JPS59138948A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To suppress the heat generation of an ultrasonic probe and to detect information on the inside of a living body with high sensitivity by forming a high acoustic impedance member and piezoelectric ceramic whose thickness are about one fourth as large as wavelengths at their operation frequencies. CONSTITUTION:The plate type acoustic impedance member 15 is provided between the piezoelectric ceramic 11 and a packing material 12. Then, the thickness of the piezoelectric ceramic 11 and high acoustic impedance member 15 are one fourth as large as the wavelengths of ultrasonic waves of their operation frequency. Consequently, the electric power is consumed almost entirely for effective ultrasonic radiation to a subject.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an ultrasonic probe that generates ultrasonic waves into a medium by electrically driving a piezoelectric ceramic.

[Technical background of the invention]

In a medical ultrasonic diagnostic device or an ultrasonic flaw detector, an ultrasonic probe emits ultrasonic waves into a subject, and the reflected sound waves from inside the subject are detected again by the ultrasonic probe. At this time, as the intensity of the emitted ultrasonic wave increases, the reflected signal increases in proportion to the intensity, and more information inside the subject can be obtained.

However, when the intensity of the emitted ultrasonic waves is increased, the temperature of the ultrasonic probe increases due to acoustic loss or electrical loss within the ultrasonic probe.
There are problems, such as the high temperature making it inappropriate to contact the object and deteriorating the performance of the ultrasonic probe. For example, in the case of medical ultrasound diagnostic equipment, ultrasound waves are attenuated by living tissue, so the further the distance from the living body's surface, the lower the intensity of the echoing ultrasound waves, eventually reaching the level of noise. Put it away. For this reason, how deep information can be obtained depends on the excitation voltage applied to the ultrasound probe, and the thicker the excitation voltage, the deeper information can be obtained inside the living body. Become.

However, when the excitation voltage is increased in this way, acoustic and electrical losses within the ultrasonic probe turn into heat, causing the entire temperature of the ultrasonic probe to rise. If the surface temperature of the ultrasound probe becomes much higher than the human body's body temperature, it not only gives the subject a sense of anxiety, but also causes minor burns if it is fixed in the same area for a long time. Therefore, in practice, it is desirable to keep the surface temperature of the ultrasonic probe below 140°C.

Therefore, it is possible to reduce the various losses within the ultrasonic probe that cause such temperature rises, suppress the temperature rise due to heat generation to below 40℃, and obtain information from deep inside the living body. We are looking for an excellent ultrasonic probe.

[Problems with background technology]

In ultrasonic diagnostic equipment and ultrasonic flaw detectors, the resolution in the direction in which ultrasonic waves propagate (distance resolution) is determined by the length of the ultrasonic pulse, and the shorter the pulse, the better the root resolution. In order to realize short ultrasonic pulses, a conventional ultrasonic probe has a backing material 2 placed on the back side of a piezoelectric ceramic 1, as shown in FIG. u, one or more acoustic matching layers 6 for achieving acoustic matching with the subject, and an acoustic lens 4 for focusing the entire ultrasonic wave.

Generally, the closer the acoustic impedance value of the backing material 2 is to the acoustic impedance of the piezoelectric ceramic 1, the more
・The pulse width of the emitted ultrasonic waves becomes shorter and the distance resolution improves. The ultrasonic waves radiated to the backing material 2 are reflected by the back surface of the banking material 2, and the piezoelectric ceramic 1
When Vc is reached, the signal becomes unnecessary, so the heart wall condition is that the backing material 2 has a large propagation attenuation so that it absorbs all of the ultrasonic waves.

In many ultrasound diagnostic devices currently on the market,
As a piezoelectric material, the acoustic impedance is 60 to 35
I Q@Kf/m2・S piezoelectric ceramic material and the backing material 2 have an acoustic impedance of 5 to 10.
A combination of 106 Kg/m2° is used.

There are roughly two causes of heat generation in such an ultrasonic probe. One of these is electrical loss due to the dielectric loss of the ceramic material, and the other is due to the mechanism in which the ultrasonic waves once emitted are attenuated and converted to heat.
That is, it is an acoustic loss.

FIG. 2(α)(b) shows the characteristics of an ultrasound probe conventionally generally used in ultrasound diagnostic equipment.
FIG. 2 (α) shows the frequency characteristics of the human conductance, and FIG. 2 Cb) shows the frequency dependence of the voltage pulse that drives the ultrasonic probe.

When the ultrasound probe is left in the air, the power consumption P of the ultrasound probe is . Here, G(f) is the input conductance of the ultrasonic probe of 5 V (f> is the frequency spectrum of the driving voltage.

The double hatched area in FIG. 2 (α) is the conductance component due to the dielectric loss of the ceramic material, that is, the acoustic radiation conductance. As can be seen from this Figure 2 (α),
Most of the power consumed within an ultrasound probe is used to generate sound waves. That is, in the conventional ultrasonic probe shown in FIG. 1, radiation is emitted not only to the subject but also to the backing material 2. Therefore, in the combination of the piezoelectric ceramic 1, which is a piezoelectric material, and the backing material 2, the sound waves radiated to the backing material 2 are thicker than the sound waves radiated to the subject. This backing material 2
The radiation of sound waves into the air is a major cause of heat generation.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic probe capable of suppressing heat generation of the ultrasonic probe and detecting in-vivo information with high sensitivity.

[Summary of the invention]

To achieve the above object, the US invention provides an ultrasonic probe in which a backing material is provided on one side of a piezoelectric ceramic, which is a piezoelectric material, and an acoustic matching layer and an acoustic lens are provided on the other side. A high acoustic impedance section made of a material with high acoustic impedance such as metal or ceramic is provided between them, and the thickness of each of the high acoustic impedance member of the bracket and the piezoelectric ceramic is approximately 1/4 of the wavelength of the operating frequency at the operating frequency. It is characterized in that almost all the power consumption km is consumed for effectively emitting ultrasonic waves to the specimen.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a side view of the present invention, in which 11 is a piezoelectric ceramic, 12 is a backing material, 16 is an acoustic matching, 14 is an acoustic lens, and the piezoelectric ceramic 11 and the backing material 12 are shown in FIG.
A plate-shaped acoustic impedance member 15 is provided between them.

In such a configuration, the thickness of the piezoelectric ceramic 11 and the acoustic impedance member 15 are each formed to be 1/4 vc of the wavelength of the ultrasonic wave at the operating frequency.

Next, the features of this configuration will be explained in comparison with the conventional ultrasonic probe shown in FIG.

Thickness t of piezoelectric ceramic 1 in the conventional configuration shown in FIG.
is the frequency at which ultrasonic waves are effectively emitted, ie, the operating frequency f. When λ0 1 −− = − fo 2 . Here, υ is the sound velocity of the piezoelectric ceramic 1, and λ0 is the wavelength at the operating frequency foVc.

In contrast to the VC, in the present invention, the high acoustic impedance member 15 is formed to have a thickness tl, and the piezoelectric ceramic 11 is formed to have a thickness t2.

Here vl+υ2. λ′o1. λ'02 is the sound velocity in the high acoustic impedance member 15 and the piezoelectric ceramic 11, respectively;
This is the wavelength at the operating frequency f'o.

In this way, the thickness ffi of the high acoustic impedance member 15
By setting '++thickness of piezoelectric ceramic 11'frlz, the acoustic impedance seen from the piezoelectric ceramic 11 toward the high acoustic impedance member 15 becomes very sharp at the operating frequency f'oVC. Therefore, these end faces become nodes of vibration and hardly move. That is, the radiation of ultrasonic waves from the piezoelectric ceramic 11 toward the backing side becomes extremely small, and most of the ultrasonic waves from the piezoelectric ceramic 11 are radiated toward the subject side. The existence of such a vibration mode is known as λ/4 drive of a piezoelectric material.

However, piezoelectric ceramic 1 in ultrasound probe
Regarding No. 1, there has been no study on adaptation of λ/4 drive. The reason for this will be explained with reference to FIGS. 4 and 5. That is, Fig. 4 (α), Cb) shows the frequency response characteristics of a conventional ultrasonic probe, and computer simulation results showing the transmitting and receiving pulse waveforms excited by impulse voltage. ) are simulation results showing the frequency response characteristics of the present invention and transmission/reception pulses excited by an impulse voltage. In this simulation, a ceramic having the same acoustic impedance as the piezoelectric ceramic is used as the high impedance member.

Comparing all of Fig. 4.5, the frequency response characteristic of Fig. 5 (α), that is, the frequency band of the present invention is slightly narrower. You can see that it is a little longer.

That is, in the case of the present invention, the effective frequency band is a little narrow V% and the waveform of the excited ultrasonic pulse is a little long, resulting in a slightly inferior distance resolution.
In other words, it seems that research into the present invention was not conducted.

However, such a problem hardly becomes a practical problem as explained based on FIG. 4.5. Rather, the advantage of being able to suppress heat generation is far greater.

In the present invention, a high acoustic impedance member 15 is provided between the piezoelectric ceramic 11 and the backing material 12, and the thickness of each of the high acoustic impedance members 15 and the left piezoelectric ceramic 11 is formed to be 1/4 of the wavelength λ at the operating frequency. , almost all the power consumption can be used for effective ultrasonic radiation to the temporary specimen.

Therefore, in the present invention, it is possible to exceed all the conventional operating limits due to heat generation, and it is possible to obtain better overall high sensitivity characteristics.

In the embodiment shown in FIG. 3, the backing material 12 is arranged, but the acoustic impedance condition of the backing material 12 is such that the high acoustic impedance member 15
It only needs to be sufficiently small compared to the current, and in extreme cases, it may be air. Further, although the embodiment shown in FIG. 3 shows a single acoustic matching layer 16, it is of course possible to use a multilayer acoustic matching layer having two or more layers.

FIG. 6 shows a so-called array-type ultrasonic probe that uses a large number of micro-oscillators arrayed. A backing material 22 is provided on one side, and a small strip-shaped acoustic matching layer 2 is provided on the other side of the piezoelectric ceramic 21.
In the array type ultrasonic probe in which the acoustic lens 24 is provided on the acoustic matching layer 26 and the piezoelectric ceramic 21 is placed in close contact with each other, a small rectangular high acoustic impedance member 25 is provided between the piezoelectric ceramic 21 and the backing material 22. The thickness of the valleys of the acoustic impedance member 25 and the piezoelectric ceramic 21 is formed to be 1/4 of the wavelength of the operating frequency.

〔Effect of the invention〕

As explained above, a high acoustic impedance member is provided between the piezoelectric ceramic and the backing material, and the thickness of the high acoustic impedance member and the piezoelectric ceramic is set to 174 of the wavelength λ of the operating frequency, that is, λ/4. Therefore, the power consumed by the ultrasonic probe can be effectively used to excite ultrasonic waves to the subject. Therefore, the ultrasonic probe generates heat due to the radiation of sound waves to the conventional backing material, for example, at an upper limit of 40 degrees Celsius, and can be driven at a high voltage that exceeds the performance of conventional structures, providing an ultrasonic probe with overall high sensitivity. can do. In addition, it is possible to provide an ultrasonic probe with comprehensive high sensitivity characteristics when obtaining information on the deep parts of a living body or detecting extremely weak signals such as blood flow Doppler signals.

[Brief explanation of the drawing]

Figure 1 is a side view of a conventional ultrasonic probe, Figure 2 is a characteristic diagram of Shibago's ultrasonic probe, and (α) is a frequency -
Figure 6 shows a human conductance characteristic diagram, Figure 6 shows a frequency spectrum characteristic diagram, Figure 6 shows a side view of the ultrasonic probe of the present invention, and Figure 4 shows the characteristics of a conventional ultrasound probe. Figure (α) shows a frequency response characteristic diagram, Figure (b) shows a transmission/reception pulse waveform diagram, Figure 5 shows the characteristics of the ultrasonic probe of the present invention, and Figure (α) shows a frequency response characteristic diagram. , Cb) of the same figure is a diagram of transmission and reception pulse waveforms, and FIG. 6 is a perspective view of an array type ultrasonic probe which is another embodiment of the present invention. 1.11.21...Piezoelectric ceramic, 2,12
゜22゜1. Backing material, 3.13.23...
acoustic matching layer, 4,14.24...acoustic lens,
15°25...High acoustic impedance member. Agent Patent attorney Kensuke Chika (1m or 1 person) Haq
La leather hand J (/-BHz 12 1 piece 111
314 Funeral 4 Zu Shu 1 Reibu (Ml-h) (b) ~0. S@C (G) FE'EF! U (Hm) (b)

Claims (3)

[Claims] (1) In an ultrasonic probe in which an acoustic matching layer is provided on one side of the piezoelectric ceramic, a high acoustic impedance member is provided on the other side of the piezoelectric ceramic, and the thickness of the high acoustic impedance member and the piezoelectric ceramic is 1. An ultrasonic probe characterized in that each waveform is approximately 1/4 K of a wavelength at an operating frequency. (2) The piezoelectric ceramic, the acoustic matching layer, and the high acoustic impedance member are each formed into minute pieces, and the minute pieces are brought into close contact with each other to be integrated. ultrasonic probe. (3) The ultrasonic probe according to claim 1 or 2, wherein the acoustic matching layer is composed of a plurality of layers.