JPH05153696A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To improve focusability of an ultrasonic wave, and also, to suppress a side beam level, and to widen a frequency band characteristic by forming a composite piezoelectric vibrator to the concave surface, and constituting the ultrasonic probe so that thickness of an acoustic matching layer becomes thinner toward the peripheral part, and thickness of a first ultrasonic propagation material body becomes thicker toward the periphery. CONSTITUTION:A composite piezoelectric vibrator 8 is constituted by cutting and separating piezoelectric ceramics like a die, and filling a cut groove with a high polymer material, and the concave surface of a prescribed curvature is formed in the (z) direction on the (xz) surface. By forming the vibrator 8 like the concave surface, an ultrasonic beam on the (xz) surface can be focused to a distance corresponding to its curvature. As for an acoustic matching layer 9, the vibrator 8 side, and the side of a body Q to be examined are formed to the convex surface and a plane, respectively on the (xz) surface. The matching layer 9 radiates efficiently an ultrasonic wave, and also, receives efficiently a reflected echo. As for a first ultrasonic propagation material body 10, a material having prescribed ultrasonic attenuation is used. Also, by constituting the surface of the side of the body Q to be examined in a concave surface shape, a side lobe of an ultrasonic radiation directional characteristic on the (xz) surface can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe such as an ultrasonic diagnostic apparatus which suppresses side lobes to a low level and focuses an ultrasonic beam having a wide range of ultrasonic frequency characteristics.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing the structure of an ultrasonic probe used in a conventional and generally used ultrasonic diagnostic apparatus. As shown in the figure, the ultrasonic probe has a plurality of strip-shaped piezoelectric vibrators 2 _i (i = 1, 2, 3, ...
Are arranged in parallel in the y direction, the first and second acoustic matching layers 3 and 4 are formed on the ultrasonic wave emitting surface of the piezoelectric vibrator, and the acoustic matching layer 4 and the subject Q are covered with each other. The acoustic lens 5 having an ultrasonic wave propagation speed slower than that of the sample Q and made of a substance such as silicon rubber is formed in a convex shape on the xz plane orthogonal to the array of the piezoelectric vibrators 2 _i . , Which is orthogonal to the y direction in which the piezoelectric vibrators are arranged by utilizing the difference in the propagation speed of ultrasonic waves between the acoustic lens 5 and the subject Q.
Ultrasonic diagnosis is performed by focusing the ultrasonic beam on the z-plane.

[0003]

However, in the configuration of the conventional ultrasonic probe described above, the side lobe level rises due to the attenuation of the ultrasonic signal in the acoustic lens 5, and
Due to the frequency band characteristic, a decrease in the gain of high frequency components occurs.

That is, generally, the side lobe in the ultrasonic probe is determined by the opening of the piezoelectric vibrator 2 _i , and the sound pressure at the center of the surface is controlled by controlling the voltage applied to the opening or changing the radiation area. The side lobe level is reduced by increasing the height and decreasing toward the periphery.

In the ultrasonic probe as shown in FIG. 6, the thickness of the acoustic lens 5 is xz which is orthogonal to the arrangement direction y of the piezoelectric vibrators 2 _i.
In terms of surface, the central portion of the opening is thicker and thinner toward the peripheral portion, so that the sound pressure increases from the central portion to the peripheral portion due to the ultrasonic wave propagation attenuation caused by the acoustic lens 5. Since the lobe level increases and the attenuation characteristic increases in proportion to the frequency of the ultrasonic wave, there is a drawback that the gain of the high frequency component is reduced due to the frequency band characteristic.

The drawbacks of the ultrasonic probe as described above are that the resolution is lowered and the pseudo echo is generated, the ultrasonic diagnostic image is remarkably deteriorated, and it causes a misdiagnosis.

The present invention solves the problems of the conventional ultrasonic probe as described above, focuses the ultrasonic beam on a predetermined position, suppresses the side beam level, and has a wide frequency band characteristic. The purpose is to provide an ultrasonic probe.

[0008]

The present invention comprises a piezoelectric ceramic and a polymer material, slit electrodes are arranged on one surface and a common electrode is formed on the other surface. A composite piezoelectric vibrator formed in a concave shape in the ultrasonic wave emitting direction in a plane orthogonal to each other, in contact with the surface in the ultrasonic wave emitting direction, the surface is formed in a convex shape, and the surface on the subject side is formed in a flat surface. And a first acoustic matching layer having a predetermined ultrasonic attenuation characteristic, which is in contact with the plane of the acoustic matching layer and whose surface on the side of the subject is concave on the surface orthogonal to the arrangement direction of the strip electrodes. The ultrasonic wave propagating material body and a surface in contact with the first ultrasonic wave propagating material body are formed in a convex shape in a plane orthogonal to the array direction of the slit-shaped electrodes, and the ultrasonic attenuation is almost zero. It is characterized by being composed of ultrasonic wave propagation material body. To.

[0009]

According to the present invention, since the ultrasonic beam is focused to a predetermined depth by the concave surface of the composite piezoelectric vibrator, and the thickness of the acoustic matching layer is thin from the central portion to the peripheral portion in the ultrasonic radiation direction, The band characteristic is broadened, and the deterioration of the image quality due to the decrease of the high frequency component is suppressed to the minimum.

Further, since the first ultrasonic wave propagating material body is made thicker from the central portion in the ultrasonic wave radiating direction toward the peripheral portion to form a large attenuation, the sound pressure is higher toward the central portion and accordingly lower toward the peripheral portion. The deterioration of the resolution of the ultrasonic image,
Sidelobe output that causes pseudo echo is suppressed.

Since the second ultrasonic wave propagating material body having almost no ultrasonic attenuation is provided between the first ultrasonic wave propagating material body and the object, the object to be inspected without impairing the frequency band characteristic. The contact with is improved.

Further, since the acoustic impedances of the ultrasonic wave propagating material body and the subject are made substantially equal, the reflection of the ultrasonic wave generated at the boundary between the two bodies is reduced to efficiently focus the ultrasonic wave in the subject. It is possible.

[0013]

FIG. 1 is a perspective view showing the structure of an ultrasonic probe according to an embodiment of the present invention.
In addition (in the Z direction in the drawing), slit-shaped electrodes 7 _i (i = 1, 2, 3 ...) Are formed in the y direction on one surface made of piezoelectric ceramics for voltage-acoustic conversion and a polymer material. The electrodes are arranged and a common electrode is formed on the other surface, and a concave surface (ultrasonic wave emission) is formed in the ultrasonic wave emission direction (z direction) on the xz plane orthogonal to the arrangement direction (y direction) of the slit electrodes 7 _i. A composite piezoelectric vibrator 8 having a surface), and an acoustic matching layer 9 having a surface on the composite piezoelectric vibrator 8 side that is a convex surface on the xz plane on the ultrasonic wave emitting surface and whose surface on the subject Q side is a flat surface. A first ultrasonic propagation material body 10 having a concave surface on the subject Q side on the subject Q side and having a predetermined ultrasonic attenuation, and a first ultrasonic propagation material body 10 provided on the subject Q side; The surface of the ultrasonic wave propagating material body 1 of 1 is a convex surface, and the ultrasonic wave attenuation is constituted by the second ultrasonic wave propagating material body 11 of almost zero. To have.

Here, the composite piezoelectric vibrator 8 is composed of a one-component piezoelectric ceramic PbTiO ₃ , a two-component piezoelectric ceramic PbZrO ₃ -PbTiO ₃ , and a three-component piezoelectric ceramic P.
b (Mg1 / 3Nb2 / 3) O ₃ --PbZrO ₃ --PbTiO ₃ etc. are cut and separated in a die shape with a predetermined width-to-thickness ratio, and the cutting groove is filled with a polymer material such as epoxy resin. And
A concave surface having a predetermined radius of curvature is formed in the z direction on the xz surface.

FIG. 2 is a characteristic diagram showing the acoustic impedance of the above-described composite piezoelectric vibrator. The acoustic impedance (vertical axis) of the composite piezoelectric vibrator 8 changes depending on the volume ratio of the piezoelectric ceramics and the polymer material (horizontal axis). However, it is desirable to bring the acoustic impedance close to the acoustic impedance of the subject Q without lowering the piezoelectric characteristics.
10 to 15 MRayl is used.

Since the composite piezoelectric vibrator 8 has flexibility, it is easy to form the above radius of curvature into a predetermined concave surface. As described above, by forming the composite piezoelectric vibrator 8 in a concave shape, it is possible to focus the ultrasonic beam on the xz plane at a distance corresponding to the radius of curvature thereof.

For the acoustic matching layer 9, a material obtained by mixing a metal powder such as tungsten with a polymer material such as epoxy resin or vinyl chloride in a predetermined ratio is brought into close contact with the ultrasonic wave emitting surface of the composite piezoelectric vibrator 8. In the xz plane, the one in which the composite piezoelectric vibrator 8 side is formed as a convex surface and the subject Q side is formed as a flat surface is used.

FIG. 3 is a diagram showing the acoustic impedance characteristics of the acoustic matching layer 9 and shows that the acoustic impedance changes depending on the mixing ratio of tungsten.
Figures (a) and (b) show the acoustic impedance (vertical axis) with respect to the mixing weight ratio of epoxy resin and tungsten to vinyl chloride (horizontal axis), respectively.

As described above, the acoustic impedance of the acoustic matching layer 9 changes depending on the mixing ratio of the metal powder to the polymer material, and in the present invention, the mixing ratio is set to the composite piezoelectric vibrator 8 and the subject Q. It is selected as an intermediate value of the acoustic impedance value.

Since the acoustic impedance material composed of the above polymer material and metal powder has fluidity, it is relatively easy to form it into various shapes.

The acoustic matching layer 9 thus constructed can efficiently radiate ultrasonic waves to the subject Q and also efficiently receive reflected echoes from the subject Q.

It is generally considered that it is desirable that the thickness t _n of the acoustic matching layer 9 be set to λ / 4 where λ is the wavelength of the ultrasonic wave, and the ultrasonic frequency f and the sound velocity v _{n of the} acoustic matching layer 9 are set.
Therefore, λ can be obtained by the equation 1.

[0023]

## EQU1 ## λ = v _n / f Further, the relation between the thickness t _n of the acoustic matching layer 9 and the ultrasonic frequency f is given by Equation 2, and the thickness of the acoustic matching layer 9 and the passing ultrasonic frequency have a relation. I understand.

[0024]

T _n = λ / 4 = v _n / 4 · f Therefore, as in the present invention, one is convex in the xz plane,
The thickness t _n (x) of the acoustic matching layer 9 having the other planar shape is as shown in Equation 3 in the x direction as shown in FIG. However,
R is the radius of curvature, a is the short axis opening length of the composite piezoelectric vibrator 8, and t is
₀ is the minimum thickness of the acoustic matching layer.

[0025]

[Equation 3]

Since the thickness of the acoustic matching layer 9 is not uniform as can be seen from the above mathematical formula 3, the ultrasonic frequency passing therethrough changes with each thickness, and therefore the ultrasonic probe having a wide frequency range. The child will be configurable.

For the first ultrasonic wave propagation material body 10, a material such as silicon rubber having an acoustic impedance substantially equal to that of the subject Q and having a predetermined ultrasonic attenuation is used. Also,
For the second ultrasonic wave propagating material body 11, a material having an acoustic impedance close to 0, such as butadiene rubber or natural rubber, is used. That is, the acoustic impedance of the first and second ultrasonic wave propagating material bodies is made substantially equal to that of the subject Q to maintain the acoustic matching condition, and the ultrasonic attenuation of the first ultrasonic wave propagating material body is utilized to The ultrasonic wave emitted from the acoustic probe is weighted.

Assuming that the attenuation coefficient at the ultrasonic frequency f of the first ultrasonic propagation material body 10 having the thickness t is α, the ultrasonic attenuation amount A is expressed by the equation 4.

[0029]

## EQU00004 ## A = .alpha..multidot.f.multidot.t As is clear from this equation 4, the ultrasonic wave attenuation amount A for a specific frequency is proportional to the thickness t of the first ultrasonic wave propagation material body 10. Therefore, by forming the surface of the first ultrasonic wave propagation material body 10 on the object Q side in the xz plane in a concave shape by a predetermined function as in the present invention, ultrasonic attenuation is reduced to the central portion and to the peripheral portion. Since it can be increased as it becomes, side lobes of the ultrasonic radiation directivity characteristic on the xz plane can be suppressed.

[0030]

[Table 1]

[0031]

[Table 2]

Table 1 shows a typical window function, and FIG. 5 is a standardized figure of the window function of Table 1. Table 2 shows the result of simulating the relationship between the window function and the side lobe level in Table 1. From this result, if the Hamming function is a window function, the first sidelobe level is -84.
It can be seen that the level is 5 dB, which is about 56 dB lower than the case of Rectagular where no weighting is performed at all.

Therefore, if the shape of the first ultrasonic wave propagating material body 10 is shaped so that the thickness becomes the Hamming function in the xz plane, the side lobes are significantly suppressed, and the second ultrasonic wave is generated. By using a material whose ultrasonic attenuation is close to 0 as the propagation material body 11, the contactability with the subject Q is enhanced without impairing the weighting effect in the first ultrasonic propagation material body 10, and The function of the probe is improved.

[0034]

As described above, the ultrasonic probe of the present invention is a stable ultrasonic probe having an excellent function because each component of the ultrasonic probe functions as follows.

(1) Since the surface of the composite piezoelectric vibrator in the ultrasonic wave radiation direction is formed as a concave surface with a predetermined curvature, the ultrasonic beam can be focused to a predetermined depth.

(2) Since the thickness of the acoustic matching layer is reduced from the central portion to the peripheral portion in the ultrasonic wave radiation direction, acoustic matching can be achieved in a wide range of ultrasonic frequency regions. Therefore, the frequency band characteristic is broadened, and the deterioration of the image quality due to the reduction of the high frequency component due to the attenuation of the first ultrasonic wave propagation material body can be suppressed to the minimum.

(3) The thickness of the first ultrasonic wave propagating material body having a predetermined ultrasonic wave propagation attenuation is formed as a concave surface on the side of the object to be examined, and as a whole, from the central portion to the peripheral portion in the ultrasonic wave radiating direction. Since the sound pressure is made thicker and the attenuation is increased, the sound pressure becomes higher toward the central part and becomes lower toward the peripheral part, and the deterioration of the resolution of the ultrasonic image and the side lobe output that causes the pseudo echo are suppressed. ..

(4) Since the second ultrasonic wave propagating material body whose ultrasonic attenuation is close to 0 is provided between the first ultrasonic wave propagating material body and the subject, the frequency of the ultrasonic probe is increased. The contact property with the subject is improved without impairing the band characteristic.

(5) Since the acoustic impedances of the first and second ultrasonic wave propagating material bodies and the subject can be made substantially equal, the reflection of ultrasonic waves at the interface between the ultrasonic probe and the subject is reduced. Thus, the ultrasonic waves can be efficiently focused inside the subject.

(6) Since the composite piezoelectric vibrator made of the piezoelectric ceramics and the polymer material is used, the concave shape can be easily processed, and therefore the composite piezoelectric vibrator having stable characteristics can be formed.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of an ultrasonic probe according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing acoustic impedance of a composite piezoelectric vibrator.

FIG. 3 is a diagram showing acoustic impedance characteristics of an acoustic matching layer.

FIG. 4 is a diagram showing a change in thickness of an acoustic matching layer.

FIG. 5 is a diagram showing a standardized standard window function.

FIG. 6 is a perspective view showing a structural example of a conventional ultrasonic probe.

[Explanation of symbols]

6 ... Holder, 7 _i (i = 1, 2, 3 ...) ... Slit electrode, 8 ... Composite piezoelectric vibrator, 9 ... Acoustic matching layer, 10
... 1st ultrasonic wave propagation material body, 11 ... 2nd ultrasonic wave propagation material body, Q ... Subject.

Claims (4)

[Claims] 1. A piezoelectric ceramic and a polymer material, wherein slit-shaped electrodes are arranged on one surface and a common electrode is formed on the other surface, and ultrasonic waves are generated in a plane orthogonal to the arrangement direction of the slit-shaped electrodes. A composite piezoelectric vibrator formed in the radial direction in a concave shape, and an acoustic matching layer in contact with the surface in the ultrasonic radiation direction, the surface is formed in a convex shape, and the surface on the subject side is formed in a flat surface, A first ultrasonic wave propagation material body having a predetermined ultrasonic wave attenuation characteristic, which is in contact with the plane of the acoustic matching layer and whose surface on the side of the subject is concavely formed on the surface orthogonal to the array direction of the strip-shaped electrodes, The second ultrasonic wave propagation material has a surface that is in contact with the first ultrasonic wave propagation material body and has a convex shape in a plane that is orthogonal to the array direction of the slit-shaped electrodes, and the ultrasonic attenuation is almost zero.
And an ultrasonic wave propagating material body. 2. The ultrasonic probe according to claim 1, wherein the value of the acoustic impedance of the acoustic matching layer is approximately the middle of the acoustic impedance values of the composite piezoelectric vibrator and the subject. 3. The ultrasonic probe according to claim 1, wherein the acoustic impedances of the first ultrasonic wave propagation material body and the subject are substantially equal to each other. 4. The ultrasonic probe according to claim 1, wherein the first ultrasonic wave propagation material body has a concave surface shape defined by a predetermined function.