JPS6131128A - Ultrasonic probe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

[Background of the invention]

Conventionally, zircon-lead titanate (PZT) ceramics have been widely used as materials for piezoelectric vibrators in ultrasonic probes. However, these piezoelectric ceramics (i) have significantly higher acoustic impedance than the human body, so for diagnostic purposes, it is necessary to devise an acoustic matching layer, etc.;
(ii) Because the dielectric constant is extremely large, the piezoelectric voltage constant g is small, making it impossible to obtain a high voltage when exposed to ultrasonic waves.(Ri) It is difficult to create a curvature that matches the shape of the human body. There is. 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, the US N.
Awnham et al. reported that a composite structure in which columnar PZT 12 is embedded in an organic material 11 as shown in Figure 1 is effective (Materials Research Press Vol. 13, pp. 525-536 (1978) )). Actually P
By combining ZT with organic substances such as silicone rubber and epoxy, materials with low acoustic impedance and high piezoelectric voltage constant g have been obtained.

However, experiments by the inventors have revealed that when these composite piezoelectric materials are used in ultrasonic probes, there is a problem with acoustic noise. Ultrasonic waves are generated using a composite piezoelectric material as shown in Figure 1.

When detecting, it is desirable that the organic matter and the columnar piezoelectric body are displaced uniformly. However, since organic matter is generally much softer than the columnar piezoelectric body, the organic matter part is displaced as shown schematically in Figure 2. Actual results have revealed that the columnar piezoelectric body portion 22 is displaced more than the columnar piezoelectric body portion 21.

For this reason, when the columnar piezoelectric bodies are arranged periodically as shown in FIG. 1, acoustic noise called a so-called grating lobe is generated when ultrasonic waves are generated. This causes deterioration of the ultrasonic image due to unnecessary ultrasonic waves emitted in a direction determined by the pitch of the array of columnar piezoelectric bodies in addition to the main ultrasonic waves.

[Purpose of the invention]

Therefore, the object of the present invention is to provide a system with sufficiently low acoustic noise level.
An object of the present invention is to provide an ultrasonic probe using a composite piezoelectric material.

[Summary of the Invention] The sensitivity of an ultrasonic probe using a composite piezoelectric material as shown in Fig. 1 depends on the size of the columnar piezoelectric materials and the distance between the columnar piezoelectric materials1. is set to be. As a result of systematic research on the structure and sensitivity of composite piezoelectric materials, the average value of the 51 composite piezoelectric materials is determined to be the optimum value even if the size and distance of the columnar piezoelectric materials are changed. It has become clear that the sensitivity will hardly decrease if the values are approximately equal to each other. The present invention is based on such experimental results, and the sensitivity can be improved by changing at least one of the size of the columnar piezoelectric bodies and the distance between the columnar piezoelectric bodies in the arrangement direction to make the columnar piezoelectric bodies array non-periodic. We were able to create an ultrasonic probe with sufficiently low acoustic noise levels without reducing the noise level. The present invention will be described in detail below with reference to Examples.

[Embodiments of the invention]

A PZT ceramic plate of 10 cm square and 0.4 mm thick, which was polarized uniformly in the thickness direction, was bonded to a ferrite substrate with electron wax. These ceramic plates were cut into a mesh shape as shown in FIG. 3 using a blade having a thickness of 0.2 mm and changing the pitch between 0.3 and 0.501. The grooves created by cutting were filled with silicone rubber, and the resulting plate-shaped composite piezoelectric material was peeled off from the ferrite substrate by melting the electron wax. In this way, a composite piezoelectric body was created in which the size of the columnar piezoelectric bodies and the distance between the columnar piezoelectric bodies were varied. The average values of the size of the columnar piezoelectric bodies and the distance between the columnar piezoelectric bodies in these composite piezoelectric bodies are almost the same as those formed by cutting with a 0.2 nm blade at a pitch of 0.4I.

By depositing chromium and gold as electrodes on both sides of these composite piezoelectric bodies and applying an electric field, ultrasonic waves were emitted into the water and the ultrasonic beam patterns were measured. As a result, it was revealed that the acoustic noise level, including the influence of the grating lobes, was less than -50 dB for transmitting and receiving with respect to the central main beam. The acoustic noise level exceeded 150 dB, which was a practical problem), and the sensitivity of the main beam was almost the same as that of a probe cut at an equal pitch of 0.4 m.

In this example, the size of the columnar piezoelectric bodies and the distance between the columns are changed simultaneously to give them non-periodic properties. Considering that the effect of the invention is due to the non-periodic nature of the arrangement of the columnar piezoelectric bodies, For example, it is obvious that the same effect can be obtained even if the size of the columnar piezoelectric bodies is kept constant and only the distance between the columns is changed.

〔Effect of the invention〕

As explained above, in a composite piezoelectric material having a structure in which a large number of columnar piezoelectric bodies are embedded perpendicularly to the plate surface in a plate-like organic material, at least one of the size of the columnar piezoelectric bodies and the distance between the columnar piezoelectric bodies is changed. It is clear that an ultrasonic probe with high sensitivity and low acoustic noise level can be realized by using a composite piezoelectric material in which the arrangement of columnar piezoelectric materials is made non-periodic.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the concept of a composite piezoelectric body, FIG. 2 is a cross-sectional view showing the displacement distribution within the composite piezoelectric body, and FIG. 3 is a diagram showing a method for manufacturing the composite piezoelectric body in an embodiment of the present invention. . 31... Ferrite substrate, 32... Columnar p z 'r
Ceramics.

Claims (1)

[Claims] In a composite piezoelectric body having a structure in which a large number of columnar piezoelectric bodies are embedded perpendicularly to the plate surface in a plate-like organic material, at least one of the size of the columnar piezoelectric bodies and the distance between the columnar piezoelectric bodies is defined as the arrangement direction of the columnar piezoelectric bodies. An ultrasonic probe characterized in that it uses a composite piezoelectric material in which the arrangement of columnar piezoelectric materials is made non-periodic by changing the .