JPH09247796A - Ultrasonic wave transducer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ultrasonic wave transducer in which a side lobe is suppressed without being limited by a shape and a size of a piezoelectric element and a sharp ultrasonic wave image with high resolution is obtained over a wide range. SOLUTION: In the ultrasonic wave transducer driven by a piezoelectric element 2, an electrode is formed to both sides of the piezoelectric element 2, and outer shape R of a 5-leaf electrode 6 in the electrodes at least on one side is formed according to equation R=R0 ×[ cos(nθ)+m}/(m+1)]×f(θ), R0 is the maximum value of an electrode radius, n is a natural number being 2 or over, m is the number of leaves, and f(θ) is a function whose maximum value is 1 with respect to the polar coordinate R-θ, taking one point of the 5-leaf electrode 6 as the origin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer used in a medical or non-destructive ultrasonic diagnostic apparatus.

[0002]

2. Description of the Related Art A conventional ultrasonic transducer has a structure as shown in, for example, "Medical Ultrasonic Equipment Handbook", (Corona Publishing Co., Ltd., first edition published April 20, 1985), page 186. There is. That is, in this ultrasonic transducer, a piezoelectric element made of a PZT (lead zirconate titanate) -based piezoelectric ceramics plate having electrodes formed on both surfaces thereof via an insulating layer is adhered on a back damping material, and an acoustic matching layer and an acoustic matching layer are formed. The acoustic lens is glued.

The ultrasonic transducer is driven by applying a driving pulse of a voltage of about 100 to several hundreds of volts from a pulser (not shown) to the piezoelectric element to rapidly deform the piezoelectric element by the inverse piezoelectric effect. The ultrasonic pulse excited by this is oscillated through the acoustic matching layer and the acoustic lens.

The oscillated ultrasonic pulse is reflected at the interface between tissues in the body for medical use, and after being reflected from a discontinuous portion such as a scratch inside the object to be measured for nondestructive inspection. It re-enters the piezoelectric element through the acoustic lens and the acoustic matching layer, and vibrates it.

This mechanical vibration is converted into an electric signal by the piezoelectric effect and sent to an observation device (not shown) to be imaged.

The ultrasonic pulse oscillated as described above is focused by an acoustic lens and shaped into a thin ultrasonic beam, and high resolution in the scanning direction is obtained. However, even in this case, it was not possible to eliminate the surplus ultrasonic sound field (side lobe) generated around the main ultrasonic beam (main lobe).

For this reason, especially at a very short distance, the ultrasonic image captured by the main lobe and the ultrasonic image captured by the side lobe are superposed, and a good image cannot be obtained. However, since the shape and number of lesions, defects, etc. cannot be accurately grasped, a situation may occur in which judgment based on the ultrasonic image is erroneous.

On the other hand, the shape of the electrode of the piezoelectric element is formed over the entire center of the piezoelectric element, and a multi-leaf electrode continuous with the central electrode is formed around the electrode. A method has been devised in which the area is gradually reduced toward the outer peripheral portion of the element.

It is said that, as a result, a strong main lobe can be transmitted from the center, and the transmission of ultrasonic waves around the piezoelectric element, especially the edges, which causes the side lobe, can be effectively suppressed.

For example, as disclosed in Japanese Patent Laid-Open No. 57-52299, four-leaf electrodes are formed on the piezoelectric body of an ultrasonic transducer for flaw detection having a circular contact surface. X- that divides the shape of the leaf into four equal parts
For each quadrant of the y orthogonal coordinate axis, y = R ₀ · exp (−x ²
/ _R0 ² ) and x = R ₀ · exp (−y ² / r0 ² ), and a substantially pincushion type electrode surrounded by these curves, or as described in this application. It is known to use more multi-leaf electrodes.

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The shape of the electrodes of the piezoelectric element disclosed in Japanese Patent No. 52299 is effective in suppressing the side lobes, but has the following problems.

That is, the manufacturing method is limited to the case where the electrode shape is only four leaves, and when a large-sized ultrasonic transducer is manufactured, a portion where electrodes are not formed becomes large as compared with the wavelength, so that a sound field is generated. There is a possibility that the ultrasonic image formed by using this ultrasonic transducer will be deformed without being formed axisymmetrically:

Further, since the shape of the piezoelectric element is limited to a perfect circle and lacks flexibility in design, it is inconvenient especially for an ultrasonic probe having a small diameter which is desired to be rectangular.

Therefore, there is a problem that the above-mentioned conventional technique has a narrow application range and is difficult to use in a wide range of products.

The present invention has been made to solve the above-mentioned problems, and the invention according to claims 1 to 5 is not limited to the shape and size of the piezoelectric element, and side lobes can be suppressed. An object of the present invention is to provide an ultrasonic transducer capable of obtaining a high-resolution clear ultrasonic image over a wide range and a manufacturing method thereof.

[0016]

According to the first aspect of the present invention,
In an ultrasonic transducer driven by using a piezoelectric element, the piezoelectric element forms electrodes on both surfaces thereof, and at least one of the electrodes has an outer shape R,
Regarding the curved coordinate R-θ with one point on the electrode as the origin, R
₀ is the maximum value of the electrode radius, n is a natural number of 2 or more, f (θ)
Is a function with a maximum value of 1, R = R ₀ × [{cos
The present invention is characterized in that it is configured as n multi-leaf electrodes defined by (nθ) + m} / (m + 1)] × f (θ).

According to a second aspect of the present invention, in an ultrasonic transducer driven by using a piezoelectric element, the piezoelectric element forms electrodes on both surfaces thereof, and at the same time one of the electrodes is an entire surface electrode, an acoustic radiation surface is formed. To the side, and at the same time, the outer shape of the other electrode is curved coordinate R with one point on the electrode as the origin
With respect to −θ, when R ₀ is a maximum value of the electrode radius, n is a natural number of 2 or more, and f (θ) is a maximum value of 1, R = R
₀ × [{cos (nθ) + m} / (m + 1)] × f
It is characterized in that it is configured as n multi-leaf electrodes defined by (θ).

The invention according to claim 3 is characterized in that the function f (θ) defining the outer shape of the electrode in the ultrasonic transducer according to claim 1 or 2 is a constant 1.

The invention according to claim 4 is characterized in that the function f (θ) defining the outer shape of the electrode in the ultrasonic transducer according to claim 1 or 2 is an ellipse having a major axis 2.

According to a fifth aspect of the present invention, in a method of manufacturing an ultrasonic transducer driven by using a piezoelectric element, electrodes are formed on both surfaces of the piezoelectric element, and at least one of the electrodes is formed. Is formed as a partial leaflet-shaped electrode that does not cover the entire surface of the piezoelectric element, and at least the side where the leaflet-shaped electrode is formed is held by a conductive elastic body so as to cover the electrode-unformed portion, It is characterized in that the element is polarized.

According to the invention described in claim 1, one or both surfaces of the electrodes formed on both surfaces of the piezoelectric element are curved coordinates with one point on the electrode as an origin as described in claim 1. R
Regarding −θ, R = R ₀ × [{cos (nθ) + m} /
Since it is composed of n multi-leaf electrodes defined by (m + 1)] × f (θ), it is possible to shape the ultrasonic beam emitted from this piezoelectric element and obtain an ultrasonic beam beam with few side lobes. This makes it possible to obtain a high-resolution clear ultrasonic image over a wide range.

According to the second aspect of the invention, one of the electrodes formed on both sides of the piezoelectric element is a full-scale electrode, and the other electrode is directed toward the acoustic radiation surface side during assembly and the other electrode is placed on the electrode. Regarding the curved coordinate R-θ with one point as the origin, R = R ₀ × [{cos (nθ) + m} / (m +
1)] × f (θ) defined as n multi-leaf electrodes, the ultrasonic beam radiated from this piezoelectric element is shaped similarly to the invention described in claim 1, and an ultrasonic beam with less side lobes is formed. An acoustic beam can be obtained, and a high-resolution clear ultrasonic image can be obtained over a wide range.

The invention according to claim 3 is a function f (θ) which defines the outer shape of the electrode in the invention according to claim 1 or 2.
Is set to a constant 1, the envelope of the outer shape of the electrode becomes a perfect circle electrode, and an axially symmetric sound field with few side lobes can be realized.

According to a fourth aspect of the invention, a function f (θ) that defines the outer shape of the electrode in the first or second aspect of the invention is provided.
Is an ellipse with a major axis of 2, the outermost electrode can be an ellipse, and side lobes can be reduced even in a non-axisymmetric sound field.

According to the fifth aspect of the present invention, since the portion of the piezoelectric element in which the multi-leaf electrode is not formed is polarized, the strain caused by the polarization between the electrode-formed portion and the unformed portion is reduced. Therefore, it is possible to manufacture an ultrasonic transducer capable of obtaining a high-resolution clear ultrasonic image over a wide range.

[0026]

Embodiments of the present invention will be described below in detail. (Embodiment 1) (Structure) Embodiment 1 will be described with reference to FIGS. 1 to 7. FIG. 1 shows a piezoelectric element 2 according to the first embodiment. This piezoelectric element 2 has one surface of a piezoelectric ceramic 4 and
A full-face electrode 5 and a multi-leaf electrode (5 leaves in this example) 6 are formed on the other face by silver baking. Here, the piezoelectric ceramic 2 has a diameter of 6 mm and a frequency of 12 MH.
It was for z.

The outer shape of the multi-leaf electrode 6 has a curved coordinate R-θ with the center of the piezoelectric ceramic 2 as an origin.
Electrode radius R ₀ = 3 mm, n = 5, f (θ) = 1 (constant), m = 4, R = R ₀ × [{cos (nθ) +
m} / (m + 1)] × f (θ) was defined as five multi-leaf electrodes.

As a result, the electrode-unformed portion 7 is formed especially on the peripheral portion of the piezoelectric element 2.

After forming the full-face electrode 5 and the multi-leaf electrode 6, a voltage of 3 kV per 1 mm thickness was applied between them to polarize the piezoelectric ceramics 4.

The ultrasonic transducer 13 shown in FIG.
Is a structure in which an acoustic matching layer or acoustic lens 3 and the back braking material 1 are bonded to the piezoelectric element 2.

The ultrasonic transducer 13 is mounted in a case (not shown) and is connected to a pulsar and an image processing device (both not shown), and an ultrasonic medium such as water (not shown) is used. It is immersed in (omitted), and ultrasonic waves are transmitted and received via the acoustic radiation surface 8 as shown in FIG. Here, the acoustic matching layer 3 was formed by using a low-density resin as a matrix, and dispersing a small amount of high-density powder as a filler in the matrix.

Here, alumina ceramic powder was used as the powder, and epoxy thermosetting resin was used as the matrix. The back braking material 1 used was one in which tungsten particles were dispersed in an epoxy resin having a low cross-linking density.

[Operation] The ultrasonic transducer 13
The intensity distribution of the ultrasonic waves transmitted from is shown in FIG. 3 as a conceptual diagram. As can be seen from the figure, the sound pressure distribution 9 of the ultrasonic waves transmitted by the ultrasonic transducer 13 shown in this example
Indicates a distribution state in which the central portion where the multilobal electrode 6 is formed is high, the multilobal electrode 6 gradually decreases toward the edge portion where it is not formed, and becomes 0 at the edge portion. .

On the other hand, the sound pressure distribution 10 of the ultrasonic waves transmitted by the ultrasonic transducer which is generally used and which uses the conventional piezoelectric element having the entire surface electrodes formed on both sides is as follows:
Although the central part is high, the sound pressure does not decrease significantly even at the peripheral part. On the contrary, the edge component transmitted from the outer circumference of the piezoelectric element becomes large.

Therefore, the ultrasonic transducer 1
A relatively strong ultrasonic wave is also emitted from the peripheral portion of No. 3. A sound field 12 of ultrasonic waves transmitted from the ultrasonic transducer 13 is shown in a conceptual diagram in FIG.

Due to the characteristics of each electrode described above, in the case of using the piezoelectric element having the whole surface electrode (conventional example), as shown by the dotted line in FIG.
Becomes

On the other hand, in the sound field 12 using the piezoelectric element 4 of the multi-leaf electrode 6 shown in the first embodiment, the turbulence near the acoustic radiation surface 8 becomes small, and the side lobe is suppressed. In addition, since the change in sound pressure at the edge is small and the absolute value is close to 0, the divergence of the sound field at the edge and its vicinity is suppressed, and the sound field 12 is thin as a whole.

[Effect] Since the disturbance of the sound field at the close range from the ultrasonic transducer 2 of the first embodiment is suppressed, the resolution and the S / N ratio at the close range are improved. Moreover, since a thin sound field 12 is obtained as a whole,
The loss due to the diffusion of acoustic energy is reduced and the reaching distance is increased, so that the observation range is expanded and the overall resolution is also improved.

In the first embodiment, the piezoelectric element 4 is shown as a flat disk for simplification, but it is also possible to use a concave piezoelectric element 14 as shown in FIG. In this case, an ultrasonic transducer having a clear focus position can be obtained as compared with the case where the planar piezoelectric element 4, the acoustic lens 3 and the acoustic matching layer are used.

Besides the circle, the first embodiment can be applied to a regular polygon such as a square. It is also possible to use piezoelectric ceramics that is sufficiently larger than the portion that constitutes the electrode, and form the multi-leaf electrode 6 described in the first embodiment only in that portion.

Similarly, in the first embodiment, the electrode shape is constituted by five leaves. However, when a small piezoelectric element having a diameter of 2 mm or less is used, n = 4 or It is possible to use 3 or 4 leaves (3 leaf electrode 15 is shown in FIG. 6).

Since the width of the electrode-unformed portion 7 can be made sufficiently large, the electrode-unformed portion 7 is covered with the electrode material due to bleeding of the electrode material when a small piezoelectric element is used. It is possible to prevent such a situation.

On the contrary, when a particularly large piezoelectric element is used, by setting n = 8 or the like in the above formula, a multi-leaf electrode such as the 8-leaf electrode 16 as shown in FIG. Can be configured. As a result, the electrode-unformed portion 7 can be made as small as several times the wavelength, so that the acoustic field is formed axially symmetrical and an ultrasonic image that is not deformed can be obtained.

In addition to the silver baking shown in the first embodiment, the material of the electrodes is silver palladium baking.
It goes without saying that it is possible to prevent migration and improve reliability, and to form highly accurate electrodes as a thin film by vapor deposition, sputtering, ion plating or the like.

Although not shown in the drawing, the entire surface electrode 5 facing the multi-leaf electrode 6 is at least the multi-leaf electrode 6.
Extremely, since it only needs to be formed in the same part as
Regarding the facing surface of the electrode non-formed portion 7, the electrode is not formed,
It is also possible to configure both surfaces as the multi-leaf electrodes 6.

When such a structure is adopted, the leakage electric field between the multi-leaf electrode 6 and the full-face electrode 5 in the vicinity of the edge portion of the multi-leaf electrode 6 is compared with the case where one face is the full-face electrode 5. Since it can be eliminated, the sound pressure distribution and sound field of the transmitted ultrasonic waves can be controlled more strictly.

On the contrary, as shown in the first embodiment, one surface of the piezoelectric element 2 is used as the whole surface electrode 5, and this surface is assembled so as to face the outside of the ultrasonic transducer 13, and the whole surface electrode 5 is formed. It is also possible to adopt a configuration in which is the ground potential. In this case, since the entire surface electrode 5 can be provided with an effect of preventing the electromagnetic noise from being mixed, the effect of improving the S / N ratio can be exhibited.

In the first embodiment, the surface electrode formed on the polarization of the piezoelectric element 2 is used, but especially on the surface on which the multi-lobed electrode 6 is formed, a rubber mixed with carbon or metal particles ( By using a flexible conductor represented by conductive rubber) and applying it to the entire surface of the piezoelectric element 2 for polarization, it is possible to polarize the piezoelectric element 2 in a portion where no electrode is formed.

By adopting such a process, the strain generated between the portion with the electrode and the portion without the electrode due to the polarization is reduced, so that the crack inside the piezoelectric ceramic 4 caused by this strain is prevented. You can do it. As a result, it is possible to improve the life and reliability of the ultrasonic transducer for high frequency band, in which the piezoelectric element 2 is thinned to 100 μm or less.

[Second Embodiment] The second embodiment will be described with reference to FIGS. 8 and 9. In the description of the configuration and the drawings, the same elements as those in the first embodiment described above are designated by the same reference numerals, and duplicate description will be omitted.

(Structure) The second embodiment is characterized in that the shape of the piezoelectric element 17 is such that its planar shape is not axially symmetric.

In the following, an example of using the rectangular piezoelectric element 17 as an example will be described. Piezoelectric element 17
The structure of is shown in FIG. In this piezoelectric element 17, the whole surface electrode 5 is provided on one surface of the rectangular piezoelectric ceramics 20, and the multi-leaf electrode 19 (four leaves in the second embodiment) is provided on the other surface.
Formed by silver baking. Here, the piezoelectric ceramic 20 has a size of 2 mm × 5 mm and is for 12 MHz.

The outer shape of the multi-leaf electrode 19 has a curved coordinate R-θ with the center of the piezoelectric ceramic 20 as the origin.
When R ₀ is 3 mm, n = 5, m = 4, and f (θ) is the following equation 1, R = R ₀ × [{cos (nθ) + m} /
(M + 1)] × f (θ). In the following mathematical expression 1, b is the ratio of the minor axis to the major axis of the ellipse inscribed in the piezoelectric element 17.

[0054]

[Equation 1]

(Operation) According to the second embodiment, the piezoelectric ceramic 20 having a non-axial (point) symmetric shape different from that of the first embodiment described above has a high center and is attenuated toward the edges. However, the multi-leaf electrode 19 that can have a sound pressure distribution that becomes approximately 0 at the peripheral portion is formed.
The effect of the sound pressure distribution of the multi-leaf electrode 19 is similar to that of the first embodiment.

[Effect] According to the second embodiment, the piezoelectric element 17 having a shape other than the axial symmetry such as a rectangle or an ellipse or the point symmetry.
In the same manner as in the case where the symmetric disk-shaped piezoelectric element 2 is used, the disturbance of the sound field from the ultrasonic transducer at a close range is suppressed, and the resolution and S / N ratio at the close range are suppressed. And a narrow sound field can be obtained as a whole, so that the observation range can be expanded and the resolution can be improved.

As a result, the resolution can be improved even in an ultrasonic transducer using a piezoelectric element such as a rectangle, an ellipse, or an ellipse which is often used in an ultrasonic probe having a small diameter of 3 mm or less.

Although not shown in particular in the second embodiment, the concave cylindrical piezoelectric element 18 is formed by using the concave piezoelectric element ceramics 21 as shown in FIG. 9 similarly to the first embodiment. It is needless to say that the multi-leaf electrode 19 can be formed into a shape other than four-lobed by forming the above, and that an electrode material other than silver baking can be used.

Further, in the second embodiment, the function f
Although (θ) is an ellipse which is a line-symmetrical function, it is limited to a line-symmetrical function as long as the function satisfies the condition that the maximum value is 1 described in claim 1 such as an ellipse. It is not something that will be done. It is also possible to apply a different type of function to each quadrant.

[0060]

According to the invention of claim 1, even in an ultrasonic transducer using piezoelectric elements of various shapes, it is possible to obtain a clear ultrasonic image with high resolution over a wide range. Can be provided.

According to the second aspect of the present invention, it is possible to provide an ultrasonic transducer having excellent electromagnetic noise resistance and capable of obtaining a clear ultrasonic image with high resolution over a wide range.

According to the third aspect of the present invention, there is provided an ultrasonic transducer capable of obtaining a high-resolution clear ultrasonic image over a wide range, in particular, in a configuration in which an electrode having an outermost external shape is axisymmetric. Can be provided. be able to.

According to the invention as defined in claim 4, an ultrasonic transducer capable of obtaining a clear ultrasonic image of high resolution over a wide range, in particular, by adopting a constitution in which the outermost shape is an axisymmetric electrode. Can be provided.

According to the invention described in claim 5, the strain caused by the polarization between the electrode forming portion and the non-molding portion can be reduced, the life and reliability can be particularly improved, and a high resolution can be achieved over a wide range. It is possible to manufacture an ultrasonic transducer capable of obtaining a clear ultrasonic image of.

[Brief description of drawings]

FIG. 1 is a perspective view showing a piezoelectric element according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an ultrasonic transducer according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an ultrasonic intensity distribution of the ultrasonic transducer according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a sound field of the ultrasonic transducer according to the first embodiment of the present invention.

FIG. 5 is a perspective view showing a modified example of the piezoelectric element according to the first embodiment of the present invention.

FIG. 6 is a perspective view showing another example of the piezoelectric element according to the first embodiment of the present invention.

FIG. 7 is a perspective view showing still another example of the piezoelectric element according to the first embodiment of the present invention.

FIG. 8 is a perspective view showing a piezoelectric element according to a second embodiment of the present invention.

FIG. 9 is a perspective view showing a modified example of the piezoelectric element according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Back damping material 2 Piezoelectric element 3 Acoustic lens 4 Piezoelectric ceramics 5 Full-surface bridge 6 Multileaf electrode 7 Electrode unformed portion 8 Acoustic emission surface 13 Ultrasonic transducer 14 Piezoelectric element 15 3 Leaf electrode 16 8 Leaf electrode 17 Piezoelectric element 19 Poly Leaf electrode

Claims (5)

[Claims] 1. An ultrasonic transducer driven by using a piezoelectric element, wherein the piezoelectric element forms electrodes on both surfaces thereof, and
Regarding at least one of the outer shapes R of the electrodes with respect to a curved coordinate R-θ with one point on the electrode as an origin, R ₀ is the maximum value of the electrode radius, n is a natural number of 2 or more, and f (θ) is When the function has a maximum value of 1, R = R ₀ × [{cos (nθ) +
An ultrasonic transducer characterized by being configured as n multi-leaf electrodes defined by m} / (m + 1)] × f (θ). 2. An ultrasonic transducer driven by using a piezoelectric element, wherein the piezoelectric element forms electrodes on both surfaces thereof, and when one of the electrodes is an entire surface electrode and is directed toward the acoustic radiation surface side, the other simultaneously. With respect to the outer shape of the electrode of the above, with respect to the curved coordinate R-θ with one point on the electrode as the origin, R ₀ is the maximum value of the electrode radius, n is a natural number of 2 or more, and f (θ) is a function of the maximum value 1. When R = R ₀ × [{cos (nθ) + m} / (m +
1)] × f (θ) defined as n multi-leaf electrodes, which is an ultrasonic transducer. 3. The ultrasonic transducer according to claim 1, wherein the function f (θ) that defines the outer shape of the electrode is a constant 1. 4. The ultrasonic transducer according to claim 1, wherein the function f (θ) that defines the outer shape of the electrode is an ellipse having a major axis 2. 5. A manufacturing method for manufacturing an ultrasonic transducer driven by using a piezoelectric element, comprising forming electrodes on both surfaces of the piezoelectric element,
At least one of the electrodes is formed as a partial multi-lobed electrode that does not cover the entire surface of the piezoelectric element, and at least the side on which the multi-lobed electrode is formed is covered with a conductive elastic body to cover the electrode-unformed portion. A method of manufacturing an ultrasonic transducer, wherein the piezoelectric element is polarized in a state of being held.