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DESCRIPTION JP2001285995

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DESCRIPTION JP2001285995
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe used in an ultrasonic diagnostic apparatus and the like.
[0002]
2. Description of the Related Art An ultrasound probe is used in an ultrasound diagnostic
apparatus for a living body. As a conventional ultrasound probe, for example, there is one
disclosed in Japanese Patent Application Laid-Open No. 8-122310. FIG. 5 is a longitudinal
sectional view showing the structure of the ultrasonic probe disclosed in this publication. In the
figure, the piezoelectric element 11 is formed in a plate shape, electrodes are attached on both
sides of the plate surface, an AC voltage is applied between both electrodes to transmit ultrasonic
waves, and ultrasonic waves are received to receive both electrodes. It is an element for inducing
a voltage between them.
[0003]
An acoustic matching layer 15 made of a conductor is laminated on one surface of the
piezoelectric element 11, that is, on the upper surface of the drawing. The acoustic matching
layer 15 is for efficiently transmitting and receiving ultrasonic waves to and from the subject
(living body). In addition, a conductor layer 14 is formed on one surface of the polymer film 14 a
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by vapor deposition or the like, and the polymer film 14 a is laminated in a state where the
conductor layer 14 is in contact with the acoustic matching layer 15. An acoustic lens 16 for
focusing the ultrasonic waves is mounted on the other surface of the polymer film 14a. An FPC
17 having a conductive pattern formed thereon is stacked on the other surface of the
piezoelectric element 11, that is, the lower surface of the drawing, and a back load material 18 is
stacked on the outer surface of the FPC 17.
[0004]
With this configuration, even if the piezoelectric element 11 is broken due to mechanical impact
from the outside, the piezoelectric element 11 is electrically connected, has a structure in which
failure is reduced and the quality is stabilized. ing.
[0005]
However, in the above-mentioned conventional ultrasonic probe, the acoustic matching layer 15
is required to be a conductor and a material having excellent processability.
Therefore, it is difficult to select a material having a desired acoustic impedance as the acoustic
matching layer 15, and there is a problem that it is difficult to achieve a wide band of the
acoustic characteristics desired for the ultrasonic probe, particularly the frequency
characteristics.
[0006]
The present invention has been made to solve the above-mentioned problems, and the value of
the acoustic impedance can be freely selected, and it is possible to widen the acoustic
characteristics required for the ultrasonic probe, particularly the frequency characteristics. It is
an object of the present invention to provide an ultrasound probe having good sensitivity.
[0007]
According to the first aspect of the present invention, there is provided a piezoelectric element
having electrodes formed on both sides of a plate surface formed into a plate shape, and a
conductor laminated on one of the electrodes of the piezoelectric element. Layer, at least one
acoustic matching layer laminated on the outside of the conductor layer, an electric terminal
extraction film in contact with the other electrode surface of the piezoelectric element, and the
side of the electric terminal extraction film opposite to the piezoelectric element And a back load
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material laminated on the outside of the other electrode surface of the piezoelectric element.
[0008]
The invention according to claim 2 is the ultrasonic probe according to claim 1, wherein the
conductor layer is copper, aluminum, nickel, gold or another metal film, or a multilayer in which
these metal films are laminated. It is a film.
[0009]
The invention according to claim 3 is the ultrasonic probe according to claim 1 or 2, wherein the
thickness of the conductor layer is 1/90 or less of the wavelength of the ultrasonic wave
generated by the resonant vibration of the piezoelectric element. is there.
[0010]
The invention according to claim 4 relates to the ultrasonic probe according to any one of claims
1 to 3, wherein one of the electrodes formed on the piezoelectric element is a ground electrode,
and the conductor layer has a planar shape than that of the piezoelectric element. And a side
electrode as a terminal of the ground electrode.
[0011]
The invention according to claim 5 is the ultrasonic probe according to any one of claims 1 to 4,
in which the polymer on the surface of the conductor layer on the side of the piezoelectric
element of the portion led out laterally from the piezoelectric element It is made of materials.
[0012]
According to a sixth aspect of the present invention, in the ultrasonic probe according to the fifth
aspect, the insulating layer is formed on the side surface of the piezoelectric element on the side
where the conductor layer is led out laterally.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described in detail with reference to the drawings.
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FIG. 1 is a longitudinal sectional view showing the configuration of a first embodiment of an
ultrasonic probe according to the present invention.
In the figure, the piezoelectric element 1 is formed in a plate shape using a piezoelectric ceramic
such as PZT system or a single crystal such as PZN or KNbO 3, thereby transmitting and
receiving ultrasonic waves.
Gold or silver is sputtered on one surface of the piezoelectric element 1, that is, the upper surface
of the drawing, or silver is baked to form the ground electrode 2.
Gold or silver is sputtered on the other surface of the piezoelectric element 1, that is, the lower
surface of the drawing in the same manner as the ground electrode 2, or silver is formed to form
the signal electrode 3 There is.
[0014]
A conductive layer 4 is bonded on the surface of the ground electrode 2 of the piezoelectric
element 1 so as to be electrically connected.
The conductive layer 4 has a lateral end, that is, an extending end which extends in the lateral
direction of the drawing.
The first acoustic matching layer 5 is stacked on the outer side of the conductive layer 4 as
viewed from the piezoelectric element 1, and the second acoustic matching layer 6 is stacked on
the outer side thereof.
[0015]
On the other hand, on the surface of the signal electrode 3 of the piezoelectric element 1, an FPC
(Frexible Print Circuit) 7 as an electric terminal extraction film is adhered so that the printed
wiring is electrically connected to the signal electrode 3. The back load material 8 is attached so
as to sandwich the FPC 7 with the piezoelectric element 1.
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The backing material 8 has a function to attenuate unnecessary ultrasonic waves and to hold
useful ultrasonic waves. Even if the FPC 7 as an electric terminal output film is adhered to a part
of the surface of the signal electrode 3 of the piezoelectric element 1 and the back load material
8 is attached to a part of the signal electrode 3 and the FPC 7 The same effect is obtained.
Further, although not shown, an acoustic lens or the like for converging the ultrasonic beam is
provided on the second acoustic matching layer 6.
[0016]
Here, the conductor layer 4 is electrically connected to the ground electrode 2 by bonding an
adhesive such as an epoxy resin very thinly and bonded, or bonded to the ground electrode 2 by
a conductive adhesive. There is a method of connecting to, but it is sufficient if it can be
electrically connected by any method. Further, the constituent material of the conductor layer 4
may be a material having a low electric resistance, for example, a metal film made of a metal such
as copper, nickel, aluminum, gold, silver or an alloy of these metals, or A so-called multi-layered
film in which metal films are laminated is desirable. Further, since the conductor layer 4 is
electrically connected to the ground electrode of the piezoelectric element 1 and the conductor
layer 4 is connected to the ultrasonic diagnostic apparatus through the cable, the conductor layer
4 is formed longer than the piezoelectric element 1, It extends to the side of 1 to facilitate
electrical connection.
[0017]
On the other hand, since the conductor layer 4 is provided between the piezoelectric element 1
and the first acoustic matching layer 5, the frequency characteristic (bandwidth) of the acoustic
characteristic and the sensitivity are affected. Therefore, setting of the thickness of the conductor
layer 4 is important. 2 and 3 are diagrams showing calculation results of the influence. This is a
change in the relative band (-6 dB) when the thickness converted to the wavelength is changed
using, for example, copper (density: 8.9 kg / m 3, sound speed: 4.7 km / s) as the material of the
conductor layer 4 Is shown in FIG. 2 and the change in sensitivity is shown in FIG. As apparent
from FIGS. 2 and 3, as the thickness of the conductor layer 4 increases, both the specific band
and the sensitivity decrease. Although it is desirable that the deterioration of these characteristics
is small, the characteristics may vary in the process of actual production, but there is no problem
as long as there is no difference in ultrasonic images even if there are variations. Being in a
situation where
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[0018]
The level of problem-free variation is about -7.5% in the fractional band of the frequency
response and 1.5 dB in the sensitivity. However, since the value of the level of these allowable
variations is the value of the entire ultrasonic probe, and includes the variations of each material,
the variations of each adhesive layer, etc., the thickness of the conductor layer 4 is more It is
necessary to keep it small. From such a point of view, it is desirable to limit the conductor layer 4
to a thickness of -3.5% at least in the specific band and a sensitivity of about -1.0 dB. Therefore, it
is desirable that the thickness of the conductor layer 4 satisfying this characteristic be about
1/90 wavelength or less.
[0019]
Next, the first acoustic matching layer 5 and the second acoustic matching layer 6 are selected
from materials having acoustic impedance values between the piezoelectric element 1 and the
living body as the subject. More specifically, the value of the acoustic impedance greatly changes
the bandwidth of the frequency characteristic, and the material is selected according to the
desired characteristic. In this case, it is strongly desirable to widen the frequency bandwidth in
that the ultrasound image can be made high resolution and high sensitivity. Generally, since the
piezoelectric element 1 uses PZT-based piezoelectric ceramics, this acoustic impedance is about
30 Mrayl, and the acoustic impedance of a living body is about 1.6 Mrayl. Therefore, a material
having an acoustic impedance of, for example, around 8 Mrayl is used as the first acoustic
matching layer 5, and a material having an acoustic impedance of, for example, around 3 Mrayl
is used as the second acoustic matching layer 6.
[0020]
According to this configuration, any material can be selected as the material of the first acoustic
matching layer 5 regardless of the conductor or the insulator. Among these, graphite is used for
the conductor, and a polymer is used for filling the polymer for the insulator. Materials which can
be adjusted, or glass-based or machinable ceramics may be used. Further, as the second acoustic
matching layer 6, a polymer material represented by epoxy resin is used. The thickness of each
of the first acoustic matching layer 5 and the second acoustic matching layer 6 is basically
selected to be 1⁄4 wavelength. However, these thicknesses may deviate from the quarter
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wavelength depending on the desired properties.
[0021]
As described above, according to the first embodiment of the ultrasonic probe according to the
present invention, since the conductor layer 4 is provided between the piezoelectric element 1
and the first acoustic matching layer 5, As the acoustic matching layer 5 of 1 is free from the
restriction that it is a conductor and excellent in processability as required for the conventional
device, and the material can be freely selected by paying attention to the value of the acoustic
impedance. It is possible to provide an ultrasonic probe having a good sensitivity, as well as to
make it possible to broaden the acoustic characteristics, particularly the frequency
characteristics, required for the above. As a result, it is possible to realize high resolution and
high sensitivity of the image of the ultrasonic diagnostic apparatus.
[0022]
FIG. 4 is a longitudinal sectional view showing the configuration of a second embodiment of the
ultrasonic probe according to the present invention. In the figure, the same reference numerals
are given to the same elements as in FIG. 1 showing the first embodiment, and the explanation
will be omitted. This is because the polymer material layer 9 is adhered to the surface on the side
of the piezoelectric element 1 where the conductor layer 4 stacked on the piezoelectric element 1
protrudes in the lateral direction than the piezoelectric element 1, and the conductor layer 4 The
configuration is different from that of the first embodiment in that an adhesive 10 having a
predetermined thickness is applied as an insulating layer to the side surface of the piezoelectric
element 1 in the direction of protruding laterally beyond the piezoelectric element 1.
[0023]
Here, when the polymer material layer 9 makes the conductor layer 4 a thin film-like one, the
conductor layer of a portion other than the portion which is in surface contact with the
piezoelectric element 1 in the process of manufacturing the ultrasonic probe. The conductor 4
and the conductor layer of the FPC 7 when the conductor layer 4 is finally arranged along the
side surface of the FPC 7 and the side surface of the back load member 8 because 4 is easily
broken. And 4 have a function of electrically insulating them from each other, and are preferably
flexible. The polymer material layer 9 is preferably made of, for example, polyimide, polyethylene
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terephthalate (PET) polysulfone or the like, and the thickness may be about 10 to 50 μm, for
example, as long as it is flexible and can be bent. These polymeric material layers 9 may be
directly adhered to the conductor layer 4 or may be adhered using an adhesive.
[0024]
On the other hand, the adhesive 10 is applied to the side surface of the piezoelectric element 1
and is also applied to the polymer material layer 9 at the base of the conductor layer 4
protruding laterally from the piezoelectric element 1. . As a result, when the conductor layer 4 is
bent and fixed to the side surfaces of the FPC 7 and the backing material 8, the function of
preventing damage to the extended base of the conductor layer 4 and the polymer material layer
9 is achieved. The adhesive 10 may be a general adhesive typified by an epoxy resin etc., but the
hardness is about 80 or more in Shore hardness, the effect of the adhesive 10 is sufficient . In
particular, it is the piezoelectric element 1, the conductor layer 4, the first acoustic matching
layer 5, and the second acoustic matching layer 6 which exhibit the effect in such a
configuration, for example, in the direction orthogonal to the sheet of FIG. This is the case of a socalled array-type ultrasound probe in which several hundreds are arranged side by side at a pitch
of 0.1 mm to 0.3 mm.
[0025]
According to the second embodiment described above, since the conductor layer 4 is provided
between the piezoelectric element 1 and the first acoustic matching layer 5, the conventional
device is required as the first acoustic matching layer 5. As described above, there is no
restriction of being a conductor and excellent in processability, and it is possible to freely select
the material paying attention to the value of the acoustic impedance. An ultrasound probe having
the same can be provided. As a result, it is possible to realize high resolution and high sensitivity
of the image of the ultrasonic diagnostic apparatus.
[0026]
Further, the polymer material layer 9 is adhered to the surface on the side of the piezoelectric
element 1 where the conductor layer 4 laminated on the piezoelectric element 1 protrudes
sideward than the piezoelectric element 1, and the conductor layer 4 is a piezoelectric element
Since the adhesive 10 of a predetermined thickness is applied to the side surface of the
piezoelectric element 1 in the direction of protruding in the lateral direction more than 1, when
the conductor layer 4 is bent and fixed to the side surfaces of the FPC 7 and the backing material
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8, The effect of being able to prevent damage to the extending base of the conductor layer 4 and
the polymer material layer 9 can also be obtained.
[0027]
In each of the above embodiments, the first acoustic matching layer 5 and the second acoustic
matching layer 6 are provided outside the conductor layer to form two layers, but if the desired
frequency characteristics and sensitivity can be satisfied, the acoustic matching is achieved. The
same effect as described above can be obtained by using one layer or three or more layers as
needed.
[0028]
As apparent from the above description, according to the present invention, by providing the
conductor layer between the piezoelectric element and the acoustic matching layer, the acoustic
matching layer is a conductor, and the processability is improved. There is no restriction that it
must be an excellent material, and it is possible to freely select materials focusing on acoustic
impedance, and to enable broadening of the acoustic characteristics, particularly frequency
characteristics, desired for each ultrasonic probe, An ultrasound probe with good sensitivity can
be provided.
As a result, it is possible to increase the resolution and sensitivity of the image of the ultrasonic
diagnostic apparatus.
[0029]
In addition, the conductor layer is formed larger than the piezoelectric element, and the polymer
material is adhered to the surface of the conductor layer on the side of the piezoelectric element
on the side portion which is led out, so that the conductor layer is bent and the back surface is
loaded. When fixed to the side surface of the material, an effect that breakage of the extended
base of the conductor layer can be prevented can also be obtained.
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