JP2563650B2 - Composite piezoelectric body and ultrasonic probe - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite piezoelectric body and an ultrasonic probe used for sensors such as sonar and ultrasonic diagnostic equipment.

2. Description of the Related Art As an ultrasonic probe for sonar and ultrasonic diagnostic equipment for water and living organisms, studies have been conducted to obtain high resolution ultrasonic images by using a multi-ring type ultrasonic transducer. There is. Conventionally, as a structure of this multi-ring type ultrasonic transducer, for example, there is one disclosed in Japanese Patent Laid-Open No. 61-77497.

Hereinafter, an ultrasonic transformer juice having a conventional configuration will be described with reference to FIGS. 5 (a) and 5 (b). This ultrasonic transformer juice is a so-called 1-3 type composite piezoelectric device in which a plurality of columnar piezoelectric ceramics 22 are arranged with a space between each other and a polymer 23 such as polyurethane is filled between the piezoelectric ceramics 22. 24n is arranged on one surface of the body 21 at equal intervals, and the common electrode 25 is formed on the other surface. As a result, the composite piezoelectric body of the Aniura array type is formed. Further, lead wires are taken out from the respective electrodes 24a, 24b ... 24n, a back load material is provided on the side of the electrodes 24a, 24b ... 24n as necessary, and further, an acoustic matching layer, an acoustic lens are provided on the common electrode 25 side. Is provided, but it is not shown here.

Then, the multi-ring type electrodes 24a, 24b ... 24n and the common electrode
By applying a time difference to each of the electrodes 24a, 24b, ... 24n in the voltage applied between 25, the ultrasonic beam to be transmitted can be arbitrarily focused in a wide region in the time axis direction, that is, the depth direction of the subject. it can. Therefore, by mechanically operating this ultrasonic transducer, it is possible to scan the ultrasonic beam in a fan shape and obtain an ultrasonic image with high resolution.

However, in the above conventional example, the ring-shaped electrode 24a,
Since 24b ... 24n are divided at equal intervals, the respective electrode areas are different, and the area of the outer electrode 24n has the largest area, and becomes smaller toward the center.
That is, the electrical impedance between each of the electrodes 24a, 24b ... 24n and the common electrode 25 also differs due to the difference in electrode area.
For example, in the case where the whole is divided into four equidistantly diameter disks 20 mm, the area of each electrode 24a is 19.63mm ^2, 4b 3
9.2 mm ^2, 4c is 58.9mm ^2, 4n is 137.44Mm ² becomes, in the electrode 4a and the outer electrode 4n, 1: a 7 ratio. Therefore, since the electric 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 portions 4a, 4b ... 4n, the difference in the efficiency of conversion into ultrasonic waves becomes large. Therefore, when a voltage is applied to each of the electrodes 4a, 4b ... 4n from the transmitter circuit, ultrasonic waves are efficiently transmitted from the electrodes that match the electrical impedance of the transmitter / receiver circuit. It is at most one of 24a, 24b ... 24n, and the other cannot match the electrical impedance, so that the conversion efficiency to ultrasonic waves becomes poor.
Therefore, it becomes difficult to form a good ultrasonic beam. Then, the sound field has a large side lobe, and there is a drawback that a high-resolution ultrasonic image cannot be obtained.

Therefore, the present invention is to solve the above-described problems of the related art, and an object of the present invention is to set the electrical impedance of each electrode formed in a ring shape on a composite piezoelectric body to a desired value and It is to obtain a composite piezoelectric body and an ultrasonic probe that can perform efficient transmission and reception by reducing reflection due to impedance mismatching.

Means for Solving the Problems The present invention has been made to achieve the above object, and the invention of claim (1) provides two or more kinds of piezoelectric bodies having different dielectric constants, and each piezoelectric body. A composite piezoelectric body characterized by having an organic polymer material filled between them.

The invention of claim (2) is the composite piezoelectric body according to the invention of claim (1), characterized in that two or more kinds of piezoelectric bodies are piezoelectric ceramics.

The invention of claim (3) is characterized in that, in the invention of claim (1), a plurality of columnar piezoelectric bodies of two or more types are arranged, and an organic polymer material is filled between the piezoelectric bodies. It is a composite piezoelectric body.

According to the invention of claim (4), a plurality of ring-shaped electrodes provided on one surface, a common electrode provided on the other surface, two or more kinds of piezoelectric bodies provided between the both surfaces, and each piezoelectric element. And a composite piezoelectric body made of an organic polymer material filled between the bodies, and the value of the dielectric constant of the piezoelectric body for each ring-shaped electrode is changed according to the area of each ring-shaped electrode. It is an ultrasonic probe characterized by the following.

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

According to a sixth aspect of the present invention, a plurality of ring-shaped electrodes provided on one surface, a common electrode provided on the other surface, two or more kinds of piezoelectric bodies provided between the both surfaces, and each piezoelectric element. A composite piezoelectric body made of an organic polymer material filled between the bodies,
Corresponding to the area of each ring-shaped electrode, for each region of the composite piezoelectric body corresponding to each ring-shaped electrode, the volume ratio of the piezoelectric body and the organic polymer material contained in the composite piezoelectric body. The ultrasonic probe is characterized by changing the.

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

The invention of claim (1), the invention of claim (2), and the invention of claim (3) relate to a composite piezoelectric body and the invention of claim (4) relating to an ultrasonic probe, It is used for the main part of the invention of claim (5).

According to the invention of claim (1), the dielectric constants have different values.
By having more than one kind of piezoelectric body, the impedance value can be set to a desired value even if the area of the electrodes of each piezoelectric body is different. The electrodes may be provided separately in contact with the piezoelectric body, or the ends of the piezoelectric body may serve as the electrodes. When a separate electrode is provided, the impedance value can be selected by selecting a piezoelectric body connected in parallel by the electrode. The invention of claim (2) and the invention of claim (3) have substantially the same actions as the invention of claim (1).

The invention of claim (4) has a plurality of ring-shaped electrodes, so that the composite piezoelectric body exists for each ring-shaped electrode. Then, by changing the value of the dielectric constant of the piezoelectric body corresponding to the area of each ring-shaped electrode, the impedance of each ring-shaped electrode, that is, the impedance of each composite piezoelectric body to a desired value, for example, approximately Can be the same value. The invention of claim (5) has substantially the same operation as the invention of claim (4). The inventions of claims (1) to (3) can be used in the ultrasonic probe of the inventions of the fourth and fifth aspects.

The invention according to claim (6) differs from the invention according to claim (5) in that the value of the dielectric constant of the piezoelectric body is changed, and the impedance of each ring-shaped electrode is changed by changing the volume ratio of the piezoelectric body.
That is, the impedance of each composite piezoelectric body can be set to a desired value, for example, substantially the same value. The invention of claim (7) has substantially the same operation as the invention of claim (6).

First Embodiment A first embodiment of the ultrasonic probe of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a front view of an ultrasonic probe of the present invention, and FIG. 2 is a sectional view thereof. An organic polymer 3 such as silicone rubber, polyurethane, or epoxy resin is filled between a plurality of columnar piezoelectric bodies 2 and the piezoelectric body 2 to form a composite piezoelectric body 1. Then, ring-shaped electrodes 4a, 4b, 4c, 4d (in this embodiment, four divisions) are provided at equal intervals on one surface of the composite piezoelectric body 1 by a method such as vapor deposition, baking, and plating. A common electrode 5 is provided on the other surface of the composite piezoelectric body 1 in the same manner as the ring-shaped electrodes 4a, 4b, 4c, 4d, and divided into four composite piezoelectric bodies to form an ultrasonic probe. . In order to make the electric impedance when a voltage is applied between the ring-shaped electrodes 4a, 4b, 4c, 4d and the common electrode 5, respectively, a desired value, for example, the same value, the ring-shaped electrodes 4a, 4b, 4c, 4d The piezoelectric bodies 2a, 2b, 2c, 2d of the composite piezoelectric body 1 corresponding to the portions are formed by selecting materials having different dielectric constants. For example, when the electrode 4 is divided into a disk having a diameter of 20 mm at equal intervals, the electrodes 4a, 4b, 4
c, the area of ^{4d, 19.63mm 2, 39.2mm 2,} 58.9mm 2, 137.44mm 2
Becomes In order to make the electrical impedances of the electrodes 4a, 4b, 4c, 4d having different areas substantially equal to each other, the respective composite piezoelectric bodies 1 (1a, 1b, 1) corresponding to the respective electrodes 4a, 4b, 4c, 4d
The permittivity ε of c, 1d) may be adjusted. That is, with respect to one composite piezoelectric body 1, the electrical impedance Z and the dielectric constant ε have a relationship as shown in the equation (1).

Z = 1 / ω _{o co} , co _o = ε · s / t (1) where ω _o is the angular frequency, and ω _o = 2πf. c _o is the capacitance of the composite piezoelectric transducer 1, S is the area of the electrode 4 composite piezoelectric transducer 1, t is the thickness of the composite piezoelectric transducer 1 (common here).

Therefore, by adjusting the dielectric constant ε of the composite piezoelectric body 1 corresponding to the area S of each electrode 4 with respect to the electrodes 4a, 4b, 4c, 4d, the electrical impedance Z of each electrode 4 is made approximately the same value. It becomes possible. As a method of changing the dielectric ε of the composite piezoelectric body 1 corresponding to the area S of each electrode 4, the piezoelectric body 2
Select a, 2b, 2c, 2d materials. Usually, piezoelectric bodies 2a, 2b, 2c, 2
There are many types of PZT-based, lead titanate-based, and PCM-based piezoelectric ceramics used as d, and the dielectric constants ε are distributed in a wide range of 180 to 6000. , 2c and 2d may be selected from these piezoelectric ceramics. For example, an electrode with a small electrode area
As the piezoelectric body 2a of the composite piezoelectric body 1 used for 4a, piezoelectric ceramics having a large dielectric constant ε may be used, and conversely, for the electrode 4d having a large electrode area, piezoelectric ceramics having a small dielectric constant may be used. Here, since the electrode 4 is divided into four, four types of piezoelectric bodies 2 are used. In other words, by selecting the dielectric constant ε of each piezoelectric body 2 of the composite piezoelectric body 1 corresponding to the portions of the electrodes 4a, 4b, 4c, 4d provided on the composite piezoelectric body 1 as a parameter, 4b,
Even if there is a difference between the areas S of 4c and 4d, the electric impedance Z can be set to a desired value, for example, substantially the same value.

Therefore, it becomes possible to adjust the electrical impedance Z of each of the ring-shaped electrodes 4a, 4b, 4c, 4d to substantially the same value or a desired value by the composite piezoelectric body 1, and the electrical impedance Z of the transmission / reception system circuit or the cable can be adjusted. Since the value can be almost the same, efficient transmission / reception can be performed. In addition, since a desired ultrasonic sound field can be formed, the ultrasonic probe using the composite piezoelectric body of the present embodiment can efficiently form an ultrasonic sound field with a small side lobe, and An ultrasonic image with high resolution can be obtained.

In the present embodiment, the case where the ring-shaped electrode 4 is divided into four at equal intervals has been described, but it is clear that the same effect can be obtained when the ring-shaped electrodes 4 are not equally spaced.

In addition, in the present embodiment, the case where a plurality of piezoelectric bodies 2 are provided for one ring-shaped electrode 4 has been described, but the same applies to the case where a single piezoelectric ceramic is used for one ring-shaped electrode. It is clear that the effect can be obtained.

Further, in the present embodiment, the case where four types of the piezoelectric body 2 of the composite piezoelectric body 1 are used has been described.
It is obvious that the same effect can be obtained when two types, three types, and more than five types of the piezoelectric body 2 are used.

Second Embodiment Hereinafter, an ultrasonic probe of the present invention will be described in detail with respect to a second embodiment with reference to FIG. The figure is a cross-sectional view of the present embodiment. Similar to the first embodiment, a columnar piezoelectric body 2 and an organic polymer 3 such as silicone rubber, polyurethane, or epoxy resin are filled between the piezoelectric bodies 2. Composite piezoelectric body 1
To form. Then, the ring-shaped electrodes 4a, 4b, 4c, 4d of the conductor are provided at equal intervals on one surface of the composite piezoelectric body 1 by a method such as vapor deposition, plating, baking or the like.
The common electrode 5 is provided on the other surface of the ring-shaped electrodes 4a, 4b,
The ultrasonic probe is provided by the same method as in 4c and 4d and divided into four composite piezoelectric bodies. The ring-shaped electrodes 4a, 4b, 4c, 4
When a voltage is applied between the d and the common electrode 5, for example, the ring electrodes 4a, 4b, 4c, 4d are used to set the electric impedances Za, Zb, Zc, Zd of the ring electrodes 4a, 4b, 4c, 4d to desired values. ,Four
In order to make the electric impedances Z of b, 4c, and 4d almost the same (Za = Zb = Zc = Zd), each ring-shaped electrode 4
Composite piezoelectric body 1 (1a, 1b, 1c, 1 corresponding to a, 4b, 4c, 4d part
It is possible to change the value of the dielectric constant ε by changing the volume ratio of the piezoelectric body 2 and the organic polymer material 3 in d). That is, the dielectric constant ε of each composite piezoelectric body 1 can be adjusted by the volume ratio of the piezoelectric body 2 and the organic polymer 3. The dielectric constant εc of the piezoelectric body 2 has a value larger than the dielectric constant εp of the organic polymer material 3 by 1 to 2 digits or more. The permittivity ε of the composite piezoelectric body 1 changes substantially in proportion to the volume ratio Vc, Vp of the piezoelectric body 2 and the organic polymer material 3 as shown in the following formula (2).

ε = Vc · εc + Vp · εp (Vc + Vp = 1.0) (2) where Vc and εC are the volume ratio of the piezoelectric body 2, the dielectric constant, and Vp, ε.
p is the volume ratio and the dielectric constant of the organic polymer 3.

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

When the ring-shaped electrodes 4a, 4b, 4c, 4d are equidistant, the outer electrode area is larger than the inner electrode area. The volume ratio Vc of the piezoelectric body 2 of No. 1 may be reduced to select the dielectric constant ε.

For example, the volume ratio Vc of the piezoelectric body 2a (here, the piezoelectric ceramics C-6) of the composite piezoelectric body 1a corresponding to the portion of the electrode 4a is 70 vol% where the dielectric constant ε is large because the area of the ring-shaped electrode 4a is small. And Similarly, the portion corresponding to the electrode 4b is 50 vol%, the electrode 4c is 25 vol%, the electrode 4d is 10 vol%, and so on.
Piezoelectric body 2 of composite piezoelectric bodies 1a, 1b, 1c, 1d corresponding to 4d
It is possible to arbitrarily adjust each electric impedance Z by selecting the volume ratio Vc.

In the present embodiment, the PZT-based piezoelectric ceramics have been described as the piezoelectric body 2, but other piezoelectric bodies 2 may be PCM-based, lead cyanate-based piezoelectric ceramics and LiNbO 2.
It is clear that the same effect can be obtained when a single crystal such as ₃ is used.

In this embodiment, the case where one type of PZT-based piezoelectric ceramic is used as the piezoelectric body 2 has been described.
Besides, it is apparent that the same effect can be obtained when two or more kinds of materials are used as 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 obvious that the same effect can be obtained when the ring-shaped electrode 4 is disassembled at unequal intervals. .

In this embodiment, as the composite piezoelectric body 1, a plurality of columnar piezoelectric bodies 2 having a one-dimensional connection are arranged with a space between each other, and an organic polymer material having a three-dimensional connection between the piezoelectric bodies 2. The case of using a so-called 1-3 type composite piezoelectric body having a structure filled with 3 has been described, but in addition to this, a 0-3 type or a three-dimensional structure in which granular piezoelectric bodies are dispersed in an organic polymer material. It is clear that the same effect can be obtained also when a composite piezoelectric body such as a 3-3 type in which an organic polymer material is filled between piezoelectric bodies formed in a typical mesh state is used.

EFFECTS OF THE INVENTION As is apparent from the above description, according to the invention of claim (1), the invention of claim (2), or the invention of claim (3), two or more types having different values of dielectric constants are used. By including the piezoelectric body, the electric impedance value of the composite piezoelectric body can be set to a desired value. If such a composite piezoelectric body is used in an ultrasonic probe configured by arranging it in a plurality of rings, the impedance of each composite piezoelectric body can be made to be, for example, approximately the same value, and impedance matching is improved and efficiency is improved. Good transmission and reception.

Further, according to the invention of claim (4) or the invention of claim (5), the impedance of the plurality of composite piezoelectric bodies forming the ultrasonic probe is determined by the value of the dielectric constant of the piezoelectric body in each composite piezoelectric body. In the invention according to claim (6) or the invention according to claim (7), the volume ratio of the piezoelectric body is similarly changed to obtain substantially the same value, and the electrical impedance of the transmission / reception circuit is matched. Therefore, the conversion efficiency of ultrasonic waves can be improved, a desired ultrasonic beam can be formed, and an ultrasonic image with high resolution can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing an embodiment of an ultrasonic probe of the present invention, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a sectional view of another embodiment. FIG. 4 is a diagram showing the relationship between the dielectric constant of the composite piezoelectric body and the volume ratio of the piezoelectric body, FIG. 5 (a) is a front view of a conventional composite piezoelectric body, and FIG. 5 (b) is the same figure. It is sectional drawing of (a). 1,1a, 1b, 1c, 1d …… Composite piezoelectric body, 2,2a, 2b, 2c, 2d …… Piezoelectric body, 3 …… Organic polymer material, 4a, 4b, 4c, 4d …… Ring-shaped electrode 5 ... Common electrode.

Continuation of the front page (56) Reference JP-A-1-120998 (JP, A) JP-A-3-270282 (JP, A) JP-A-3-270597 (JP, A) JP-A-3-92141 (JP , A) JP-B 64-10998 (JP, B2)

Claims (7)

(57) [Claims] 1. A composite piezoelectric body comprising: two or more types of piezoelectric bodies having different values of inductivity; and an organic polymer material filled between the piezoelectric bodies. 2. The composite piezoelectric body according to claim 1, wherein the two or more types of piezoelectric bodies are piezoelectric ceramics. 3. A composite piezoelectric body according to claim 1, wherein a plurality of columnar piezoelectric bodies are arranged with a space between each other, and an organic polymer material is filled between the respective piezoelectric bodies. 4. A plurality of ring-shaped electrodes provided on one surface, a common electrode provided on the other surface, and two or more types of piezoelectric bodies provided between the two surfaces, and between each piezoelectric body. And a composite piezoelectric body made of an organic polymer material filled in a ring shape, wherein the value of the dielectric constant of the piezoelectric body for each ring-shaped electrode is changed according to the area of each ring-shaped electrode. And ultrasonic probe. 5. The ultrasonic probe according to claim 4, wherein the two or more kinds of piezoelectric bodies are piezoelectric ceramics. 6. A plurality of ring-shaped electrodes provided on one surface, a common electrode provided on the other surface, and two or more kinds of piezoelectric bodies provided between the both surfaces and between each piezoelectric body. And a composite piezoelectric body made of an organic polymer material filled in each of the ring-shaped electrodes corresponding to the area of each ring-shaped electrode. An ultrasonic probe characterized in that the volume ratio of the piezoelectric material and the organic polymer material contained in is changed. 7. The ultrasonic probe according to claim 6, wherein the piezoelectric body is a piezoelectric ceramic.