JPS60197099A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To obtain a ultrasonic wave of 10-200mHz with high performance by receiving and transmitting a ultrasonic wave on an electrode surface of a polariized piezoelectric body obtained by impressing a voltage between adjacent electrodes and by making the piezoelectric body under electrode into a body for absorbing a ultrasonic wave. CONSTITUTION:An electrode 6 is formed on a ceramic 5 in such a manner that corrosion-resistant metals such as Au and Ni are deposited or spattered, because the electrode 6 is immersed in a ultrasonic wave propagating medium 7 and exposed in steam in air. When a voltage is impressed on the electrode 6, the produced ultrasonic wave propagates the ceramic 5 and the medium 7, while a ultrasonic wave for propagating the medium 7 reaches a body 8 to be measured, and is reflected or transmitted after obtaining of information of the object to be measured. On the other hand, a ultrasonic wave for propagating the ceramic 5 is reflected at end face 9, whereby unwanted waves are produced. This can be prevented if a length L of the ceramic 5 is selected so that a ultrasonic wave will be attenuated in propagation and will turn out to be negligible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the configuration of a probe for an apparatus that uses ultrasonic waves to measure the internal structure and physical properties of an object to be measured.

[Background of the invention]

Recently, devices such as medical ultrasonic diagnostic equipment and ultrasound microscopes that transmit ultrasonic waves of several MHz to several 100 MHz to a measured object, receive reflected waves or transmitted waves, and examine the inside of the object in detail have become significantly more popular. Progress is being made.

Conventionally, the electroacoustic transducers, or probes, used in these devices utilize the thickness expansion and contraction vibration of a piezoelectric material, so there are restrictions on the frequency of use based on the manufacturing method of the piezoelectric material. It was getting worse. That is, assuming that the sound velocity in the thickness direction is v (m/s) and the thickness of the piezoelectric body is 1 (m), the fundamental co-grip frequency f (Hz) is expressed by the following equation.

'O-v/(2t) Since ceramics are usually used in medical diagnostic equipment and it is difficult to reduce the thickness to about 200 μm or less, f is the height of 10 MHz.

However, V = 4000 m/s. However, for use in endoscopes or ophthalmology, the frequency has become even higher.
There is a strong desire for high-resolution diagnosis, and improvements have been desired. On the other hand, in ultrasonic microscopes, on the contrary, a piezoelectric semiconductor such as ZnO is grown on a lens matrix made of sapphire or the like by sputtering, so only extremely thin lenses can be produced, and the resonant frequency is 100 MHz.
It was only used in higher-level areas. However, if ultrasonic waves of about 10 MHz to 200 MHz are used, it is possible to reduce attenuation in the ultrasonic propagation medium as well as attenuation inside the sample. It can be expected to have a wide range of applications in various fields.

[Purpose of the invention]

The present invention was made in view of these points, and its purpose is to provide a high-performance probe that can be used in the ultrasonic band from 10 MHz to several 1100 MHz and uses ceramic itself as an unnecessary ultrasonic absorber. It is in.

Vero. FIG. 1 shows a cross section of a ceramic and, by way of example, an interdigital electrode formed thereon. Lead wires 1 and 2 are alternately connected to electrodes 4 on ceramics 3. Unlike ordinary surface acoustic wave elements, this ceramic is polarized by applying a voltage between lead wires 1 and 2, so the degree of polarization is strongest below the electrodes and gradually weakens as you move away from the electrodes. It has become. The direction is shown by the arrow. Once the ceramic has been polarized in this way, the voltage for ultrasonic excitation is applied to the lead wires 1 and 2.
When applied between the electrodes, the polarization direction and the applied voltage direction match for the area under the electrodes, so they all expand and contract in the same phase.
Vertical imaging occurs in the thickness direction. However, in the region between the electrodes, the directions of polarization are alternately opposite, so the lateral vibrations cancel each other out and become extremely small. It can be seen that for the above reasons, longitudinal thickness vibration mainly occurs. In this case, the polarized region does not have clear boundaries and exhibits non-resonant characteristics. Therefore, since the resonant frequency f (Hz) of such a probe depends on the change in electrical impedance accompanying lateral imaging, the period of the electrode is J (m), and the sound velocity in the lateral direction is v (m/s). ) is given by the following formula.

f = v / l In the case of ceramics, it is about V-4000 m / s, and the period of the electrode can be miniaturized to about 1 μm using photolithography or X-ray phosphorography, so f = IG
Hz. In reality, the particle size of ceramics is 0.5 μm.
Therefore, J = 5 μm is considered to be the limit at present, and in this case f = 400 MHz. It goes without saying that this value naturally increases as the particle size becomes smaller.

Now, when the frequency increases, if the ultrasonic wave is emitted from the back of the electrode, the internal loss of the ceramic itself causes the ultrasonic wave generated under the electrode to attenuate while propagating through the ceramic, resulting in a significant deterioration in sensitivity. Another disadvantage is that at low frequencies, unnecessary signals are generated due to internal multiple reflections.

Therefore, by using a construction method in which the electrode surface is used as the ultrasonic emission surface and the ceramic under the electrode is used as the backing material, the above-mentioned drawbacks were solved and a high-performance probe was achieved.This will be explained below with reference to examples. .

[Embodiments of the invention]

FIG. 2 shows an embodiment of the present invention, and shows the structure of a probe for an ultrasound microscope. Forming an electrode 6 on the ceramic 5,
The same polarization treatment as in FIG. 1 was performed. Since the electrode 6 is not only immersed in the ultrasonic propagation medium 7 but also exposed to water vapor in the air, it is formed by vapor deposition or sputtering of a corrosion-resistant metal such as Au or Nl. However, if the electrode surface is covered with a protective film by sputtering glass or the like, a metal such as AJ may be used. Now, when voltage is applied to electrode 6,
The generated ultrasonic waves propagate through 5 and 7.

The ultrasonic wave propagating through 7 reaches the object to be measured 8, obtains information about 8, and is reflected or transmitted. Although this n is a useful ultrasonic component, on the other hand, the ultrasonic wave propagating through 5 reaches 6 again after being reflected by end face 9, which is not preferable because it generates an unnecessary signal. However, if the length L (m) of the ceramic 5 is selected so that the ultrasonic waves attenuate during propagation and can be sufficiently ignored, no unnecessary signals will be generated. Figure 3 is a diagram showing the relationship between propagation loss and frequency for lead titanate with a particle size of 1 μm. Attenuation of 0.1 dB/crIL was obtained at 10 MHz, and the amount of attenuation is almost the same as the frequency. It can be seen that it increases in proportion to the square of the square. Furthermore, it is known that the amount of attenuation is proportional to the cube of the grain size, so for example, if ceramics with a grain size of 5 μm and a thickness of 2 mm are used, it is possible to achieve a round trip attenuation of 5 QdB at 10 MHz. , unnecessary reflected waves from the end face can be almost ignored. The thickness and type of ceramic may be selected depending on the required amount of attenuation.

Note that the dotted line in FIG. 2 indicates the ultrasonic propagation region.

The electrode shapes are as shown in Fig. 4 (a), (b), (
In addition to the shape shown in C), a combination of these shapes can be considered.

In FIG. 4, 10 and 11 represent electrodes, and 12 represents ceramics.

FIG. 5 shows another embodiment of the present invention, and shows a probe having a structure in which the electrode surface has a curvature so that ultrasonic waves are focused. A lens 14 is created on the ceramic 13, and an electrode 1 is placed on it.
5 is formed. The generated ultrasonic waves are focused as shown by the dotted line in the figure and reach the object to be measured 16. The electrodes can be formed as follows. A thin metal film is formed on the entire concave surface of the ceramic by vapor deposition or sputtering, and then a resist is applied, and then electrodes of arbitrary shapes are baked into the optical system shown in FIG. That is, light source 1
The light from 7 is converted into parallel light by a lens 18, passes through a mask 19, is condensed by a condenser lens 20, and forms an image on a ceramic surface 21. The shape of the electrode is determined by the mask 19. Here, since the ceramic surface has a curvature, it is necessary that the mask also have the same curve.

After the electrodes are baked in this manner, they are etched, and a Fresnel zone plate is used as the electrode in the configuration example shown unnecessarily to focus the ultrasonic waves.

Although FIG. 7(b) shows an ideal intensity distribution of polarization, in reality, polarization may be performed by binarizing as shown in FIG. 7(C).

Note that the polarization intensity distribution To(x) in FIG. 7(b) is To(
x) = O+Ac0''' (kx2/Zo). However, 0 is the DC component, k is the wave number, and ZO is the distance to the focal point. The term width Δ may be selected as shown in the following equation.

Note that in the electrodes shown here, since the distance between the electrodes becomes narrower toward the ends, it is necessary to polarize each adjacent ring.

FIG. 8 shows another embodiment of the present invention, in which ceramics 22
A plurality of electrodes 23 are arranged side by side on the top. As the shape of the electrode, those shown in FIG. 2, FIG. 5, and FIG. 7 can be used. By using a probe in which a plurality of electrodes are formed in this manner, information from many areas can be obtained in a short period of time, so that the measurement speed can be increased.

〔Effect of the invention〕

As described above, the present invention enables the detection of frequencies that are difficult to obtain with probes of conventional configurations (for example, 10 MHz to 200 MHz).
) can obtain high-performance ultrasonic waves.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the operation of the ceramics used in the present invention, Figure 2 is a diagram showing an example of the present invention, Figure 3 is a diagram showing the relationship between attenuation and frequency, and Figure 4 is a diagram showing the relationship between attenuation and frequency. FIG. 5 is a diagram showing another embodiment of the present invention; FIG. 6 is a diagram showing an optical system for baking the electrode; FIG. 7(a)
7(b) and 7(b) are diagrams showing other embodiments of the present invention.
FIG. 8C is a diagram showing the polarization intensity, and FIG. 8 is a diagram showing another embodiment of the present invention. Agent Patent attorney Katsuo Ogawa l So: + 2 Tatsukyo tM/4z);J-4'@2 (6) Ya 5 Figure! Deya 6 Figure + 7 Figure 10B Continuation of concave 1st page @ Inventor Kageyoshi Katakura Kuniyoshi” Minoru Gakuo Research Institute

Claims (1)

[Claims] 1. Transmission and reception of ultrasonic waves across the electrode surface of a piezoelectric material that has inter-digital electrodes, concentric annular electrodes, or a combination of these electrodes and is polarized by applying a voltage between adjacent electrodes. and an ultrasonic probe in which the piezoelectric body under the electrode is an ultrasonic absorber. 2. The probe according to claim 1 of the utility model registration, characterized in that the electrode surface has a curvature. 3. The probe according to claim 1, wherein the concentric annular electrode has a Fresnel zone plate shape.