JPS5929816B2 - ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a probe for a non-destructive testing device, an ultrasonic diagnostic device, etc. that uses ultrasonic waves, and in particular, it simultaneously solves the conventional disadvantages of high loss and narrow bandwidth. The purpose is to solve the problem.

FIG. 1 shows the configuration of a typical conventional probe.

In the figure, 1 is a piezoelectric plate, 2 is an electrode, 3 is a matching plate such as a quarter wavelength plate, 4 is a back load generally called a damper, and 5 is a lead wire. Examples of the piezoelectric plate 1 include piezoelectric ceramics such as PZT, quartz, and piezoelectric crystals such as LiNbO3. Matching layer 3 and damper 4
A common example is a resin such as epoxy mixed with an appropriate amount of tungsten powder. Next, an example of the use of the conventional probe will be explained based on FIG. In the figure, 21 is the probe shown in FIG. 1, 22 is a test object such as a human body, 23 is a high-frequency pulse oscillation source, 24 is a high-frequency receiver,
25 is a signal indicator. The high-frequency pulse 26 generated by the high-frequency pulse oscillation source 23 is converted into an ultrasonic wave by the probe 21, becomes an ultrasonic pulse 2T, travels through the object 22, hits the object 28, and becomes a reflected pulse. 29. This reflected pulse 29 is again converted into a high frequency pulse by the probe 21, which is detected by the high frequency receiver 24, subjected to appropriate signal processing, and then displayed by the signal display 25. Used for searching for various internal information.
In order to improve contact between the probe 21 and the subject 22, a lubricating substance 211 such as oil is interposed between the probe 21 and the subject 22. The disadvantages of the conventional non-destructive inspection apparatus using the probe described in FIGS. 1 and 2 will be described below.

The first drawback is the high loss of conventional probes. The reason for this large loss is roughly due to two causes. The first is that, in FIG. 1, the sound waves generated by the piezoelectric plate 1 are directed not only toward the subject but also toward the damper 4. That is, a considerable amount of the generated sound waves is consumed by the damper 4. The second cause is poor electrical matching conditions of the piezoelectric plate 1.
That is, the high frequency signal is not well absorbed by the piezoelectric plate 1. The second drawback is the poor high frequency response characteristics of the conventional probe, in other words, the narrow frequency bandwidth of the probe 21.

This is due to poor electrical matching conditions of the piezoelectric plate 1 and poor characteristics of the damper 4 and matching layer 3. In order to eliminate the first drawback, the acoustic impedance of the damper layer 4 can be lowered or removed, but this will worsen the frequency characteristics of the probe, which will lead to the second drawback. Increasingly.

The first drawback will be specifically explained using the frequency characteristics of the transducer gain (hereinafter referred to as T.G.).

Changes in frequency characteristics of transducer gain (hereinafter referred to as T.G.) are used as the best representation of the characteristics of the probe.

T. G. is a conversion gain that indicates how efficiently the electric power supplied as input can be converted into sound waves and supplied into the subject.
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This is explained on page 2 of the January 1969 issue of S0nics magazine, so detailed explanation will be omitted here. In FIG. 3, a curve 31 shows a piezoelectric plate 1 with a coupling coefficient of 0.5 and an acoustic impedance of 30.3×105 CGS, and a w powder so that the acoustic impedance becomes the geometric mean value of that of the subject and the piezoelectric plate 1. 1/ made by mixing and adjusting epoxy resin
T. of the probe consisting of a four-wavelength matching layer 3 and a damper 4. G. This is the frequency characteristic of

In order to improve the matching between the probe and the electrical system, an inductance and a resistance are connected in parallel. In the figure, FO is the anti-resonance frequency of the piezoelectric plate 1, and f is the frequency of the high-frequency pulse applied to the probe. As can be seen from this characteristic diagram, the gain of the probe always exists at least about -7DB,
Moreover, when the frequency bandwidth is widened, the gain further deteriorates.

That is, improvement in gain and improvement in frequency bandwidth cannot be achieved at the same time. This tendency is not limited to the above-mentioned example, but the same can be said for other general cases.

That is, in the conventional probe, a considerable amount of input is absorbed by the damper layer 4, resulting in a large loss. In addition to the above, in reality,
Many more problems arise.

Among them, the major problem is the materials of the matching layer 3 and damper 4. The damper layer 4 and mating layer 3 that have been used in the past are both made by mixing tungsten powder into synthetic resin and solidifying it. Because it takes time for the synthetic resin to solidify, it is difficult to mix the tungsten powder uniformly. As a result, non-uniformity occurs in the quality of the finished material. As a result of this, the loss of the probe further increases. A second drawback, frequency bandwidth, which is also related to the first drawback mentioned above, again requires a suitable homogeneous matching layer and damper.

In addition to this, the material constants of the piezoelectric body itself become a problem. What is particularly important is that the electromechanical coupling coefficient be large and the dielectric constant be appropriate.
For two- and three-component piezoelectric ceramics such as plates, there was no one with a particularly appropriate dielectric constant. The present invention eliminates these drawbacks, and the embodiment shown in FIG. 4 will be described in detail.

In FIG. 4, a piezoelectric plate 41 is made of a piezoelectric ceramic material whose dielectric constant value matches the electrical impedance of the probe well with the impedance of the circuit system.

Examples of such piezoelectric ceramics include PbTiO3 as shown in Japanese Patent Laid-Open No. 48-30097.
Ceramics are used. The piezoelectric plate 41 has a resonant structure due to x wavelength thickness longitudinal vibration, the surface is parallel polished, and a metal electrode 42 of Au, A9, Ni, Al, etc. is formed thereon by plating or vapor deposition. A matching layer 43 is made of a material having an acoustic impedance value close to the geometric mean value of the acoustic impedances of the piezoelectric plate 41 and the load 45.

This material is AS2S3 glass plate or Ges2
A glass plate or the like is preferably used, and a glass plate polished to have a surface shape approximately the same as that of the piezoelectric plate 41 and a thickness of 1/4 wavelength is used. The acoustic impedance of AS2S3 glass is 8.
3X105c9s, the acoustic impedance of GeS2 is 7
．． 0x105c9s, which is approximately equal to the geometric mean value of the acoustic impedance of the aforementioned PbTiO3 ceramic and a load such as the human body. After shaping the aforementioned piezoelectric plate 41 and matching layer 43 to a predetermined size and thickness, they are acoustically adhered with chalcogen glass containing sulfur, and lead wires 44 are attached to form a probe. .

In the probe according to the present invention having such a structure, the matching layer 43 is not a mixture of powder and resin as in the conventional example, but is a glass body having a uniform structure. Therefore, the uniformity of the material is good, the material constant always takes a constant value, and as long as the thickness is accurate, an ideal matching layer can always be obtained, so a damper layer is not necessary. Without the damper layer, all of the sound waves generated by the piezoelectric plate 41 would proceed toward the load, that is, the object 45. Therefore, the loss due to the damper layer (as shown by curve 31 in Figure 3), as in the conventional probe, would be reduced. Ba7
(more than dB) is eliminated, and the sensitivity of the probe is greatly improved.

Curves 32 and 33 in FIG. 3 indicate the T.I. of such a probe according to the invention. G. This is the frequency characteristic of A curve 32 is a characteristic diagram when AS2S3 is used as the matching layer 43, and a curve 33 is a characteristic diagram when Ges2 is used as the matching layer 43. Note that when the clamping capacity of the piezoelectric plate 41 is CO, 1/
2πFOCO=1. As can be seen from curves 32 and 33, regardless of whether AS2S3 or Ges2 is used as the matching layer 43, T. G. The value of is 0
．． The average difference between 7f0 and 1.2f0 is about -1 dB, which is extremely large compared to conventional probes.

Moreover, the bandwidth is very wide, 3 dB wide and about 0.6 f0.
As described above, the probe of the present invention has a high electromechanical coupling coefficient and an appropriate dielectric constant value of the ceramic used, and eliminates the loss caused by the damper caused by the conventional structure, resulting in high efficiency and wide band. , it becomes possible to produce high-sensitivity characteristics with a relatively simple configuration.

INDUSTRIAL APPLICABILITY The present invention is extremely useful for non-destructive testing and ultrasonic diagnosis used on the human body.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the configuration of a conventional probe, Figure 2 is a block diagram showing an example of how the probe is used, and Figure 3 is a diagram showing the gain frequency characteristics of the present invention and the conventional probe. , FIG. 4 is a sectional view showing the structure of a probe in an embodiment of the present invention. 41... Piezoelectric plate, 42... Electrode, 43
. . . Matching layer, 44 . . . Lead wire, 45 . . . Load (subject).

Claims (1)

[Claims] 1. A flat plate of a material having an acoustic impedance close to the geometric mean value of the acoustic impedance of the piezoelectric plate and the subject is adhered to one surface of the piezoelectric plate via a metal electrode, and a flat plate of a material having an acoustic impedance close to the geometric mean value of the acoustic impedance of the piezoelectric plate and the subject is bonded to the other surface of the piezoelectric plate. An ultrasonic probe characterized by forming a metal electrode. 2. The ultrasonic probe according to claim 1, wherein the flat plate is made of chalcogen glass containing sulfur.