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DESCRIPTION JP2015115684

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DESCRIPTION JP2015115684
An object of the present invention is to suppress spurious resonances in a plane other than
resonance in the thickness direction of a piezoelectric body while improving electrical matching
with the system side of a device, and to generate spurious within the band of output ultrasonic
waves. The present invention provides a composite piezoelectric body, an ultrasonic probe and
an ultrasonic diagnostic imaging apparatus capable of suppressing high frequency and obtaining
high sensitivity characteristics in a wide band. An aspect ratio of a piezoelectric body is set to
satisfy the following formulas (1) to (3) or the following formulas (4) to (6). 0.5 ≦ W / H ≦ 0.65
(1) D / H W W / H (2) D / H ((13 W / H) / 3-13 / 6 (3) ) 0.5 ≦ D / H ≦ 0.65 (4) D / H ≦ W / H
(5) W / H ≧ (13 D / H) / 3-13 / 6 (3) 6) where H represents the thickness of the piezoelectric
body, W represents the length of one side perpendicular to the thickness direction, and D
represents the length of one side perpendicular to the thickness direction and W. [Selected
figure] Figure 3
Composite piezoelectric body, ultrasonic probe and ultrasonic diagnostic imaging apparatus
[0001]
The present invention relates to a composite piezoelectric body, an ultrasonic probe and an
ultrasonic diagnostic imaging apparatus.
[0002]
Ultrasound generally refers to sound waves of 16000 Hz or more, and is applicable to various
fields such as inspection of defects and diagnosis of diseases because it can be inspected
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nondestructively, harmlessly and substantially in real time.
One of them is an ultrasonic diagnostic imaging apparatus that scans the inside of a subject with
ultrasound and images the internal state of the inside of the subject based on a reception signal
generated from a reflected wave of the ultrasound propagating from the inside of the subject. is
there. This medical diagnostic ultrasound system has various features such as small size and low
cost compared to other medical imaging devices for medical use, and no radiation exposure such
as X-rays and high safety. There is. For this reason, the ultrasound imaging apparatus includes a
circulatory system (eg, coronary artery of heart, etc.), a digestive system (eg, gastrointestinal
tract, etc.), an internal medicine system (eg, liver, pancreas, spleen, etc.), a urinary system (eg, It
is widely used in the kidney and bladder, etc.) and in obstetrics and gynecology.
[0003]
An ultrasound probe that transmits and receives ultrasound to and from a subject is used in the
ultrasound diagnostic imaging apparatus. The ultrasonic probe mechanically vibrates based on
the electric signal of transmission by utilizing the piezoelectric phenomenon to generate an
ultrasonic wave, and receives the reflected wave of the ultrasonic wave generated by the
difference in acoustic impedance inside the object. A plurality of ultrasonic transducers that
generate received electric signals are provided, and the plurality of ultrasonic transducers are
arranged, for example, in a one-dimensional array or a two-dimensional array.
[0004]
Conventionally, as this piezoelectric element, a single ceramic material such as PZT (lead
zirconate titanate) has been applied, but in recent years, the ceramic material is arranged at equal
intervals and an epoxy resin or the like is interposed therebetween. The composite piezoelectric
body configured by filling the polymer of (1) has come to be used.
[0005]
In such a composite piezoelectric body, it is known to make the aspect ratio of the columnar
piezoelectric ceramic sintered body (piezoelectric body) in the range of 0.1 to 0.5 so as to obtain
a preferable dielectric constant and acoustic impedance. (For example, patent document 1).
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Here, the length of the minor axis of the structure / the length of the major axis is defined as the
aspect ratio.
[0006]
Patent No. 4528383 gazette
[0007]
However, in the case of a composite piezoelectric body as disclosed in Patent Document 1
described above, when it is intended to output an ultrasonic wave of a desired frequency, the
thickness of the piezoelectric body is determined, so the width of the element is limited to a
constant. Becomes thin and the effective area decreases, so it is possible to obtain a high
electromechanical coupling coefficient that matches the aspect ratio, but the electrical impedance
rises and it becomes difficult to achieve electrical matching with the system side of the device, It
may be difficult to obtain a large signal output.
On the other hand, if the aspect ratio of the piezoelectric body is made too large, unnecessary
resonance in the plane other than the resonance in the thickness direction of the piezoelectric
body causes a spurious within the band of the output ultrasonic wave, and a wide band It
becomes difficult to obtain high sensitivity characteristics.
[0008]
The object of the present invention is to improve electrical matching with the system side of the
device while suppressing unnecessary resonance in the plane other than resonance in the
thickness direction of the piezoelectric body, and spurious within the band of the output
ultrasonic wave. An object of the present invention is to provide a composite piezoelectric
material, an ultrasonic probe and an ultrasonic diagnostic imaging apparatus capable of
suppressing generation and obtaining a wide band and high sensitivity characteristics.
[0009]
In order to solve the above problems, the invention according to claim 1 comprises a plurality of
columnar piezoelectric bodies arranged at predetermined intervals in an array, and a
nonconductive polymer positioned between the piezoelectric bodies. In the composite
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piezoelectric body, the aspect ratio of the piezoelectric body satisfies the following formulas (1)
to (3) or the following formulas (4) to (6).
0.5 ≦ W / H ≦ 0.65 (1) D / H W W / H (2) D / H ((13 W / H) / 3-13 / 6 (3) ) 0.5 ≦ D / H ≦
0.65 (4) D / H ≦ W / H (5) W / H ≧ (13 D / H) / 3-13 / 6 (3) 6) where H represents the
thickness of the piezoelectric body, W represents the length of one side perpendicular to the
thickness direction, and D represents the length of one side perpendicular to the thickness
direction and W.
[0010]
According to a second aspect of the present invention, in the composite piezoelectric body
according to the first aspect, the surface roughness of the piezoelectric body and the polymer is
0.2 μm or less on at least the piezoelectric body and one surface on which the polymer is
exposed. It is characterized by being.
[0011]
The invention according to claim 3 is characterized in that, in the composite piezoelectric body
according to claim 1 or 2, the grain size of the piezoelectric body is 3 μm or less.
[0012]
The invention according to claim 4 is an ultrasonic probe, comprising a backing layer, the
composite piezoelectric body according to any one of claims 1 to 3 and an acoustic matching
layer laminated in this order. It is characterized by
[0013]
The invention according to claim 5 is the ultrasonic probe according to claim 4, wherein the
composite piezoelectric body is divided at a predetermined interval by a first dividing groove
along the arrangement direction of the piezoelectric bodies. And each of the elements is divided
into a plurality of parts by a second dividing groove which is parallel to the first dividing groove
and shallower than the first dividing groove.
[0014]
The invention according to claim 6 is the ultrasonic diagnostic imaging apparatus, wherein the
ultrasonic probe according to claim 4 or 5 and a transmission signal for applying a voltage to the
composite piezoelectric material are the ultrasonic waves. A transmitter configured to transmit to
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a probe, a receiver configured to receive an electrical signal converted by the ultrasonic probe as
a received signal, and ultrasonic image data generated based on the received signal received by
the receiver And a display unit for displaying an ultrasound image based on the ultrasound image
data generated by the image processing unit.
[0015]
According to the present invention, while achieving good electrical matching with the system
side of the device, unnecessary resonance in the plane other than resonance in the thickness
direction of the piezoelectric body is suppressed, and spurious noise is generated within the band
of the output ultrasonic wave. It is possible to suppress generation and obtain high sensitivity
characteristics in a wide band.
[0016]
It is a perspective view which shows the external appearance structure of the ultrasound
diagnostic imaging apparatus based on this Embodiment.
It is a block diagram which shows the functional structure of an ultrasound diagnostic imaging
apparatus.
It is sectional drawing which shows the structure of an ultrasonic transducer | vibrator typically.
It is a graph which shows the conditions of the aspect ratio of a piezoelectric material.
It is a figure which shows the frequency spectrum of the ultrasonic wave output from a
piezoelectric material.
It is a graph explaining a roughness curve.
It is a graph which shows the relationship between the surface roughness of a composite
piezoelectric material, and the bandwidth of an ultrasonic probe. It is the enlarged view which
looked at the ultrasonic transducer | vibrator from the major axis direction.
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[0017]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. However, the scope of the invention is not limited to the illustrated example. In the
following description, components having the same function and configuration are denoted by
the same reference numerals, and the description thereof is omitted.
[0018]
As shown in FIG. 1, the ultrasound diagnostic imaging apparatus 1 according to the present
embodiment includes an ultrasound probe 2 and a diagnostic apparatus main body 4, which are
connected via a cable 3. The ultrasonic probe 2 transmits ultrasonic waves (transmission
ultrasonic waves) to a subject such as a living body (not shown) and receives ultrasonic waves
(reflected ultrasonic waves) reflected by the subject. In the present embodiment, the ultrasound
probe 2 is configured by arranging a plurality of ultrasound transducers 21 (see FIG. 2) in an
array. The diagnostic device body 4 causes the ultrasonic probe 2 to transmit an ultrasonic wave
by transmitting a transmission signal of an electric signal through the cable 3 and converts the
ultrasonic wave received by the ultrasonic probe 2 Based on the received signal, the internal
state inside the subject is imaged as a tomographic image.
[0019]
The diagnostic device body 4 includes an operation input unit 11 and a display unit 16 at the
top. The operation input unit 11 includes switches, buttons, a trackball, a mouse, a keyboard, etc.
for performing various setting operations, etc., and can input commands such as a command to
start diagnosis and data such as personal information of a subject . The display unit 16 displays a
support image for an operation by the operation input unit 11, an ultrasonic image created based
on a reception signal, and the like. Further, a holder 7 for holding the ultrasound probe 2 when
not in use is provided at an appropriate position of the operation input unit 11 or the diagnostic
device body 4.
[0020]
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Next, the functional configuration of the diagnostic device body 4 will be described with
reference to FIG. In addition to the operation input unit 11 and the display unit 16 described
above, the diagnostic device body 4 includes, for example, a transmission unit 12, a reception
unit 13, a signal processing unit 14, an image processing unit 15, a control unit 17 and a voltage
control unit 18. There is.
[0021]
The transmission unit 12 is a circuit that generates a transmission pulse as a transmission signal
to the ultrasound probe 2 according to the control of the control unit 17. The transmitter 12
outputs a transmission pulse to the voltage controller 18 via the controller 17. The transmission
pulse is amplified in amplitude by the voltage control unit 18 and transmitted to the ultrasound
probe 2. The ultrasound probe 2 outputs transmission ultrasound according to the received
transmission pulse. At this time, the transmission unit 12 forms a transmission beam so that the
transmission ultrasonic waves from the ultrasonic transducers 21 converge at a predetermined
focal position. The above-mentioned transmission ultrasonic wave may be constituted by a
plurality of encoded pulses expanded in the time axis direction.
[0022]
The receiving unit 13 is a circuit that receives a received signal of an electrical signal from the
ultrasound probe 2 via the cable 3 according to the control of the control unit 17, and outputs
the received signal to the signal processing unit 14.
[0023]
The signal processing unit 14 detects the reflected ultrasound from the output of the receiving
unit 13.
[0024]
The image processing unit 15 is a circuit that generates data (ultrasound image data) of an image
of the internal state of the subject based on the reception signal processed by the signal
processing unit 14 under the control of the control unit 17.
[0025]
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The display unit 16 is a device that displays an ultrasound image of the subject based on the
ultrasound image data generated by the image processing unit 15 under the control of the
control unit 17.
The display unit 16 is realized by a display device such as a CRT (Cathode-Ray Tube) display, an
LCD (Liquid Crystal Display), an organic EL (Electronic Luminescence) display, an inorganic EL
display, a plasma display, or a printing device such as a printer. Ru.
[0026]
The control unit 17 includes a microprocessor, a memory element, and peripheral circuits
thereof, and the operation input unit 11, the transmission unit 12, the voltage control unit 18,
the reception unit 13, the signal processing unit 14, the image processing unit 15, and the like. It
is a circuit which performs overall control of the ultrasound diagnostic imaging apparatus 1 by
controlling the display unit 16 according to the function.
[0027]
As shown in FIG. 3, for example, the ultrasonic transducer 21 is configured by laminating a
backing (back) layer 22, a piezoelectric layer 24, and an acoustic matching layer 25 from the
lower side in a front view in the figure, and each is an epoxy adhesive Etc. are bonded with an
adhesive.
An acoustic lens may be stacked above the acoustic matching layer 25 as necessary.
[0028]
The backing layer 22 is an ultrasonic absorber that supports the piezoelectric layer 24 and can
absorb unnecessary ultrasonic waves.
That is, the backing layer 22 is provided on the opposite side of the piezoelectric layer 24 to the
direction in which ultrasonic waves are transmitted to and received from the subject, and is
generated from the opposite side of the direction of the subject to the piezoelectric layer 24 and
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reaches the backing layer 22 Absorbs ultrasound.
In the present embodiment, the backing layer 22 may not be provided.
[0029]
As a backing material which constitutes backing layer 22, vinyl chloride, polyvinyl butyral (PVB),
ABS resin, polyurethane (PUR), polyvinyl alcohol (PVAL), polyethylene (PE), polypropylene (PP),
polyacetal (POM), polyethylene Thermoplastic resins such as terephthalate (PETP), fluorocarbon
resin (PTFE), polyethylene glycol, polyethylene terephthalate-polyethylene glycol copolymer,
natural rubber, ferrite rubber, epoxy resin, silicone resin powder such as tungsten oxide, titanium
oxide, ferrite A composite material which has been pressed and molded, and further, the
composite material is pulverized and then mixed with the above-described thermoplastic resin,
epoxy resin or the like to be cured can be used. In order to adjust the acoustic impedance, an
inorganic material such as macor glass or a porous material having an air gap can also be used.
[0030]
A preferable backing material is a rubber composite material and / or an epoxy resin composite
material, and the shape thereof is appropriately selected according to the shape of the
piezoelectric layer 24 and the ultrasonic probe 2 including the same. be able to.
[0031]
In the present embodiment, the piezoelectric layer 24 is formed of a composite piezoelectric
material in which prismatic piezoelectric materials and polymer layers are alternately arranged in
a one-dimensional array.
[0032]
As materials of the piezoelectric body, conventionally used quartz, piezoelectric ceramics PZT,
PZLT, thin films such as piezoelectric single crystals PZN-PT, PMN-PT, LiNbO3, LiTaO3, KNbO3,
ZnO, AlN, etc. In addition to inorganic piezoelectric materials, polyvinylidene fluoride and
polyvinylidene fluoride copolymers, polyvinylidene cyanide and vinylidene cyanide copolymers,
odd nylon such as nylon 9 and nylon 11, aromatic nylon, alicyclic nylon, poly Examples thereof
include lactic acid, polyhydroxycarboxylic acids such as polyhydroxybutyrate, cellulose
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derivatives, and organic piezoelectric materials such as polyurea.
Furthermore, composite materials in which an inorganic piezoelectric material and an organic
piezoelectric material, and an inorganic piezoelectric material and an organic polymer material
are used in combination are also included.
In the present embodiment, in particular, a piezoelectric material having a grain size of 3 μm or
less is preferable. When the grain size is 3 μm or less, it is possible to reduce the surface
roughness caused by the detachment of the grain during processing of the piezoelectric material.
Moreover, since the increase in the volume to be lost can be suppressed, the loss of the
piezoelectricity can be suppressed, the loss of the effective area and the capacitance can be
suppressed, and the high piezoelectricity can be maintained.
[0033]
The piezoelectric material mentioned above can use a commercially available thing as an
inorganic piezoelectric material, For example, C-6, C-6H, C-62, C-63, C-63, C-64, C made from
Fuji ceramic company -601, C-7, C-8, C-82, C-83 H, C-84, C-9, C-91, C-91 H, C-92 H, C-93, C-94,
or Tayka L-1A, L-6A, L-201F, L-11, L-9, L-155N, L-155NF, L-145N, L-13 and the like. Further, as
an organic piezoelectric material, a PVDF film manufactured by Tokyo Sensor, a poly (vinylidene
fluoride-co-trifluoroethylene) film manufactured by Kureha, a poly (vinylidene fluoride-cohexafluoro) manufactured by Aldrich as a reagent Propylene) and the like.
[0034]
As the polymer constituting the polymer layer, thermosetting resins such as epoxy resin, phenol
resin, urea resin, melamine resin, polyester, polysilicon, polyurethane, silicone resin, polyolefin,
polyacetal, polycarbonate, polyphenylene sulfide, polyamide And thermoplastic resins such as
polyimide, polyamide imide, and polyether ether ketone. Further, fine particles may be mixed
with the above-mentioned materials. Examples of the fine particles include those made of
inorganic materials such as ferrite, zinc oxide, silica, glass, carbon, etc., and organic materials
such as polymers, and those having a flat shape or anisotropy other than spherical shape. It may
be In addition, it may be a hollow particle shape or a composite composed of two or more kinds
of materials.
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[0035]
The piezoelectric layer 24 configured as described above is manufactured by a known
manufacturing method. That is, the piezoelectric materials such as the piezoelectric ceramic and
the single crystal are cut in an array to form grooves at predetermined intervals. Alternatively,
the piezoelectric material may be cut into a predetermined size to form a plurality of
piezoelectric bodies by providing gaps at predetermined intervals. Further, a plurality of
piezoelectric bodies may be molded by a mold. Then, the polymer is filled and cured in the gaps
between the plurality of piezoelectric members to form a polymer layer. Then, the upper and
lower surfaces of the integrated piezoelectric body and polymer layer are ground so as to have a
predetermined thickness. Specifically, for example, a piezoelectric material and a polymer layer
integrated in a disk-like flat lapping machine are disposed, and a liquid abrasive mixed with free
abrasives and a liquid is poured into the lapping machine from above and below Polishing is
performed by sliding while applying pressure. Thus, a composite piezoelectric body is formed.
Electrodes are sandwiched between upper and lower surfaces of the ground composite
piezoelectric body, and a predetermined polarization voltage is applied to perform polarization
processing.
[0036]
At this time, in the present embodiment, the composite piezoelectric body is formed such that the
aspect ratio of the piezoelectric body satisfies the following formulas (7) to (9) or the following
formulas (10) to (12). 0.5 ≦ W / H ≦ 0.65 (7) D / H W W / H (8) D / H ((13 W / H) / 3-13 / 6
(9) ) 0.5 ≦ D / H ≦ 0.65 (10) D / H ≦ W / H (11) W / H ≧ (13 D / H) / 3-13 / 6 12) where H
represents the thickness of the piezoelectric body, W represents the length of one side
perpendicular to the thickness direction, and D represents the length of one side perpendicular to
the thickness direction and W.
[0037]
The condition of the aspect ratio of the piezoelectric body can be represented by a range
surrounded by a solid line A in FIG.
[0038]
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In the present embodiment, by configuring the piezoelectric body as described above,
unnecessary resonance in the plane other than resonance in the thickness direction of the
piezoelectric body is suppressed, and spurious is generated in the band of the output ultrasonic
wave. Can be obtained and broadband and high sensitivity characteristics can be obtained.
In addition, electrical alignment with the system side of the diagnostic device body 4 can be
obtained well. For example, when the aspect ratio exceeds the above-mentioned conditions, in
addition to the resonance in the thickness direction of the piezoelectric body, unnecessary
resonance may occur in the plane, causing spurious within the desired band and narrowing the
band. , The sensitivity decreases. FIG. 5 shows frequency spectra in the case where a spurious is
generated in the ultrasonic wave output from the piezoelectric body and in the case where the
generation of the spurious is suppressed as in the present embodiment. In FIG. 5, the frequency
spectrum when the generation of the spurious is suppressed is indicated by a solid line P, and the
frequency spectrum when the spurious is generated is indicated by a broken line Q. As shown in
FIG. 5, it can be seen that, when the spurious occurs, the high frequency part in the band is cut
off, the band becomes narrow, and the sensitivity is also reduced. In addition, when the aspect
ratio of the piezoelectric body falls below the above-mentioned condition, the electrical
impedance rises, and it becomes difficult to obtain the electrical matching with the system side of
the diagnostic device body 4, and it becomes difficult to obtain a large signal output. There is a
case. In addition, since the thickness of the piezoelectric body is defined by the frequency of the
ultrasonic wave to be output, the piezoelectric body must be extremely thinned to obtain a
desired frequency when the aspect ratio of the piezoelectric body is less than the abovedescribed condition. It may be difficult to process as designed, such as product variation.
[0039]
The acoustic impedance of the piezoelectric layer 24 made of a composite piezoelectric body is
determined based on the volume ratio of the piezoelectric body and the polymer layer
constituting the piezoelectric layer 24. Assuming that the acoustic impedance of the piezoelectric
body is Z A (MRayls), the volume ratio is V A (volume%), the acoustic impedance of the polymer
layer is Z B (MRayls), and the volume ratio V B (volume%) The acoustic impedance V TOTAL
(MRayls) is defined by the following equation (13). V TOTAL =(Z A ×V A +Z B ×V
B )/100・・・(13)
[0040]
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By the way, in the grinding process described above, pressure is applied to the upper and lower
surfaces of the integrated piezoelectric body and polymer layer. Therefore, the polymer layer is
shrunk at the time of grinding due to this pressure, and is ground in that state. Therefore, when
the pressure is released and the grinding process is finished, the contraction of the polymer layer
may be restored, and the polymer layer may protrude from the piezoelectric body to cause a step.
When other components are stacked in this state, the adhesive layer may be thickened due to the
unevenness, which may reduce the sound propagation efficiency of the ultrasonic wave.
Therefore, in the present embodiment, the composite piezoelectric body is further subjected to a
process of polishing both surfaces thereof using a polishing film in which abrasive particles are
coated on a base film, as follows. Note that such a process is preferable because it can improve
the sound propagation efficiency, but may not be performed.
[0041]
Examples of base films applicable in the present embodiment include polyesters such as
polyimide, polyamide, polyimideamide, polyethylene terephthalate (PETP), polyethylene
naphthalate (PEN), and polymethyl methacrylate (PMMA). Films of plastics such as polyacrylates,
polymethacrylates, polycarbonate resins, polyurethanes, cycloolefin polymers, etc. are applicable.
Moreover, as abrasive particles that can be applied in the present embodiment, silicon carbide
(SiC), aluminum oxide (Al 2 O 3), chromium oxide (Cr 2 O 3), iron oxide (FexO y), diamond ( C)
Inorganic materials such as cerium oxide (CeO 2) and silicon oxide (SiO 2), organic materials
such as phenol resin and epoxy resin, or materials obtained by combining the above-mentioned
inorganic materials and organic materials are applicable. is there. In addition, the particle size of
the abrasive particles is 9 μm or less, preferably 3 μm or less. In the present embodiment, at
least three randomly selected piezoelectric and polymer layers on both sides of the composite
piezoelectric body, and the surface roughness (Ra) in the area of 0.2 mm × 0.2 mm is 0.2 μm or
less. Polish the composite piezoelectric body until it reaches Although in the present
embodiment, the polishing process is performed on both surfaces of the composite piezoelectric
body, the polishing process may be performed only on one side (the surface facing the backing
layer 22). Here, surface roughness (Ra) refers to arithmetic mean roughness. For example, as
shown in FIG. 6, the arithmetic mean roughness is obtained by measuring the surface roughness
at a plurality of locations with a measuring device such as a scanning confocal laser microscope
to obtain a roughness curve. The method of measuring the surface roughness may be contact or
non-contact. Then, only a reference length (l) is extracted from the roughness curve in the
direction of the average line, the X axis is taken in the direction of the average line of the
extracted portion, and the Y axis is taken in the direction of longitudinal magnification. When it
represents with y = f (x), what represents the value calculated | required by following formula
(14) with a micrometer (micrometer) turns into surface roughness (Ra). This is the surface
roughness in a one-dimensional straight line, but the surface roughness (Ra) of the present
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invention is also included in the case where this concept is developed on a two-dimensional
plane.
[0042]
According to the present embodiment, the exposed portions of the piezoelectric body and the
polymer layer of the composite piezoelectric body can be simultaneously polished, and moreover,
the polarized composite piezoelectric body does not depolarize. In addition, the protruding
portion of the polymer layer can be appropriately polished. Therefore, it becomes possible to
form a composite piezoelectric material which can form a low-cost, highly reliable electrode and
which has a surface roughness close to that of a mirror surface.
[0043]
Here, the relationship between the surface roughness of the composite piezoelectric body and
the bandwidth of the ultrasonic probe 2 will be described. The layer thickness of the adhesive
layer formed by the adhesive used when adhering the piezoelectric layer 24 depends on the
surface roughness of the composite piezoelectric body of the piezoelectric layer 24; the larger
the surface roughness, the more the layer thickness of the adhesive layer Is in a relationship of
becoming larger. And as the layer thickness of the adhesive layer is larger, the high frequency
side of the band of the ultrasonic probe 2 tends to narrow and narrow in the high frequency side,
so the smaller the surface roughness, the wider the band can be maintained. . Here, FIG. 7 shows
the relationship between the surface roughness of the composite piezoelectric body and the
relative bandwidth of −6 dB of the ultrasound probe 2. As shown in FIG. 7, it can be seen that
when the surface roughness of the composite piezoelectric material is 0.3 μm or more, the
relative bandwidth of −6 dB drops significantly. Therefore, according to FIG. 7, although it can
be said that the surface roughness of the composite piezoelectric body is preferably 0.3 μm or
less, when the surface roughness of the composite piezoelectric body is larger than 0.2 μm, The
change of bandwidth by -6 dB due to product variation is large. Therefore, in the present
embodiment, the composite piezoelectric body is polished until the surface roughness becomes
0.2 μm or less.
[0044]
As described above, in the present embodiment, since the surface roughness of the composite
piezoelectric material is 0.2 μm or less, the layer thickness of the adhesive layer can be reduced,
and it is suitably used for an ultrasonic probe for high frequency applications. And can maintain
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high sensitivity.
[0045]
In order to form the electrode layer on the composite piezoelectric body prepared as described
above, first, a base metal such as titanium (Ti) or chromium (Cr) is formed to a thickness of 0.02
to 1.0 μm by sputtering. Subsequently, a part of the insulating material is optionally combined
with a metal material consisting mainly of a metal element or a metal material thereof or an alloy
thereof to form a thickness of 1 to 10 μm by a suitable method such as a sputtering method. Is
done.
As the metal material, gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu), nickel (Ni),
tin (Sn) or the like is used. Electrode formation can also be performed by apply | coating the
conductive paste which mixed the metal powder of fine powder and low melting glass with
screen printing, the dipping method, the thermal-spraying method etc. besides said sputtering
method.
[0046]
An FPC (Flexible Printed Circuits) 27 is sandwiched between the backing layer 22 and the
piezoelectric layer 24, and the FPC 27 sends a transmission signal from the voltage control unit
18 to the piezoelectric layer 24. Further, the reception signal generated by the piezoelectric layer
24 is given to the receiving unit 13 by the FPC 27.
[0047]
The acoustic matching layer 25 matches the acoustic impedance between the piezoelectric layer
24 and the subject to suppress reflection at the interface. The acoustic matching layer 25 is
disposed on the object side of the piezoelectric layer 24 in the direction in which transmission
and reception of ultrasonic waves are performed. The acoustic matching layer 25 has an acoustic
impedance substantially intermediate between the piezoelectric layer 24 and the subject.
[0048]
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Materials used for the acoustic matching layer 25 include aluminum, aluminum alloy (for
example, AL-Mg alloy), magnesium alloy, macor glass, glass, fused quartz, copper graphite, PE
(polyethylene), PP (polypropylene), PC (polycarbonate) ), ABC resin, ABS resin, AAS resin, AES
resin, nylon (PA6, PA6-6), PPO (polyphenylene oxide), PPS (polyphenylene sulfide: may be
contained in glass fiber), PPE (polyphenylene ether), PEEK (poly Ether ether ketone), PAI
(polyamide imide), PETP (polyethylene terephthalate), an epoxy resin, a urethane resin etc., and
the composite material which mixed these and other materials can be used. Preferably, it is
molded by adding zinc flower, titanium oxide, silica or alumina, bengara, ferrite, tungsten oxide,
ytterbium oxide, barium sulfate, tungsten, molybdenum, organic fine particles, etc. as a filler to a
thermosetting resin such as epoxy resin Can be applied.
[0049]
The acoustic matching layer 25 may be a single layer or a plurality of layers, but is preferably
two or more layers, more preferably four or more layers. The layer thickness of the acoustic
matching layer 25 is preferably determined to be λ / 4, where λ is the wavelength of the
ultrasonic wave transmitted through the matching layer. The thickness of such an acoustic
matching layer depends on the center frequency, but generally, a thickness in the range of about
20 to 500 μm is used. The acoustic matching layer 25 is formed by lamination bonding or
multilayer coating in the thickness direction, and the acoustic impedance is matched by
weighting the acoustic impedance in the thickness direction by making each material
configuration different in each layer. The weighting direction of the acoustic impedance in the
acoustic matching layer 25 is not limited to the thickness direction, but may be horizontal.
[0050]
As shown in FIG. 8, in the laminated body configured as described above, main die grooves (first
divided grooves) 31 are inserted at predetermined intervals along the minor axis direction (the
arrangement direction of the piezoelectric members) by dicing. Thereby, it is divided into a
plurality of (for example, 192) elements (ultrasonic transducer 21). Specifically, a dicing blade is
installed along the minor axis direction to the above-mentioned laminate, and dicing is performed
from the acoustic matching layer 25 side to the backing layer 22 at a predetermined interval in
the major axis direction (azimuth direction) Thus, the acoustic matching layer 25, the
piezoelectric layer 24, and a part of the backing layer 22 are divided, and the plurality of
ultrasonic transducers 21 are formed in a one-dimensional array. A gap between the adjacent
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ultrasonic transducers 21 formed in this manner is a main die groove 31.
[0051]
Furthermore, in the present embodiment, two sub-die grooves (second divided grooves) 32
parallel to the main die groove 31 and shallower than the main die groove 31 are inserted into
each of the divided ultrasonic transducers 21. Thus, each ultrasonic transducer 21 is divided into
three fine elements. In the sub die groove 32, for example, a dicing blade is installed parallel to
the main die groove 31 in the laminate, and the acoustic matching layer 25 is diced from the
acoustic matching layer 25 side to a predetermined depth of the piezoelectric layer 24. And a
part of the piezoelectric layer 24 are divided into fine elements. In this embodiment, one
ultrasonic transducer 21 is divided into three fine elements, but the number of divisions can be
set arbitrarily. According to the present embodiment, by dividing one element into a plurality of
fine elements, it becomes possible to obtain a desired frequency without being subject to
dimensional constraints. In the present embodiment, it is possible not to perform microelement
formation.
[0052]
Hereinafter, the present invention will be described in more detail by way of examples, but of
course the present invention is not limited to these examples.
[0053]
<Preparation of Composite Piezoelectric> As shown in Table 1 below, processing was performed
under the conditions shown in A to E to prepare composite piezoelectrics of Examples 1 to 6 and
Comparative Examples 1 to 4.
That is, grooves having a width B μm and a depth of 0.4 mm were continuously formed along
long sides at pitch C μm intervals in a general-purpose ceramic piezoelectric material A (10 mm
× 60 mm × 1 mm), and this was cleaned. The aspect ratio (D / H, W / H) of the piezoelectric
body at this time was as shown in Table 1 below. Then, the processed groove was filled with an
epoxy resin, and the temperature was gradually raised from room temperature to completely
cure the filled epoxy resin. Thereafter, the upper and lower surfaces of the ceramic piezoelectric
material filled with the epoxy resin were ground to expose the ceramic piezoelectric material and
the epoxy resin on both surfaces, and the upper and lower surfaces of the composite
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piezoelectric material were further ground until the thickness was 125 μm. Thereafter, the
upper and lower surfaces of the composite piezoelectric material were further polished using a
polishing film in which artificial diamond abrasive particles of 3 μm in particle size were coated
on a substrate film, and the thickness was made 120 μm. Thereafter, this composite
piezoelectric material was cut out to a size of 4.6 mm × 42.5 mm, electrodes were formed, and
polarization processing was performed to prepare composite piezoelectric bodies of Examples 1
to 6 and Comparative Examples 1 to 4, respectively.
[0054]
<Fabrication of Ultrasonic Probe> First, four acoustic matching materials were laminated to
produce an acoustic matching layer. The acoustic matching materials of the respective layers
were produced by kneading and curing the epoxy resin and the ferrite or the fine powder of the
silicone resin so as to satisfy the following conditions. That is, the acoustic matching material of
the uppermost layer, which is the outermost layer on the acoustic radiation side, has an acoustic
impedance of 2.0 MRayls and a thickness of 40 μm, and the acoustic matching material of the
second layer has an acoustic impedance of 4.0 MRayls and a thickness of 40 μm, The acoustic
matching material of the third layer had an acoustic impedance of 6.0 MRayls and a thickness of
50 μm, and the acoustic matching material of the fourth layer (bottom layer) had an acoustic
impedance of 11.0 MRayls and a thickness of 60 μm. The acoustic matching material of each
layer thus prepared is laminated in the above-mentioned order and bonded by heat curing with
an epoxy adhesive under a pressure condition of 2.94 MPa, and then the size of 4.6 mm × 42.5
mm It was molded into an acoustic matching layer.
[0055]
Next, using the composite piezoelectric body of Example 1 prepared as described above, along
the longitudinal direction of the insulating groove in the vicinity of both ends of the short axis on
the back side so that the effective opening in the short axis direction is 4.0 mm. A signal
electrode and a ground electrode were formed to form a piezoelectric layer of Example 1.
[0056]
Thereafter, while the patterned FPC, the backing layer and the fixing plate are laminated and
adhered under the same adhesion conditions as described above, the piezoelectric layer and the
acoustic matching layer manufactured as described above are laminated in order And glued.
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The acoustic matching layer was bonded such that the acoustic matching layer having high
acoustic impedance was in contact with the piezoelectric layer. Then, the laminated body
manufactured in this manner is divided into elements by performing main dicing that completely
divides the piezoelectric layer at intervals of pitch E μm in the longitudinal direction (azimuth
direction) with a blade having a thickness of D μm. The divided elements were subjected to subdicing in which the acoustic matching layer was completely divided by the above-described
blade, and divided by the number of microelements n to fabricate a transducer.
[0057]
After that, an insulating layer of about 3 μm made of polyparaxylylene was provided on the
surface of the transducer, and an acoustic lens was laminated on the acoustic radiation surface of
this insulating layer and adhered to produce a vibrating portion.
[0058]
Next, after connecting a connector to the FPC, the vibration unit manufactured as described
above was housed in a case to manufacture an ultrasonic probe of Example 1.
[0059]
Subsequently, instead of the composite piezoelectric material of Example 1, the composite
piezoelectric materials of Examples 2 to 6 and Comparative Examples 1 to 4 are respectively
used, and the other members and the manufacturing process are the same. The ultrasound
probes of Examples 1 to 4 were produced respectively.
[0060]
(Evaluation) The following conditions evaluated the -6 dB ratio zone (BW6 (%)) of the ultrasonic
probe of Examples 1-6 manufactured as mentioned above and comparative examples 1-4.
The measurement system is constructed by general-purpose function generator (33220A
manufactured by Agilent), power amplifier (8447D manufactured by HP), and an oscilloscope
(TP5032 manufactured by Tektronix), and a reflector made of SUS is installed in degassed water
did.
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Then, the ultrasonic probe was fixed at a position where the focal length of the ultrasonic probe
matches the distance to the reflecting plate and the transmission / reception sensitivity of the
ultrasonic probe is the highest.
And the signal was transmitted by burst wave drive of Vpp80 [V], and the comparison of
transmission / reception sensitivity was performed. The results are shown in Table 1. In addition,
about piezoelectric material A in following Table 1, C-84 is made by Fuji Ceramics, L-11, L-201F,
and L-155NF are made by Tayca. Moreover, about the grain size of the piezoelectric material A,
in the cross section cut and processed by the braid | blade, 20 grain traces which detached |
desorbed were extracted and it computed from the average value of those magnitude | sizes.
[0061]
[0062]
(Result) In this manner, by adjusting the aspect ratio of the piezoelectric body to a range defined
in the present invention, unnecessary resonance in the plane other than resonance in the
thickness direction is suppressed, and spurious within a desired band. It has been found that an
ultrasonic wave having a wide band and high sensitivity characteristics can be output without
generation.
On the other hand, it was found that when the aspect ratio of the piezoelectric body is out of the
range defined in the present invention, the high frequency part of the band is narrowed to
narrow the band.
[0063]
As described above, according to the present embodiment, the aspect ratio of the piezoelectric
body satisfies the above formulas (7) to (9) or the above formulas (10) to (12). To suppress
unwanted resonances in the plane other than resonance in the thickness direction of the
piezoelectric body, and to suppress generation of spurious within the band of the output
ultrasonic wave, while achieving good electrical matching with the The sensitivity characteristic
can be obtained.
[0064]
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Further, according to the present embodiment, since the composite piezoelectric body has a
surface roughness of 0.2 μm or less on at least one surface on which the piezoelectric body and
the polymer are exposed, the cost is low and the reliability is low. Electrode formation is possible.
In addition, the surface roughness of the composite piezoelectric body can be reduced, and the
thickness of the adhesive layer produced by the adhesive can be reduced when the composite
piezoelectric body is adhered to the other member with the adhesive. Therefore, in particular, it
can be suitably used for an ultrasonic probe for high frequency applications, and high sensitivity
can be maintained.
[0065]
Further, according to the present embodiment, since the grain size of the piezoelectric body is 3
μm or less, it is possible to reduce the surface roughness caused by the detachment of the grain
at the time of processing of the piezoelectric body. Further, since it is possible to suppress an
increase in grain volume to be lost, loss of piezoelectricity can be suppressed, loss of effective
area and dielectric constant is suppressed, processing deterioration can be suppressed, and high
piezoelectricity can be maintained. become.
[0066]
Further, according to the present embodiment, the composite piezoelectric body is divided at a
predetermined interval by the main die groove 31 along the arrangement direction of the
piezoelectric bodies and divided into a plurality of elements, and each element is respectively a
main die groove Since a plurality of sub-die grooves 32 which are parallel to 31 and shallower
than the main die groove 31 are used, a desired frequency can be obtained without dimensional
constraints.
[0067]
The description in the embodiment of the present invention is an example of the ultrasound
diagnostic imaging apparatus according to the present invention, and the present invention is not
limited to this.
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The detailed configuration and the detailed operation of each functional unit constituting the
ultrasound diagnostic imaging apparatus can be appropriately changed.
[0068]
Reference Signs List 1 ultrasound image diagnostic apparatus 2 ultrasound probe 12
transmission unit 13 reception unit 15 image processing unit 16 display unit 21 ultrasound
transducer 24 piezoelectric layer
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