JP3655794B2 - Ultrasonic transducer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer mainly used in an ultrasonic endoscope that images a tomography in a living body using an ultrasonic echo.
[0002]
[Prior art]
2. Description of the Related Art In recent years, an ultrasonic diagnostic apparatus that obtains an ultrasonic tomographic image by irradiating a living body with ultrasonic waves, receiving reflected ultrasonic waves reflected by a changing portion of acoustic impedance in the living body, converting them into electrical signals, and imaging them. Became widely used.
[0003]
An ultrasonic endoscope in which an ultrasonic transducer is provided at the distal end of an endoscope insertion portion that can be inserted into a body cavity and an ultrasonic tomographic image can be obtained by this ultrasonic transducer has been put into practical use. .
[0004]
The piezoelectric body of the ultrasonic vibrator used in the ultrasonic endoscope is formed of a piezoelectric material such as lead zirconate titanate (PZT) or lead titanate (PbTiO ₃ ), for example. The impedance was as large as about 30 × 10 ⁶ Kg / m ² · s. For this reason, even when a concave acoustic lens that also serves as an acoustic matching layer having an acoustic impedance optimized to about 4 to 5 × 10 ⁶ Kg / m ² · s is arranged on the piezoelectric body, the solid line in FIG. As shown in the band characteristics of the 7.5 MHz piezoelectric material, the ratio band at a gain of −6 dB was about 40%. For this reason, there was almost no effect on wideband by using the concave acoustic lens in which the thickness dimension of the acoustic lens was continuously changed.
[0005]
The −6 dB ratio band is a quotient relationship between a difference between a higher frequency fh and a lower frequency fl at a gain of −6 dB and a center frequency fc between the frequency fh and the frequency fl. It can be expressed as
[0006]
−6 dB ratio band = (frequency fh−frequency fl) / center frequency fc
The center frequency fc = (frequency fh + frequency fl) / 2.
[0007]
Further, in order to widen the specific band of the piezoelectric material formed of PZT, PbTiO3, etc., the piezoelectric material 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 Kg / There is also a configuration in which the second matching layer of m ² · s and the acoustic lens are provided to increase the bandwidth. However, even in this configuration, the specific band at -6 dB was about 60 to 70 percent.
[0008]
It is known that the matching layer has a three-layer structure, so that the specific band becomes about 90%, but it is also known that there are many problems such as a great deal of labor for pasting the matching layer.
[0009]
For this reason, in the ultrasonic endoscope, in order to increase the bandwidth and enable observation from the surface of the body cavity to the deep part, as shown in FIG. 5B, the distal end of the insertion part of the ultrasonic endoscope 90 For the purpose of observing a deep portion in the tip cap 92 disposed at 91, a frequency 7.5 MHz (with a band characteristic shown by the solid line in FIG. 10A), a fixed focus type ultrasonic transducer 93 for long-distance observation, For the purpose of observing the vicinity of the surface of the body cavity, an ultrasonic transducer 94 having a frequency of 12 MHz (with the band characteristics shown by the broken line in FIG. 10A) or a fixed focus type ultrasonic transducer 94 of 20 MHz is attached. It was arranged and observed.
[0010]
[Problems to be solved by the invention]
However, as described above, the distal end portion of the ultrasonic endoscope has a large diameter by arranging the ultrasonic transducer for long-distance observation and the ultrasonic transducer for short-distance observation on the distal end portion of the insertion portion. It became a factor that deteriorated the insertability.
[0011]
The present invention has been made in view of the above circumstances, without causing the decrease in sensitivity can observation until the body cavity surface or RaFukashi unit, ultra wideband attained a diameter of the insertion portion of the ultrasonic endoscope An object is to provide an ultrasonic transducer that has been made multi-frequency.
[0012]
[Means for Solving the Problems]
The ultrasonic transducer according to the present invention is formed of a plurality of columnar piezoelectric bodies and an organic substance filled in a gap between the columnar piezoelectric bodies, and has an acoustic impedance of 7 to 15 × 10 ⁶ kg / m ² · s. A composite piezoelectric body in which the volume filling rate of the columnar piezoelectric body is set to 20 to 45%, and the acoustic impedance of the composite piezoelectric body is set to a value within a predetermined range smaller than the acoustic impedance of the composite piezoelectric body. , an acoustic matching layer comprising a single layer which is set at a predetermined thickness from the acoustic radiation surface of the composite piezoelectric body, wherein are formed disposed on the acoustic emission face side of the acoustic matching layer, the thickness of the central portion, the It is set to zero with respect to the acoustic radiation surface at the predetermined thickness position of the acoustic matching layer, and is formed in a spherical shape that changes so that the thickness dimension continuously increases from the central portion toward the peripheral direction. ago In the same acoustic impedance as the acoustic matching layer, characterized by comprising an acoustic lens which sound velocity condition is set to a speed higher than water.
[0013]
According to this configuration, ultrasonic waves over a wide frequency band such as 7.5 MHz, 12 MHz, or 20 MHz are radiated from the composite piezoelectric body through the acoustic lens without lowering the sensitivity.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
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 illustrating a schematic configuration of an ultrasonic transducer, FIG. 2 is a diagram illustrating a configuration of a composite piezoelectric body, and FIG. FIG. 4 is a diagram illustrating the characteristics of the ultrasonic transducer, and FIG. 4 is a diagram illustrating the distal end portion of the ultrasonic endoscope in which the ultrasonic transducer is arranged.
[0015]
1A is a perspective view illustrating the configuration of the ultrasonic transducer, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A.
[0016]
As shown in FIGS. 1A, 1B, and 2, the ultrasonic transducer 1 according to this embodiment includes a large number of prismatic or cylindrical columnar piezoelectric bodies 2a,..., 2a, and the columnar piezoelectric body 2a. ,..., 2a are filled with a resin member 2b such as polyurethane or epoxy and formed into a predetermined shape, and the composite piezoelectric body 2 emits ultrasonic waves or transmits / receives ultrasonic waves. The front electrode 3a formed by sputtering gold on the sound wave emitting surface or the ultrasonic wave transmitting / receiving surface (also simply referred to as the front surface) and the surface opposite to the ultrasonic wave emitting surface of the composite piezoelectric body 2 (referred to as the rear surface with respect to the front surface). In order to eliminate a gap between the acoustic impedance of the rear electrode 3b formed by sputtering gold and the composite piezoelectric body 2 laminated via the front electrode 3a of the composite piezoelectric body 2 and the acoustic impedance of the living body. Efficiency An acoustic matching layer 4 provided with an acoustic lens 4a that serves as a focusing means for focusing and focusing the ultrasonic wave emitted from the composite piezoelectric body 2 on the central axis of the ultrasonic transducer 1 and emitting an ultrasonic beam; Backing material 5 (acoustic impedance is 5-6 × 10 ⁶ Kg / m ² .multidot.2) formed of ferrite-containing rubber or the like for attenuating the ultrasonic wave radiated to the rear side of the composite piezoelectric body by being provided via the rear electrode 3b of the piezoelectric body ^2. s) and parylene (which has excellent water resistance and chemical resistance covering the surface of the composite piezoelectric body 2, the front electrode 3a, the rear electrode 3b, the acoustic matching layer 4, the acoustic lens 4a, and a part of the backing material 5). And a protective film 6 made of polyparaxylylene) or the like.
[0017]
The central axis is the effective surface central axis of the composite piezoelectric body 2, that is, the ultrasonic sound axis. A ground wire 7 is electrically connected to the front electrode 3a, and a signal line 8 is electrically connected to the rear electrode 3b. The electric wires 7 and 8 are collectively extended as a lead wire 9 and connected to a signal terminal and an earth terminal of an observation apparatus (not shown).
[0018]
As shown in FIG. 2, the composite piezoelectric body 2 is formed of a plurality of columnar piezoelectric bodies 2a,..., 2a and a resin member 2b having an acoustic impedance of 2 to 5 × 10 ⁶ Kg / m ² · s. The volume filling rate of the columnar piezoelectric bodies 2a, ..., 2a is set to 20 to 45%. As a result, the acoustic impedance of the composite piezoelectric body 2 is set to 7 to 15 × 10 ⁶ Kg / m ² · s, which is close to the bioimpedance.
[0019]
The acoustic matching layer 4 is an epoxy resin having an acoustic impedance of 2 to 4.5 × 10 ⁶ Kg / m ² · s, which is lower than the acoustic impedance of the composite piezoelectric body 2, and the thickness dimension excluding the acoustic lens 4a portion is λ / It is formed in a cylindrical shape of 4 (λ is the wavelength of the center frequency of the ultrasonic wave, hereinafter the same).
[0020]
The acoustic lens 4a provided on the acoustic matching layer 4 is formed and arranged with respect to the acoustic matching layer 4 formed to have a predetermined thickness, and the epoxy resin of the same member as the acoustic matching layer 4 is acoustically matched. For example, the layer 4 is formed in a concave curved surface shape that is laminated on the ultrasonic radiation surface of the layer 4 so that the thickness dimension continuously increases from the central portion in the circumferential direction.
[0021]
In the present embodiment, the thickness dimension of the central portion of the acoustic lens 4 a is set to zero with respect to the ultrasonic radiation surface of the acoustic matching layer 4. That is, the central part of the acoustic lens 4a and the ultrasonic radiation surface of the acoustic matching layer 4 are coincident. Further, the sound speed condition of the acoustic lens 4a is set faster than water (living body).
[0022]
When the composite piezoelectric body 2 of the ultrasonic vibrator 1 configured as described above is driven to emit ultrasonic waves, an extremely wide band characteristic as shown in FIG. 3 is obtained. At this time, since the higher frequency fh at the gain of −6 dB is 20 MHz and the lower frequency fl is 3 MHz,
−6 dB ratio band = (frequency fh−frequency fl) / center frequency fc
The center frequency fc = (frequency fh + frequency fl) / 2.
[0023]
By substituting the frequency fh = 20 MHz and the frequency fl = 3 MHz into the above equation, the ratio band at −6 dB is required to be an ultra-wide band of about 150%.
[0024]
That is, this ultrasonic transducer 1 has the functions of a fixed focus type long-distance observation ultrasonic transducer having a frequency of 7.5 MHz and a fixed focus type short-distance observation ultrasonic transducer having a frequency of 12 MHz or 20 MHz.
[0025]
Accordingly, as shown in FIG. 4, by placing only one ultrasonic transducer 1 in the distal end cap 12 of the insertion portion distal end portion 11, the insertion portion distal end portion 11 has a small diameter and is deep from the body cavity surface. The ultrasonic endoscope 10 that can perform the observation up to is configured. At this time, of course, only one lead wire 9 extends from the ultrasonic transducer 1.
[0026]
As described above, the thickness of the composite piezoelectric body formed with the columnar piezoelectric body having a predetermined volume filling rate so that the acoustic impedance approaches the impedance of the living body, that is, the acoustic impedance becomes a small value, on the ultrasonic radiation surface side. By arranging an acoustic matching layer that also serves as an acoustic lens whose acoustic impedance is smaller than the acoustic impedance of the composite piezoelectric material in a shape that the thickness dimension increases continuously from the central portion in the circumferential direction, the specific bandwidth at −6 dB is reduced to about -6 dB. An ultrasonic transducer with a long focal range can be configured by increasing the bandwidth to 150%. Therefore, this single ultrasonic vibrator has the function of a multi-frequency vibrator.
[0027]
Further, by arranging this ultrasonic transducer at the distal end of the insertion portion, it is possible to configure an ultrasonic endoscope that can observe from the body cavity surface to the deep portion by reducing the diameter of the insertion portion.
[0028]
As shown in the perspective view of FIG. 5A and the cross-sectional view of FIG. 5B, a part of the front electrode 3a formed on the front surface of the composite piezoelectric body 2 is exposed to the side surface of the composite piezoelectric body 2. The ultrasonic transducer 1 </ b> A may be configured by providing the electrode 31 and connecting the ground wire 7 to the surrounding electrode 31.
[0029]
As a result, the composite piezoelectric body 2 and the acoustic matching layer 4 can be joined without arranging the ground wire 7 on the joint surface between the front electrode 3a and the acoustic matching layer 4, so that the joining workability can be improved. In addition, the composite piezoelectric body 2 and the acoustic matching layer 4 can be joined with high accuracy.
[0030]
6 and 7 relate to the second embodiment of the present invention, FIG. 6 is a diagram for explaining the configuration of the ultrasonic transducer, and FIG. 7 is a diagram for explaining the operation of the ultrasonic transducer.
6A is a perspective view of the ultrasonic transducer, FIG. 6B is a cross-sectional view taken along the line BB of FIG. 6B, and FIG. 6C is a diagram illustrating the configuration of the rear electrode. FIG. 7A is a diagram illustrating a state in which a small transducer opening is formed and radiating ultrasonic waves, and FIG. 7B is a diagram illustrating a state in which a large transducer aperture is formed and radiating ultrasonic waves.
[0031]
In the present embodiment, the configurations of the ultrasonic transducer 1 and the rear electrode 3a of the first embodiment are different.
[0032]
As shown in FIG. 6C, the rear electrode 3b constituting the ultrasonic transducer 1B of the present embodiment includes a first electrode 32 having a disk shape and a small diameter disposed in the center portion, and the first electrode 32. The second electrode 33 having a substantially donut plate shape disposed on the outer periphery. The first electrode 32 constituting the rear electrode 3b is connected to the signal line 8 of the first lead wire 9a, and the second electrode 33 is connected to the signal line 8 of the second lead wire 9b. The ground wires 7 of the wires 9a and 9b are connected to the front electrode 3a.
[0033]
Therefore, 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 is omitted.
[0034]
By configuring the ultrasonic transducer 1B as described above, when the composite piezoelectric body 2 is driven by the first electrode 32, as shown in FIG. An ultrasonic wave with a narrow beam width set at a short distance is radiated from the acoustic lens 4a.
[0035]
On the other hand, when the composite piezoelectric body 2 is driven by the first electrode 32 and the second electrode 33, as shown in FIG. 7B, the vibrator aperture is enlarged and the focal position is set to a long distance. Are emitted from the acoustic lens 4a.
[0036]
As described above, the rear electrode is constituted by the first electrode having a small diameter and the doughnut-shaped second electrode arranged on the outer periphery of the first electrode, and the composite piezoelectric body is driven by combining each electrode alone or in combination. To provide an ultrasonic transducer having a long focal range from a short distance to a long distance by changing the focal position of an ultrasonic wave with a narrow beam width to a short distance or a long distance, or by combining them. Can do. Other operations and effects are the same as those in the first embodiment.
[0037]
In the present embodiment, the rear electrode is composed of two electrodes, but the rear electrode may be composed of more electrodes.
[0038]
Further, in the present embodiment, the description of the frequency when driving the composite piezoelectric body 2 is omitted. However, by driving the composite piezoelectric body 2 by applying a high frequency f1 to the first electrode 32, FIG. As shown in (a), it is possible to radiate high-resolution ultrasonic waves from the acoustic lens 4a by setting the focal position to a short distance from a small vibrator opening.
[0039]
Further, by driving the composite piezoelectric body 2 by applying a low frequency f0 to the first electrode 32 and the second electrode 33, the focal position is moved away from a large vibrator opening as shown in FIG. 8B. Ultrasonic waves that have been set and improved in depth speed can be emitted from the acoustic lens 4a.
[0040]
That is, as shown in the characteristic diagram showing the relationship between sensitivity and frequency in FIG. 8C, an ultrasonic transducer having high sensitivity characteristics can be obtained by switching the frequency.
[0041]
As described above, when the rear electrode is composed of the first electrode having a small diameter and the doughnut-shaped second electrode disposed on the outer periphery of the first electrode, when driving the composite piezoelectric body by combining each electrode alone or in combination, Furthermore, an ultrasonic transducer capable of changing the focal position to a short distance or a long distance by appropriately switching and setting the frequency and radiating highly sensitive ultrasonic waves is provided. it can. Other operations and effects are the same as those of the above-described embodiment.
[0042]
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 the line CC in FIG. 9A.
[0043]
In the present embodiment, the configuration of the acoustic lens 4b provided in the ultrasonic transducer 1 of the first embodiment and the acoustic matching layer 4 is different.
[0044]
As shown in FIGS. 9 (a) and 9 (b), different members are used on the ultrasonic radiation surface side of the acoustic matching layer 4 formed in a predetermined thickness dimension constituting the ultrasonic transducer 1C of the present embodiment. An acoustic lens 4b having a first lens portion 41 and a second lens portion 42 formed to have a curvature is formed and arranged.
[0045]
The first lens portion 41 is a so-called central lens disposed in the central portion, and changes with a predetermined lens curvature radius (R1) so that the thickness dimension continuously increases from the central portion in the circumferential direction. It is formed in a concave curved shape. And the thickness dimension of the center part is set to zero with respect to an ultrasonic radiation surface similarly to the acoustic lens 4a of 1st Embodiment. The sound speed condition of the first lens unit 41 is set to a sound speed V1 that is faster than the water (biological) sound speed V0.
[0046]
On the other hand, the second lens portion 42 is a so-called peripheral lens having a substantially donut shape disposed around the first lens portion 41, and the thickness dimension increases continuously from the inner peripheral surface to the outer peripheral surface. The first lens portion 41 is formed in a concave curved 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 a sound speed V2 that is faster than the sound speed V0 of water (living body) and smaller than the sound speed V1 of the first lens part 41.
[0047]
That is, there is a relationship of V0 <V2 ≦ V1, R1 <R2 between the sound velocities V0, V1, V2 and the lens curvature radii 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 is omitted.
[0048]
By configuring the ultrasonic transducer 1C as described above, when the composite piezoelectric body 2 is driven, the focal position is set to a short distance from the first lens portion 41 having a small opening as shown in FIG. On the other hand, an ultrasonic wave having a narrow beam width is emitted from the second lens part 42 having a large aperture, while an ultrasonic wave having a narrow beam width is radiated.
[0049]
As described above, the acoustic lens provided in the acoustic matching layer is configured by the first lens portion disposed in the central portion having different lens curvature radii and the second lens portion disposed around the first lens portion, and the respective lenses. By setting the relationship of V0 <V2≤V1, R1 <R2 between the parts, the focal position can be lengthened by providing two types of focal positions, short distance and long distance, and the short distance and long distance Thus, it is possible to provide an ultrasonic transducer capable of emitting highly sensitive (deep speed) ultrasonic waves by switching the driving frequency. Other operations and effects are the same as those of the above-described embodiment.
[0050]
In this embodiment, the acoustic lens is composed of two lens portions, but the acoustic lens may be composed of more lens portions.
[0051]
It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.
[0052]
[Appendix]
According to the embodiment of the present invention as described above in detail, the following configuration can be obtained.
[0053]
(1) A composite piezoelectric element formed of a plurality of columnar piezoelectric bodies and an organic material filled in a gap between the columnar piezoelectric bodies and having a volume filling rate of the columnar piezoelectric bodies set so that an acoustic impedance is in a predetermined range. Body,
An acoustic matching layer that is disposed on the radiation surface side of the composite piezoelectric body and has a thickness dimension that continuously changes from the central portion toward the peripheral direction, serving as an acoustic lens, and having an acoustic impedance set to a predetermined range;
An ultrasonic transducer comprising:
[0054]
(2) The acoustic impedance of the composite piezoelectric material is in the range of ⁷ × 10 ⁶ Kg / m ² · s to 15 × 10 ⁶ Kg / m ² · s, and the acoustic impedance of the acoustic matching layer is equal to the acoustic impedance of the composite piezoelectric material. The ultrasonic transducer according to appendix 1, which is in a range of 1/5 to 1/2.
[0055]
(3) The ultrasonic transducer according to appendix 2, wherein a volume filling factor of the columnar piezoelectric body is set to 20 to 45% in order to set an acoustic impedance of the composite piezoelectric body within a predetermined range.
[0056]
(4) One of the electrodes arranged in the composite piezoelectric body is divided into a plurality of predetermined shapes, and the size of the vibrator opening is changed by driving the composite piezoelectric body through the electrodes. Ultrasonic vibrator.
[0057]
(5) The ultrasonic transducer according to appendix 1 or appendix 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.
[0058]
(6) The ultrasonic transducer according to appendix 1, wherein the acoustic lens is formed by laminating at least two members having different sound speeds in the circumferential direction.
[0059]
【The invention's effect】
According to the present invention described above, without causing the decrease in sensitivity can observation until the body cavity surface or RaFukashi unit, ultra wide band attained a diameter of the insertion portion of the ultrasonic endoscope (multifrequency The ultrasonic transducer can be provided.
[Brief description of the drawings]
FIG. 1 to FIG. 4 relate to a first embodiment of the present invention, FIG. 1 is a diagram showing a schematic configuration of an ultrasonic transducer, and FIG. 2 is a diagram for explaining a configuration of a composite piezoelectric material. The figure which shows the characteristic of the ultrasonic transducer | vibrator by a frequency and a gain. FIG. 4 is a figure explaining the front-end | tip part of the ultrasonic endoscope which has arrange | positioned the ultrasonic vibrator. FIG. FIGS. 6 and 7 are related to the second embodiment of the present invention, and FIG. 6 is a diagram for explaining the configuration of the ultrasonic transducer. FIG. 7 is a diagram for explaining the operation of the ultrasonic transducer. 8 is a diagram for explaining another operation of the ultrasonic transducer. FIG. 9 is a diagram for explaining the configuration of the ultrasonic transducer according to the third embodiment. FIG. 10 is a diagram of a conventional ultrasonic transducer and an ultrasonic endoscope. The figure explaining the ultrasonic transducer arranged in the tip part
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic vibrator 2 ... Composite piezoelectric body 2a ... Columnar piezoelectric body 2b ... Composite piezoelectric body 3b ... Rear electrode 4 ... Acoustic matching layer 4a ... Acoustic lens

Claims (3)

The columnar piezoelectric body is formed of an organic material filled in a plurality of columnar piezoelectric bodies and gaps between these columnar piezoelectric bodies, and the volume filling rate of the columnar piezoelectric bodies is 20 so that the acoustic impedance is 7 to 15 × 10 ⁶ kg / m ² · s. A composite piezoelectric body set to ~ 45%;
It is arranged on the acoustic radiation surface side of the composite piezoelectric body, and the acoustic impedance is set to a value within a predetermined range smaller than the acoustic impedance of the composite piezoelectric body, and a single thickness set with a predetermined thickness from the acoustic radiation surface of the composite piezoelectric body. An acoustic matching layer including a layer;
The formed disposed on the acoustic emission face side of the acoustic matching layer, the thickness of the central portion is set to zero with respect to the acoustic radiation surface at said predetermined thickness position of the acoustic matching layer, near from the central portion An acoustic lens having the same acoustic impedance as the acoustic matching layer formed in a spherical shape that changes so that the thickness dimension continuously increases toward the direction, and the speed of sound is set to a speed faster than water ;
An ultrasonic transducer comprising:   One electrode arranged in the composite piezoelectric body is divided into a plurality of shapes with a predetermined shape, and the size of the vibrator opening is changed by driving the composite piezoelectric body through the electrode. The ultrasonic transducer according to claim 1.   The acoustic lens is disposed at a central portion, and a first lens portion formed with a first lens curvature, and a second lens disposed around the first lens portion and different from the first lens curvature. The ultrasonic transducer according to claim 1, comprising: a second lens portion formed with a lens curvature of:

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