JPH0118639B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is applicable to a device that transmits ultrasonic waves to an object to be measured, receives reflected waves or transmitted waves, and measures the internal structure and physical properties of the object to be measured. The present invention relates to the configuration of an ultrasonic probe.

[Background of the invention]

Recently, it has become possible to examine the inside of living organisms or objects in detail using ultrasonic waves of several MHz to several 100 MHz using medical ultrasound diagnostic equipment and ultrasound microscopes. Among these, the probes conventionally used in the former type of diagnostic equipment use thickness stretching vibrations of PZT (lead zirconate titanate) ceramics, PbTiO ₃ (lead titanate) ceramics, etc., so the resonant frequency is low. is almost determined by the thickness of the piezoelectric material, and its upper limit is said to be around 10MHz. However, there is a strong desire to increase the frequency and diagnose living organisms with higher resolution, and improvements have been essential. on the other hand,
In the latter type of ultrasound microscope, on the other hand, piezoelectric semiconductors such as ZnO are grown on a lens base material made of sapphire or the like by sputtering, so only extremely thin products can be produced, and the frequency is also low.
Only frequencies above 100MHz are widely used. However, if ultrasonic waves of several tens of MHz to 200 MHz are used, the attenuation inside the sample is relatively small and the configuration of the device is simple, making it possible to apply it to a wide range of fields that do not require high resolution, such as biological samples.

[Purpose of the invention]

The present invention has been made in view of these points,
The purpose is to provide a high-performance probe that can be used in the ultrasonic band from about 10 KHz to several 100 MHz, and in which the piezoelectric body itself doubles as an acoustic lens.

[Summary of the invention]

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 connected to electrodes 4 on ceramics 3.
are connected alternately. This ceramics is
Unlike ordinary surface acoustic wave elements, lead wires 1,
Since polarization is achieved by applying a voltage between the electrodes, the degree of polarization is strongest below the electrodes and becomes weaker as the distance from the electrodes increases. Its direction is indicated by arrow _A1 . Therefore, the directions of polarization under adjacent electrodes are perpendicular to the electrodes and opposite to each other, while those between the electrodes are polarized parallel to the electrodes, and these are also in opposite directions like the under polarization. When a voltage is applied between the lead wires 1 and 2 of such a piezoelectric material, the direction of polarization and the direction of the applied voltage match exactly in the region under the electrode, so they all expand and contract in the same phase, causing thickness vibration. arise. However, in the region between the electrodes, the direction of polarization and the direction of the applied voltage are the same, and the directions of polarization are opposite to each other, so the lateral vibrations of adjacent regions cancel each other out and become extremely small.

It can be seen that for the above reasons, mainly thickness vibration (indicated by arrow _A2 in the figure) occurs. In addition,
Since the polarized region is not clearly partitioned, it exhibits non-resonant characteristics with respect to thickness vibration. Therefore, the resonant frequency of such a probe is determined not by the mechanical natural vibration of the thickness method, but by the change in electrical impedance associated with lateral vibration (indicated by arrow A ₃ in the figure). Therefore, it essentially has excellent pulse response characteristics in the thickness direction.
The resonance frequency is determined by the period l of the electrode and the velocity of sound in the lateral direction v
It is expressed as =v/l. In the case of ceramics, v=4000 m/s. Currently, the electrode period can be reduced to about 1 μm using photolithography or X-ray lithography, but
Since the particle size of ceramics is also about the same, a period of about 5 μm is the limit for obtaining uniform electrodes.
The resonant frequency at this time is 400MHz. but,
If the particle size is made finer, it can be used in even higher frequency bands.

Even if a probe has such excellent characteristics, if an acoustic lens is attached to the front surface like conventional ceramics, the characteristics cannot be fully utilized.

For example, consider attaching an acoustic lens to the side of ceramics that contacts the object to be measured. Frequency 15M
Hz, and ECCOBOND24, a low-viscosity epoxy adhesive manufactured by Emerson & Cumming, was used as the adhesive. Since the speed of sound is approximately 2000 m/s, in order for the adhesive layer to be sufficiently ignored, it must be less than 1/10 wavelength, that is, 13 μm. It is not easy to produce such an adhesive layer uniformly and without leaving any bubbles. Needless to say, as the frequency increases, the difficulty increases.

However, it has been discovered that if ceramics itself is used as an acoustic lens, these problems can be resolved and a construction method that can fully bring out the above-mentioned characteristics can be achieved. That is, an area that generates ultrasonic waves,
If the lens that focuses the ultrasonic waves is formed in the same ceramic matrix, there will be no acoustic mismatch inside the probe, and excellent pulse response characteristics can be obtained.

[Embodiments of the invention]

This will be explained below with reference to Examples.

FIG. 2 shows an example of a probe for an ultrasonic microscope as an embodiment of the present invention. A metal electrode 6 made of Cr, Au, Al, or the like was formed on the ceramic piezoelectric body 5 by vapor deposition or plating, and a voltage was applied between the electrodes to polarize the electrode. Polarization voltage is 40-70kV/cm,
A suitable polarization temperature is about 100 to 170°C. Note that the distance between the lens 7 and the electrode 6 is usually selected to be approximately a ² /λ.

Here, λ represents the wavelength, and a represents the effective radius of the electrode region. The side surface 8 of the probe is preferably roughened to avoid unnecessary reflected waves from this surface. With this configuration, when a voltage is applied to the electrode 6, the ultrasonic waves generated in the polarized region immediately below the electrode 6 propagate through the ceramics 5 and reach the lens 7.
The light is focused by the dotted line in FIG. 2 to form a focal point. During wave reception, on the contrary, when an ultrasonic wave is incident, a voltage is generated in the electrode 6.

As for the shape of the electrode, in addition to the shapes shown in FIG. 3a, b, and c, various combinations of these shapes can be considered. however,
3 is a diagram showing electrodes 9 and 10 formed on ceramics 3. FIG.

FIG. 4 shows another embodiment of the present invention, and shows an example of a probe used in a diagnostic device or the like. An electrode 12 was formed on the ceramic 11, and the same treatment as in the embodiment shown in FIG. 2 was performed. It is inserted into body cavities such as the stomach or rectum for the purpose of taking high-resolution images of internal organs.
The frequency of the probes used until now is at most
Although the frequency is approximately 10 MHz, the frequency can be further increased in the configuration example shown in FIG. Furthermore, since backing is not required, a small and lightweight probe is obtained, which is suitable for insertion into body cavities. Of course, lens 13
On the front of the oscillator, 1/
A four-wavelength acoustic matching layer can also be formed. This probe can be used not only for insertion into a body cavity but also for ordinary diagnostic equipment.

FIG. 5 shows another embodiment of the invention. A plurality of lenses 16 are formed on ceramics 14, and electrodes 15 are formed directly below them. If such a probe is used in an ultrasonic microscope, a wide measurement area can be assigned to each lens, and the measurement time can be extremely shortened. Moreover, with ZnO, which has been used up until now, it is difficult to create resonators with uniform performance over a wide area, whereas with ceramics, it is possible to suppress the variation to less than 0.1% even in large areas of several centimeters. is not very difficult. Therefore, it becomes possible to measure a wide range of samples.

〔Effect of the invention〕

As described above, according to the present invention, the pulse response characteristics are excellent over the band from 10 KHz to several 100 MHz, and
A probe with stable characteristics can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an electrode and the polarization state immediately below the electrode for explaining the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing a probe according to the present invention. FIG. 4 is a diagram showing the shape of the electrode used, FIG. 4 is a diagram showing another embodiment of the present invention used in a diagnostic device, and FIG. 5 is a diagram showing another embodiment of the present invention.

Claims (1)

[Claims] 1. An inter-digital electrode, a plurality of concentric annular electrodes, or a combination of these electrodes are provided on one surface, and a region is polarized by applying a voltage between adjacent electrodes. An ultrasonic probe comprising a piezoelectric material, wherein at least a portion of the other surface of the piezoelectric material is curved so that the piezoelectric material itself functions as an acoustic lens. 2. The ultrasonic probe according to claim 1, wherein the piezoelectric body has a roughened side surface.