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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe which is used in a medical ultrasonic diagnostic apparatus or the like to
transmit and receive ultrasonic waves. (Prior Art) Generally, a piezoelectric material of a zirconlead titanate system is used as a piezoelectric transducer material of an ultrasonic probe. In these
materials, when used as a longitudinal wave converter, the coupling coefficient of this transverse
effect is 31 as large as 0.2 to 0.3, which makes unnecessary vibration easy to occur and can
obtain good characteristics. In particular, in the array type probe used in the ultrasonic
diagnostic apparatus etc., as shown in FIG. The ratio W / T of the width dimension W needs to be
reduced to 0, 6 or less, and when the frequency of the probe is increased, the width of the
imaging moving element becomes small, which causes a problem that manufacturing becomes
difficult . Referring to FIG. 6, the structure of a general ultrasonic probe will be described.
Reference numeral 61 denotes a rectangular plate-shaped transducer made of zircon-lead
titanate piezoelectric ceramic for electro-mechanical energy conversion. 62 and 63 are acoustic
matching layers, which are provided to obtain acoustic impedance matching of the object (human
body, water, or steel) with largely different pumping ceramics and acoustic impedance, and the
broadband of the probe, It contributes to low loss. The acoustic impedance of the matching layer
is usually set to a value intermediate between the acoustic impedances of the piezoelectric
ceramic and the subject. The entire configuration is a configuration in which upper acoustic
matching layers 62, 63 of a plurality of rectangular plate-like transducers 61 disposed at
predetermined intervals are formed. On the other hand, “Ultrasonic probe using lead titanate
ceramic material” by Honda, Yamashita, Uchida (Technical report US81-20 (1981) of the
Institute of Electronics and Communication Engineers) or by bone, by Nakatani, Izumura In
“Application of PbTi01 series ceramics to high frequency ultrasonic probe” (Technical report
of the Institute of Electronics and Communication Engineers TJ884-7 (1984)), PbTi0. It is stated
that the probe using the piezoelectric ceramic material is superior to the one using the
conventional lead zirconate titanate. That is, since the coupling coefficient of the transverse effect
is extremely small in the PbTiOs-based piezoelectric ceramic material, unnecessary vibration is
drastically reduced, and when the material of f is applied to an ultrasonic probe, the vibration
energy by the transverse effect is considerably weak. It can be expected that near-ideal
transmission and reception characteristics with almost no influence can be expected. The pbTios
piezoelectric ceramic of course has a W / T of 0.6 or less, and in particular, a W / T of 1.2 to 2.
Also in this case, good thickness and vibration characteristics without spurious emission can be
obtained, which is extremely advantageous in the case of achieving high frequency of an array
type probe using a rectangular plate-like imaging moving member. (Problems of the prior art) As
described above (PbTiO3 based ceramic ceramics have a large anisotropy of one-machine
mechanical coupling coefficient, and in actual use, the thickness warp coupling coefficient has a
lateral effect of 0, 50 or more. A coupling coefficient of 1 css of 0.05 or less is obtained, and is
considered to be an extremely excellent material as a material of an ultrasonic probe, but the
induction ratio dL rate εL / ε. There is only about 200, and the zircon-lead titanate
piezoelectric ceramic is not more than about 11/10. In particular, the polarization area becomes
smaller in the array type probe of the electronic scanning type, and ε 3 Ts / ε when PbTiO 3 based pressure ceramics are used. The impedance of the probe is about 10 times larger than that
of the probe using zircon / lead titanate-based piezoelectric ceramic because The ultrasound
probe is usually connected to the diagnostic device body via a cable so that the PbTi0. If it is a
material having a low dielectric constant, such as piezoelectric ceramic, the first problem is that
the S / N ratio is degraded due to the influence of the capacity of the cable. Second, PbTi0. In the
case of thread ball ceramic, since the piezoelectric d constant is also small because the dielectric
constant is small, there is a disadvantage that a sufficient skirt width can not be obtained unless
the driving pressure is increased. That is, the Onion ceramic has such a defect and
has been an obstacle to practical use of the probe. Furthermore, although the actual ultrasonic
probe requires a certain fixed center frequency such as 3.5 MHz, 7-5 MHz, etc., the conventional
transducer has a drawback that frequency adjustment can not be performed because the
electrode is on the surface There is. OBJECTS OF THE INVENTION The present invention relates
to PbTi0. To solve the above-mentioned various defects of piezoelectric ceramics, obtain an
ultrasonic probe which has a small impedance, excellent spurious characteristics, a large effective
mechanical coupling coefficient, and can easily perform frequency feasting. The purpose is to
(Constitution of the Invention) In the present invention, a plurality of planar internal electrodes
are formed at predetermined intervals inside a PbTiO3-based piezoelectric ceramic plate, and
each internal electrode is an external surface formed on the two side surfaces of the ceramic
plate. Is a d-type structure connected to a pole and one layer, and the ceramic layer inserted in
the inner 'dt pole is alternately reversely polarized in the direction of the iN layer.
It is an ultrasonic probe which is in the standby state of being equipped with the piezoelectrics of
l14'lii, the electrons, and the acoustic coupling layer formed on the surface of one layer
perpendicular to the lamination direction of the transducers. (Detailed Description of
Configuration) The PbTi0. The ultrasonic probe using yarn ball core ceramics solves the
problems of the prior art by having an electrode inside the ceramics as described above.
Hereinafter, it demonstrates according to drawing. FIG. 2 shows an example of the laminated
structure in the state of a green sheet of the pbTios-based piezoelectric ceramic transducer used
for the probe of the present invention. The structure of the transducer and an example of the
manufacturing method will be described in detail below. In FIG. 2, 20 is a green sheet made of an
organic binder and PbTiO3 yarn ceramic powder, and 21 is a conductive paste, which becomes
an internal electrode after firing. Such a green sheet is laminated as shown in the drawing and
crimped to form a green sheet laminate. In this case, the gap portion 22 to which the conductive
paste is not applied is left so that the pole 21 can pull out the electrical terminals in parallel
every other layer. The green sheet laminate is fired. Thereafter, as shown in FIG. 3, electrodes are
applied to two side surfaces parallel to the yz plane of the sintered PbTiO3 piezoelectric ceramic
laminate by a method such as baking, vapor deposition, or plating. In this case, the internal
electrode has a four-layer structure 7, "other than 0" "3", "5" threat, 6) sound, and so on. It is
good. In FIG. 3, 30 is PbTi0. 31 is an internal electrode, 32.32 'is an external electrode provided
on the side surface after firing, and 33, 33' is a surface ceramic layer. The PbTi0... Internally
regressed by polarization by applying a 1σ flow high electric field between the outer electrodes
32, 32 '. Each layer of the ceramic is polarized to impart piezoelectricity. At this time, it is
desirable to set the thicknesses d, d, d smaller than the gap tItt so that a sufficient voltage is
applied between the layers so that no ceramic crack occurs when one force is polarized. Also, the
arrow indicates the polarization direction in FIG. The frequency A adjustment of the present
converter can be easily performed by grinding the surface ceramic 1833 or 33 'to reduce the
thickness. A rectangular plate-like transducer used for array type probe numbering can be easily
obtained by cutting in the y direction parallel to the xz plane of FIG. The transducer according to
the invention as shown in FIG. 3 has the following advantages:
First of all, the piezoelectric transducer according to the present invention has an effective
electric machine compared to the thickness of the transducer having the polarization provided on
only the surface having no internal electrode and the coupling coefficient of the transducer. The
coupling coefficient kaff can be increased up to one additional degree. This is due to the mass
effect of the surface-provided ceramic layer. The electromechanical coupling coefficient ke (r2 is
defined by the ratio of mechanical vibrational energy output to electrical input energy, which is
expressed by the following equation as another expression. However, the “resonance frequency
r, 1 anti-resonance frequency”, according to the present invention, the transducer according to
the present invention can increase the resonance anti-coincidence frequency difference f, −f
with respect to a constant resonance frequency, The present invention is particularly effective
when used for an ultrasonic probe having excellent pulse response characteristics. The second
piezoelectric ceramic piezoelectric transducer according to the present invention has a plurality
of internal electrodes, and in the structure that the internal electrodes are accommodated in
parallel every other layer, the conventional piezoelectric ceramic veneer is used. A much smaller
impedance can be realized compared to the converter made by. Now, in order to simplify the
description, a stacked converter in which two poles are provided at equal intervals will be
specifically described as an example. In the case of a converter having an (n + 1) layer of internal
electrodes, the effective area is almost n times as close as the electrodes are connected in parallel
according to a simple calculation, and the electrode spacing is n for the plate thickness The free
volume -i is about n2 times as large as a single plate. The impedance of the transducer having the
internal electrode of the (n + 1) layer is compared with that of a single piezoelectric plate, since
@ff is never lost in the effective electromechanical coupling coefficient by such a laminated
structure. In about 12 minutes, it decreases sharply. Also, this is true, considering the dielectric
constant of PbT103-based pressure ceramics, the real dielectric constant II of the transducer
laminated with equal electrode spacing. (Alternative electrode converted as if there are both
principal surfaces t and this electrode of the converter) is approximately 9εT s -J- for the fourlayer electrode, and about 258'ss for the six-layer electrode In the electrode of the (n + 1) layer, it
increases approximately in proportion to the square of (number of the electrode layers-1) and
approximately n ′ ′ g :. As mentioned above, about the converter in which the electrodes were
laminated at equal intervals, but the transducers in which the electrodes were multiplied at
uneven intervals were the same? If it is the number of d pole layers, the effective dielectric
constant ε 33 becomes slightly larger than the transducers stacked at equal intervals. In
addition, a converter having a narrow thickness in the central region of the converter and an
inner region and a gap between the electrodes can obtain larger ke (f) than the converter in
which the electrodes are stacked at equal intervals.
However, this type of converter is somewhat disadvantageous when there is a demand to apply
large voltages and perform large loss width excitation imaging as compared with a converter in
which electrodes are stacked at equal intervals. Therefore, the piezoelectric transducer in the
present invention can obtain an effective dielectric constant equal to or more than that of a
transducer made of a conventional zircon-lead titanate piezoelectric ceramic, in other words,
obtain a small impedance equal to or less than the same. it can. Next, the converter used in the
present invention can be adjusted in frequency by polishing the surface ceramic layer. さらに
PbTi0. Piezoelectric ceramic 1. 28 (ffiJllHj "& '6f, =? The H.1 knowledge C.sub.11 has an
advantage that a good thickness and a resonant response can be obtained. (Example) As an
example of an ultrasound probe according to the present invention, a central station 1-reciprocal
3.5 MHz near-array medical ultrasound probe having a triple / matching layer shown in FIG. I
will talk about the feeler. FIG. 1 (7) is a side view of the probe, and FIG. 1 (a) is a cross-sectional
view of the probe. In the present embodiment, the piezoelectric transducer 10 has PbTi0. It has a
laminated structure in which four layers of the electrode 31 are embedded inside the thread ball
ceramic. The ceramic used was a composition of Pbo, ss Ca (1, 15 Ti 0.95 (Mn 3 AS b X) o, os O
3, and the production was carried out by the method using the above-mentioned green sheet. The
polarization was performed by applying a DC high electric field between the external 'electrodes
32 and 32'. In the transducer immediately after polarization, the thickness of the ceramic layers
33 and 33 'on the surface was about 40% with respect to the total plate thickness, but polishing
33, 33' gave a resonance frequency of 3.5 MHz. The thickness of the ceramic layers 33 and 33
'on the surface at this time is 23% of the total plate thickness. In this converter, @ (f is 0.553,
PbTi 0. The electromechanical coupling coefficient of a single plate of piezoelectric ceramic is 8%
larger and the effective relative permittivity εT / ε. Is 179 ° and about 9 times the value of a
single plate of PbTiO 3 based piezoelectric ceramic and copper. In FIG. 1, 11, 12, 13 are acoustic
matching layers, and 44 is a backing. The acoustic matching layer was tuned to about one
quarter of the resonant wavelength. 11 is a urethane resin of acoustic impedance 1.92 X 10 'kgm
1 type, 12 is an epoxy resin 1 mixed with an appropriate amount of fine powder of quartz glass,
but also an acoustic impedance 7: x, 4.12 X 10' Jc 9 mlsec, 13 is an acoustic impedance 14.2 x
10 'kFim /!
It is an optical glass of eC. The shape of one manufactured piezoelectric transducer is in the order
of 0.6 ++ 11 uXO, 3tl + lX1.3. The transducers were arranged at predetermined intervals and
configured in a linear array of about 10 to 13 C1 rL in length to form a probe. Next, using this
probe, underwater 3C! The frequency characteristics (round tripinsertion 1 oss% property) when
an ultrasonic wave returning toward the Ae reflector plate with rL and 1t is received by the same
probe are shown by a solid line in FIG. The zero passband characteristic shown by the dotted line
in Fig. 4 is the same for both of the frequency characteristics of the probe when the zircon and
lead titanate based piezoelectric ceramic single plate type piezoelectric transducer is used for the
piezoelectric transducer part. Although the characteristics are shown, in the probe using zirconlead titanate based piezoelectric ceramics out of the band, a large ripple is recognized due to the
spurious of the transverse effect. Furthermore, in order to test the resolution of both contactors,
the diameter Q embedded in a gel-like material having ultrasonic attenuation characteristics (0, 7
dBA 7 rL / i 徂 7) equivalent to that of a living body and acoustic impedance The force 1 was
evaluated to what extent a 3 mu nylon wire was disassembled. A probe using a conventional
piezoelectric ceramic single plate has a depth of 12 (at most a LO mm distance at 1 m (it can not
be seen that the embedded nylon wire can be seen, but a depth of 0.7 m I could see the nylon
wire embedded in the space clearly separated. In another embodiment according to the present
invention, the entire surface of the green sheet is coated with an electric paste without leaving
gaps 22 and then laminated in the same manner as in FIG. 2 and pressure bonded and fired to
manufacture a PbTi01 ceramic laminate. Do. Further, an insulator 51 is formed on the side
surface of the laminate, external 'electrodes 32 and 32' are provided, and a DC high electric field
is applied between 32 and 32 'to perform polarization. Thus, as shown in FIG. 5 (a piezoelectric
transducer having a shape in which the internal electrode spreads in a row can be obtained. Since
the piezoelectric transducer shown in FIG. 5 does not have the gap 22, the impedance can be
slightly lowered by that amount compared to the transducer shown in FIG. When a probe having
a triple matching layer as shown in FIG. 1 was manufactured using the piezoelectric transducer
shown in FIG. 5, one having characteristics equivalent to the characteristics shown by the solid
line in FIG. 4 was obtained. The Thus, the overlapping length of the internal electrodes is
desirably about the same as the length of the piezoelectric transducer (at least 80 inches or
more). (Effects of the Invention) As described above, the probe according to the present invention
maintains the advantage that the energy of the spurious vibration due to the transverse effect
which is an inherent feature of the PbTiO3 based piezoelectric ceramic is extremely small, and
the dielectric of this ceramic is 'Cable' that occurs because the rate is small.
It is possible to eliminate the defects that are sensitive to capacity and 0 '. Furthermore, it has an
excellent feature that the effective electromechanical coupling coefficient keff can be increased,
and the frequency can be adjusted, and a probe with an excellent resolution compared to a
conventional probe is obtained. be able to.
Brief description of the drawings
1 (7) and 1 (A) are schematic views of an ultrasonic probe showing an embodiment of the
present invention, and FIG. 2 shows an example of a laminated structure of a piezoelectric
transducer portion used in the probe of the present invention. Figure.
Fig. 3 is a perspective view showing an example of a laminated piezoelectric transducer
according to the present invention, Fig. 4 is a frequency characteristic diagram of an ultrasonic
probe, and Fig. 5 is a view showing another embodiment of the present invention. FIG. 2 is a view
showing an example of a conventional ultrasonic probe. In the figure, lO is a laminated
piezoelectric transducer, 11, 12, 13 is an acoustic matching layer, 14 is a backing, 20 is a green
sheet, 21 is a conductive paste, 22 is a gap, 30 is a PbTiO3 based pressure fiber, 31 is an internal
electrode, 32 ° 32 'is an external electrode, 33, 33' is a surface ceramic layer, 51 is an insulator,
61 is a rectangular plate-like transducer, 62, 63 is an acoustic matching layer, and arrows
indicate polarization directions.
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description, jps6169300
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