JPH0759765A - Ultrasonic transducer - Google Patents

Abstract

PURPOSE:To provide an ultrasonic transducer which meets both of wide band frequency characteristic and large depth of focus characteristic to obtain an ultrasonic image with a higher resolution. CONSTITUTION:An piezo-electric body 1 is formed in such a manner that the center part thereof becomes thinner while becomes thicker toward the outside to make an ultrasonic radiation surface concave. An acoustic matching layer 2 is provided on the concave side of the piezo-electric body 1. The acoustic matching layer 2 has a value of 1/10 to 1.5/10 of an acoustic impedance value of the piezo-electric body 1 and is formed so that the center part thereof becomes thicker while becomes thinner toward the outside to be made uneven in thickness. A wide band frequency characteristic can be obtained by setting the shape of the piezo-electric body 1 and the acoustic impedance of the acoustic matching layer 2. A large depth of focus characteristic can be obtained depending on the shape of the piezo-electric body 1. The surface of the acoustic matching layer 2 is made almost flat thereby achieving better contacting properly with living body an a specimen 4.

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 as a sensor for a sonar or ultrasonic diagnostic apparatus for water or living bodies.

[0002]

2. Description of the Related Art Conventionally, in this type of ultrasonic transducer, in order to obtain an ultrasonic image with high resolution, a structure for frequency characteristic of a wide band using a material of a composite piezoelectric material, an electromechanical coupling coefficient A configuration is being considered in which the ultrasonic waves are given a sound pressure distribution by giving a distribution, and weighting (apodization) is performed to increase the depth of focus (longer focal depth).

Here, the relationship between the resolution, the frequency characteristic, and the depth of focus characteristic will be briefly described. The resolution is roughly divided into a propagation direction of ultrasonic waves, that is, a depth direction and a scanning direction in which an ultrasonic transducer is scanned. The frequency characteristic is a characteristic that greatly affects the resolution in the depth direction. Since the frequency characteristic is obtained by Fourier transforming the pulse response characteristic, when the bandwidth of the frequency characteristic becomes wide, the tail of the pulse response characteristic is suppressed and a short pulse is obtained, so that the resolution is improved. Further, if the frequency characteristic is a Gaussian-type unimodal characteristic, the tail of the pulse response characteristic falls straight, so the resolution is further improved in the depth direction. From the above, it is desirable that the frequency characteristics of the ultrasonic transducer have a wide band and a Gauss type. On the other hand, in the scanning direction, the resolution is improved by narrowing the ultrasonic beam transmitted from the ultrasonic transducer as much as possible and not narrowing it at any depth. This means that the longer the focal depth of the ultrasonic beam, the higher the resolution.

As an example of the ultrasonic transducer as described above, the document "Proc. IEEE, 1985, Ultrasonics Symposiu" is used.
The structure as described in P648-P651 of "m" and Japanese Patent Application No. 2-513975 is known.

In the former case, as shown in FIG. 4, a composite piezoelectric body 11 in which a columnar piezoelectric ceramic 11a and a polymer 11b are composited is formed, and a ground electrode 12 is provided on one surface of the composite piezoelectric body 11. The structure is a so-called array type transducer in which the electrodes 13 arranged in an array are provided on the other surface.

Since the composite piezoelectric body 11 can bring the acoustic impedance close to that of a living body and has a high electromechanical coupling coefficient almost equal to that of the piezoelectric ceramic alone, it has high sensitivity and a wide frequency band. It has the characteristic that the characteristics can be obtained.

On the other hand, in the latter, as shown in FIG. 5, the piezoelectric ceramic 1 between the ground electrode 12 and the electrode 13 is formed.
5 are arranged in an array, the polarization strength of the piezoelectric ceramic 15 is adjusted in a direction perpendicular to the arrangement direction, and a distribution is formed in the electromechanical coupling coefficient so that ultrasonic waves have a sound pressure distribution. It is composed.

Therefore, the sound field in the direction perpendicular to the arrangement direction of the piezoelectric ceramics 15 (acoustic lens direction) has a small side lobe, and further, a characteristic that the depth of focus is long in the depth direction is obtained. ing.

[0009]

However, among the conventional ultrasonic transducers as described above, the former configuration shown in FIG. 4 can obtain ultrasonic characteristics in a wide band, but has a curved surface shape for the depth of focus. Since it is formed or provided with an acoustic lens to focus the ultrasonic waves, it becomes a single-point focusing, and the focused focal portion can focus the ultrasonic beam, but the beam diverges in other portions, There was a problem of degrading resolution.

On the other hand, in the latter configuration shown in FIG. 5, the depth of focus becomes longer, contrary to the former, but since the electromechanical coupling coefficient of the piezoelectric body is lowered to give the sound pressure distribution, the frequency characteristic, In particular, there is a problem that the band characteristic is narrowed and the pulse response characteristic is deteriorated.

The present invention solves any of the conventional problems described above, and is capable of satisfying both the broadband frequency characteristic and the long focal depth characteristic, thus obtaining an ultrasonic image with high resolution. It is an object of the present invention to provide an ultrasonic transducer capable of performing the above.

[0012]

Means for Solving the Problems The technical means of the present invention for achieving the above-mentioned object is that the thickness of the central portion is thin, and becomes thicker toward the outside, the thickness is uneven, and the ultrasonic wave transmitting / receiving side is concave. A piezoelectric body formed to have a shape and a concave surface portion of the piezoelectric body having a nonuniform thickness having a value of 1/10 to 1.5 / 10 of the acoustic impedance value of the piezoelectric body. And an acoustic matching layer.

The acoustic matching layer in the above technical means is formed in a shape in which the thickness of the central portion is thick and becomes thinner toward the outside, and the acoustic matching layer has a substantially flat surface in contact with the subject. It is preferable to form so that

[0014]

Therefore, according to the present invention, since the thickness of the piezoelectric body is made non-uniform, it is possible to vibrate in a wide frequency band, and moreover, the acoustic impedance value of the piezoelectric body is 10% on the concave surface of the piezoelectric body. Since the acoustic matching layer set to a value of 1/10 to 1.5 / 10 is provided, a wide band frequency characteristic can be obtained. In addition, the surface of the piezoelectric body in the ultrasonic transmission / reception direction has a concave shape, and the thin portion of the central portion of the piezoelectric body has a high frequency, and the thicker portion toward the outside has a lower frequency. The ultrasonic beam transmitted and received from the vicinity of the portion has a high frequency component and is focused on the near distance portion, and the outer portion has a low frequency component and is focused on the far distance despite having the same curved surface. as a result,
The ultrasonic beam can be focused from a short distance to a long distance, and the depth of focus becomes long.

[0015]

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

First, a first embodiment of the present invention will be described. FIG. 1 is a schematic sectional view showing an ultrasonic transducer according to the first embodiment of the present invention.

In FIG. 1, 1 is a piezoelectric body for transmitting and receiving ultrasonic waves, 2 is an acoustic matching layer provided on the surface of the piezoelectric body 1 on the ultrasonic transmitting and receiving side, and 3 is opposite to the acoustic matching layer 2 of the piezoelectric body 1. The backing material 4 provided on the back surface of the side is a living body or an object to be examined such as water, and ultrasonic waves propagate from the piezoelectric body 1 through the acoustic matching layer 2 to the living body or water (acoustic impedance is 1 .5 to 1.65 MRayl) is propagated to the subject 4.

The details of the above configuration will be described below.
As the piezoelectric body 1, a piezoelectric material such as PZT-based or lead titanate-based piezoelectric ceramics or a composite piezoelectric body is used. The surface of the piezoelectric body 1 on the backing material 3 side is formed into a substantially flat surface shape, and the ultrasonic wave transmitting / receiving surface on the opposite side is formed into a concave shape having a certain curvature with respect to the subject 4 side. That is, the piezoelectric body 1 has the thinnest thickness in the vicinity of the center thereof, the thickness gradually increases toward the outside (or the periphery), and becomes the thickest in the outermost portion (or the outermost peripheral portion). Is formed. Therefore, the piezoelectric body 1 has a high frequency component near the thin central portion and a low frequency component near the thick outer portion, and has a wide frequency band component.

The acoustic matching layer 2 is made of a material such as epoxy resin and is provided on the entire concave surface of the piezoelectric body 1 on the ultrasonic wave receiving side. Contrary to the case of the piezoelectric body 1, the acoustic matching layer 2 is thickest in the vicinity of the central portion, becomes gradually thinner toward the outside (or the periphery), becomes thinner at the outermost portion, and becomes closer to the subject 4 side. The contact surface is formed into a substantially flat surface. Therefore, the acoustic matching layer 2
Has a non-uniform thickness, not a uniform thickness.

In the structure of such an ultrasonic transducer, for example, a lead titanate-based piezoelectric ceramic M-6 manufactured by Fuji Ceramics Co., Ltd. is used as the piezoelectric body 1, and one surface has a width of 10 mm and a curved surface with a radius of curvature of 50 mm. When the opposite surface is flat and the thickness of the thinnest central portion is 0.36 mm, the thickest outermost peripheral portion of the piezoelectric body 1 has a thickness of 0.61 mm. Therefore, the height of the concave shape of the piezoelectric body 1 is 0.25 mm, which is the difference between the thickest thickness and the thinnest thickness. The frequency constant Nt at the antiresonance frequency of the thickness longitudinal vibration of the piezoelectric body 1 made of the above material has a value of about 2470 Hz · mm, and the acoustic impedance has a value of about 34 MRayl. Therefore, the piezoelectric body 1 having the above shape has a thickness of 0.61 mm.
The anti-resonance frequency of about 4.05MHz in the part of, and 6.86MHz in the part of thickness 0.36mm becomes 4.05MHz.
It has a frequency pair of ~ 6.86 MHz. However, in reality, about 80% for this anti-resonance frequency
The center frequency is near the low frequency. Therefore, the center frequency of the piezoelectric body 1 having the above shape is 5.45 MHz × 0.8.
Becomes about 4.4 MHz.

The piezoelectric body 1 as described above is used, and the acoustic matching layer 2 is provided on the concave surface portion thereof, and the acoustic impedance of 1.5 to
When ultrasonic waves are transmitted / received to / from a living body or a subject 4 having a value of 1.65 MRayl, the value of the acoustic impedance of the acoustic matching layer 2 greatly affects the frequency characteristics. In order to improve the resolution, it is ideal that the frequency characteristic is wide band and the Gaussian distribution type single-peak characteristic. Therefore, the frequency characteristics of the reflected wave from the aluminum reflection plate installed by filling the concave surface of the piezoelectric body 1 with different acoustic impedance values of the acoustic matching layer 2 and using the subject 4 as water are measured. did. As a result, the tendency of frequency characteristics as shown in FIG. 2 was obtained. In addition, in FIG. 2, (1), (2),
In (3), (4), (5), (6), and (7), the acoustic impedance values of the acoustic matching layer 2 are 2.8, 3.
3, 3.5, 5.0, 7.0, 7.8, 11.0MRa
It is yl. The acoustic matching layer 2 having each acoustic impedance used here was prepared by changing the filling material and the filling amount based on the epoxy resin. Moreover,
As far as possible, a material having a value close to the sound velocity was used.

As is clear from FIG. 2, the acoustic matching layer 2
It was confirmed that the frequency characteristics greatly changed depending on the value of the acoustic impedance of. Here, as described above, the frequency characteristic is a characteristic that the frequency characteristic is wideband and has a Gaussian-type unimodal characteristic is important for improving the resolution. When the characteristics are evaluated, the numbers (2) to (4), that is, the value of the acoustic impedance of the acoustic matching layer 2 is 3.3 to.
It can be said that 5.0 MRayl is a desirable characteristic. The acoustic impedance of the acoustic matching layer 2 is 2.8 MRayl, number (1) has a single-peaked characteristic, but the frequency band is narrow, and the tail of the pulse response characteristic becomes worse. Also, 7.0 MRa
When the number is (5) to (7) above yl, the band is wide,
It has a bimodal frequency characteristic. This deteriorates the tailing characteristic of the pulse response, and as a result, reduces the resolution in the depth (ultrasonic wave propagation direction) direction.

Here, the value of the acoustic impedance and the frequency characteristic of the acoustic matching layer 2 are described, but these frequency characteristics are the piezoelectric body 1, the acoustic matching layer 2, and the subject 4.
The optimum value of the acoustic impedance of the acoustic matching layer 2 has been found from the relationship between the respective acoustic impedances of and.
Therefore, in the present embodiment, when the subject 4 having an acoustic impedance of 1.5 to 1.65 MRayl is targeted, the acoustic impedance of the acoustic matching layer 2 is 1/10 to 10 minutes of the acoustic impedance of the piezoelectric body 1. We have found that a value of 1.5 is optimal.

When the thickness of the piezoelectric body 1 changes, the piezoelectric body 1 has a frequency corresponding to each thickness, and the acoustic matching layer 2 has a thickness of a quarter wavelength with respect to each frequency of the piezoelectric body 1. Is generally formed. However, when the acoustic matching layer 2 is formed to have a thickness corresponding to each frequency as described above in the shape of the piezoelectric body 1 as in this embodiment, the shape of the surface in contact with the subject 4 has a smaller curvature. The surface becomes concave, and the contact with the subject 4 becomes worse. In the present embodiment, the contact property with the subject 4 can be greatly improved in this way, and the frequency characteristic can be obtained in a wide band and a unimodal frequency characteristic close to a Gaussian distribution type. , One with a long depth of focus can be obtained.

Further, the surface of the piezoelectric body 1 in the ultrasonic wave transmitting / receiving direction has a concave shape, and the thin portion at the center of the piezoelectric body 1 has a high frequency and the thicker portion toward the outside has a low frequency. Therefore, the ultrasonic beam transmitted and received from the vicinity of the central portion has a high frequency component and is focused in a short distance portion, and the outer peripheral portion has a low frequency component, which is the same curved surface. Focus on a long distance. As a result, the ultrasonic beam can be focused from a short distance to a long distance, and the depth of focus becomes long.

As described above, according to this embodiment, since it has a wide band Gaussian distribution type frequency characteristic and a long focal depth ultrasonic beam characteristic, it is possible to obtain an ultrasonic image with high resolution. Since the contact property with the subject 4 becomes good, good operability can be obtained.

In this embodiment, the surface of the piezoelectric body 1 in contact with the backing material 3 is formed as a flat surface, but the same characteristics can be obtained in the case of a curved surface.

Further, in the present embodiment, the case where the curved surface of the piezoelectric body 1 has a cylindrical shape has been described, but in addition to this, the same characteristics can be obtained when the curved surface has a spherical shape.

In the present embodiment, the case where the piezoelectric body 1 is a single body has been described. In addition to this, as shown in FIG. 3 as a second embodiment, the piezoelectric bodies 1 are arranged in an array, that is, so-called. Similar characteristics can be obtained in the array type ultrasonic transducer.

[0030]

As described above, according to the present invention, the acoustic impedance value of the piezoelectric body is 1 on the concave side of the piezoelectric body having a nonuniform thickness and a concave shape in the ultrasonic wave radiation direction.
Since the material of the acoustic matching layer having a value of 1/0 to 1/10 is provided in a non-uniform thickness, it is possible to obtain a wide band frequency characteristic and a long focal depth characteristic. it can. Therefore, an ultrasonic image with high resolution can be obtained.

Further, by forming the acoustic matching layer so that the contact surface with the subject is substantially flat, the contactability with the subject such as a living body is improved and the operability can be improved. it can.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an ultrasonic transducer according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between acoustic impedance of an acoustic matching layer and frequency characteristics in the ultrasonic transducer.

FIG. 3 is a schematic perspective view showing an ultrasonic transducer according to a second embodiment of the present invention.

FIG. 4 is a schematic perspective view showing an example of a conventional ultrasonic transducer.

FIG. 5 is a schematic perspective view showing another example of a conventional ultrasonic transducer.

[Explanation of symbols]

 1 piezoelectric body 2 acoustic matching layer 3 backing material 4 subject

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04R 17/00 J 332 A

Claims (3)

[Claims] 1. A piezoelectric body formed so that a central portion thereof has a small thickness and becomes thicker toward the outside, and a transmitting and receiving side of ultrasonic waves has a concave shape, and a piezoelectric body provided on the concave surface portion of the piezoelectric body. 1/10 of the acoustic impedance value of the body
Ultrasonic transducer with a non-uniform thickness acoustic matching layer having a value of 1.5 min. 2. The ultrasonic transducer according to claim 1, wherein the acoustic matching layer is formed in a shape in which the thickness of the central portion is large and the thickness becomes thinner toward the outside. 3. The ultrasonic transducer according to claim 1, wherein the acoustic matching layer is formed such that the surface in contact with the subject is a substantially flat surface.