JP2001178719A - Ultrasonic vibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a super-broadband (multi-frequency) ultrasonic vibrator allowing observation from a coelom surface to a deeper part from the coelom surface without causing reduction of sensitivity, and allowing reduction of a diameter of an insertion part in an ultrasonic endoscope. SOLUTION: This ultrasonic vibrator 1 mainly comprises a composite piezoelectric body 2 composed of columnar piezoelectric bodies 2a, etc., and a resin member 2b; and an acoustic matching layer 4 eliminating a difference between an acoustic impedance of the composite piezoelectric body 2 and an acoustic impedance of a living body, provided with an acoustic lens 4a for emitting an ultrasonic beam. The acoustic impedance of the composite piezoelectric body 2 is set to 7-15×106 kg/m2.s by setting a volume filling rate of the plural columnar piezoelectric bodies 2a, etc., to 20-45%. The acoustic impedance of the acoustic matching layer 4 is set to be smaller than that of the composite piezoelectric body 2. The acoustic lens 4a has a concave curve shape such that a thickness continuously increases from the center toward the periphery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer mainly used for an ultrasonic endoscope for imaging a tomographic image in a living body using an ultrasonic echo.

[0002]

2. Description of the Related Art In recent years, an ultrasonic tomographic image is obtained by irradiating an ultrasonic wave to a living body, receiving reflected ultrasonic waves reflected at a portion where the acoustic impedance changes in the living body, converting the reflected ultrasonic wave into an electric signal, and forming an image. The resulting ultrasonic diagnostic devices have become widely used.

[0003] An ultrasonic endoscope provided with an ultrasonic transducer at the distal end of an endoscope insertion portion that can be inserted into a body cavity and capable of obtaining an ultrasonic tomographic image with the ultrasonic transducer has been put into practical use. Have been.

A piezoelectric body of an ultrasonic transducer used in an ultrasonic endoscope is formed of a piezoelectric material such as lead zirconate titanate (PZT) or lead titanate (PbTiO ₃ ). The acoustic impedance of the body is about 30 × 10 ⁶
It was as large as Kg / m ² · s. For this reason, even when a concave acoustic lens which also serves as an acoustic matching layer and whose acoustic impedance is optimized to about 4 to 5 × 10 ⁶ Kg / m ² · s is disposed on the piezoelectric body, the solid line in FIG. 7.5 MH
As shown by the band characteristic of the z piezoelectric body, the ratio band at a gain of -6 dB was about 40%. For this reason, the use of the concave acoustic lens in which the thickness dimension of the acoustic lens is continuously changed has little effect on broadening the band.

[0005] The -6 dB ratio band is a gain-
Higher frequency fh and lower frequency f at 6 dB
1 and the quotient of the center frequency fc between the frequency fh and the frequency fl, and can be expressed by the following equation.

-6 dB ratio band = (frequency fh-frequency f
1) / center frequency fc center frequency fc = (frequency fh + frequency fl) / 2.

In order to widen the relative band of the piezoelectric body formed of PZT, PbTiO3 or the like, the piezoelectric body has a first matching layer having an acoustic impedance of 8 to 10 × 10 ⁶ Kg / m ² · s and an acoustic impedance of ^{2 to 3} × 10 ^{6 6} kg / m ²
There is also a configuration in which the second matching layer of s is provided and the acoustic lens to widen the band. However, even with this configuration, -6 dB
Was about 60-70 percent.

It is known that the ratio band is about 90% when the matching layer has a three-layer structure, but it is also known that there are many troubles such as a great deal of labor for bonding the matching layer. ing.

For this reason, in order to widen the bandwidth and enable observation from the surface of the body cavity to the deep part, the ultrasonic endoscope 90 is inserted as shown in FIG. In order to observe a deep part in the distal end cap 92 disposed at the distal end portion 91, a frequency of 7.5 MHz (see FIG.
(The band characteristic indicated by the solid line in (a)) The fixed focus type ultrasonic transducer 93 for long-distance observation, and the frequency of 12 MHz for the purpose of observing the vicinity of the body cavity surface (the band characteristic indicated by the broken line in FIG. ) Or a 20 MHz fixed focus type ultrasonic transducer 94 for short-range observation is arranged for observation.

[0010]

However, as described above, the ultrasonic transducer for long-distance observation and the ultrasonic transducer for short-distance observation are bonded and arranged at the distal end of the insertion portion, so that the ultrasonic The end portion of the endoscope has a large diameter, which is a factor of deteriorating the insertability.

The present invention has been made in view of the above circumstances, and enables observation from the surface of a body cavity to a depth deeper than the surface of the body cavity without causing a decrease in sensitivity, and a reduction in the diameter of an insertion portion of an ultrasonic endoscope. It is an object of the present invention to provide an ultra-wideband (multi-frequency) ultrasonic transducer that can be achieved.

[0012]

SUMMARY OF THE INVENTION An ultrasonic transducer according to the present invention is formed of a plurality of columnar piezoelectric members and an organic material which fills gaps between the columnar piezoelectric members so that the acoustic impedance falls within a predetermined range. A composite piezoelectric body in which the volume filling ratio of the columnar piezoelectric body is set, and an acoustic lens which is arranged on the radiation surface side of the composite piezoelectric body and whose thickness dimension continuously changes from a central portion toward a peripheral direction. And an acoustic matching layer whose acoustic impedance is set within a predetermined range.

According to this structure, for example, 7.5M is passed through the acoustic lens from the composite piezoelectric body without lowering the sensitivity.
Ultrasonic waves are radiated over a wide frequency band such as Hz, 12 MHz or 20 MHz.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 relate to a first embodiment of the present invention, FIG. 1 is a diagram showing a schematic configuration of an ultrasonic vibrator, FIG. 2 is a diagram for explaining a configuration of a composite piezoelectric body, and FIG. FIG. 4 shows characteristics of an ultrasonic transducer.
FIG. 3 is a diagram illustrating a distal end portion of an ultrasonic endoscope on which an ultrasonic transducer is arranged.

FIG. 1A is a perspective view illustrating the structure of an ultrasonic transducer, and FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A.

As shown in FIGS. 1 (a), 1 (b) and 2, the ultrasonic vibrator 1 according to the present embodiment has a large number of prisms 2a,... A composite piezoelectric body 2 formed into a predetermined shape by filling a resin member 2b of polyurethane, epoxy or the like in the gaps and surroundings of the piezoelectric bodies 2a,. A front electrode 3a formed by sputtering gold on a transmitting / receiving ultrasonic radiation surface or an ultrasonic transmitting / receiving surface (also simply referred to as a front surface) and a surface of the composite piezoelectric body 2 opposite to the ultrasonic radiation surface (rear surface with respect to the front surface) The gap between the acoustic impedance of the composite piezoelectric body 2 and the acoustic impedance of the living body which are stacked via the rear electrode 3b formed by sputtering gold and the front electrode 3a of the composite piezoelectric body 2 is eliminated. Yo An acoustic matching layer provided with an acoustic lens 4a serving as a focusing means for increasing the efficiency of sound and converging the ultrasonic waves radiated from the composite piezoelectric body 2 to the central axis of the ultrasonic vibrator 1 and emitting an ultrasonic beam. 4 and a backing material 5 made of rubber containing ferrite or the like which attenuates ultrasonic waves radiated to the rear side of the composite piezoelectric body by being provided through the rear electrode 3b of the composite piezoelectric body 2 (acoustic impedance is 5 to ⁶ × 10 ⁶ Kg / m ² · s) and water resistance and chemical resistance covering the composite piezoelectric body 2, the front electrode 3 a, the rear electrode 3 b, the acoustic matching layer 4, the surface of the acoustic lens 4 a and a part of the backing material 5. And a protective film 6 made of parylene (polyparaxylylene) or the like, which is excellent in quality.

The central axis is the central axis of the effective surface of the composite piezoelectric element 2, that is, the sound axis of the ultrasonic wave. Also, a ground line 7 is electrically connected to the front electrode 3a, and a signal line 8 is electrically connected to the rear electrode 3b.
These wires 7 and 8 are collectively extended as a lead wire 9 and connected to a signal terminal and a ground terminal of an observation device (not shown).

As shown in FIG. 2, the composite piezoelectric body 2
, 2a and the acoustic impedance
Is 2-5X10⁶ Kg / m^Two · Shaped with s resin member 2b
, 2a.
The filling rate is set to 20 to 45%. This allows
The acoustic impedance of the composite piezoelectric body 2 is 7 to 15 × 10 ⁶ 
Kg / m^Two ・ Make it closer to bio-impedance
I have.

The acoustic matching layer 4 is an epoxy resin having an acoustic impedance lower than the acoustic impedance of the composite piezoelectric body 2 having an acoustic impedance of 2 to 4.5 × 10 ⁶ Kg / m ² · s,
It is formed in a cylindrical shape whose thickness except for the acoustic lens 4a is λ / 4 (λ is the wavelength of the center frequency of the ultrasonic wave, the same applies hereinafter).

The acoustic lens 4a provided on the acoustic matching layer 4 is formed and arranged on the acoustic matching layer 4 having a predetermined thickness. Is laminated on the ultrasonic wave radiating surface of the acoustic matching layer 4 to form a concave curved surface shape that changes in thickness continuously from the center to the circumferential direction, for example.

In this embodiment, the acoustic lens 4
The thickness dimension of the central part of a is set to zero with respect to the ultrasonic wave emitting surface of the acoustic matching layer 4. That is, the acoustic lens 4
The central portion of “a” coincides with the ultrasonic radiation surface of the acoustic matching layer 4. The sound speed condition of the acoustic lens 4a is set faster than water (living body).

When the composite piezoelectric body 2 of the ultrasonic vibrator 1 configured as described above is driven to emit ultrasonic waves, an ultra-wide band characteristic as shown in FIG. 3 is obtained. At this time, the higher frequency fh at a gain of -6 dB is 20 MHz.
Since the lower frequency fl is 3 MHz, the ratio band is −6 dB = (frequency fh−frequency fl) / center frequency fc center frequency fc = (frequency fh + frequency fl) / 2.

By substituting the frequency fh = 20 MHz and the frequency fl = 3 MHz into the above equation, -6 dB is obtained.
Is required to be an ultra-wide band of about 150%.

That is, this ultrasonic transducer 1 has the functions of a fixed-focus type ultrasonic transducer for long-distance observation at a frequency of 7.5 MHz and a fixed-focus ultrasonic transducer for fixed-field observation at a frequency of 12 MHz or 20 MHz. Having.

As a result, as shown in FIG. 4, the ultrasonic transducer 1 is placed in the distal end cap 12 of the distal end portion 11 of the insertion portion.
By arranging only one, the insertion portion tip 1
The ultrasonic endoscope 10 is configured such that the diameter of the ultrasound endoscope 1 is small and can be observed from the surface of the body cavity to the deep part. At this time, naturally, only one lead wire 9 extends from the ultrasonic transducer 1.

As described above, the ultrasonic wave emitting surface side of the composite piezoelectric body formed by setting the columnar piezoelectric body to a predetermined volume filling ratio so that the acoustic impedance approaches the impedance of the living body, that is, the acoustic impedance becomes a small value. In addition, by arranging an acoustic matching layer which also serves as an acoustic lens having a thickness dimension continuously increasing from the center to the circumferential direction and having an acoustic impedance smaller than the acoustic impedance of the composite piezoelectric material, the ratio at −6 dB can be obtained. An ultra-wide band of about 150% can be provided to form an ultrasonic transducer having a long focal range. Therefore, one ultrasonic transducer has the function of a multi-frequency transducer.

By arranging the ultrasonic transducer at the distal end of the insertion section, the diameter of the insertion section can be reduced, and an ultrasonic endoscope capable of observing from the surface of a body cavity to a deep portion can be formed. it can.

The perspective view of FIG. 5A and the view of FIG.
As shown in the cross-sectional view, a part of the front electrode 3a formed on the front surface of the composite piezoelectric body 2 is provided as a wraparound electrode 31 exposed on the side surface of the composite piezoelectric body 2, and the ground wire 7 is connected to the wraparound electrode 31. The ultrasonic transducer 1A may be connected to form an ultrasonic transducer 1A.

Thus, the ground wire 7 is not disposed on the joint surface between the front electrode 3a and the acoustic matching layer 4,
Since the joining between the composite piezoelectric body 2 and the acoustic matching layer 4 can be performed, the joining workability can be improved, and the joining between the composite piezoelectric body 2 and the acoustic matching layer 4 can be performed with high accuracy.

FIGS. 6 and 7 relate to a second embodiment of the present invention. FIG. 6 is a view for explaining the configuration of the ultrasonic vibrator, and FIG. 7 is a view for explaining the operation of the ultrasonic vibrator. FIG.
6A is a perspective view of the ultrasonic transducer, and FIG.
6B is a cross-sectional view taken along the line BB, FIG. 6C is a diagram illustrating the configuration of the rear electrode, and FIG. 7A is a diagram illustrating a state in which a small vibrator aperture is formed to emit ultrasonic waves. FIG. 7B is a diagram showing a state in which a large transducer aperture is formed and ultrasonic waves are emitted.

In this embodiment, the configuration of the ultrasonic transducer 1 of the first embodiment and the rear electrode 3a are different.

As shown in FIG. 6 (c), the rear electrode 3b constituting the ultrasonic vibrator 1B of the present embodiment comprises a disc-shaped small-diameter first electrode 32 disposed at the center and A substantially donut-shaped second electrode 3 arranged on the outer periphery of the electrode 32
3 is comprised. The first electrode 32 constituting the rear electrode 3b is connected to the signal line 8 of the first lead 9a, and the second electrode 33 is connected to the signal line 8 of the second lead 9b. The ground wire 7 of the wires 9a and 9b is connected to the front electrode 3a.

Accordingly, the composite piezoelectric body 2 is driven by the first electrode 32 and the second electrode 33. Other configurations are the same as those of the first embodiment, and the same members are denoted by the same reference numerals and description thereof will be omitted.

When the composite piezoelectric body 2 is driven by the first electrode 32 by forming the ultrasonic vibrator 1B as described above, the vibrator aperture is reduced as shown in FIG. Ultrasonic waves with a narrow beam width whose focal position is set to a short distance are radiated from the acoustic lens 4a.

On the other hand, the first electrode 32 and the second electrode 33
When the composite piezoelectric body 2 is driven by the
As shown in (1), an ultrasonic wave having a narrow beam width, in which the aperture of the transducer is enlarged and the focal position is set at a long distance, is emitted from the acoustic lens 4a.

As described above, the rear electrode is a small-diameter first electrode, and the donut-shaped second electrode is disposed on the outer periphery of the first electrode.
By configuring the electrodes and driving the composite piezoelectric body alone or in combination with each electrode, it is possible to change the focal position of the ultrasonic beam having a narrow beam width to a short distance or a long distance and emit the ultrasonic wave, Alternatively, by combining them, it is possible to provide an ultrasonic transducer having a long focal range from a short distance to a long distance. Other functions and effects are the same as those of the first embodiment.

In this embodiment, the rear electrode is 2
Although the back electrode is constituted by one electrode, the rear electrode may be constituted by more electrodes.

In the present embodiment, the description of the frequency at which the composite piezoelectric body 2 is driven has been omitted, but by driving the composite piezoelectric body 2 by applying a high frequency f 1 to the first electrode 32. As shown in FIG. 8A, it is possible to radiate high-resolution ultrasonic waves from the acoustic lens 4a by setting the focus position to a short distance from the small transducer aperture.

Further, the first electrode 32 and the second electrode 3
By driving the composite piezoelectric body 2 by applying a low frequency f0 to the piezoelectric element 3, an ultrasonic wave whose depth velocity is improved by setting the focal position from a large vibrator aperture to a long distance as shown in FIG. From the acoustic lens 4a.

That is, as shown in the characteristic diagram showing the relationship between the sensitivity and the frequency in FIG. 8C, it is possible to obtain an ultrasonic transducer having high sensitivity characteristics by switching the frequency.

As described above, the rear electrode is a small-diameter first electrode, and the doughnut-shaped second electrode is disposed on the outer periphery of the first electrode.
When the composite piezoelectric body is driven by individually or in combination with each other, the focus position can be changed to a short distance or a long distance by appropriately switching and setting the frequency, and It is possible to provide an ultrasonic transducer that can emit highly sensitive ultrasonic waves. Other functions and effects are the same as those of the above-described embodiment.

FIG. 9 is a view for explaining the configuration of an ultrasonic transducer according to the third embodiment. 9A is a perspective view illustrating the configuration of the ultrasonic transducer, and FIG. 9B is a cross-sectional view taken along line CC of FIG. 9A.

In this embodiment, the acoustic lens 4b provided on the ultrasonic transducer 1 and the acoustic matching layer 4 of the first embodiment is used.
Is different.

As shown in FIGS. 9A and 9B, different members are provided on the ultrasonic wave emitting surface side of the acoustic matching layer 4 formed to have a predetermined thickness to constitute the ultrasonic transducer 1C of the present embodiment. An acoustic lens 4b including a first lens portion 41 and a second lens portion 42 having different curvatures is formed and arranged.

The first lens portion 41 is a so-called center lens disposed at the center, and has a predetermined lens radius of curvature (R1) such that the thickness dimension increases continuously from the center to the circumferential direction. It is formed in a concave curved surface shape that changes with. The thickness of the central portion is set to zero with respect to the ultrasonic wave emitting surface, similarly to the acoustic lens 4a of the first embodiment. The sound speed condition of the first lens unit 41 is set to a sound speed V1 higher than the water (biological) sound speed V0.

On the other hand, the second lens section 42 is
This is a so-called peripheral portion lens having a substantially donut shape disposed around the lens portion 41, and the first lens has a thickness that continuously increases from the inner peripheral surface to the outer peripheral surface.
The lens portion 41 is formed in a concave curved surface shape that changes with a lens curvature radius (R2) larger than the lens curvature radius R1. The sound speed condition of the second lens unit 42 is set to be higher than the sound speed V0 of water (living body) and lower than the sound speed V1 of the first lens unit 41.

That is, between the sound speeds V0, V1, V2 and the lens radii R1, R2, V0 <V2≤V1.
, R1 <R2. Other configurations are the same as those of the first embodiment, and the same members are denoted by the same reference numerals and description thereof will be omitted.

By driving the composite piezoelectric body 2 by configuring the ultrasonic vibrator 1C as described above, as shown in FIG. Ultrasonic waves with a narrow beam width set at a distance are emitted, while ultrasonic waves with a narrow beam width at a focal position set at a long distance are emitted from the second lens unit 42 having a large aperture.

As described above, the acoustic lens provided on the acoustic matching layer is constituted by the first lens portion disposed at the center portion having a different radius of curvature of the lens and the second lens portion disposed around the first lens portion. V0 <V2 ≤ between each lens part
By setting the relationship of V1 and R1 <R2, the focal position can be extended by providing two types of focal positions, a short distance and a long distance, and the driving frequency can be switched between a short distance and a long distance to increase the focal length. It is possible to provide an ultrasonic vibrator capable of emitting ultrasonic waves having high sensitivity (at a high velocity).
Other functions and effects are the same as those of the above-described embodiment.

In the present embodiment, the acoustic lens is composed of two lens parts, but the acoustic lens may be composed of more lens parts.

It should be noted that the present invention is not limited to only the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

[Appendix] According to the above-described embodiment of the present invention, the following configuration can be obtained.

(1) A plurality of columnar piezoelectric bodies and an organic substance filling gaps between the columnar piezoelectric bodies and the like, and the volume filling ratio of the columnar piezoelectric bodies is set so that the acoustic impedance is within a predetermined range. A composite piezoelectric body, which is arranged on the radiation surface side of the composite piezoelectric body and whose thickness dimension continuously changes from the central portion to the peripheral direction. And a matching layer.

(2) The acoustic impedance of the composite piezoelectric body is 7 × 10 ⁶ Kg / m ² · s to 15 × 10 ⁶ K
^{2. The} ultrasonic transducer according to claim 1, wherein the acoustic impedance of the acoustic matching layer is in the range of 1/5 to 1/2 of the acoustic impedance of the composite piezoelectric material.

(3) The ultrasonic transducer according to appendix 2, wherein the volume filling factor of the columnar piezoelectric body is set to 20 to 45% in order to set the acoustic impedance of the composite piezoelectric body in a predetermined range.

(4) One of the electrodes disposed on the composite piezoelectric body is divided into a plurality of parts in a predetermined shape, and the size of the vibrator opening is changed by driving the composite piezoelectric body via the electrodes. 2. The ultrasonic transducer according to 1.

(5) The ultrasonic vibrator according to Appendix 1 or 4, wherein the composite piezoelectric body is driven by a high-frequency pulse or a burst wave, or a low-frequency pulse or a burst wave.

(6) The acoustic lens is formed by laminating at least two members having different sound speeds in the circumferential direction.
The ultrasonic transducer as described.

[0059]

As described above, according to the present invention, it is possible to perform observation from the surface of a body cavity to a portion deeper than the surface of the body cavity without lowering the sensitivity, and to reduce the diameter of the insertion portion of the ultrasonic endoscope. An ultrasonic transducer having an ultra-wide band (multi-frequency) can be provided.

[Brief description of the drawings]

FIGS. 1 to 4 relate to a first embodiment of the present invention, and FIG. 1 is a diagram showing a schematic configuration of an ultrasonic transducer.

FIG. 2 is a diagram illustrating a configuration of a composite piezoelectric body.

FIG. 3 is a diagram showing characteristics of an ultrasonic transducer according to frequency and gain.

FIG. 4 is a diagram illustrating a distal end portion of an ultrasonic endoscope on which an ultrasonic transducer is arranged.

FIG. 5 is a diagram illustrating another configuration example of the front electrode.

FIG. 6 and FIG. 7 relate to a second embodiment of the present invention, and FIG. 6 is a view for explaining a configuration of an ultrasonic transducer.

FIG. 7 is a diagram illustrating the operation of an ultrasonic transducer.

FIG. 8 is a view for explaining another operation of the ultrasonic transducer.

FIG. 9 illustrates a configuration of an ultrasonic transducer according to a third embodiment.

FIG. 10 is a view for explaining a conventional ultrasonic transducer and an ultrasonic transducer disposed at the distal end of an ultrasonic endoscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultrasonic vibrator 2 ... Composite piezoelectric substance 2a ... Columnar piezoelectric substance 2b ... Composite piezoelectric substance 3b ... Rear electrode 4 ... Acoustic matching layer 4a ... Acoustic lens

[Procedure amendment]

[Submission Date] October 25, 2000 (2000.10.
25)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] FIG.

[Correction method] Change

[Correction contents]

FIG. 10

Claims (1)

[Claims] 1. A volume filling ratio of a plurality of columnar piezoelectric bodies and an organic material filling gaps and the like between the columnar piezoelectric bodies, and the volume impedance of the columnar piezoelectric bodies is set such that an acoustic impedance is within a predetermined range. An acoustic matching member, which is arranged on the radiation surface side of the composite piezoelectric material and whose thickness dimension continuously changes from a central portion to a peripheral direction, also serves as an acoustic lens, and has an acoustic impedance set within a predetermined range. An ultrasonic transducer, comprising: a layer;