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DESCRIPTION JP2004072755

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DESCRIPTION JP2004072755
An object of the present invention is to provide a composite piezoelectric body having a structure
in which a plurality of piezoelectric elements are arranged in a dielectric, enabling ultrasonic
transmission and reception in a wide band while having a constant thickness. A composite
piezoelectric body 1 comprising a plurality of piezoelectric elements 2 arranged and a dielectric
portion (resin 3) positioned between the plurality of piezoelectric elements 2, the plurality of
piezoelectric elements 2 The shape of each piezoelectric element 2 is determined in accordance
with the in-plane position so that at least one piezoelectric element 2 has a resonant frequency
different from that of the other piezoelectric elements 2. [Selected figure] Figure 1
Composite piezoelectric body
[0001]
The present invention relates to a composite piezoelectric used in an ultrasonic probe or the like,
in particular, a composite piezoelectric having an in-plane resonant frequency distribution, a
method of manufacturing the same, and the composite piezoelectric in the short axis direction.
The present invention relates to an ultrasonic probe and an ultrasonic diagnostic apparatus
capable of aperture control.
[0002]
Conventionally, as an ultrasonic probe which can perform aperture control in the short axis
direction of the ultrasonic probe and has a wide band resonant frequency characteristic, for
example, the one described in Patent Document 1 is known.
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1
[0003]
The conventional ultrasonic probe 100 shown in FIG. 16 includes a piezoelectric body 101
whose thickness increases along the minor axis direction.
A matching layer 102 is provided on the sound wave emitting surface side of the piezoelectric
body 101.
A large number of such transducers constituted by the piezoelectric body 101 and the matching
layer 102 are arranged along the azimuthal direction indicated by the arrows in the figure, and
supported by the back load member 103.
[0004]
Each piezoelectric body 101 is thin at the central portion in the short axis direction, and is
thicker toward both ends. By using the piezoelectric body having such a structure, it becomes
possible to transmit and receive high frequency ultrasonic waves at the central portion in the
minor axis direction of the vibrator and to transmit and receive low frequency ultrasonic waves
at the peripheral portion. As a result, the resonance frequency characteristic of the ultrasonic
transducer is broadened.
[0005]
Further, in the ultrasonic transducer shown in FIG. 16, the aperture size in the short axis
direction is smaller for high frequency ultrasonic waves and wider for low frequency ultrasonic
waves. Therefore, a narrow ultrasonic beam can be formed from near distance to far distance,
and high resolution can be obtained from short distance to far distance. JP-A-7-107595
[0006]
However, in the conventional ultrasonic probe as shown in FIG. 16, it is necessary to process the
surface of the piezoelectric body into a concave shape. In addition, it is necessary to further form
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matching layers with different curvatures on the concave surface of the piezoelectric body. It is
very difficult to manufacture such an ultrasound probe, but even if possible, it is not realistic in
terms of yield and cost.
[0007]
The present invention has been made in view of the above problems, and an object thereof is a
composite piezoelectric body which can transmit and receive ultrasonic waves in a wide band
while being a piezoelectric body having a constant thickness, and a manufacturing method
thereof To provide.
[0008]
Another object of the present invention is to provide an ultrasonic probe provided with such a
composite piezoelectric material.
[0009]
The composite piezoelectric body of the present invention is a composite piezoelectric body
having a plurality of piezoelectric elements arranged in a row and a dielectric portion located
between the plurality of piezoelectric elements, and at least at least one of the plurality of
piezoelectric elements. The cross-sectional area perpendicular to the ultrasonic radiation
direction in one piezoelectric element changes along the ultrasonic radiation direction.
[0010]
In a preferred embodiment, the at least one piezoelectric element has a resonant frequency
different from that of the other piezoelectric elements.
[0011]
In a preferred embodiment, the resonance frequencies of the plurality of piezoelectric elements
have a distribution in which the difference between the minimum value and the maximum value
is 10% or more of the average value.
[0012]
In a preferred embodiment, each of the plurality of piezoelectric elements has a size in a
direction perpendicular to the ultrasonic radiation direction having a certain size along the
ultrasonic radiation direction.
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[0013]
In a preferred embodiment, each of the plurality of piezoelectric elements has a constant
thickness along the ultrasonic radiation direction.
[0014]
In a preferred embodiment, the plurality of piezoelectric elements are two-dimensionally
arranged along a plane perpendicular to the sound wave emitting direction of the piezoelectric
elements, and the resonant frequency of the plurality of piezoelectric elements is the surface It
changes according to the position in the inside.
[0015]
In a preferred embodiment, the plurality of piezoelectric elements have a substantially constant
height.
[0016]
In a preferred embodiment, the resonance frequency of the piezoelectric element at the
periphery of the surface is lower than the resonance frequency of the piezoelectric element at the
center of the surface perpendicular to the sound wave emitting direction of the piezoelectric
element.
[0017]
In a preferred embodiment, the area of the cross section perpendicular to the sound wave
emitting direction of at least one of the plurality of piezoelectric elements is larger at the end face
of the piezoelectric element than at the center of the piezoelectric element.
[0018]
In a preferred embodiment, the area of the cross section perpendicular to the sound wave
emitting direction of at least one of the plurality of piezoelectric elements is smaller at the end
face of the piezoelectric element than at the center of the piezoelectric element.
[0019]
In a preferred embodiment, each of the plurality of piezoelectric elements has a pair of columnar
parts extending in the sound wave radiation direction, and a thickness of a bridging part
connecting the columnar parts at the center is that of the piezoelectric element. It changes in the
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plane perpendicular to the sound wave radiation direction.
[0020]
In a preferred embodiment, each of the plurality of piezoelectric elements has an opening at the
center, and the size of the opening is changed in a plane perpendicular to the sound wave
emitting direction of the piezoelectric element. .
[0021]
In a preferred embodiment, the shapes of the plurality of piezoelectric elements are selected such
that the resonant frequencies of the plurality of piezoelectric elements have a predetermined inplane distribution.
[0022]
In a preferred embodiment, the ratio of the size of the sound wave emitting direction of the
piezoelectric element to the minimum size S of the cross section perpendicular to the sound wave
emitting direction of the piezoelectric element is 5 or more.
[0023]
In a preferred embodiment, the dielectric portion is formed of a resin.
[0024]
In a preferred embodiment, the elastic modulus of the resin has a predetermined distribution in
accordance with the position in the plane perpendicular to the sound wave emitting direction of
the piezoelectric body element.
[0025]
The unit composite sheet of the present invention is a unit composite sheet having a resin layer
and a plurality of piezoelectric elements arranged on the resin layer, wherein the plurality of
piezoelectric elements are located depending on the position on the resin layer. It has different
shapes.
[0026]
In the composite sheet laminate of the present invention, a plurality of unit composite sheets
each having a resin layer and a plurality of piezoelectric elements arranged on the resin layer are
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laminated, and the piezoelectric elements are formed by the resin layer. The positional
relationship is fixed by being pinched, and the plurality of piezoelectric elements included in each
unit composite sheet have different shapes depending on the position on the resin layer.
[0027]
In the composite piezoelectric body of the present invention, a plurality of unit composite sheets
each having a resin layer and a plurality of piezoelectric elements arranged on the resin layer are
stacked, and the piezoelectric elements are sandwiched by the resin layer. The plurality of
piezoelectric elements included in each unit composite sheet have different shapes depending on
the position on the resin layer, and the composite sheet laminate is in a state where the
arrangement relationship is fixed by being carried out; It was produced by cutting so as to cross
the sound wave emission direction of the piezoelectric element.
[0028]
In a preferred embodiment, the piezoelectric element is surrounded by a resin.
[0029]
In a preferred embodiment, the resin is obtained by flowing and curing a part of the resin layer
of the unit composite sheet.
[0030]
The ultrasonic probe according to the present invention is a composite piezoelectric body having
a plurality of piezoelectric elements arranged and a dielectric portion located between the
plurality of piezoelectric elements, the plurality of piezoelectric elements And a pair of electrodes
formed on the composite piezoelectric body, wherein the cross-sectional area perpendicular to
the direction of ultrasonic radiation in at least one of the piezoelectric elements is changed along
the direction of ultrasonic radiation. Have.
[0031]
In a preferred embodiment, a matching layer is formed on the composite piezoelectric body, and
the thickness of the matching layer is changed along the direction in which the resonance
frequency of the piezoelectric element in the composite piezoelectric body changes. .
[0032]
An ultrasonic inspection apparatus according to the present invention includes an ultrasonic
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probe, a transmitting unit that transmits a signal to the ultrasonic probe, and a receiving unit that
receives an electrical signal output from the ultrasonic probe. In the ultrasonic inspection
apparatus, the ultrasonic probe is a composite piezoelectric body having a plurality of
piezoelectric elements arranged and a dielectric portion located between the plurality of
piezoelectric elements. A composite piezoelectric body in which a cross-sectional area
perpendicular to an ultrasonic wave radiation direction in at least one piezoelectric body element
of the plurality of piezoelectric body elements changes along the ultrasonic wave radiation
direction, and formed on the composite piezoelectric body And a pair of electrodes.
[0033]
The method for producing a unit composite sheet according to the present invention comprises
the steps of (a) preparing a composite plate having a resin layer formed on one surface of a platelike piezoelectric material, and (b) for the piezoelectric material of the composite plate. Forming a
plurality of grooves from the plate-like piezoelectric body without completely dividing the resin
layer, and including the step of forming a plurality of piezoelectric elements from the plate-like
piezoelectric body; Different shapes are given to the piezoelectric element of the book depending
on the position on the resin layer.
[0034]
The method for producing a unit composite sheet according to the present invention comprises
the steps of (a) temporarily fixing a plate-like piezoelectric body on a substrate with an adhesive
sheet, and (b) forming a plurality of grooves in the plate-like piezoelectric body. Including the
steps of: forming a plurality of thin wire-like piezoelectric bodies from a plate-like piezoelectric
material; and (c) transferring the plurality of thin wire-like piezoelectric bodies fixed to the
substrate to a resin layer b) gives different shapes to the plurality of piezoelectric elements
depending on the position on the resin layer.
[0035]
In a preferred embodiment, the plurality of grooves are formed by sand blasting.
[0036]
The method for producing a composite piezoelectric material according to the present invention
is a unit composite sheet including (a) a resin layer and a plurality of piezoelectric elements
arranged on the resin layer, wherein the plurality of piezoelectric elements are the resin.
Preparing a plurality of unit composite sheets having different shapes depending on the position
on the layer; (b) laminating the plurality of unit composite sheets; and (c) stacking the plurality of
units. Integrating the composite sheet.
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[0037]
In a preferred embodiment, the method includes: cutting the integrated plurality of unit
composite sheets transversely to the piezoelectric element.
[0038]
According to the present invention, in a composite piezoelectric body having a structure in which
a plurality of piezoelectric body elements are arranged in a dielectric, since the piezoelectric body
elements have different shapes depending on the position, the resonant frequency in the sound
wave emission plane of the composite piezoelectric body Can be different.
According to the composite piezoelectric body of the present invention, it is possible to transmit
and receive ultrasonic waves in a wide band while using a flat composite piezoelectric body.
Further, the resonance frequency of the ultrasonic waves to be transmitted and received can be
given a predetermined distribution in the plane of the composite piezoelectric body, so that the
resolution of the ultrasonic probe can be enhanced.
[0039]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0040]
Embodiment 1 FIG. 1 is a view showing a first embodiment of a composite piezoelectric body
according to the present invention.
In the composite piezoelectric body 1 of the present embodiment, a plurality of piezoelectric
body elements 2 are two-dimensionally arranged in the XY plane of the coordinates shown in
FIG.
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A resin 3 is filled between the piezoelectric elements 2 and the positional relationship between
the piezoelectric elements 2 is fixed to each other, thereby forming an integrated composite
piezoelectric body 1.
[0041]
Each piezoelectric element 2 in the present embodiment has a substantially columnar shape with
the Z direction as the longitudinal direction (ultrasonic radiation direction), and emits ultrasonic
waves in the Z direction by expanding and contracting in the Z direction. Can.
Both end faces of the piezoelectric element 2 are located on the upper and lower surfaces of the
composite piezoelectric body 1.
The upper and lower surfaces of the composite piezoelectric body 1 are perpendicular to the Z
direction and parallel to the XY plane.
In the present specification, the upper surface of the composite piezoelectric body 1 shown in
FIG. 1 is referred to as an “ultrasonic emission surface”.
[0042]
In FIG. 1, both sides of the piezoelectric element 2 are described as exposed, but electrodes (not
shown) are formed on the upper and lower surfaces of the composite piezoelectric body 1,
respectively. The piezoelectric element 2 is polarized in the Z-axis direction.
[0043]
The material of the piezoelectric element used in the composite piezoelectric body 1 of the
present embodiment is not particularly limited as long as it has piezoelectricity, and piezoelectric
ceramics, piezoelectric single crystals, and the like are suitably used.
As piezoelectric ceramics, lead zirconate titanate, lead titanate, barium titanate and the like are
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used.
Further, as the piezoelectric single crystal, quartz crystal, lithium niobate, lead zirconate titanate
single crystal, or the like is used.
In this embodiment, as the piezoelectric body, lead zirconate titanate (PZT) ceramic having high
piezoelectricity and relatively easy processing is used.
[0044]
The resin constituting the composite piezoelectric body 1 may be any material as long as it can
fix the positional relationship of the piezoelectric elements 2 and can be integrated, and epoxy
resin, acrylic resin or the like can be used.
In the present embodiment, an epoxy resin is used in consideration of adhesion to the
piezoelectric ceramic.
[0045]
The electrodes provided on both end faces perpendicular to the Z direction of the composite
piezoelectric body 1 are preferably formed of a material having low electric resistance and
excellent adhesion.
As an electrode material, general metals such as gold, silver, nickel and the like can be used.
Further, as a method of forming the electrode, plating, sputtering, vapor deposition, or the like
can be used.
In the present embodiment, a two-layer metal film of nickel and gold is formed by electroless
plating.
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The thickness of the nickel plating layer can be set to 2 μm, and the thickness of the gold plating
layer can be set to 0.1 μm.
[0046]
Hereinafter, the structure of the composite piezoelectric body 1 will be described in more detail.
[0047]
FIG. 2 shows a cross section taken along line A-A 'of the composite piezoelectric body of FIG.
As shown in FIG. 2, among the plurality of piezoelectric elements constituting the composite
piezoelectric body 1, the piezoelectric elements arranged along the Y direction each have the
same shape.
Therefore, the resonance frequency characteristics of the piezoelectric element 2 are constant
along the Y direction, and there is no change in the resonance frequency in the composite
piezoelectric body along the Y direction.
[0048]
FIG. 3 shows a cross section taken along line B-B 'of the composite piezoelectric body of FIG.
As shown in FIG. 3, among the plurality of piezoelectric body elements 2 constituting the
composite piezoelectric body 1, the piezoelectric body elements 2 arranged along the X direction
have different shapes according to the position (X coordinate) The resonance frequency
characteristics of each piezoelectric element 2 change (have a distribution) along the X direction.
[0049]
Hereinafter, the structure of the piezoelectric element 2 will be described in detail.
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[0050]
In the present embodiment, the length L of each piezoelectric element 2 measured in the Z
direction, that is, the thickness of the composite piezoelectric body 1 is set to about 0.25 mm
(250 μm).
Among the piezoelectric elements 2 shown in FIG. 3, the piezoelectric elements 2 located at the
center in the X direction have a uniform shape (straight columnar shape) in the Z direction.
The width (size S measured along the X direction) of this piezoelectric element 2 in FIG. 3 is
about 0.05 mm (50 μm).
Therefore, the ratio (L / S: aspect ratio) of the length (height) L to the size (minimum size) S of
the piezoelectric element 2 is about 5.
[0051]
The resonance frequency (the resonance frequency in the thickness direction) of such a
piezoelectric element 2 in the Z direction is about 5.7 MHz, and the antiresonance frequency is
7.7 MHz.
Also, the electromechanical coupling factor in this vibration mode is about 0.7.
[0052]
On the other hand, among the piezoelectric elements 2 shown in FIG. 3, the piezoelectric
elements 2 located at the periphery in the X direction have a cross-sectional shape similar to the
alphabet “I (eye)” character.
The piezoelectric element 2 of the I-type structure has a central portion having a constant width
common to the respective piezoelectric elements 2, and an upper end and a lower end connected
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to both ends of the central portion.
The Z-direction size of the central portion of the I-type piezoelectric element 2 is 0.15 mm, the Zdirection size of the upper end is 0.05 mm, and the Z-direction size of the lower end is 0.05 mm.
The X-direction sizes of the upper end portion and the lower end portion of the piezoelectric
element 2 of the I-shaped structure change along the X-direction, as can be seen from FIG.
The X-direction size of the upper end and the lower end of the piezoelectric element 2 closest to
the end of FIG. 3 is 0.1 mm.
[0053]
According to the piezoelectric element 2 having such a shape, the upper end portion and the
lower end portion exert the function of weight, so that the resonant frequency in the Z direction
decreases as the size in the X direction of the upper end portion and the lower end portion
increases. become.
In the case of the above-described piezoelectric element 2 having the upper end and the lower
end with the size in the X direction of 0.1 mm, the resonant frequency (the resonant frequency in
the thickness direction) in the Z direction is about 3.1 MHz.
The antiresonance frequency is 4.1 MHz, and the electromechanical coupling coefficient is about
0.68.
[0054]
The resonance frequency of the piezoelectric element 2 between the center and the end of the
composite piezoelectric body 1 in the X direction is to adjust the size in the X direction of the
upper end and the lower end in the range of 0.05 to 0.10 mm. Can be set to a value in the range
of 3.1 to 5.7 MHz.
[0055]
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Of the one row of piezoelectric elements 2 arranged along the X direction, the size in the Y
direction of each piezoelectric element 2 is uniform.
In addition, the size in the Y direction of each piezoelectric element 2 does not change along the
Z direction.
In other words, the shape of the plane in which each piezoelectric element 2 is projected onto the
Z-Y plane is substantially rectangular, and is uniform regardless of the position of the
piezoelectric element 2 in the X direction.
Further, in the present embodiment, the shape of the projection plane is uniform regardless of
the position of the piezoelectric element 2 in the Y direction (FIG. 2).
[0056]
Although only eight piezoelectric elements 2 are illustrated in FIG. 3 for the sake of simplicity,
actually, the size of the composite piezoelectric element 1 in the X direction is 12 mm, and the
arrangement pitch of the piezoelectric elements 2 is 0.15 mm. In this case, 80 piezoelectric
elements 2 are arranged in the X direction.
[0057]
In FIG. 3, two sets of piezoelectric element 2 having four types of shapes are shown.
The piezoelectric elements 2 are arranged symmetrically with respect to an axis (axis parallel to
the Z direction) passing through the central portion of the composite piezoelectric body 1, but
the present invention is not limited to such a structure.
The number of types of shapes of the piezoelectric elements 2 included in the plurality of
piezoelectric elements 2 arranged in parallel in the X direction may be five or more.
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Also, two or more piezoelectric elements 2 having the same shape may be continuous along the X
direction.
That is, even if the shape of the piezoelectric element 2 is gradually changed according to the
position in the X direction (X coordinate) to arrange one by one from the center to the periphery,
several piezoelectric elements having the same shape are arranged. It may be arranged.
[0058]
In this embodiment, the resonance frequency is designed to be highest at the center of the
composite piezoelectric body 1 and to decrease from the center toward the periphery along the X
direction, but the present invention is not limited to this.
Depending on the application, it is possible to set the distribution of resonant frequencies
arbitrarily.
[0059]
An ultrasonic probe and an ultrasonic diagnostic apparatus using the above-mentioned
composite piezoelectric body 1 will be described with reference to FIG.
[0060]
FIG. 4 is a diagram showing the configuration of an ultrasound probe and an ultrasound
diagnostic apparatus.
In FIG. 4, the ultrasonic probe 6 includes a composite piezoelectric body 1, an acoustic matching
layer 4 formed on the ultrasonic wave emitting surface of the composite piezoelectric body 1,
and a back surface provided on the back surface of the composite piezoelectric body 1. A load 5
is provided.
The composite piezoelectric body 1 has the configuration shown in FIG. 1 to FIG.
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[0061]
The acoustic matching layer 4 is for efficiently propagating the ultrasonic wave generated in the
composite piezoelectric body 1, and the acoustic matching layer 4 in FIG. 4 has a thickness
corresponding to the resonance frequency of the composite piezoelectric body 1 just below it.
have. The acoustic matching layer 4 is required to satisfy the following two conditions regarding
acoustic impedance and thickness described below.
[0062]
Acoustic impedance is determined by the product of sound velocity and density. The acoustic
impedance Zm of the acoustic matching layer 4 preferably satisfies the following equation (1),
where Zp is the acoustic impedance of the composite piezoelectric body 1 and Zs is the acoustic
impedance of a human body or the like as a sound wave propagation medium.
[0063]
Zm = (Zp × Zs) <(1/2)> (Equation 1)
[0064]
The thickness of the acoustic matching layer 4 is preferably set to 1⁄4 of the wavelength of
ultrasonic waves to be transmitted and received.
[0065]
By setting the acoustic impedance Zm of the acoustic matching layer 4 and the thickness of the
acoustic matching layer 4 to optimal values, the reflection of the acoustic wave at the interface of
the ultrasonic probe 6 and the human body as the propagation medium is reduced, It is possible
to enable highly sensitive ultrasound.
[0066]
In the present embodiment, the acoustic matching layer 4 is formed of epoxy resin.
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Since the speed of sound of epoxy resin is about 2500 m / s, the thickness is set to about 0.4 mm
at the center and about 0.8 mm at the periphery according to the resonance frequency of the
ultrasonic wave transmitted and received by the composite piezoelectric body 1 .
[0067]
The back load member 5 provided on the back side of the composite piezoelectric body 1 has a
function of generating ultrasonic waves generated in the composite piezoelectric body 1 and
propagating in the direction opposite to the sound wave radiation direction.
The back load member 5 prevents reflection of ultrasonic waves from the back side, and
contributes to broadening the resonant frequency characteristics of the ultrasonic probe 6.
That is, by providing the back surface load member 5, transmission and reception of ultrasonic
pulses with a short pulse width can be performed, so that high-resolution ultrasonic inspection
can be realized. In the present embodiment, the back load material 5 made of rubber in which
iron powder is dispersed is used.
[0068]
According to the ultrasonic probe 6 of the present embodiment, while the thickness of the
composite piezoelectric body 1 is constant, high frequency ultrasonic waves are transmitted and
received in the central portion, and low frequency ultrasonic waves are transmitted and received
in the peripheral portion. Because it can be performed, it is possible to operate in a wide
resonance frequency band. This is because, as shown in FIGS. 1 to 3, piezoelectric elements 2
having different resonance frequencies are two-dimensionally arranged in the composite
piezoelectric body 1.
[0069]
In the case of an ultrasonic probe in which an acoustic matching layer having a uniform
thickness is provided on a piezoelectric body with a normal flat plate-like piezoelectric ceramic,
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when the resonance frequency is 4 MHz, The band defined by the resonant frequency exhibiting
a value of 6 dB is approximately 2.8 to 5.2 MHz, and the relative band is approximately 60%. On
the other hand, the ultrasonic probe of the present embodiment has a relative bandwidth of
about 60% at 3.1 to 5.7 MHz. For this reason, the ultrasonic probe as a whole has a wide
frequency band of 1.9 to 6.9 Mz. When the central resonance frequency is set to 3.4 MHz, which
is a median value of 1.9 to 6.9 MHz, and the relative band is calculated, it is understood that it
has a very wide frequency ratio band of about 150%.
[0070]
The ultrasound probe 6 is used by being connected to the ultrasound diagnostic apparatus main
body 7 shown in FIG. The ultrasonic diagnostic apparatus main body 7 includes a transmitting
unit 8 for transmitting an ultrasonic signal to the ultrasonic probe 6, a receiving unit 9 for
receiving a voltage signal output from the ultrasonic probe, and various kinds of transmission
and reception of the ultrasonic signal. System control unit 10 for controlling the image, an image
configuration unit 11 for forming an image based on the obtained ultrasound signal, and an
image display unit 12 for displaying an image based on the image signal output from the image
configuration unit 11. And have.
[0071]
The ultrasound diagnostic apparatus 1 of the present embodiment operates as follows.
[0072]
By applying the drive pulse generated by the transmission unit 8 to the electrodes provided on
both sides of the composite piezoelectric body 1, the composite piezoelectric body 1 is deformed
in the thickness direction to generate an ultrasonic wave.
The generated ultrasonic waves propagate through the acoustic matching layer 4 to a human
body (not shown) which is a subject. The ultrasonic waves scattered and reflected in the human
body return to the composite piezoelectric body 1 soon. The reflected ultrasonic wave received
by the composite piezoelectric body 1 is converted into an electric signal, is imaged through the
receiving unit 9, and is displayed on the image display unit 12.
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[0073]
Since the signal received immediately after applying the drive pulse is a signal from a short
distance, the filter converts the image of only the high frequency signal into a selected image.
Thus, it is possible to construct a high resolution image in which the ultrasonic beam is focused
at a short distance.
[0074]
A signal received after a predetermined time is a far distance signal, and a low frequency signal is
received by the filter and imaged to form a high resolution image in which the ultrasound beam
is focused at the far distance. be able to. In this way, it is possible to form an image in which the
ultrasonic beam is focused at each point from the near distance to the far distance.
[0075]
Since the composite piezoelectric body 1 of the present embodiment has a uniform thickness, it is
easy to form an acoustic matching layer thereon. Moreover, since transmission and reception of
ultrasonic waves from low frequency to high frequency are possible and the frequency band is
broadened, transmission and reception of short pulse ultrasonic waves are possible, and
resolution in the depth direction is improved.
[0076]
According to the composite piezoelectric body 1 of the present embodiment, the size of the
opening is high-frequency transmission / reception in the narrow opening region in the central
portion and low-frequency ultrasonic waves transmission / reception in the wide opening region
in the peripheral portion. Can be controlled according to the resonance frequency of the
ultrasonic wave. By doing so, it becomes possible to form a narrow ultrasonic beam in a wide
range from a short distance to a long distance and to improve the resolution in the azimuthal
direction.
[0077]
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Second Embodiment A second embodiment of the present invention will be described with
reference to FIGS. 5 (a) to 5 (d). The difference between the present embodiment and the first
embodiment is the difference between the individual shapes of the piezoelectric element 2. The
other points are the same as in the first embodiment.
[0078]
FIGS. 5A to 5D are cross-sectional views corresponding to FIG. 2 and show cross sections of five
types of composite piezoelectric materials. Since each composite piezoelectric body 1 has a
uniform structure in the Y direction, the cross section cut at any position along the Y direction is
described in FIGS. 5 (a) to 5 (d). It is the same as the cross section.
[0079]
In the composite piezoelectric body 1 of FIG. 5A, the area of the cross section perpendicular to
the longitudinal direction (Z direction) of the piezoelectric element 2 is smaller in the both end
faces of the piezoelectric element than in the center of the piezoelectric element 2 doing. In
addition, the area of the cross section perpendicular to the longitudinal direction at the center of
the piezoelectric element 2 changes along the X direction. Of the plurality of piezoelectric
elements 2 arranged along the X direction, the resonance frequency of the piezoelectric element
2 located at the central portion of the composite piezoelectric body 1 is the same as that of the
piezoelectric element 2 located at the peripheral portion of the composite piezoelectric body 1 It
is designed to be higher than the resonant frequency.
[0080]
In the composite piezoelectric body 1 of FIG. 5B, each piezoelectric element 2 has a pair of
columnar portions, and a bridge portion (bridge portion) connecting the pair of columnar
portions is provided between the pair of columnar portions. . The thickness of the bridge portion
of the piezoelectric element 2 changes along the X direction. Specifically, the bridging portion of
the piezoelectric element 2 is relatively thick in the central portion in the X direction, and thinner
as it approaches the peripheral portion in the X direction. By adopting such a structure, it is
possible to relatively increase the resonance frequency in the in-plane central portion of the
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composite piezoelectric body.
[0081]
In the composite piezoelectric body 1 of FIG. 5C, each piezoelectric element 2 has an opening at
the center, and the size of the opening changes in the X direction. In this structure, as opposed to
the structure shown in FIG. 5B, the smaller the opening, the heavier the ends of the piezoelectric
element, and the lower the resonance frequency.
[0082]
In the composite piezoelectric body 1 of FIG. 5D, the area of the cross section perpendicular to
the longitudinal direction of the piezoelectric element is constant along the X direction, but has
different values depending on the position in the plane. Specifically, the piezoelectric element 2 is
thinner as it approaches the periphery of the composite piezoelectric body. Even if such a
structure is adopted, it is possible to transmit and receive a high frequency at the central portion
of the composite piezoelectric body and a low frequency ultrasonic wave at the end portion.
[0083]
Third Embodiment The present embodiment is characterized in that the material of the dielectric
portion is formed of different materials along the X direction. FIG. 6 is a cross-sectional view
corresponding to FIG.
[0084]
As shown in FIG. 6, in the central portion in the X direction, a dielectric material is formed using
a hard material having a high elastic modulus, and in the peripheral region a dielectric material is
formed using a soft material having a low elastic modulus. There is.
[0085]
In the present embodiment, since the periphery of the piezoelectric element at the central
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portion becomes hard, the substantial sound velocity of the piezoelectric element becomes fast,
and the resonance frequency becomes high.
On the other hand, since the periphery of the piezoelectric element in the peripheral portion is
soft, the resonant frequency of the piezoelectric element is close to that when the piezoelectric
element is in the free state, and is lower than the resonant resonant frequency of the
piezoelectric element located at the center.
[0086]
As a dielectric having a relatively high elastic modulus, an epoxy resin mixed with a ceramic filler
can be used. As a dielectric material used for a peripheral part, an epoxy resin single-piece | unit,
silicone resin, rubber | gum, etc. can be selected suitably, and can be used.
[0087]
According to the composite piezoelectric body of the present embodiment, the wide band and the
high resolution can be realized as in the above-described embodiment.
[0088]
Embodiment 4 In this embodiment, a method of manufacturing the composite piezoelectric body
of Embodiments 1 to 3 will be described.
[0089]
First, FIG. 7 will be referred to.
FIG. 7 shows the composite plate 15 in which the resin layer 14 is attached to one surface of the
plate-like piezoelectric body 13.
The plate-like piezoelectric body 13 is made of, for example, lead zirconate titanate (PZT). The
thickness of the plate-like piezoelectric body 13 used in the present embodiment is about 0.05
mm. Piezoelectric ceramics of such a thickness can be easily and inexpensively manufactured by
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sintering plate-like PZT ceramics at low price, ceramic green sheets (thickness: about 0.07 mm).
The ceramic green sheet is a sheet before sintering composed of ceramic powder and resin, and
is produced by a method such as doctor blade method, and when a thin layer or layer structure
piezoelectric body (laminated substrate etc.) is formed Are preferably used. Although the platelike piezoelectric body 13 can be produced by cutting a block-like ceramic, this method requires
a high cost process such as a cutting and polishing process. On the other hand, the method of
producing a plate-like piezoelectric body from a ceramic green sheet is advantageous in terms of
cost reduction because steps such as cutting and polishing are unnecessary.
[0090]
In the case of producing the plate-like piezoelectric body 13 by sintering the ceramic green
sheets, generally, a large number of ceramic green sheets are stacked and simultaneously
sintered from the viewpoint of reducing the cost of equipment. In this case, powder such as MgO,
which is said to be exfoliated powder, is piled up between the ceramic and green sheets so as not
to bond the stacked upper and lower ceramic and green sheets during sintering. The sintered
plate-like piezoelectric bodies 13 are washed one by one in order to remove the peeling powder.
When the size of the plate-like piezoelectric body 13 is about 15 mm square, in order to facilitate
handling such as handling, it is necessary to set its thickness to about 30 μm or more and to
ensure sufficient strength. In the case of a thin plate-like piezoelectric member 13 whose
thickness does not reach about 30 μm, its handling is difficult, so cracking or chipping is likely
to occur during handling, which may lower the manufacturing yield and increase cost. is there.
[0091]
As the resin layer 14, one in which an epoxy resin is formed into a sheet in a semi-cured state is
commercially available, and such a material can be usefully used. The composite plate 15 can be
manufactured by disposing the resin layer 14 made of such a resin sheet on the plate-like
piezoelectric body 13 and raising the temperature and curing while pressing. Specifically, an
epoxy semi-hardened resin (resin layer 14) having a release film attached on one side is
laminated on the plate-like piezoelectric body 13, and 120 sheets of this are laminated by a
piston-like jig, and then plate-like piezoelectric The laminate of the body 13 and the resin layer
14 is pressurized while being placed in a jig. For example, pressure may be applied for 5 minutes
while applying a pressure of about 1 MPa in an air atmosphere at 120 ° C. and 0.1 Torr or less.
Thereafter, the atmosphere is returned to the atmosphere to release the pressure, and then
maintained at 150 ° C. for 1 hour. After curing the resin layer 14 in this manner, the laminate is
taken out of the jig and the peelable film is peeled off, whereby 120 composite plates 15 can be
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obtained.
[0092]
Instead of using a resin sheet as the resin layer 14, the resin layer 14 can be formed by applying
a liquid resin on the plate-like piezoelectric body 13 by spin coating or the like and curing it.
[0093]
When the resin layer 14 is attached to one surface of the piezoelectric body 13, the thin platelike piezoelectric body 13 which is relatively easily damaged is protected by the resin layer 14,
so that the handling of the piezoelectric body 13 becomes easy.
[0094]
Each of the piezoelectric body 13 and the resin layer 14 used in the present embodiment has a
size of 15 mm in the X direction and a size of 15 mm in the Y direction.
The Z direction of the piezoelectric body 13 and the resin layer 14 is 0.05 mm and 0.025 mm,
respectively.
Thus, the thickness of the resulting composite plate is 0.075 mm.
[0095]
As shown in FIG. 8, a mask 16 for processing is formed on the exposed surface of the plate-like
piezoelectric body 13 of the composite plate 15 of FIG. The mask 16 used in the present
embodiment has a pattern for producing the composite piezoelectric body of the first
embodiment. That is, the mask 16 has a pattern in which the cross sections of the piezoelectric
element 2 shown in FIG. 3 are repeatedly and continuously arranged along the Z direction. When
a composite piezoelectric body having the configuration of FIGS. 5A to 5D is manufactured, a
mask having a pattern in which the cross sections of FIGS. 5A to 5D are repeatedly and
continuously arranged may be used. . The exposed surface of the plate-like piezoelectric body 13
on which the mask 16 of FIG. 8 is formed is parallel to the XZ plane perpendicular to the Y
direction, and the vibration direction of the composite piezoelectric body finally manufactured is
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the Z direction. .
[0096]
The mask 16 includes line-shaped pattern elements having an X-direction size (width) of 0.05
mm at the center in the X-direction. At both ends in the X direction, rectangular lands of 0.10
mm × 0.2 mm are added at intervals of 0.15 mm along the Z direction to the line elements of
the same width as the central portion.
[0097]
In a region between the central portion in the X direction and both end portions in the X
direction, rectangular land portions of 0.05 to 0.10 mm are arranged to have a size
corresponding to the position in the X direction.
[0098]
The mask 16 is formed by attaching a photosensitive resin sheet to the plate-like piezoelectric
body 13 and then exposing and developing the resin sheet using a photomask.
A light shielding pattern which defines the pattern shown in FIG. 8 is formed on the photomask.
Exposure and development of the photosensitive resin sheet can be performed using a known
photolithography technique. By changing the photomask pattern, the pattern and shape of the
mask 16 can be set arbitrarily.
[0099]
Next, sand blasting is performed on the surface of the composite plate 15 on which the
processing mask 16 is formed. Sand blasting is a process in which fine particles (abrasive
particles such as alumina and diamond) are sprayed together with compressed air to process
while breaking the workpiece by impact.
[0100]
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According to sand blasting, soft materials such as resin can be broken selectively and hard
materials such as ceramics can be broken without being broken. Therefore, by sandblasting using
the processing mask 16 made of resin, it is possible to selectively remove only the region of the
surface of the plate-like piezoelectric body 13 which is not covered by the processing mask.
[0101]
As the sand blasting progresses, the resin layer 14 disposed on the back side of the plate-like
piezoelectric body 13 is exposed, but the resin layer 14 is hardly broken like the processing
mask 16. In this manner, in the present embodiment, as shown in FIG. 9A, a plurality of
piezoelectric elements 2 can be formed from one plate-like piezoelectric body 13. Although eight
piezoelectric body elements 2 are shown in FIG. 9, in reality, several hundred piezoelectric body
elements 2 are formed from one plate-like piezoelectric body 13.
[0102]
According to the above-described sandblasting, the wide surface of the plate-like piezoelectric
body 13 can be collectively processed at high speed and precisely. However, in sandblasting, the
ratio of the depth to the width of the opening of the processing mask 16 ( If the aspect ratio is
large, this is an inappropriate processing method. However, in the present embodiment, the
depth direction of the cutting groove formed by sandblasting is not parallel but perpendicular to
the longitudinal direction of the piezoelectric element 2 to be formed. For this reason, when the
depth of the cutting groove formed by processing is D and the width of the cutting groove is W,
the ratio D / W in this embodiment is about 1. The ratio D / W defines the aspect ratio of the
cutting groove, and although depending on the material of the piezoelectric body, it is preferable
to set in a range of about 1 to 2. And when especially fine processing is required, it is desirable to
set ratio D / W to 1 or less.
[0103]
In the present embodiment, as described above, in order to process the piezoelectric material
from the direction perpendicular to the longitudinal direction (Z direction) of the columnar
piezoelectric material element 2, “aspect ratio of the piezoelectric material element 2” is 5
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Even if the size is exceeded, the aspect ratio of the cutting groove can be reduced. For this
reason, it becomes possible to easily form a columnar piezoelectric body having an aspect ratio
which has hitherto been considered impossible. Also, any structure not possible in the prior art,
such as thickening or thinning the central portion in the Z direction, can be formed.
[0104]
After processing, by peeling off the mask 16, as shown in FIG. 9B, a unit composite sheet 17
having a configuration in which the plurality of piezoelectric elements 2 are held by the resin
layer 14 can be obtained. In addition, if it is a method which can process the plate-like
piezoelectric material 13 into a predetermined shape, it will not be limited to sandblasting
processing, Ultrasonic processing, a laser processing method, etc. can also be used.
[0105]
Next, 300 unit composite sheets formed by the above-mentioned method are prepared, and the
process of lamination and integration is performed. In addition, according to the sandblasting
method, since a large amount of processing is possible at once, the time required to process the
composite plate of the above-mentioned size is very short, 2 hours or less. For this reason, the
manufacturing time of the unit composite sheet can be shortened to reduce the cost.
[0106]
Next, as shown in FIG. 10, a unit composite sheet is laminated | stacked, interposing the resin
layer 14 'different from the resin layer 14 which comprises a unit composite sheet. In FIG. 10,
although five unit composite sheets 17 are stacked for the sake of simplicity, 300 unit composite
sheets 17 are actually stacked. In lamination, the piezoelectric bodies of the respective layers are
arranged substantially parallel to each other, and the epoxy semi-cured resin having the same
size in the X and Y directions as the composite plate at the top and a thickness of 0.025 mm The
sheet is placed.
[0107]
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By applying heat to the thus formed laminate and curing and integrating the resin, it is possible
to obtain a composite piezoelectric block 18 which is a laminate of unit composite sheets.
Specifically, the laminate is left for 10 minutes while applying a pressure of about 0.1 MPa at
120 ° C., 0.1 Torr or less, then returned to atmospheric pressure, and at 180 ° C. without
applying a pressure. Heat for 1 hour. By curing the resin layers 14 and 14 'in this way and
integrating the laminates, it is possible to obtain the composite piezoelectric block 18, which is a
composite sheet laminate. The obtained composite piezoelectric block 18 has a rectangular
parallelepiped shape with X-direction size: 15 mm, Y-direction size: 30 mm, Z-direction size: 15
mm, and in one composite piezoelectric body block 30, 30, The 000 piezoelectric elements 2 are
held substantially parallel by the resin.
[0108]
Next, as shown in FIG. 11, the composite piezoelectric block 18 is cut and separated into a
plurality of composite piezoelectric members 19 along a plane perpendicular to the Z direction.
At this time, the cutting pitch is set to 0.35 mm, the cutting margin is set to 0.1 mm, and the
cutting start position is set to be the central portion of the piezoelectric body with the increased
diameter.
[0109]
Under such cutting conditions, a composite piezoelectric body 19 having a size of 15 mm in the
X direction, a size of 30 mm in the Y direction, and a size of 0.25 mm in the Z direction is
obtained from a composite piezoelectric block of 15 mm in the X direction, 30 mm in the Y
direction, and 15 mm in the Z direction. 42 pieces are obtained. In FIG. 11, only four composite
piezoelectric members 19 are shown for simplification.
[0110]
Next, electrodes are formed on the upper and lower surfaces (both end surfaces perpendicular to
the Z direction) of the obtained composite piezoelectric body 19 and polarization processing is
performed to obtain a composite piezoelectric body exhibiting piezoelectric characteristics.
[0111]
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According to the manufacturing method of the present embodiment, it is possible to easily form a
composite piezoelectric body having columns of piezoelectric bodies having complicated shapes,
and to easily form a composite piezoelectric body having a resonant frequency distribution.
In addition, since a thin plate-like piezoelectric material is attached to a resin layer and
processed, there is no need to dispose the piezoelectric material or handle it alone, and it
becomes possible to manufacture in a short time with a good yield.
[0112]
Fifth Embodiment In the composite piezoelectric body shown in FIG. 11, a void portion exists
between the piezoelectric elements 2 arranged on each unit composite sheet, and the void
portion is filled with air. Since air is also a dielectric, there is no need to fill the void with another
dielectric material in order to function as a composite piezoelectric. However, it is preferable to
embed the void portion with a hardenable dielectric material and harden it, because the
mechanical strength of the composite dielectric can be increased, and the vibration mode of the
composite piezoelectric can be properly adjusted. .
[0113]
In the present embodiment, first, a piezoelectric block manufactured by the same method as the
manufacturing method of the fourth embodiment is prepared. Then, the resin as the dielectric
material is filled in the void portion formed between the piezoelectric elements 2 in the
piezoelectric block to increase the mechanical strength of the composite piezoelectric body.
Specifically, the filling resin is impregnated in the void portion of the piezoelectric block and
cured. After that, in the same manner as each of the above-described embodiments, the cutting
process, the electrode forming process, and the polarization process of the composite
piezoelectric body 10 are performed.
[0114]
According to the present embodiment, breakage in a process such as cutting is less likely to
occur, and the yield is improved. As a result, the manufacturing cost can be further reduced. In
addition, when the void portion is filled with resin, the two surfaces on which the electrode is
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formed are not in communication with each other through the void portion. Therefore, even if
the electrode is formed using electroless plating, the two electrodes A short circuit can be easily
prevented. For this reason, electrodes can be formed collectively for a large amount of composite
piezoelectric materials, and cost reduction can be further promoted.
[0115]
Sixth Embodiment In the present embodiment, as shown in FIG. 12A, a unit composite sheet is
formed by performing a step of temporarily fixing a plate-like piezoelectric body 13 to a glass
substrate 21 with an adhesive sheet 20. Do. As the adhesive sheet 20, a thermal release sheet can
be used. However, the pressure-sensitive adhesive sheet 20 is not limited to a heat-releasing
sheet, and holds the plate-like piezoelectric body 13. When processing the piezoelectric body, the
plate-like piezoelectric body does not separate from the pressure-sensitive adhesive sheet and
breaks the piezoelectric body after processing. What is necessary is just what can be made to
exfoliate by a certain effect, without doing.
[0116]
Next, as shown in FIG. 12B, the plate-like piezoelectric body 13 is processed by sand blasting to
form the piezoelectric body element 2 having a desired shape. Before sandblasting, a mask (not
shown) is formed on the piezoelectric body 13 in the fourth embodiment. Thus, as shown in FIG.
12B, it is possible to obtain a structure in which the row of piezoelectric elements 2 is
temporarily fixed to the substrate 21 by the adhesive sheet 20.
[0117]
Next, as shown in FIG. 12C, the piezoelectric element 2 temporarily fixed to the substrate 21 is
made to face the sheet-like resin layer 14, and heat and pressure are simultaneously applied to
the resin layer 14. Thus, peeling of the piezoelectric element 2 from the adhesive sheet 20 and
adhesion to the resin layer 14 are simultaneously performed. A unit composite sheet can be
obtained by the above steps.
[0118]
The subsequent steps are carried out by the same method as described above, and finally, the
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composite piezoelectric shown in FIG. 1 is produced.
[0119]
In the unit composite sheet of the present embodiment, since the resin layer has not passed
through the heat history of complete curing, the adhesive strength is still maintained, and it is
not necessary to interpose a new adhesive sheet when constructing the laminate.
In addition, by applying a relatively high pressure, a part of the unit composite sheet can be
made to flow and cure during the laminating step, and the resin can be filled in the space (void)
of the piezoelectric body.
[0120]
Seventh Embodiment Each of the composite piezoelectric bodies 1 according to the above
embodiments has a uniform thickness, and has a structure in which the resonant frequency
changes stepwise only in the X direction. However, the composite piezoelectric body of the
present invention is not limited to the above configuration. For example, as in the cross section
perpendicular to the X direction, the cross section perpendicular to the Y direction may have a
structure in which the resonance frequency of the piezoelectric element changes according to the
position as shown in FIG.
[0121]
In the configurations shown in FIG. 3 and FIG. 5, the resonance frequency distribution is obtained
in which the resonance frequency is highest in the central portion and low in the peripheral
portion, but the resonance frequency distribution is not limited to this. FIG. 13 shows a
configuration in which the resonant frequency changes periodically along the X direction (or Y
direction). The distribution pattern of the resonant frequency is arbitrarily set according to the
application of the composite piezoelectric material.
[0122]
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31
FIG. 14 shows a configuration in which the composite piezoelectric body does not have a plane of
symmetry perpendicular to the Z direction. According to the manufacturing method described
with reference to FIG. 9, since the shape of the mask 16 can be freely designed, it is easy to form
a piezoelectric element having the structure shown in FIG.
[0123]
The desired resonant frequency distribution can also be obtained by arranging the piezoelectric
elements of the structure as shown in FIG.
[0124]
The composite piezoelectric body 1 does not have to have a uniform thickness.
By changing the shape of the piezoelectric element, it is possible to give an arbitrary distribution
in the resonance frequency of the sound wave to be emitted while keeping the thickness of the
composite piezoelectric body constant in the plane, but for other purposes The thickness of the
piezoelectric body may be changed according to the position. For example, the composite
piezoelectric body 1 having a structure as shown in FIG. 15 (a) or FIG. 15 (b) may be
manufactured for the purpose of focusing or diverging ultrasonic waves. Also in this case, the
resonance frequency is changed by appropriately changing the shape of the piezoelectric
element (not shown), the elastic modulus of the dielectric portion and the like according to the
position.
[0125]
It is a perspective view which shows the compound piezoelectric material in Embodiment 1 of
this invention. FIG. 5 is a cross-sectional view of the composite piezoelectric body according to
Embodiment 1 along the line A-A ′. FIG. 7 is a cross-sectional view of the composite
piezoelectric body in Embodiment 1 along the line B-B ′. It is a sectional view showing an
example of composition of an ultrasound probe and an ultrasound diagnostic device of the
present invention. (A) to (d) are cross-sectional views related to the second embodiment and
showing various configurations of the composite piezoelectric body according to the present
invention. It is sectional drawing which shows the composite piezoelectric material in
Embodiment 3 of this invention. It is a figure which shows the manufacturing process of the
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composite piezoelectric material of this invention. It is a figure which shows the manufacturing
process of the composite piezoelectric material of this invention. (A) And (b) is a figure which
shows the manufacturing process of the composite piezoelectric material of this invention. It is a
figure which shows the manufacturing process of the composite piezoelectric material of this
invention. It is a figure which shows the manufacturing process of the composite piezoelectric
material of this invention. (A) to (c) is a figure which shows the other manufacturing process of
the composite piezoelectric material of this invention. It is sectional drawing which shows the
further another structural example of the composite piezoelectric material of this invention. It is
sectional drawing which shows the further another structural example of the composite
piezoelectric material of this invention. It is a figure which shows the other structure of the
composite piezoelectric material of this invention. It is a perspective view which shows the
conventional ultrasonic probe.
Explanation of sign
[0126]
DESCRIPTION OF SYMBOLS 1 composite piezoelectric material 2 piezoelectric material element
(column-like piezoelectric material) 3 resin 4 acoustic matching layer 5 backing material 6
ultrasonic probe 7 ultrasonic diagnostic apparatus main body 8 transmission unit 9 reception
unit 10 system control unit 11 image formation unit 12 Image display portion 13 plate-like
piezoelectric body 14 resin layer 15 composite plate 16 processing mask 17 unit composite
sheet 18 composite piezoelectric body block 19 composite piezoelectric body 20 adhesive sheet
21 substrate 100 ultrasonic probe 101 piezoelectric body 102 matching layer 103 back surface
Load material
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