JPS6153900A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To provide an ultrasonic probe with excellent characteristics by imbedding a number of needle shaped crystal of antimony sulfaiodide in a sheet shaped organic material to form a composite piezoelectrc material. CONSTITUTION:The needle shape crystal of antimony sulfaiodide is produced by the vapor growth method. A number of the needle shaped crystal 12 is imbedded in the sheet shaped organic material 11 to form the composite piezoelectric material. The composite piezoelectric material thus produced facilitates the manufacture of uniform one, and has better piezoelectric characteristics than one made of PZT ceramic fiber. Therefore, this type of composite piezoelectric material provides the ultrasonic probe with excellent characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ultrasonic probe used in an ultrasonic diagnostic apparatus or the like.

[Background of the invention]

Conventionally, ceramics based on zirconate and lead titanate (PZT) are often used as materials for piezoelectric vibrators in ultrasonic probes. However, these piezoelectric ceramics (
i) Since the acoustic impedance is significantly larger than that of the human body, it is necessary to take measures such as an acoustic matching layer for diagnostic purposes.
It has disadvantages such as (it) the piezoelectric voltage constant g is small because the dielectric constant is extremely large, making it impossible to obtain a high voltage when subjected to ultrasonic waves, and (tit) it is difficult to create a curvature that matches the shape of the human body. . In order to solve these problems, so-called composite piezoelectric materials, which are composites of organic matter and piezoelectric materials, have been proposed. As an example, Newham et al. of the United States have reported that it is effective to embed columnar P Z T 1.2 in organic matter 11 as shown in Figure 1 (Materials Research Preprints). (1978), Vol. 13, pp. 525-536 (1978)
In fact, by combining PZT with organic substances such as silicone rubber and epoxy, materials with low acoustic impedance and high piezoelectric voltage constant g have been obtained.

In such a case, the piezoelectric properties of the piezoelectric material vary greatly depending on the volume fraction of the piezoelectric material in the organic substance. Further, even if the volume fraction is the same, it is desirable to make the size of the columnar piezoelectric body as small as possible so that the composite piezoelectric body can be considered uniform in terms of the operating frequency. For this reason, there is a method in which PZT ceramics in the form of fibers with a small diameter are created, these are arranged with gaps between them, and resin is poured into the gaps to harden them. However, P with a small diameter (<0.5w+)
It is very difficult to create ZT ceramic fibers, and even if they can be created, their mechanical strength is weak and they break during the arranging process, resulting in extremely low production yields. Therefore, recently, a method has been developed for manufacturing composite piezoelectric materials especially for high frequencies, in which a PZT ceramic plate is cut into a mesh shape using a blade of an appropriate thickness, and the resulting grooves are filled with organic matter and hardened. There is.

However, in order to obtain good piezoelectric properties, it is necessary to make the width W of the column smaller than the height h, so even with this, the frequency is 5
Cutting becomes difficult when exceeding M T (z). For example, at 7 or 5 MHz, the height of the PZT ceramic column is about 0.2+++n+, so it is necessary to cut the width to be smaller than 0.2wn.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a composite piezoelectric material that is uniform, easy to manufacture, and has superior properties to those using PZT ceramic fibers, and an ultrasonic probe using the same.

[Summary of the invention]

The inventors have discovered that a ferroelectric substance called antimony sulfide (SbST) has a needle-shaped crystal extending in the C-axis direction by a vapor-phase growth method, and has an electromechanical coupling coefficient k for longitudinal vibration in the C-axis direction. It was noted that the PZT ceramic was 0.8 to 0.9, which was higher than that of PZT ceramic, and a composite piezoelectric material was constructed using this material. As a result, the cross section of the acicular crystal of 5bST is 0.5×0.5wn”
It was found that the following materials were easily obtained, the mechanical strength was greater than that of PZT ceramic fiber, and the composite process was easy. Furthermore, since the value of k3a was larger than that of PZT, it was found that the properties as a composite piezoelectric material were also superior to those using PZT. The present invention is based on such experimental results. The present invention will be described in detail below with reference to Examples.

[Embodiments of the invention]

Example l Acicular crystals of SbSI were created by vapor phase growth.

A mixture of antimony sb, sulfur S, and iodine was placed in a pyrex ampoule and sealed in vacuum.

This was placed in an electric furnace, heated to 550°C, and left for one week with a temperature gradient in the longitudinal direction of the ampoule (410°C in the high temperature part, 320°C in the low temperature part). As a result, the length is 140-20m
A large number of needle-shaped crystals with a cross-sectional area of 0.2 mm angle to 0.7 mm angle were obtained.

Next, needle-like crystals 21 with a length of 15 mm and a cross-sectional area of about 0.3 x 0.3 e'' were arranged as shown in FIG. 2, and an epoxy resin was poured and solidified to form a composite with a diameter of 10 mm. This was cut and polished to a thickness of about 0.5+an,
Two layers of chromium and gold were deposited on both sides as electrodes. Finally, a polarization process was performed by cooling through the Curie temperature (approximately 20° C.) while applying a DC electric field of 500 V/l between the electrodes.

Using the composite piezoelectric material thus prepared, an experiment of transmitting and receiving ultrasonic pulses was conducted underwater as shown in FIG. As a result, it was found that the total transmitting and receiving sensitivity was 5 to 1.0 dB higher than that of a composite piezoelectric material using PZT ceramic fiber.

As explained above, a composite piezoelectric material having a structure in which a large number of antimony sulfide 5bST needle crystals are embedded in a plate-like organic material is easy to manufacture uniformly and has good piezoelectric properties.
It is clear that this is superior to a composite piezoelectric material using ZT ceramic fiber, and that an ultrasonic probe using this material exhibits extremely excellent performance.

Example 2 A second composite piezoelectric body of the present invention is characterized in that a lithium niobate single crystal is used as the piezoelectric body.

Like PZT ceramics, lithium niobate has a large piezoelectric property, and is particularly suitable for use with 36° rotated Y plates (crystal plates in which the direction perpendicular to the plate surface is perpendicular to the crystal axis or the crystal axis Y and the angle formed with the crystal axis Y is 36°). ) vibrates in the thickness direction and has a large electromechanical coupling coefficient of approximately 0.5.

Furthermore, the resonance frequency constant is 3200 Hz-m, which is about twice as large as that of PZT ceramic (1500 Hz-m), so even after making it into a columnar composite, a higher frequency can be achieved with the same height and thickness. As a result of focusing on these characteristics of lithium niobate and attempting to combine it with organic matter, we found that 5MT (z
The above-mentioned high-frequency materials can be easily realized and have the same characteristics as PZ.
It became clear that it was comparable to that using T ceramics. The present invention is based on such experimental results. The present invention will be described in detail below with reference to Examples.

Area 10X1. A 36° rotated Y plate of lithium niobate single crystal with a thickness of 0.4+nm was bonded to the ferrite substrate-L with electron wax. It was cut into a mesh shape as shown in Figure 4. In Figure 4,
41 is a ferrite substrate, and 42 is a cut lithium niobate single crystal. After filling and solidifying the epoxy resin into the grooves created by cutting, the electron wax was melted and the plate-shaped composite piezoelectric material was peeled off from the ferrite substrate. In this way, a piezoelectric composite of lithium niobate and epoxy resin was obtained, in which the volume fraction of lithium niobate was 25% and the width of the pillars was 1/2 of the height. After chromium and gold were vapor-deposited as electrodes on both surfaces of this composite piezoelectric material, an experiment of transmitting and receiving ultrasonic pulses was conducted in the same manner as in the first embodiment described above.

From the frequency response, the resonant frequency is approximately 7.5 MHz
It turned out to be. This is a P of the same shape and size.
This is approximately twice the frequency when ZT ceramic is used. Furthermore, the wave transmitting and receiving sensitivity was almost the same as that using PZT ceramics.

Next, a similar experiment was conducted on a Y-plate rotated 20' to 50'' every 5 degrees.As a result, the resonance frequency of the composite piezoelectric material was almost constant at 7 to 8 MHz, but below 20 degrees, The transmitting and receiving sensitivity deteriorates rapidly above 40';
Significant trailing was observed in the ultrasonic pulse at angles below 36° and above 40°. This is considered to be due to the effect of shearing vibration, which is excited simultaneously with the thickness direction vibration except at around 36°.

As explained above, in a composite piezoelectric material having a structure in which a large number of columnar piezoelectric materials are embedded perpendicularly to the plate surface in an organic material,
A composite piezoelectric material in which the columnar piezoelectric material is made of a lithium niobate single crystal, and the direction perpendicular to the top and bottom surfaces of the pillar is perpendicular to the crystal axis or the crystal axis Y, and the angle formed with the crystal axis Y is in the range of 30 to 40 degrees, has excellent piezoelectric properties. It is clear that the ultrasonic probe using this method shows excellent performance.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain an ultrasonic probe using a composite piezoelectric material that is easier to manufacture and has higher performance than using conventional PZT ceramics.

[Brief explanation of the drawing]

Fig. 11 is a diagram showing the concept of a composite piezoelectric body, Fig. 2 is a diagram showing a part of the manufacturing process of an embodiment of the present invention, Fig. 21...S
bSI needle-shaped crystal, 31... water sore, 32... probe, 33... reflector, 34... applied pulse, 35...
・Ultrasonic pulse, 41... Ferrite substrate, 42...
・Lithium niobate single crystal.

Claims (1)

[Claims] A composite piezoelectric material having a structure in which a large number of needle-like crystals of antimony sulfide SbSI are embedded in a plate-like organic material, and an ultrasonic probe using the same.