JPH0128339B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sonic probe, particularly a sonic probe suitable for use in a microscope that utilizes high frequency sonic energy.

In recent years, it has become possible to generate and detect high-frequency sound waves of up to 1 GHz, resulting in a sound wave wavelength of about 1 micron underwater, and therefore, a microscope that utilizes sound wave energy has been considered.

In such devices, it is important to create a narrow focused acoustic beam, and it is strongly desired to improve the performance of the acoustic probe. first,
A conventional sonic probe will be explained with reference to FIG.

That is, the sonic probe consists of a cylindrical crystal (sound wave propagator) 1 made of a sound wave propagation medium such as sapphire, which has one end surface polished flat and the other end surface provided with a concave hole, and this crystal 1. A lower electrode 2 made of titanium, gold, chrome, aluminum, etc. is provided on the polished end surface by vapor deposition or the like, a piezoelectric material 3 such as zinc oxide is provided on it by sputtering or the like, and an upper electrode 4 is further placed on top of it. It consists of a piezoelectric element provided by vapor deposition or the like. When an RF electric signal is applied between the upper electrode 4 and the lower electrode of such a probe, the piezoelectric material 3
As a result, a plane wave RF sound wave is radiated into the crystal 1.
This plane wave is generated by the crystal 1 formed in the concave portion.
A positive spherical lens formed at the interface between the light and the medium 5 focuses the light at a predetermined focal point S.

As is well known, if the focal length to aperture ratio, ie, the F-number of the lens, is sufficiently small, the above-described configuration can produce a significantly narrower acoustic beam.

As described above, the focused sound waves are subject to disturbances such as reflection, scattering, transmission, and attenuation by the sample 6 placed near the focal point. , it is possible to obtain an electrical signal that reflects the elastic properties of the sample.

Note that for the detection of the sound wave energy, the above-described sound wave probe may be used again, or a similar sound wave probe placed facing the confocal area may be used.

As is clear from the above explanation, the conventional example uses a positive spherical lens as its focusing principle, which utilizes the difference in sound speed between the crystal and the medium. Therefore, in order to form a spherical lens with good focusing properties, a concave hole with excellent specularity and sphericity is formed in the crystal, and the shape is made closer to a hemisphere to create a spherical lens with a low F number. That is important. Moreover, since the attenuation of sound waves in the medium from the lens surface to the focal point S is extremely large, a concave hole with a minute radius of curvature, for example 0.2 mm, is formed to reduce the distance from the lens surface to the focal point to reduce the attenuation of the sound waves. I need to avoid it.

On the other hand, it is desirable that the area of the piezoelectric element portion (upper electrode 4) that emits RF sound waves becomes smaller as the spherical surface of the lens becomes smaller. That is, as shown in FIG. 2a, the concave diameter d and the upper electrode 4 are
It is desirable that the diameters D of the two are equal to each other. This is due to the following reasons. That is, for example, the second
As shown in Figure b, the axes of the upper electrode 4 and the diameter of the concave hole are misaligned, or as shown in Figure 2c, the relationship between the diameter d of the concave hole and the diameter D of the upper electrode 4 is D>
d, the transmission of sound waves within the crystal follows the path shown by the dotted line. Therefore, the plane wave transmitted to the outside of the concave hole is diffusely reflected within the crystal and enters the piezoelectric material 3, causing unnecessary signals (noise).

As mentioned above, when the diameter of the concave hole becomes as small as about 0.2 mm, it is extremely difficult to attach the upper electrode 4 having the same diameter on the axis of the concave hole by vapor deposition as in the conventional method. It was hot. Furthermore, even if the upper electrode 4 is mounted so as to be simply geometrically aligned with the axis of the concave hole, the acoustic axes may not necessarily align due to non-uniformity within the crystal. Furthermore, it was an extremely difficult task to connect a lead wire for applying an RF signal to the upper electrode 4 having a minute area.

The present invention has been made in view of the above points, and an object of the present invention is to provide a sonic probe that can completely and accurately attach an upper electrode 4 to a piezoelectric material 3 with a predetermined cross-sectional area. .

In order to achieve this object, the sonic probe of the present invention includes a sonic wave propagating medium having a concave hole formed at one end thereof and a first sonic wave propagating medium at the other end of the sonic wave propagating medium.
In a sonic probe comprising an electrode (lower electrode), a piezoelectric element in which a piezoelectric material and a second electrode (upper electrode) are formed in order, a liquid metal ball such as mercury is used as the second electrode. By pressing this mercury bulb from the other end with a material such as a carbon rod that has electrical conductivity but does not react with mercury, an RF signal can be reliably applied to the piezoelectric material. It is characterized in that the area of contact with the piezoelectric substance can be freely changed depending on the position where the carbon rod is pressed.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a diagram showing an embodiment of the present invention. In the figure, a crystal 1, which is a sound wave propagation medium having a concave hole formed at one end, is fixed to a case 7, and a mercury bulb 9 (upper electrode) is inserted into the case 7 with a push screw 8.
An electrode holder 10 having a structure that allows the electrode to be moved horizontally is inserted. An electrode 11 made of a carbon rod is attached to this electrode holder 10. A ball hole in which a mercury ball can be stored is provided at the end of the electrode 11. With this structure, the mercury bulb 9 can be reliably brought into contact with the piezoelectric material, and since it can move in the horizontal plane, the upper electrode 4 can be moved as described in FIG. It becomes possible to set the position on the axis of the concave hole, and it becomes possible to generate ultrasonic waves under optimal conditions. In addition, by adjusting the amount of mercury used depending on the diameter of the concave hole, the diameter d of the concave hole described above can be adjusted.
and the diameter D of the upper electrode 4 can be easily set to d=D.

Furthermore, the use of a material such as a carbon rod that has electrical conductivity and does not react with mercury for the electrode 11 prevents mercury from reacting with the electrode, forming an amalgam layer, and diffusing. By selecting the material used for the electrode 11 as described above, stable operation can be achieved.

As described above, according to the present invention, it is possible to omit the upper electrode deposition process and the lead wire connection process, which were extremely difficult in the past, and at the same time, it is possible to easily equalize the area of the sound wave focusing part and the area of the sound wave emission part. You can. Furthermore, it has the advantage of perfecting electrical contact, and can be expected to be highly effective in the production of devices that use high-frequency focused sound waves, such as sonic microscopes and ultrasonic spectroscopy.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the structure of a conventional sonic probe, Fig. 2 is a schematic diagram showing how sound waves propagate within the sonic probe, and Fig. 3 shows an embodiment of the present invention. figure.

Claims (1)

[Claims] 1. A sound wave propagation medium having a concave hole formed at one end, a first electrode, a piezoelectric material, and a second electrode formed at the other end of the sound wave transmission medium in this order. In a sonic probe comprising a piezoelectric element, a liquid metal sphere is used as the second electrode, and a conductive substance that does not react with the liquid metal is used to press the liquid metal sphere from the other end onto the piezoelectric substance. and a support mechanism that supports the member so as to be movable in any direction within the plane on which the piezoelectric substance is provided. 2. The sonic probe according to claim 1, wherein mercury is used as the liquid metal and a carbon rod is used as the member.