JPH0457599A - Composite piezoelectric body and ultrasonic probe - Google Patents

Abstract

PURPOSE:To bring an electric impedance of a composite dielectric body to a desired impedance by providing two kinds of piezoelectric bodies or over whose dielectric constant is different. CONSTITUTION:Ring electrodes 4a-4d are formed to one face of a composite piezoelectric body 1 formed by packing an organic high polymer 3 between plural piezoelectric bodies 2 and a common electrode 5 is formed on the other face. Then piezoelectric electrodes 2a-2d whose dielectric constant differs from each other are selected by bringing an electric impedance when a voltage is applied between the electrodes 4a-4d and the common electrode 5 into a desired value. In this case, the electric impedance is made almost identical by adjusting the dielectric constant of the composite piezoelectric body 1 corresponding to the area of the electrodes 4a-4d. Thus, the electric impedance of the composite piezoelectric body 1 is adjusted to a desired value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a composite piezoelectric material and an ultrasonic probe used in sensors such as sonar and ultrasonic diagnostic equipment.

Conventional technology Studies have been conducted to obtain high-resolution ultrasonic images using multi-ring type ultrasonic transducers as ultrasonic probes for sonar and ultrasonic diagnostic equipment that target water and living organisms. There is. Conventionally, as a configuration of this multi-ring type ultrasonic transducer, for example, Japanese Patent Application Laid-Open No. 61-77.4
There is one described in Publication No. 97.

Hereinafter, an ultrasonic transducer having a conventional configuration will be explained with reference to FIGS. 5(a) and 5(b). This ultrasonic transducer consists of rings arranged at equal intervals on one surface of a so-called 1-3 type composite piezoelectric body 21, which is composed of a polymer 23 such as polyurethane, in which piezoelectric ceramics 22 are arranged in a three-dimensional arrangement. shaped electrodes 24a, 24b...
24n, and a common electrode 25 is formed on the other surface. This results in an annular array type composite piezoelectric material. Furthermore, each electrode 24a, 2
Lead wires are taken out from 4b...24n, and if necessary, a back load material is provided on the electrodes 24a, 24b...24n side, and an acoustic matching layer and an acoustic lens are provided on the common electrode 25 side. However, it is not shown here.

And multiple ring type electrodes 24a, 24b...24
The voltage applied between the common electrode 25 and the electrodes 24a, 2
By giving a time difference of 4b...24n, the transmitted ultrasound beam can be focused arbitrarily over a wide area in the time axis direction, that is, in the depth direction of the subject. Therefore, by mechanically operating this ultrasonic transducer, it is possible to scan the ultrasonic beam in a fan shape and obtain a high-resolution ultrasonic image.

Problems to be Solved by the Invention However, in the above conventional example, the ring-shaped electrode 24a
, 24b, . . . , 24n are divided at equal intervals, so each electrode has a different area, with the outer electrode 24n having the largest area and decreasing toward the center. In other words, each electrode 2
The electrical impedance between the common electrodes 4a, 24b, . . . 24n and the common electrode 25 also differs. For example, the entire diameter is 20
When a non disk is divided into four at equal intervals, the area of each electrode is 19.63 m for 24a, 39° for 2.4b, 58.9 m+n for non2.4c, and 137 m for 4n.
．． 44 embryos 2, and between the electrode 4a and the outer electrode 4n,
The ratio is 1.7. Therefore, since the electrical impedance is inversely proportional to the area, there is a large difference, and even if the same voltage is applied to each of the electrode parts 4a, 4b, . Therefore,
When a voltage is applied from the transmitting circuit to each of the electrodes 4a, 4b, . 24b...24n
There is at most one of them, and the others have poor electrical impedance matching, resulting in poor conversion efficiency to ultrasonic waves. This makes it difficult to construct a good ultrasonic beam. This has the disadvantage that it creates a sound field with large side lobes, making it impossible to obtain high-resolution ultrasound images.

Therefore, the present invention is intended to solve the above-mentioned conventional problems.The purpose of the present invention is to set the electrical impedance of each electrode formed in a ring shape on a composite piezoelectric material to a desired value, and to reduce the electrical impedance. An object of the present invention is to obtain a composite piezoelectric material and an ultrasonic probe that can perform efficient transmission and reception by reducing reflections caused by mismatching.

Means for Solving the Problems The present invention has been made to achieve the above objects.
The invention of claim (1) is a composite piezoelectric body characterized by having two or more types of piezoelectric bodies having different dielectric constant values and an organic polymer material filled between each piezoelectric body. be.

The invention according to claim (2) is the composite piezoelectric material according to the invention according to claim (1), characterized in that the piezoelectric material is made of two or more types of piezoelectric materials or piezoelectric ceramics.

The invention of claim (3) is the invention of claim (1), wherein the two or more types of piezoelectric materials have a one-dimensional connection, and the organic polymer material has a three-dimensional connection. It is a piezoelectric material.

The invention of claim (4) includes a plurality of tongue-shaped electrodes provided on one surface, a common electrode provided on the other surface, two or more types of piezoelectric bodies provided between the two surfaces, and each and a composite piezoelectric material made of an organic polymer material filled between the piezoelectric materials, and the dielectric constant value of the piezoelectric material for each ring-shaped electrode is changed in accordance with the area of each ring-shaped electrode. This ultrasonic probe is characterized by:

The invention of claim (5) is an ultrasonic probe characterized in that in the invention of claim (4), the two or more types of piezoelectric bodies are piezoelectric ceramics.

The invention of claim (6) provides a plurality of ring-shaped electrodes provided on one surface, a common electrode provided on the other surface, two or more types of piezoelectric bodies provided between the two surfaces, and each piezoelectric material. a composite piezoelectric body made of an organic polymer material filled between the bodies, and the volume ratio of the piezoelectric body for each ring-shaped electrode is changed in accordance with the area of each ring-shaped electrode. This is an ultrasonic probe featuring the following.

The invention according to claim (7) is the ultrasonic probe according to the invention according to claim (6), characterized in that the piezoelectric body is a piezoelectric ceramic.

Invention of action claim (1) 7 Invention of claim (2), claim (3)
) relates to a composite piezoelectric material, and is used as a main part of the invention of claim (4) and claim (5), which relate to an ultrasonic probe.

According to the invention of claim (1), by having two or more types of piezoelectric bodies having different permittivity values, the impedance value can be set to a desired value even if the area of the electrode of each piezoelectric body is different. . The electrode may be provided separately in contact with the piezoelectric body, or the electrode may be provided at the end of the piezoelectric body.

When separate electrodes are provided, the impedance value can also be selected by selecting piezoelectric bodies connected in parallel by the electrodes. The invention of claim (2) and the claim (
The invention of claim 3) has substantially the same effect as the invention of claim (1).

In the invention of claim (4), by having a plurality of ring-shaped electrodes, a composite piezoelectric body is present for each ring-shaped electrode. Then, by changing the dielectric constant value of the piezoelectric material in accordance with the area of each ring-shaped electrode, the impedance of each ring-shaped electrode, that is, the impedance of each composite piezoelectric material, can be set to a desired value, for example, It can be an interval value. The invention of claim (5) also has substantially the same effect as the invention of claim (4). Said claims (1) to (3)
) can be used for the ultrasonic probe of the fourth and fifth inventions.

The invention of claim (6) changes the impedance of each ring-shaped electrode by changing the volume ratio of the piezoelectric material, compared to the invention of claim (5) in which the dielectric constant value of the piezoelectric material is changed. That is, the impedance of each composite piezoelectric body can be set to a desired value, for example, a path-to-line value. The invention of claim (7) also has the same effect as the invention of claim (6).

Embodiments First Embodiment Hereinafter, a first embodiment of the ultrasonic probe of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view of the ultrasonic probe of the present invention, and FIG. 2 is a sectional view thereof. A composite piezoelectric body 1 is formed by filling an organic polymer 3 such as silicone rubber, polyurethane, or epoxy resin between a plurality of columnar piezoelectric bodies 2 and the piezoelectric body 2 . Then, ring-shaped electrodes 4a, 4b, 4c, and 4d (divided into four in this embodiment) are provided at equal intervals on one surface of the composite piezoelectric body 1 by a method such as vapor deposition, baking, or plating. Composite piezoelectric material 1
The common electrode 5 is placed on the other surface of the ring-shaped electrode 4a.
, 4b, 4c, and 4d, and are divided into four composite piezoelectric bodies to form an ultrasonic probe. In order to set the electrical impedance to a desired value, for example, the same value when a voltage is applied between the ring-shaped electrodes 4a, 4b, 4c, 4d and the common electrode 5, the ring-shaped electrodes 4a, 4b, 4c,
Piezoelectric bodies 2a and 2b of the composite piezoelectric body 1 corresponding to the portion 4d
, 2c, and 2d are formed by selecting materials having different dielectric constants. For example, if a disk with a diameter of 20 mm is divided into electrodes 4 at equal intervals, each electrode 4a,
The area of 4b, 4c, and 4d is 19.63mm 39
．． 2mm2.58.9mm2, 137.44+nm2. These electrodes 4a, 4b, 4c each have a different area.
, 4d to have almost the same electrical impedance,
The dielectric constant ε of each composite piezoelectric body 1 (la, lb, lc, ld) corresponding to each electrode 4a, 4b, 4c, 4d may be adjusted. That is, for one composite piezoelectric body 1, the electrical impedance Z and the dielectric constant ε have a relationship as shown in equation (1).

Z-1/ω. co , co =ε −s/t−(
1) Here ω. is the angular frequency and ω. -2πf.

co is the capacitance of the composite piezoelectric material 1, S is the area of the electrode 4 of the composite piezoelectric material 1, and t is the thickness of the composite piezoelectric material 1 (common here)
It is.

Therefore, by adjusting the dielectric constant ε of the composite piezoelectric material 1 corresponding to the area S of each electrode 4 for the electrodes 4a, 4b, 4c, and 4d, the electrical impedance Z of each electrode 4 can be made to be approximately the same value. It becomes possible to do so. Area S of each electrode 4
As a method of changing the dielectric constant ε of the composite piezoelectric body 1 corresponding to the above, the materials of the piezoelectric bodies 2a, 2b, 2c, and 2d are selected. There are many types of PZT-based, lead titanate-based, and PCM-based piezoelectric ceramics that are normally used as the piezoelectric bodies 2a, 2b, 2c, and 2d, and the dielectric constant ε is 180 to 6.
Since it is distributed over a wide range of 000, the piezoelectric body 2a
, 2b, 2c, and 2d may be selected from these piezoelectric ceramics. For example, piezoelectric ceramics with a high dielectric constant may be used as the piezoelectric body 2a of the composite piezoelectric body 1 used for the electrode 4a having a small electrode area, and piezoelectric ceramics with a small dielectric constant may be used for the electrode 4d having a large electrode area. It turns out. Here, since the electrode 4 is divided into four parts, four types of piezoelectric bodies 2 are used. In other words, the electrodes 4a, 4b, 4c provided on the composite piezoelectric body 1
By selecting the permittivity ε of each piezoelectric body 2 of the composite piezoelectric body 1 corresponding to the portions of , 4d as a parameter, even if the areas S of the electrodes 4a, 4b, 4c, and 4d are different, the electric It becomes possible to set the impedance Z to a desired value, for example, approximately the same value.

Therefore, it is possible to adjust the electrical impedance Z of each of the ring-shaped electrodes 4a, 4b, 4c, and 4d to approximately the same or desired value using the composite piezoelectric material 1, and the electrical impedance Z of the transmission/reception system circuit or cable. Since the values can be made almost the same, efficient transmission and reception can be performed. In addition, since a desired ultrasonic sound field can be formed, the ultrasonic probe using the composite piezoelectric material of this example can efficiently form an ultrasonic field with small side lobes, and can achieve high resolution. Ultrasound images can be obtained.

In this embodiment, a case has been described in which the ring-shaped electrode 4 is divided into four parts at equal intervals, but it is clear that the same effect can be obtained even when the ring-shaped electrodes 4 are divided into four parts at unequal intervals.

In addition, in this embodiment, the case where a plurality of piezoelectric bodies 2 are provided for one ring-shaped electrode 4 has been described, but in addition, one
It is clear that similar effects can be obtained when piezoelectric ceramics are used alone for the two ring-shaped electrodes.

Further, in this example, the case where four types of piezoelectric bodies 2 of the composite piezoelectric body 1 were used was explained, but in addition to this, two types, three types, and even five or more types of piezoelectric bodies 2 of the composite piezoelectric body 1 were used. It is clear that similar effects can be obtained in other cases as well.

Second Example Hereinafter, the ultrasonic probe of the present invention will be described in detail in the third example.
This will be explained in detail with reference to the drawings. The figure is a cross-sectional view of this embodiment, in which an organic polymer 3 such as silicone rubber, polyurethane, or epoxy resin is filled between the columnar piezoelectric bodies 2 and the piezoelectric bodies 2, as in the first embodiment. A composite piezoelectric body 1 is formed. Conductive ring-shaped electrodes 4a, 4b, 4c, and 4d are provided at equal intervals on one surface of the composite piezoelectric material 1 by a method such as vapor deposition, plating, or baking, and the other surface of the composite piezoelectric material 1 is A common electrode 5 is provided in the same manner as the ring-shaped electrodes 4a, 4b, 4c, and 4d, and is divided into four composite piezoelectric bodies to form an ultrasonic probe. When a voltage is applied between the ring-shaped electrodes 4a, 4b, 4c, 4d and the common electrode 5, each ring-shaped electrode 4a, 4b, 4c, 4d
For example, each ring-shaped electrode 4a,
In order to make each electrical impedance 2 of 4b, 4c, and 4d almost the same value (Za=Zb=Zc=Zd),
Composite piezoelectric body 1 (la.

By changing the volume ratio of the piezoelectric material 2 and the organic polymer material 3 (lb, lc, ld), it is possible to change the value of the dielectric constant ε. That is, the dielectric constant ε of each composite piezoelectric body 1 can be adjusted by adjusting the volume ratio of the piezoelectric body 2 and the organic polymer 30. The dielectric constant εC of the piezoelectric body 2 has a value that is 1 to 2 orders of magnitude larger than the dielectric constant εp of the organic polymer material 3. The dielectric constant ε of the composite piezoelectric material 1 is determined by the volume ratio Vc of the piezoelectric material 2 and the organic polymer material 3, as shown in the following equation (2).
, Vp, varies approximately proportionally.

ε=vc ・ε C+vp ・ε p (VC+V
p1, 0)... (2) Here, Vc and εC are the volume ratio and dielectric constant of the piezoelectric body 2, and V
p and εp are the volume ratio and dielectric constant of the organic polymer 3.

For example, if Fuji Ceramics' PZT-based C-6 piezoelectric ceramic is used as the piezoelectric body 2 of the composite piezoelectric body 1 and epoxy resin is used as the organic polymer material 3, the volume ratio Vc of the piezoelectric body 2 and the composite piezoelectric body A dielectric constant ε of 1 has a relationship as shown in FIG. As is clear from FIG. 4, by selecting the volume ratio Vc of the piezoelectric body 2, a desired value of the dielectric constant ε can be selected. This means that the desired electrical impedance Z can be obtained by selecting the volume ratio Vc of the piezoelectric body 2 from equation (1).

When the ring-shaped electrodes 4a, 4b, 4c, 4d are equally spaced,
The outer electrode area is larger than the inner electrode area, but in order to make the electrical impedance almost the same value, the volume ratio Vc of the piezoelectric body 2 of the composite piezoelectric body 1 is decreased as the outer electrode becomes closer to the dielectric constant. It is sufficient to select such that ε is small.

For example, since the area of the ring-shaped electrode 4a is small, the volume ratio Vc of the piezoelectric material 2a (here, piezoelectric ceramic C-6) of the composite piezoelectric material 1a corresponding to the electrode 4a is determined by the dielectric constant ε
70v is the largest.

1%. Similarly, the part corresponding to the electrode 4b is 50
vo 1%, 25v at electrode 4c.

Select the volume ratio Vc of the piezoelectric body 2 of the composite piezoelectric bodies 1a, lb, lc, and 1d in each part corresponding to the electrodes 4a, 4b, 4c, and 4d, such as 1% and 10vo 1% for the electrode 4d. By doing so, each electric impedance Z
can be adjusted arbitrarily.

In this embodiment, PZT-based piezoelectric ceramics have been described as the piezoelectric body 2, but PCM-based, lead titanate-based piezoelectric ceramics, and Li
It is clear that similar effects can be obtained when a single crystal such as NbO3 is used.

In this example, a case was explained in which one type of PZT-based piezoelectric ceramic was used as the piezoelectric body 2.
It is clear that similar effects can also be obtained when two or more types of materials are used for the piezoelectric body 2.

In this embodiment, the case where the ring-shaped electrode 4 is divided at equal intervals has been described, but it is clear that the same effect can be obtained also when the ring-shaped electrode 4 is divided at unequal intervals. .

In this example, a so-called 1-3 type piezoelectric material is used as the composite piezoelectric material 1, in which the piezoelectric materials 2 are arranged one-dimensionally in a columnar manner, and the organic polymer material 3 is arranged three-dimensionally at intervals between the piezoelectric materials 2. Although the above description has been made, it is clear that similar effects can be obtained when using other types of composite piezoelectric bodies such as 0-3 type and 3-3 type.

Effects of the Invention As is clear from the above explanation, according to the invention of claim (1), the invention of claim (2), or the invention of claim (3), two or more types of dielectric constants having different values are provided. By having the piezoelectric body, the electrical impedance value of the composite piezoelectric body can be set to a desired value. If such composite piezoelectric materials are used in an ultrasonic probe configured by arranging multiple composite piezoelectric materials in a ring shape, the impedance of each composite piezoelectric material can be set to, for example, approximately the same value, improving impedance matching and improving efficiency. can perform good transmission and reception.

According to the invention of claim (4) or the invention of claim (5), the impedance of a plurality of composite piezoelectric materials constituting an ultrasonic probe is determined by the value of the dielectric constant of the piezoelectric material in each composite piezoelectric material. In the invention of claim (6) or the invention of claim (7), by changing the volume ratio of the piezoelectric body, it is possible to obtain approximately the same value and match the electrical impedance of the transmitting/receiving circuit. It is possible to improve the ultrasound conversion efficiency, form a desired ultrasound beam, and obtain a high-resolution ultrasound image.

[Brief explanation of drawings]

Fig. 1 is a front view showing one embodiment of the ultrasonic probe of the present invention, Fig. 2 is a sectional view of Fig. 1, Fig. 3 is a sectional view of another embodiment, and Fig. 4 is a composite piezoelectric probe. Figure 5(a) is a front view of a conventional composite piezoelectric material, and FIG. 5(b) is a cross-sectional view of the same figure (a). be. 1, 1a, 1b, 1c,
1 d = composite piezoelectric material, 2.2a, 2b, 2c, 2d
...-Piezoelectric substance, 3... Organic polymer material, 4a, 4b,
4c, 4d...ring-shaped electrodes, 5...common electrode. Name of agent: Patent attorney Takahaka Awano (1 person) Figure 1 Figure 6 Volume ratio of piezoelectric material Vc% Figure 5 (a)

Claims (7)

[Claims] (1) A composite piezoelectric material comprising two or more types of piezoelectric materials having different dielectric constant values and an organic polymer material filled between the piezoelectric materials. (2) The composite piezoelectric body according to claim (1), wherein the two or more types of piezoelectric bodies are piezoelectric ceramics. (3) Two or more types of piezoelectric bodies have a one-dimensional connection,
2. The composite piezoelectric material according to claim 1, wherein the organic polymer material has a three-dimensional connection. (4) a plurality of ring-shaped electrodes provided on one surface;
The ring has a common electrode provided on the other surface, and a composite piezoelectric material made of two or more types of piezoelectric materials provided between the two surfaces and an organic polymer material filled between each piezoelectric material. An ultrasonic probe characterized in that the value of the dielectric constant of the piezoelectric material for each ring-shaped electrode is changed in accordance with the area of each ring-shaped electrode. (5) The ultrasonic probe according to claim (4), wherein the two or more types of piezoelectric bodies are piezoelectric ceramics. (6) a plurality of ring-shaped electrodes provided on one surface;
The ring has a common electrode provided on the other surface, and a composite piezoelectric material made of two or more types of piezoelectric materials provided between the two surfaces and an organic polymer material filled between each piezoelectric material. An ultrasonic probe characterized in that the volume ratio of the piezoelectric material for each ring-shaped electrode is changed in accordance with the area of each ring-shaped electrode. (7) The ultrasonic probe according to claim (6), wherein the piezoelectric body is a piezoelectric ceramic.