JPH07322393A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To obtain an ultrasonic probe which is excellent in the transmission and reception characteristic of ultrasonic waves, is large in mechanical strength and is suitable for high frequency and high band by making an acoustic matching layer metal and making the surface of the metal layer a rough surface having projecting and recessing parts as a whole. CONSTITUTION:This ultrasonic probe is composed by forming an acoustic matching layer 5 in front of a piezoelectric element 1. In this case, the acoustic matching layer 5 is made the metal composed of solder (Pb Sn). Concretely, cream solder is applied on a piezoelectric element 1, the solder is melted and solidified, and the thickness is roughly set to lambda/4. The surface of the solder is devastated as a whole and the surface is formed into a rough surface having projecting and recessing parts. Subsequently, at the opening surface of a metal container 6 which is formed into a cylindrical shape, the solder side is made a front surface and the side is temporarily fixed by adhesive 7. Further, resin as packing material 4 is flowed in from the rear end surface side of the metal container 6 and the material is hardened, the solder and the metal container 6 are connected by conductive adhesive 8, and a protective film 9 composed of the resin and insulating from a living body is formed on the surface of the solder and the metal container 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field of application of an ultrasonic probe, and more particularly to an ultrasonic probe which is suitable for high frequency and can obtain a wide band.

[0002]

BACKGROUND OF THE INVENTION An ultrasonic probe is useful as an ultrasonic wave transmitting / receiving unit in an ultrasonic diagnostic apparatus for medical use. Among these, there are one piezoelectric element (single type) and, for example, an array type in which piezoelectric elements are formed in a rectangular shape and are arranged in the width direction and are electronically sector-driven or linearly driven. . In any of these cases, in recent years, it has been desired to increase the frequency of ultrasonic waves (for example, 30 MHz or higher) to improve the distance resolution in the radiation direction of ultrasonic waves, increase the amount of information, and improve the diagnostic accuracy.

[0003]

2. Description of the Related Art FIG. 5 is a sectional view of a single type ultrasonic probe for explaining a conventional example. The ultrasonic probe is configured by using a piezoelectric element 1 such as lead zirconate titanate (commonly called PZT) or lead titanate as a source of the ultrasonic waves U. The piezoelectric element 1 has electrodes (not shown) on both main surfaces, and an acoustic matching layer 2 is provided on the front surface that serves as a wave transmission / reception surface of the ultrasonic waves U. The acoustic matching layer 2 is made of, for example, an epoxy resin and has a wavelength λ / 4 of ultrasonic waves in the acoustic matching layer. Then, the impedance Z ₁ is set to a prescribed value that allows the ultrasonic waves to be transmitted and received most effectively. For example, the acoustic impedance Z ₀ of the piezoelectric element 1 is 34.0 × 10 ⁶ Kg / m ² · s, and the acoustic impedance (Z _M ) of the acoustic medium (water, living body, etc.) 3 is 1.5 × 10 ⁶ Kg / m ²
・ When s, Z ₁ is theoretically 4.25 × 10 ⁶ Kg / m
² · s becomes the optimum impedance Z _S. As shown in the transmission / reception characteristics of FIG. 6, the bandwidth becomes narrower when the acoustic impedance becomes smaller than the specified value, and becomes bimodal when the acoustic impedance becomes larger.

Normally, a piezoelectric element 1 processed into a disk shape
Is fixed to the backing material 4 to form the acoustic matching layer 3,
It is stored in a cylindrical container (not shown). Alternatively, after the acoustic matching layer 2 is formed on the piezoelectric element 1 and temporarily fixed to the opening surface of the cylindrical container, the resin as the backing material 4 is flowed in from the rear end surface side and cured. In this case, for example, when the ultrasonic frequency is 30 MHz, the piezoelectric element 1 has a thickness of about 75 μm and the acoustic matching layer has a thickness of about 20 μm.

[0005]

However, it is physically difficult to accurately match the impedance Z ₁ of the acoustic matching layer 2 to the optimum impedance Z _S in the ultrasonic probe having the above structure. Therefore, in reality, as described above, the bandwidth may be narrowed or bimodal, resulting in ripples.

Further, even if the optimum impedance Z _S is obtained, the thickness of the piezoelectric element 1 and the acoustic matching layer 2 becomes extremely small as described above as the ultrasonic frequency becomes higher. Therefore, there is a problem that the acoustic matching layer 2 is worn or the piezoelectric element 1 is damaged when the diagnosis is performed while rubbing the front surface of the probe against the living body.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide an ultrasonic probe having good ultrasonic wave transmission / reception characteristics and high mechanical strength, which is suitable for high frequency and high band. To do.

[0008]

[Points of interest] In the present invention, if a metal is used instead of the resin-based acoustic matching layer, it is possible to reinforce its own wear and the strength of the piezoelectric element, and the impedance Z ₁ of the acoustic matching layer is set to the optimum impedance Z _S. Attention was paid to the fact that if it is made larger, the transmission / reception characteristic becomes a bimodal characteristic, but the band with respect to the center frequency becomes wider (see Japanese Patent Publication No. 3-81359).

[0009]

The basic solution of the present invention is that the acoustic matching layer is made of metal, and the metal surface is a rough surface having irregularities as a whole. Hereinafter, one embodiment of the present invention will be described together with its operation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram of an ultrasonic probe for explaining one embodiment of the present invention. It should be noted that the same parts as those of the previous conventional example are given the same numbers to simplify the description. The ultrasonic probe
Similarly to the above, the acoustic matching layer 5 is formed on the front surface of the piezoelectric element 1. In this embodiment, the acoustic matching layer 5 is made of solder (P
_b S _n ). Specifically, cream solder is applied onto the piezoelectric element 1 and melted and solidified. However,
Its thickness is set to approximately λ / 4. Then, the entire surface of the solder is roughened to form a rough surface having irregularities. After that, the solder side is temporarily fixed to the opening surface of the cylindrical metal container 6 with the adhesive 7 with the solder side as the front surface. Then, the resin as the backing material 4 flows in from the rear end surface side of the metal container 6 and is cured. Further, the solder and the metal container 6 are connected by a conductive adhesive 8, and a protective film 9 made of resin is formed on the surface of the solder and the metal container 6 to insulate the living body. Reference numeral 10 (ab) in the drawing is a lead wire, and one (9)
a) is the rear surface side electrode (not shown) of the piezoelectric element 1, and the other (9)
b) is connected to the inner circumference of the metal container 6 and led out to the outside.
Further, the ultrasonic frequency was set to 30 MHz (the thickness of the solder is about 38 μm when λ / 4).

FIG. 2 (ab) is a transmission / reception characteristic diagram for explaining the operation of the ultrasonic probe according to the present embodiment, in which the horizontal axis represents the frequency f (MHz) and the vertical axis represents the reception voltage with respect to the transmission voltage. The ratio (dB) has a maximum value of 0 dB. However, FIG. 2A is a diagram when the solder has a flat surface, and FIG. 2B is a diagram when the solder surface is a rough surface. As is apparent from these figures, when the solder has a flat surface, "FIG. 2 (a)" shows the bimodal characteristics as described above. That is,
Acoustic impedance Z _{1 of} solder is 24 × 10 ⁶ Kg / m ²
・ In s, the above-mentioned optimum impedance (4.25 × 10
⁶ Kg / m ² · s), the center frequency f
The bandwidth f _w1 in the ₀ to 6 dB attenuation range has a wide bimodal characteristic.

On the other hand, when the surface of the solder is roughened to make it rough, as shown in FIG. 2 (b), the peaks and valleys of the bimodal characteristics disappear,
_Wider bandwidth f _w2 than at optimum impedance Z _s
It is a single peak characteristic that maintains. In this example, the thickness t (λ /
When the surface roughness is about ± λ / 8 with respect to 4), 23 MH
A z bandwidth f _w2 was obtained. In addition, as a result of the simulation, it was confirmed that the bandwidth f _w2 increases according to the surface roughness.

A summary of the results of this example is as follows. That is, when the solder has a flat surface, its acoustic impedance Z ₁ is larger than the optimum impedance Z _s , and the reflection coefficient of the following expression (1) is negative. Therefore, the ultrasonic wave corresponding to λ / 4 is totally reflected to form a valley, and has a bimodal characteristic as described above. γ = (Z0−Z1) / (Z0 + Z1) (1) On the other hand, in this embodiment, as shown in the enlarged sectional view of FIG. 3, the thickness of the acoustic matching layer 2 (solder) Changes in the range of the surface roughness Δt in each part as a whole. That is, the ultrasonic frequency corresponding to these thicknesses λ / 4 ± Δt / 2 also changes. Therefore, the ultrasonic waves within these ranges are also totally reflected. From such a fact, it is presumed that the characteristic is obtained by removing the front end portion A of the unimodal characteristic (FIG. 4) and the bandwidth f _w becomes wider.

As described above, in the present embodiment, the acoustic impedance Z ₁ of the acoustic matching layer 2 is made larger than the optimum impedance Z _s , and the surface is roughened to make the bandwidth wider than that of the conventional one. It was found that the peak characteristics were obtained. Therefore, in such a structure, the acoustic matching layer 2 is soldered after obtaining a good transmission / reception characteristic with a wide band, so that the acoustic matching layer 2 is mechanically supplemented by its own wear and the strength of the piezoelectric element 1. Strengthen and prevent its damage.

[0015]

[Other Matters] In the above embodiments, the acoustic matching layer 2 is soldered and joined by melting. However, for example, thermocompression bonding of Al or sticking with an adhesive of these metals may be used. Is preferably a metal having a large value, and the method for forming the same is not limited. However, when the metal is melted or the like, it is desirable to use a metal having a Curie point temperature or lower at which the piezoelectric action of the piezoelectric element is impaired. Although the thickness of the acoustic matching layer 5 is set to λ / 4, it may be approximately an integer (n) times. When the surface roughness is ± λ / 8, 2
Although it has been stated that a bandwidth f _{w2 of} 3 MHz can be obtained, conversely, the surface roughness is related to the bandwidth, the impedance of the acoustic matching layer, etc., and is not necessarily limited to this surface roughness. It is decided accordingly. Although the electrode lead-out and holding structure is shown as an example, the structure and the like are not limited and can be freely configured as is clear from the gist of the present invention. Further, although the ultrasonic probe is a single type, it goes without saying that the same can be applied to linear or sector driven array type and other cases. In short, in the present invention, the acoustic matching layer 5 is made of a metal larger than the optimum impedance and the surface thereof is made rough so that the unimodal characteristic can be obtained. It belongs to the technical scope of the present invention. However, it is not necessary to have a perfect unimodal characteristic, and it is needless to say that there may be a valley within 6 dB, which is not a problem in practical use.

[0016]

According to the present invention, since the acoustic matching layer is made of metal and the metal surface is a rough surface having irregularities as a whole, ultrasonic wave transmitting / receiving characteristics are improved and mechanical strength is high. It is possible to provide an ultrasonic probe suitable for high frequency and high band.

[Brief description of drawings]

FIG. 1 is a sectional view of an ultrasonic probe for explaining an embodiment of the present invention.

FIG. 2 is a wave transmission / reception characteristic diagram for explaining the operation of one embodiment of the present invention. FIG. 2 (a) shows the conventional case and FIG. 2 (b) shows the case of the present embodiment.

FIG. 3 is a view for explaining the operation of one embodiment of the present invention and is a partially enlarged cross-sectional view of an acoustic matching layer.

FIG. 4 is a wave transmission / reception characteristic diagram for explaining the operation of one embodiment of the present invention.

FIG. 5 is a sectional view of an ultrasonic probe for explaining a conventional example.

FIG. 6 is a wave transmission / reception characteristic diagram for explaining a conventional example.

[Explanation of symbols]

1 piezoelectric element, 2, 5 acoustic matching layer, 3 acoustic medium, 4
Backing material, 6 metal container, 7 adhesive, 8 conductive adhesive, 9 protective film, 10 lead wire.

Claims (3)

[Claims] 1. An ultrasonic probe in which an acoustic matching layer is provided on a piezoelectric element, wherein the acoustic matching layer is made of metal, and the metal surface is a rough surface having irregularities as a whole. Ultrasonic probe. 2. The ultrasonic probe according to claim 1, wherein the melting point temperature of the metal is equal to or lower than the Curie point temperature of the piezoelectric element. 3. The ultrasonic probe according to claim 1, wherein a protective film made of resin is formed on the front surface of the metal.