily doubled by about twice.

When the quartz plates 14 and 15 in which a large amount of air bubbles are sealed in the lens material are cut and divided at the contact surface, two quartz plates each containing perfectly spherical air bubbles are obtained.

From this quartz plate, focusing on bubbles of a predetermined size, polishing is performed from the adhesive surface side based on the work order shown in FIGS. 5a to 5c until the polished surface reaches the equatorial plane of the bubbles. By further adjusting the outer shape, a spherical lens can be obtained.

〔Effect of the invention〕

In this way, by turning the lens materials during heating, the air bubbles generated from the collection of adsorbed gas existing on the contact surfaces of two overlapping lens materials are distributed throughout both lens materials, and the amount of air bubbles is multiplied. By doing so, it becomes easy to produce a large number of spherical lenses, and the effects of the present invention are truly remarkable.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an ultrasonic microscope, Figs. 2 and 3 are illustrations of a conventional method for obtaining a concave hole in a spherical lens from air bubbles, and Figs. 4 and 5 are examples of an embodiment of the present invention. FIG. 2... Piezoelectric thin film, 7... Sample, 14, 15...
quartz plate.

Claims (1)

[Claims] 1. By stacking and heating a plurality of plates of a specified lens material, air bubbles are generated in the plates, and the stacked plates are turned over and reheated to generate more bubbles, and the air bubbles inside the resulting bubbles are heated. A method for producing an acoustic spherical lens, which comprises selecting and exposing desired bubbles from the spherical surface of the lens to form a lens surface.