JPS60261440A - Ultrasonic transducer and its production - 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 the Invention The present invention relates to an ultrasonic transducer used for ultrasonic diagnosis of a living body.

In recent ultrasound diagnostic equipment, ultrasound signal amplification technology and signal processing technology such as log amplifiers have been developed, and it is now possible to display signals down to the very low level of thermal noise based on the output level of the ultrasound transducer. It has become possible to obtain high-quality images.

However, the impulse response of the ultrasonic transducer, which is the basis of the ultra-fine image quality and the sharpness of the outline, has a long tail. For example, in a 3.5 MHz disk-shaped ultrasonic transducer, - Since the time for ringing down to 40 dB was longer than 3 μs, good quality images could not be obtained. Generally, the current situation is that it is measured at -6 dB, or at least -20 dB.

Therefore, improvements in ultrasonic transducers commensurate with the improvements in the above-mentioned amplification technology and signal processing technology have come to be required.

BACKGROUND OF THE INVENTION Conventional ultrasound transducers use a conventional ultrasound transducer in which an ultrasound signal reflected back from a subject is re-reflected inside the ultrasound transducer and radiated into the subject again. This caused a phenomenon called multiple reflections, which were reflected back from inside and received by the ultrasonic transducer.
When the received ultrasonic signals were converted into an image, a significantly degraded image was obtained.In order to improve this drawback, the ultrasonic transducer was A method has been proposed in which the acoustic impedance up to the outermost layer of the transducer is configured to be equal to that of the acoustic medium in contact with the radiation surface of the ultrasonic transducer, thereby significantly reducing the multiple reflections.

The most improved method is disclosed in Japanese Patent Application No. 58-39908, and as shown in FIG.
．． . −・−
, Zbm, each with a thickness of 1/4 wavelength M
When it is assumed that the layer has an acoustic matching layer on the back side and an acoustic damper 21 having an acoustic impedance zb, and the radiation side surface layer 31 is in contact with a subject having an acoustic impedance Zt, the main layer from the surface layer 31 is The acoustic impedance Zin when looking at the outermost layer 21 of the acoustic transducer is configured to be substantially equal to the above 21 in a desired frequency band, and the radiation side matching N of the ultrasonic transducer 1 is
(Z'tl, Zt2.--, Ztn').

Back side matching layer (Zbl, Zb2.-, Zb+n)
, and the acoustic tamper (Zb) have a uniform acoustic impedance.

(C1 Problem to be Solved by the Invention) On the back side of the conventional ultrasonic transducer shown in FIG. However, since it is made up of a single acoustic damper, it is actually quite difficult to manufacture.

In view of the above-mentioned conventional drawbacks, the present invention uses a layer whose acoustic impedance changes continuously on the back side of an ultrasonic transducer, thereby substantially reducing the number of matching layers on the back side of the ultrasonic transducer. It is an object of the present invention to provide a method for easily manufacturing an ultrasonic transducer signal in which re-reflected ultrasonic signals are significantly reduced.

tdl Means for solving the problem and this purpose is such that the acoustic impedance of the acoustic damper material and/or the back side matching layer changes continuously, and A method according to the present invention, wherein the acoustic impedance of the ultrasonic transducer up to the outermost layer on the rear side is substantially equal to the acoustic impedance of the acoustic medium that is brought into contact with the radiation side surface in a desired frequency band. That is, according to the present invention, the acoustic impedance distribution of the back side continuous layer obtained by mixing a metal powder such as tungsten and a binder such as an epoxy resin and using a conventional technique such as natural sedimentation or centrifugation is Paying attention to the piecewise distribution as shown in the figure, and considering the high acoustic impedance part ■ as one layer in this distribution, and the part ■ continuing to this layer ■ as one layer, We focused on the fact that the entire structure consisting of the two layers ■ and ■ (referred to as the continuous change layer) has a two-layer structure, and by using this continuous change layer, we can create a This makes it possible to easily obtain characteristics equivalent to a matching layer with uniform acoustic impedance with a thickness of 1/4 wavelength on the side, so there is no need to form a matching layer with uniform acoustic impedance, which is difficult to manufacture. ,
This has the effect of significantly reducing the ultrasonic signals re-reflected from the ultrasonic transducer and easily obtaining an ultrasonic transducer with less multiple reflections.

In this figure, (a) indicates a continuous change layer.

(b) shows the acoustic impedance characteristics of the continuously variable layer.

(f) Example Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1(a) is a diagram showing the configuration of an ultrasonic transducer according to an embodiment of the present invention, and FIG. 1(b) is a diagram showing actually measured data of a continuously variable layer.

As is clear from FIG.
There is the continuous change layer 2 whose acoustic impedance changes continuously on the back side of the laser, and the radiation side matching layer N3 having a thickness of 174 wavelengths is provided on the radiation side.

The above-mentioned continuous change layer 2 is made by mixing tungsten powder with a particle size of 10 to 14 μm and epoxy resin at a weight ratio of approximately 3:1, and hardening the mixture by precipitation.Actually measured acoustic impedance data
The horizontal axis in (b) represents the distance (unit: μm) from the surface in contact with the piezoelectric element 1, and the vertical axis represents the acoustic impedance at the corresponding surface.

Among the actual measurement data of acoustic impedance shown in book (b),
A is a portion corresponding to a thickness of 174 wavelengths among the portions showing high acoustic impedance in the continuously variable layer 2 shown in (A), and B is a portion showing a substantially constant acoustic impedance.

From this actual measurement data, the average acoustic impedance of section A is 11.5X10°Kg/m2sec (however, n=6)
So, part B is 10XIO' Kg/m2sec (however, n
86) Therefore, the configuration of the back side according to the present invention is
Matching layer with a thickness of 174 wavelengths [acoustic impedance:
11.5X10' Kg/m2sec (however, n=6
)) and damper material [acoustic impedance: l0XI
It can be seen that it is equivalent to the ultrasonic transducer disclosed in the above-mentioned Japanese Patent Application No. 58-39908, which has a two-layer structure of 0' Kg/m2sec (n=6).

Next, the acoustic impedance Zin when looking at the outermost layer 2 on the back side in a desired frequency band from the surface of the matching layer 3 on the radiation side of the ultrasonic transducer of the present invention is determined by measuring the acoustic impedance Zin of the medium in contact with the matching layer 3 on the radiation side. In order to make the acoustic impedance equal to [in this example, paraffin is used, the acoustic impedance Zp=1.23 x 10' Kg/m2sec (however, n=6)], the acoustic impedance of the radiation side matching layer is 4 X 10'Kg/m2sec
(However, n=6).

This value can be easily determined according to the calculation formula for Zin disclosed in the above-mentioned Japanese Patent Application No. 58-39908, and the present acoustic impedance can be easily obtained by a conventional mixing method.

The characteristics of the ultrasonic transducer thus manufactured were measured using the measurement system shown in FIG.

In this measurement system, the ultrasonic transducer 5 and the reflector 6 are arranged in paraffin 4 so as to face each other, and the ultrasonic transducer 5 is driven by a drive circuit (not shown). Frequency analysis was performed on the first reflected wave C1 and the second reflected wave using a receiving circuit and a spectrum analyzer (not shown).

The above measurement results are shown in Figure 5. The symbol C2D in Figure 5 indicates the fourth
This corresponds to symbols C and D in the figure.

In order to compare the above characteristics of the ultrasonic transducer of the present invention, the characteristics of a commercially available 3.5 MHz ultrasonic transducer were measured using the measurement system shown in FIG. 4. The results are shown in FIG. It was shown to.

Symbols C and D in this figure correspond to symbol C2D in FIG.

As is clear from the results of comparing the characteristics of FIG. 5 and FIG. 6 above, in FIG. It can be seen that the ultrasonic signal is significantly attenuated in the 3.5MH2 band.

Next, on the back side of the ultrasonic transducer 1 of the ultrasonic transducer, a matching layer 22 with a thickness of 174 wavelengths and a damper material 21 are provided without using a continuous change layer, and a damper material 21 is provided on the radiation side.
FIG. 7 shows the results of measuring an ultrasonic transducer composed of a matching layer 32 having a thickness of four wavelengths using the measurement system shown in FIG. 4.

(A) of this figure shows the configuration of the ultrasonic transducer, and (B) shows the above measurement results.

(A) In the figure, matching layers 22, 32 . and damper material 2
1, the acoustic impedance Zin of the damper material 21, which is the outermost layer, viewed from the surface of the radiation side matching 7532 is equal to the acoustic impedance Zp of the radiation side acoustic medium (=1.23 XIO' Kg/m2sec) in the desired frequency band.
Matching layer 22: 9.4 x 10' Kg/m2se
c (however, n-6) matching layer 32: 3.8 XIO'
Kg/m2sec (however, n=6) Damper material 21:
7.5 xio' Kg/m2sec (However, n-6
).

These acoustic impedance values take into consideration the transmission efficiency of the ultrasonic transducer and the transmitted ultrasonic signal waveform, and satisfy the Zin calculation formula disclosed in the aforementioned Japanese Patent Application No. 58-39908. It was chosen as such.

By comparing Fig. 5 and Fig. 7 (b), it can be seen that the ultrasonic transducer employing this continuously variable layer is the same as the ultrasonic transducer disclosed in Japanese Patent Application No. 58-39908. It can be seen that multiple reflections can be sufficiently reduced to a certain degree.

Therefore, by using the present application, an ultrasonic transducer that eliminates multiple reflections can be created without increasing the cost of providing a matching layer with a thickness of 174 wavelengths on the back side of the ultrasonic transducer of the ultrasonic transducer. You will be able to get it.

However, in reality, the continuous change layer 2 explained in FIG.
The distribution of acoustic impedance of the ultrasonic transducer 1 is not always constant and varies to some extent depending on the manufacturing loft. The acoustic impedance Zin viewed from the radiation side surface of the continuously variable layer 2 is measured, and based on this measurement data,
An effective method is to determine the acoustic impedance of the matching layer 3 having a thickness of 174 wavelengths on the radiation side.

As is clear from the above, the essence of the present invention lies in the fact that it was made based on the knowledge obtained from the extensive experience of the inventor of the present application.

The present invention can also be applied to cases where the radiation-side matching layer of the ultrasonic transducer is two layers, three layers +-'1, or a continuously variable layer is provided on the radiation side, and it can also be applied to other frequencies. ,
Furthermore, it can be easily inferred that the present invention can also be applied to linear arrays, phased arrays, annual arrays, etc.

(g) Effects of the Invention As explained in detail above, the ultrasonic transducer of the present invention uses a layer in which the acoustic impedance changes continuously on the back side of the ultrasonic transducer, which makes it possible to improve the ultrasonic transducer of the present invention. This made it possible to easily obtain characteristics equivalent to a matching layer with a uniform acoustic impedance with a thickness of 174 wavelengths on the back side, which had been considered difficult. There is an effect that it is possible to easily obtain an ultrasonic transducer that significantly reduces ultrasonic signals re-reflected from the ultrasonic transducer without increasing the cost of providing the ultrasonic transducer.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an ultrasonic transducer to which the present invention is applied and the acoustic impedance characteristics of the continuously variable layer on the back side. FIG. 2 is a diagram showing the configuration of a conventional ultrasonic transducer. FIG. 3 is a diagram showing acoustic impedance characteristics of a continuously variable layer obtained by the conventional technique. FIG. 4 is a diagram showing a measurement system for measuring multiple reflections. FIG. 5 is a diagram showing spectrum data of the first and second reflections of the ultrasonic transducer shown in FIG. 1. Figure 6 shows the first general ultrasonic transducer. Figure 7 shows data of the spectrum of the second reflection.
The configuration of an ultrasonic transducer provided with a wavelength matching layer, and the first and second times in the ultrasonic transducer
A diagram showing data of the spectrum of the second reflection. It is. In the drawing, 1 is an ultrasonic transducer. 2 is a continuous change layer on the back side. 21 is a damper material, and 22 is a rear matching storage. 3.3L32 is a radiation side matching layer. 4 is paraffin. 5 is an ultrasonic transducer. 6 is a reflector, C and D are reflected waves. are shown respectively. Tea 1 Yuu 1 Um Misaki, i Woo) -v; 2 Tumine 3 Mouth (In (I)) Tea 4 Eye Tea Otsu Eye

Claims (2)

[Claims] (1) An ultrasonic transducer made of a piezoelectric element, a radiation side matching layer disposed on the radiation side of the ultrasonic transducer, and a back side disposed on the back side of the ultrasonic transducer. 1. An ultrasonic transducer having either or both of a matching layer and an acoustic damper material on the outermost layer on the back side. Alternatively, the acoustic impedance of both or at least one of the back side matching layers changes continuously, and the acoustic impedance from the radiation side surface of the ultrasonic transducer to the outermost layer on the back side of the ultrasonic transducer changes as desired. An ultrasonic transducer characterized in that the ultrasonic transducer is configured to have an acoustic impedance substantially equal to an acoustic impedance of an acoustic medium that is brought into contact with the radiation side surface in a frequency band of . (2) A plurality of layers are formed on the back side of an ultrasonic transducer composed of a piezoelectric element, and the acoustic impedance when viewed from the radiation side surface of the ultrasonic transducer at the time of formation is the outermost layer on the back side. Based on the measured values, the acoustic impedance of each of the plurality of layers provided on the radiation side of the ultrasonic transducer, from the radiation side surface to the outermost layer on the back side, is in contact with the radiation side surface in a desired frequency band. 1. A method of manufacturing an ultrasonic transducer, characterized in that the acoustic impedance of the acoustic medium is selected to be substantially equal to the acoustic impedance of the acoustic medium.