JP2720731B2 - Composite piezoelectric - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite piezoelectric element used for an ultrasonic probe which is a sensor of a sonar for detecting a target in water or an ultrasonic diagnostic apparatus for diagnosing a living body.

[0002]

2. Description of the Related Art Recently, as a piezoelectric body used for an ultrasonic probe such as a sonar or an ultrasonic diagnostic apparatus for water or a living body, a so-called one in which an organic polymer is filled in a gap in which columnar piezoelectric ceramics are arranged. A −3 type composite piezoelectric body has been studied.

[0003] As such a conventional composite piezoelectric body, P
ro. IEEE, 1985, Ultrasonics
Symp. The configuration described on pages 643-647 is known. As shown in FIG.
Is formed so that a gap between columnar piezoelectric ceramics 52 having a one-dimensional connection is filled with an organic polymer 53 so as to have a three-dimensional connection and a thickness t is uniform. Have been. The composite piezoelectric body 51 thus configured has a smaller acoustic impedance than that of the ceramics alone, and can be closer to the acoustic impedance of the subject (the acoustic impedance of the living body is 1.55 to 1.65 MRayl). In addition, a large value of the electromechanical coupling coefficient can be obtained, and efficient and wide-band frequency characteristics can be obtained. Therefore, it has a feature that a high-resolution ultrasonic tomographic image can be obtained.

[0004]

However, in such a structure of the conventional composite piezoelectric material, a wider frequency band characteristic can be obtained as compared with that of the piezoelectric ceramic alone, but it is still sufficient. The fact is that we haven't been able to get it.

The present invention solves such a conventional problem, and can obtain an even wider frequency characteristic. Therefore, when used in an ultrasonic probe, an extremely short pulse response waveform can be obtained. It is an object of the present invention to provide a composite piezoelectric body which can obtain an ultrasonic image having a high depth of examination and a high resolution.

[0006]

The technical means of the present invention for achieving the above object comprises two opposing sheets provided on both sides.
Multiple columnar piezoelectrics driven by applying a voltage with electrodes
Between the body element and these columnar piezoelectric elements
And an organic polymer.
The ratio of the column thickness to the column width, which extends in the direction
The thickness of the pillars is made uneven so that
The width of the organic polymer filling the gap between the body elements
This is changed almost in proportion to the width of the electric element .

[0007]

[0008] Further, when forming a non-uniform thickness, one surface can be formed flat and the other surface can be formed into a curved surface shape, or both surfaces can be formed into different curved surface shapes, Further, the curved surface can be formed in a concave shape.

[0009]

[0010]

[0011]

[0012]

According to the present invention, a vibration mode having a frequency corresponding to each thickness of the composite piezoelectric body is generated by the above configuration, so that a wide frequency characteristic can be obtained. Thus, an extremely short pulse response waveform can be obtained.

[0013]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a main part showing a composite piezoelectric body according to an embodiment of the present invention. In Figure 1, 1 is a composite piezoelectric body, and a plurality of columnar pressure collector element 2 and the organic polymer 3. Each piezoelectric element 2 is PZT
, PbTiO3 and other piezoelectric ceramics and LiNb
It is formed in a columnar shape by a single crystal such as O3 ,
Extends in the opposite direction of the two electrodes 4 and 5 to be formed
It has a column thickness (length) and a column width . Organic polymer 3
Silicone rubber, epoxy resin, urethane resin or the like is used for this.
Are three-dimensionally filled in the gaps and are connected to each other. Then, the entire width and thickness of each piezoelectric element 2 become a constant ratio, and the whole is formed non-uniformly so that the volume ratio becomes almost the same, and the arrangement interval of the piezoelectric elements 2 and the width of the organic polymer 3 are not uniform. It is formed uniformly, one surface is formed flat, and the other surface is formed as a concave curved surface.

In order to use the composite piezoelectric body 1 constructed as described above as an ultrasonic probe, the electrodes 4 and 5 are plated, vapor-deposited, or baked on both surfaces, in the illustrated example, flat and concave surfaces. Is provided. Although not shown,
If necessary, a back load material may be provided on the surface of the electrode 4 of the composite piezoelectric body 1, and an acoustic matching layer or a protective film may be provided on the surface of the electrode 5 of the composite piezoelectric body 1. Then, by applying a voltage to the electrodes 4 and 5, the composite piezoelectric body 1 mechanically vibrates to generate ultrasonic waves having frequencies corresponding to the respective thicknesses.

The embodiment of the present invention will be described in more detail. It is already known that when the shape ratio (w / t) of the width (w) and the thickness (t) of the piezoelectric element 2 of the composite piezoelectric body 1 changes, the electromechanical coupling coefficient, that is, the frequency characteristic greatly changes. Have been. Therefore, in the embodiment of the present invention,
As shown in FIG. 1, the shape ratio (w / t) of the piezoelectric element 2 becomes substantially the same as that of the composite piezoelectric body 1 having an uneven thickness, that is, w1 / t1 = W2 /
The width of the piezoelectric element 2 is changed to w1 <w2 <w3 <... <wn so that t2 = w3 / t3... = wn / tn.

Here, when the shape ratio (w / t) of the piezoelectric element 2 in the composite piezoelectric element 1 is set to a substantially constant value, that is, when the width and the thickness of the piezoelectric element 2 are set to a constant ratio. , The width of the organic polymer 3 (G1, G2, G3... G
n) have the same width, each region (A, B, C...)
The volume ratio of the piezoelectric element 2 of N) is A <B <C <... <N. The volume ratio of the piezoelectric element 2 in the composite piezoelectric body 1 and the characteristics of the composite piezoelectric body 1, particularly the electromechanical coupling coefficient k,
The acoustic impedance Z has a relationship as shown in FIG. As is clear from the characteristics of FIG.
, The electromechanical coupling coefficient k and the acoustic impedance Z also change. It is already known that the electromechanical coupling coefficient k and the frequency characteristic have a close relationship, and that the change in the acoustic impedance Z depends on the subject, for example, a living body (where the acoustic impedance is 1. The acoustic matching condition with 55 to 1.65 MRayl) changes, and as a result, uniform ultrasonic waves cannot be generated, and the efficiency, that is, sensitivity and frequency characteristics are adversely affected.

From the above, it is desirable that the volume ratio of the piezoelectric element 2 as the composite piezoelectric body 1 be set to the same value as much as possible, and that the electromechanical coupling coefficient k and the acoustic impedance Z be constant. The configuration of the present embodiment is intended to solve such a problem and make the frequency characteristic wider.

For example, the diameter of the composite piezoelectric body 1 is 20 mm,
The radius of curvature of the curved surface is 80 mm, the thickness of the thinnest part at the center is 0.2 mm, the thickest part of the outermost part is 0.82 mm, and the shape ratio of the piezoelectric element 2 (w /
When t) is set to 0.5, the width w1 of the piezoelectric element 2 in the thin portion t1 of the composite piezoelectric body 1 is 0.1 mm, and the width wn of the piezoelectric element 2 in the thickest portion tn is 0.5. 41
mm. That is, this means that the arrangement intervals of the piezoelectric elements 2 of the composite piezoelectric body 1 are not uniform. The width of the portion having an intermediate thickness may be changed sequentially so that the shape ratio (w / t) of the piezoelectric element 2 is changed to 0.5.

When the volume ratio of the piezoelectric element 2 of the composite piezoelectric element 1 is set to 25%, the width G1 of the organic polymer 3 adjacent to the thinnest t1 part of the piezoelectric element 2 is set to 0.1 mm, and sequentially. The width of the organic polymer 3 may be changed according to the width of the piezoelectric element 2, and the width Gn of the organic polymer 3 adjacent to the thickest portion tn of the piezoelectric element 2 may be set to 0.41 mm. Accordingly, the width G1 of the organic polymer 3 in the portion where the thickness of the composite piezoelectric body 1 is small is narrow, and the width Gn of the organic polymer 3 becomes wider as the thickness of the composite piezoelectric body 1 increases.

Although only one direction is shown in FIG. 1, the structure in the direction perpendicular to the paper is basically the same as that in FIG. Therefore, actually, the configuration shown in FIG. 1 is two-dimensionally arranged.

As described above, the width G of the organic polymer 3 is similarly changed corresponding to the width w of the piezoelectric element 2. That is, since the thickness of the piezoelectric element 2 and the thickness of the organic polymer 3 are almost the same, the volume ratio can be arbitrarily changed by changing the width of the piezoelectric element 2 and the organic polymer 3.
Can be set to a constant value.

By changing the width G of the organic polymer 3 in this manner, the volume ratio of the piezoelectric element 2 of the composite piezoelectric element 1 can be made constant. Therefore, the acoustic impedance Z of each part of the composite piezoelectric body 1 can be made constant, and the electromechanical coupling coefficient k can be set to a constant value, so that a material having a wide frequency characteristic can be obtained, and the design can be improved. Becomes easier.

Further, since the ultrasonic wave emitting surface is formed in a concave shape, it has a feature that the ultrasonic beam can be focused along this shape.

Therefore, the ultrasonic probe using the composite piezoelectric body of the present invention can obtain an extremely short pulse response waveform, so that it is possible to obtain an ultrasonic image with a large depth to be examined and high resolution. it can.

In the above embodiment, the case where one surface of the composite piezoelectric body 1 is formed in a concave shape having a certain curvature has been described. In addition, both surfaces have a curved shape. Alternatively, a wide-band frequency characteristic can be obtained in the same manner, even if it is formed into a curved surface having a plurality of radii of curvature such as an aspheric surface. Further, in the above-described embodiment, the case where the shape of the composite piezoelectric body 1 is a disk is described, but in addition, it is orthogonal to the direction of an array type electrode in which the composite piezoelectric body 1 is provided with electrodes in an array. Even when the present embodiment is used in the direction, a broadband frequency characteristic can be similarly obtained.

[0027]

As described above, according to the present invention, both
Drive by applying voltage with two opposing electrodes provided on the surface
And the columnar piezoelectric elements
An organic polymer filled in the gap between the body elements,
The piezoelectric element extends in the direction opposite to the electrodes
Pillar thickness so that the ratio of pillar thickness to pillar width is almost constant
Is formed unevenly and is filled in the gap between each piezoelectric element.
The width of the polymer is approximately proportional to the width of the adjacent piezoelectric element.
Change the volume ratio of the piezoelectric element as a composite piezoelectric
Since they have the same value, it is possible to generate a vibration mode having a frequency corresponding to each thickness, and to obtain a wide frequency band characteristic corresponding to the thickness range. Therefore, when used for an ultrasonic probe, an extremely short pulse response waveform can be obtained, so that an ultrasonic image with a large depth to be examined and high resolution can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing a composite piezoelectric body according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a volume ratio of a piezoelectric element of the composite piezoelectric body, an electromechanical coupling coefficient, and an acoustic impedance.

FIG. 3 is a perspective view showing a schematic configuration of a conventional composite piezoelectric body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Composite piezoelectric substance 2 Piezoelectric element 3 Organic polymer 4 Electrode 5 Electrode

Claims (4)

(57) [Claims] A voltage is applied between two opposing electrodes provided on both surfaces.
A plurality of columnar piezoelectric elements driven by applying
Organic polymer filling the gap between these columnar piezoelectric elements
And each of the piezoelectric elements is opposed to the electrode.
The ratio of the column thickness to the column width extending in the matching direction is almost constant
The thickness of the pillars is made uneven so that
The width of the organic polymer filling the gap is
A composite piezoelectric body characterized by being changed almost in proportion to the width . Wherein a flat on one surface, a composite piezoelectric member of claim 1 Symbol placing the other surface characterized in that it is a curved surface. 3. A composite piezoelectric element of claim 1 Symbol mounting, characterized in that both sides are different curved shapes, respectively. 4. The composite piezoelectric body according to claim 2 , wherein the curved surface has a concave shape.