JPS5821994B2 - Ultrasonic conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and transducer for generating or detecting ultrasound waves used in an ultrasound device, and more particularly to a method and transducer for generating or detecting parallel beam ultrasound waves.

Even if the medium is optically opaque, as long as it is acoustically transparent, it is possible to observe a transparent image using sound waves in the same way as using X-rays.

Ultrasonic imaging of optically opaque objects can be applied to the fields of medical diagnosis, microscopy, nondestructive testing, observation of ocean floor patterns, and earthquake research.

Conventional ultrasonic transducers that use an acoustic phase plate, an annular array, an acoustic lens, a photo-acoustic transducer, and the like have been proposed.

However, the reality is that there is still room for improvement in terms of the characteristics of the sound waves necessary for ultrasound imaging.

Further, although conventional transducers are based on the premise of converging an excited ultrasonic beam, even a parallel beam that does not converge can be sufficiently utilized for acoustic imaging by moving the beam.

Conventional devices of this type emit a parallel beam using a combination of multiple transducer elements that vibrate in bulk, and at the same time, signal processing technology is used to move the transducer to which electrical signals are applied, thereby emitting sound from the sound source. The parallel beam is moved in the X-axis direction.

However, in this conventional method, a technique is used to mechanically cut and divide a single piece of piezoelectric material to create a transducer consisting of a large number of elements, so there are problems with manufacturing reproducibility and The upper limit of frequencies used was restricted.

Therefore, an object of the present invention is to improve the above-mentioned drawbacks of the prior art, and its characteristics are that a piezoelectric material having an interdigital electrode on one surface is installed so that the electrode is in contact with a liquid, and the interdigital electrode is , has a structure in which a plurality of sets of comb tooth-like electrodes having a plurality of parallel elongated electrode fingers are arranged, and the electrode fingers of each comb tooth-like electrode are arranged in an alternately overlapping manner, and the electrodes are applied or induced. In the method of converting an alternating current signal and an ultrasonic wave, the electrode period of the interdigital electrode is uniform, an alternating current electrical signal is selectively applied to the interdigital electrode, and a selected electrode finger is connected to the electrode finger. An ultrasonic conversion method in which an ultrasonic beam is emitted from an interdigital electrode in a predetermined direction and moves horizontally in time by sequentially moving along an array of interdigital electrodes, and an ultrasonic detection method based on the same principle. It is in.

The details will be explained below with reference to the drawings. FIG. 1 shows an example of the structure of a focused ultrasound transducer according to the present invention, in which a liquid 2 is provided in a container 1, and interdigital electrodes (sometimes called interdigital electrodes) are disposed on the surface of the liquid.
A piezoelectric material 3 having 4 is produced.

Possible liquids include water, ether, acetone, glycerin, etc.

The electrode 4 consists of a single-phase electrode, which has comb-shaped electrodes arranged in an interdigital manner alternately, as shown in FIG. A three-phase electrode that connects every third digitally configured electrode and applies a three-phase AC signal from terminals ai, bi, and ci, or similarly connects every nth electrode (n is a natural number of 4 or more) to each other. A multi-phase electrode is possible, which is connected to the N-phase AC signal to apply an n-phase AC signal.

In the case of a single-phase electrode, two ultrasonic beams are generated in both directions (solid line and dotted line in FIG. 1), whereas in the case of a three-phase electrode, one ultrasonic beam in a single direction is obtained.

As for the material of the electrode, for example, a combination of Cr and Au has good water resistance and strong water resistance.The electrode is formed on the piezoelectric plate by photolithography, or by vapor deposition through a mask formed by photolithography. You can make money.

Piezoelectric materials include L1Nb03, crystal, and B i12.
G e 02 .

. Possible materials include PZT-based porcelain (for example, 91A material manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd.).

The relationship between the period d of the electrode and the direction θ of the maximum output of the ultrasonic beam is determined by sin θ = λf/d (λf is the ultrasonic wave f
is the wavelength of a sound wave in a liquid).

From this equation, it can be seen that if the electrode period d is made uniform, a parallel ultrasonic beam in the direction of the angle θ can be obtained from the interdigital electrode.

It can also be seen that by changing the frequency, the radiation direction θ changes.

Next, the experimental results of the beam radiation angle θ for each combination of piezoelectric material and liquid are shown in the following table.

From this table, it can be seen that in order to reduce the value of θ, it is sufficient to combine a liquid with a low acoustic wave velocity and a piezoelectric body with a high surface wave propagation velocity.

FIG. 3A shows the time relationship of application of an AC signal to the electrode in the case of the single-phase electrode of FIG.
As shown in FIG. 3A, alternating current signals are sequentially and selectively applied to 3t....

Therefore, the ultrasonic beam generated from the electrode temporally moves in the X-axis direction.

As a circuit for applying such an alternating current signal, for example, each tap of a tapped delay line is connected to electrode a1. a2 +
It is possible to correspond to a3 t...

FIG. 3B shows the voltages applied to the three-phase electrodes of FIG. 2B.

Electrodes ai, b placed every third electrode! , ci have the same frequency AC signals with a phase difference of 120° from each other.
The AC voltage is applied sequentially as shown in Figure B, and at a certain moment in time, the AC voltage is applied to only three electrodes as shown by diagonal lines in the figure.

Although Fig. 2A shows a configuration in which three pairs of electrodes constitute one section, if the electrodes are not made into fixed sections and the connection terminals with the signal processing taps are connected in a 1:1 ratio, a more precise X Axial beam shifting is possible.

As an experimental example of the present invention, a piezoelectric ceramic 91A material manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd. (polarized perpendicular to the substrate surface, length 70 mm, width 201 Lm, thickness 6 m11 L) was coated with an electrode period of 8.
It was observed that a good collimated sound beam was emitted by providing interdigital electrodes with a width of 56 μm/electrode overlap IQms, bringing water as a liquid into contact with the electrodes, and applying a high-frequency pulse electric signal.

At the same time, when the carrier frequency of the high-frequency pulse was changed, the direction θ of the acoustic beam from the transducer was changed as shown in FIG.

Therefore, by changing the frequency, the direction of the acoustic beam can be electrically changed.

As described in detail in the embodiments above, by applying a high frequency signal to interdigital electrodes having a uniform period while sequentially switching the electrodes, it is possible to generate an ultrasonic beam in which the beam moves in parallel.

In addition, although the above embodiment mainly describes the generation of ultrasonic waves, the same structure can also be used to detect ultrasonic waves and obtain a corresponding alternating current signal.

[Brief explanation of drawings]

FIG. 1 is an example of the structure of an ultrasonic generation (detection) device according to the present invention, FIGS. 2A and 2B are examples of the structure of interdigital electrodes, and FIG.
Figures A and 3B are time relationship diagrams of alternating current signals applied to the interdigital electrodes, and Figure 4 is a graph showing the frequency and beam direction applied to the interdigital electrodes. 1; container; 2; liquid; 3; piezoelectric material; 4; interdigital electrode.

Claims (1)

[Claims] 1. A piezoelectric material having an interdigital electrode on one surface is installed so that the electrode is in contact with a liquid, and the interdigital electrode has a comb-like shape having a plurality of parallel, elongated electrode fingers. It has a structure in which a plurality of electrodes are provided and the electrode fingers of the tooth-shaped electrodes of each comb are arranged in an alternately overlapping manner,
In the method of converting an alternating current signal applied or induced to an electrode into an ultrasonic wave, the electrode period of the interdigital electrode is uniform, the alternating current electric signal is selectively applied to the interdigital electrode, and the selected An ultrasonic conversion method characterized by generating an ultrasonic beam emitted from an interdigital electrode in a predetermined direction and moving in parallel in time by sequentially moving electrode fingers along an array of electrode fingers. 2. The ultrasonic conversion method according to claim 1, wherein the radiation direction of the ultrasonic beam is changed by changing the frequency of the AC electric signal.