JPS6169298A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To suppress the spurious oxcillation due to the lateral effect of ceram ics by providing a piezoelectric transducer which is polarized reverse alternately in the laminating direction and forming acoustic matching layers on one face of this transducer vertical to the laminating direction. CONSTITUTION:A piezoelectric transducer 10 has a three-layered structure, and electrodes 31 are buried in PbTiO3 piezoelectric ceramics 30. A DC high electric field is applied across external electrodes 32 and 32' to polarize the transducer 10. Acoustic matching layers 11, 12, and 13 and a packing 14 are provided on and under piezoelectric ceramics 30 respectively, and acoustic matching layers are adjusted to about 1/4 of the resonance wavelength. These transducers are arranged at intervals of a prescribed length into a linear array having about 10-13cm length, thus obtaining a probe.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an ultrasonic probe that is used in a medical ultrasonic diagnostic device such as an unexploded EAi-i and transmits and receives ultrasonic waves.

(Technology) Generally, a zircon/lead titanate-based piezoelectric material is used as the piezoelectric transducer material of an ultrasonic probe.

When these materials are used as longitudinal wave transducers, the coupling coefficient h1 of the interpolation effect is as large as 0.2 to 0.3, and therefore unnecessary vibrations are likely to occur, making it difficult to obtain good characteristics. Ta. In particular, with array type probes used in ultrasound diagnostic equipment, etc., in order to avoid unnecessary #J due to lateral effects,
As shown in FIG. 6, it is necessary to make the width dimension WO ratio W/T to the plate thickness T of the rectangular plate-shaped vibrator 61 0.6 or less.
To explain the structure of the ultrasonic probe for increasing the frequency of the probe, 61 is a child. 62.63 is acoustic matching,
It is designed to match the acoustic impedance of piezoelectric ceramics and objects that have significantly different acoustic impedances (human body, water, or steel), and contributes to the wide band and low loss of the probe. . 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 overall structure is such that acoustic matching layers 62 and 63 are formed on a plurality of rectangular plate-shaped vibrators 61 arranged at predetermined intervals. "Ultrasonic probe using acid-lead-based piezoelectric ceramic material" (IEICE technical research report US81-20 (1981)) or intraosseous,
Application of PbTiOx Ceramics to High-Frequency Ultrasonic Probes by Nakatani and Sadamura (Application of PbTiOx Ceramics to High-Frequency Ultrasonic Probes J)
It has been reported that probes using 3-series piezoelectric ceramic materials are inferior to those using conventional zircon-lead titanate. Due to the extremely small tQI, unnecessary vibrations are drastically reduced, and when this material is applied to an ultrasonic probe, the vibration energy due to the transverse effect is considerably weak and the actual tQI
It is said that near-ideal wave transmitting and receiving characteristics can be expected with almost no effect on vertical vibrations used in J-use applications. I'b
TiO.

The system piezoelectric ceramics can obtain good thick vertical vibration characteristics with no spurious, not only when W/T is 0.6 or less, but especially when W/T is 1.2 to 2.0, and rectangular plate vibration. This is extremely advantageous when trying to increase the frequency of an array type probe using a probe.

(Problems with the prior art) As mentioned above, (PbTiOs piezoelectric ceramics have a large anisotropy in the electromechanical coupling coefficient, and when the longitudinal coupling coefficient Kt actually used is 0.50 or more, the coupling coefficient of the transverse effect is 3. □ is 0.05 or less, and it is said that the material used for ultrasonic probes is highly immersed.
33/ff1o is only about 200, which is only about one-tenth that of piezoelectric ceramics based on zircon/lead titanate.

In electronic scanning array type probes, when using 9゜PbTiOs piezoelectric ceramics, which have a small electrode area, '33/'0 is small, so the impedance of the probe is reduced by using zircon-titanium-lead-based piezoelectric ceramics. It is about 10 times larger than the probe used. Ultrasonic probes are usually connected to the diagnostic equipment body via cables, so
If the material has a small dielectric constant, such as PbTiQ or piezoelectric ceramics, the first disadvantage is that the S/N ratio is affected by the cable capacitance. Second, Pb
Since the Ti 2 O piezoelectric ceramic has a small dielectric constant and a small piezoelectric d constant, it has the disadvantage that a sufficient vibration vibration term cannot be obtained unless the driving voltage is increased. In other words, pbTiO3-based piezoelectric ceramics have such drawbacks, which have hindered the practical use of probes (objective of the invention). It is an object of the present invention to obtain an ultrasonic probe using PbTiO3-based piezoelectric ceramics that is small and has excellent spurious characteristics (Structure of the Invention). A laminate in which one or more internal electrode layers are alternately stacked, two external electrodes are formed on two sides perpendicular to the west direction of the laminate and two other sides, The poles inside the valley are connected to one external electrode on the side surface of the laminate every other layer, and the PB sandwiched between the two planar ta
Tiox-based three I ceramic layers ij: have equal thickness,
And the four paths of 3'-technical chivalry, which are alternately polarized in opposite directions.

An ultrasonic probe characterized by comprising an acoustic matching layer formed on one surface perpendicular to the stacking direction of the pressure transducer (Detailed description of the structure) The pbTi03-based piezoelectric of the present invention Ultrasonic probes using ceramics solve the problems of the prior art by having electrodes placed inside the ceramics as described above. The explanation will be given below with reference to the drawings. Figure 2 shows an example of the laminated structure of the PbTiOs piezoelectric ceramic transducer used in the probe of the present invention in the state of a green sheet. An example will be described in detail in Fig. 5. In Fig. 2, 20 is a green sheet made of an organic binder, pb'rio, and ceramic powder), and 21 is a 4-electrode paste, which becomes the inner electrode with a firing diameter. Stack these green sheets as shown in the figure and press them together to form a green sheet) ff
Make it a layered body.

In this case, the electrodes 21 are left with gap portions 22 where no conductive paste is applied so that electrical terminals can be taken out in parallel from every other layer.Next, the green sheet laminate is fired. After that, as shown in Figure 3, electrodes are applied by baking, vapor deposition, plating, etc. on two sides perpendicular to the stacking direction and two sides parallel to the yz plane of the fired PbTiO3 piezoelectric ceramic laminate. . In this case, it has a three-layer structure, but other than that, there are two layers, four layers,
It may have a structure of 5 layers or the like. In Figure 3, 30 is p
b T i 03 series piezoelectric ceramics, 31 is the internal electrode, 32.32' was provided after firing! A high direct current electric field is applied between the external poles 32 and 32', which are the poles, to polarize each JfI of the pb'rio3 ceramic and impart piezoelectricity.At this time, there is sufficient space between each layer. It is desirable that the layer thickness t is set smaller than the gaps t and t' so that the ceramic is not cracked when a voltage is applied υ and the ceramic is polarized. Further, in FIG. 3, arrows indicate polarization directions. The piezoelectric transducer used in the play-type probe can be easily obtained by cutting parallel to the XZ plane and in the y direction as shown in FIG. For example, in a ceramic ceramic, electrodes are arranged at equal intervals in the stacking direction as shown in Figure 3. In this structure, polarization occurs with uniform strength inside the ceramic, and the vibrator is strongly excited with high voltage. Even in the case where the electric field is not concentrated in one part, such a structure can be said to be extremely durable against dielectric breakdown.

Furthermore, if the ceramic layer or 3EiI structure is used as shown in Figure 3, the electrode spacing will be one-third of the plate thickness), and since the electrodes are connected in parallel, the effective area will be reduced. is approximately three times as large, and a parallel capacitance approximately nine times that of a PbTiO3 piezoelectric ceramic single plate in which electrodes are formed only on two opposing surfaces can be obtained.

Since such a multilayer structure does not impair the effective electromechanical conversion efficiency at all (it does not increase the container/basin ratio γ of the converter at all), it is shown in Fig. 3. The impedance of the three-layer transducer is approximately 9 times the impedance of the resonator made of a PbTiO3 piezoelectric ceramic single plate.
◎In other words, P with a laminated structure in non-invention
If the number of layers is i, a bTiOx ceramic two-layer piezoelectric transducer has the same external dimensions as the number of layers, and has an impedance of 1/n compared to a PbTiO3 piezoelectric ceramic single-plate resonator with electrodes formed on opposing surfaces. Decrease sharply. In addition, this does not change, and the effective relative permittivity τ of this resonator '33/'O (the relative permittivity calculated assuming that there are electrodes only on both principal surfaces of the resonator) is a two-layer In the case of about 400.
Approximately 1800 in the case of 3/pu. 3200 in the case of 4 layers
, in the case of 5 layers, it is approximately 5ooo and proportional to the square of the number of layers,
Number of stacked layers n and effective dielectric constant E 33 / '0 = 2
0012 (11) Therefore, the transducer of the present invention has a small impedance that is equal to or lower than the impedance of a conventional di-A-con-lead titanate-based vibrator made of plastic laminate or glass. The above effective dielectric constant can be obtained.Furthermore, the resonator according to the present invention has P
Since all of the bTiO3 yarn beads and 4 ceramics are used, it has the advantage that there is essentially less unnecessary 4'a 96 and a good thick resonance response can be obtained.

In addition, in a structure with three ceramic layers, as shown in Fig. 3, one external yL pole is formed on one surface perpendicular to the lamination direction and one 11 surface, and the other external electrode is formed on the other surface perpendicular to the lamination direction. It is formed on the ti11 side of one of the ponds.

However, when the ceramic layer has two layers, four layers, etc., one O external polarization is formed on two planes and one side surface that overlap in the layer direction, and the other external polarization is formed on the other side surface. It is formed.

As an embodiment of the ultrasonic probe based on the present invention, the center frequency 35 having a mini-acoustic matching layer shown in FIG.
'r11) (Z linear array medical ultrasound probe will be described. Figure 1 (7) is a surface diagram of the probe, Figure 1 (
b) is a sectional view of the probe. In the case of this embodiment, the piezoelectric transducer 10 has a three-layer laminated structure, with PbTi
It has a structure in which an electrode 31 is embedded inside the O3 yarn ball electrode mix. Ceramitsuros is still Pbo, 85C
ao, 15Tio,, 5 (NXn1/3Sb2/3)o
, o503 was used. The production was carried out using the method described above using green sheets. Polarization is external electrode 32°3
2' by applying a high DC electric field between 11.
12 and 13 are sound #matching layers, and 14 is a backing. The sound # matching layer has an acoustic impedance of 1.92 x 10'Kpm/s e
c O urethane resin, No. 12 is an epoxy resin mixed with an appropriate amount of quartz glass fine powder, and has an acoustic impedance of 4.1.
2 x 106 Kfm/see, 13 is an optical glass with an acoustic impedance of 14.2
The 0-order flame beam (n + m did.

Using this, the frequency characteristics (round trip, Insertion loss) is shown in Fig. 4.

In addition, the frequency of conventional probes using zircon titanium grade lead-based piezoelectric ceramics that have the same low Sakaki structure as the probe of the present invention, or have electromagnetic waves formed only on opposite surfaces as piezoelectric transducers. The mouth passband characteristics shown by dotted lines in FIG. 4 are similar in both cases, but outside the band a large ripple is observed in the conventional probe due to spurious transverse effects. On the other hand, the probe of the present invention has an ultrasonic attenuation characteristic (0.7 dB/cn) equivalent to that of a living body in order to test the resolution of both probes.
It was evaluated to what extent nylon wires with a diameter of OJmm embedded at predetermined intervals in a gel-like material having acoustic impedance (1/MLb) and acoustic impedance were decomposed and visible.

The conventional probe has a depth of 1°Omm at depth 12.
! a'] Although the nylon ring embedded in the septum appeared to be separated, the probe according to the present invention was 0.7 m long.
I was able to clearly see the nylon wires embedded at m intervals.

In another embodiment according to the present invention, 4 sheets are coated on the entire green sheet surface f without leaving any gaps 22; after resting, lamination, three layers, and q formation are performed in the same manner as in FIG. 2, and pb'ri
○, a porcelain woven body is manufactured on a ball of yarn, an insulator 51 is formed on the side surface of the laminate, an external electrode 32.3 is provided, 32.32'
A DC electric field is applied in between to polarize. In this way, it is possible to obtain a piezoelectric transducer having a shape in which the internal electrodes are spread out over the entire width, as shown in FIG. The piezoelectric transducer shown in FIG. 5 has a slightly smaller braking capacity9 than the piezoelectric transducer shown in FIG. 3, and the impedance can also be reduced accordingly. Using the pressure transducer shown in Fig. 5, we manufactured a wire having the structure shown in Fig. 1, and obtained properties that were almost the same as those shown by the solid line in Fig. 4. It is desirable that the length of the overlap between the internal IL poles is approximately the same as the length of the piezoelectric transducer (at least 80% or more). (Effects of the Invention) As described above, the probe according to the present invention has , PbTiO
It has the advantage of being able to suppress spurious vibrations due to the transverse effect of piezoelectric ceramics, and has the disadvantage of being easily affected by cable capacitance due to the small dielectric constant of ceramic and loss, which can be easily affected by cable capacitance. I can do it [〉]
Re 7 older samurai 1 kyu? Figures 1 (7) and (a) are part of the present invention. A schematic diagram of an ultrasonic probe showing an actual travel example, FIG. 2 is a diagram showing an example of the laminated structure of the piezoelectric transducer part used in the probe of the present invention, and FIG. 3 is a diagram of the Shakotan piezoelectric transformer used in the present invention. FIG. 4 is a perspective view showing an example of a ladder, FIG. 4 is a diagram showing the circumference of an ultrasonic probe, and FIG. Schematic diagram of the probe.

In the figure, 10 is a laminated piezoelectric transducer, 11.12°13
14 is an acoustic matching layer, 14 is a backing, 20 is a green sheet, 21 is a conductive paste), 22H gap, 30 is Pb
TiOs-based piezoelectric ceramics, 31 is internal 1! pole, 32
．． 32' is an external electrode, 51 is an insulator, 61 is a rectangular plate-shaped vibrator, 62.63 is an acoustic matching QN (do) N) 1 Figure 72 ■ Figure 74 Frequency (MHz) Figure 75 Figure 32' Foam Addressing procedure correction Document (spontaneous) 1. Indication of the incident 1982 Patent Application No. 1909
No. 14 No. 2, Title of the invention: Ultrasonic probe 3, Relationship to the amended person's case: Applicant: 5-33-1 Shiba, Shinminato-ku, Tokyo <423) NEC Corporation ((Omote: Tadahiro Sekimoto 4) , Agent phone number: Tokyo (031456-3111 (Main representative) (Contact information: Nippon Electric Power Co., Ltd.) 5o Subject of amendment: Column for detailed explanation of the invention in the specification & Contents of amendment: F!A , ms, page 2, line 7, "largely" is corrected to "large", BA specification, page 11, line 5, r 35 MHz J
Correct the statement to "3.5■i" on page 12, line 18 of the specification: r Kgm/sec
Correct J to r Kg/m・sec J.
r 412X 10'K on page 11, line 20 of the specification
The one that says gm/5eeJ is r 4.12 x 10
Kg/ln, corrected to 5ecJ.

・ r 14.2x 106 on page 12, line 1 of the specification
Kgm/sec J and Aruno' (ir 14.2X
10 Kg/m2・5ecJ and correction mouth, -1)

Claims (1)

[Claims] 2 or more PbTiO_3 piezoelectric ceramic layers and 1 or 2
A laminate in which the above-mentioned internal electrode layers are alternately stacked, and 2
two external electrodes are formed, each internal electrode is connected to one external electrode on the side surface of the laminate at every other layer,
The PbTiO_3 piezoelectric ceramic layer sandwiched between the two planar electrodes has the same thickness, and the piezoelectric transducer has a structure in which the layers are alternately polarized in opposite directions in the stacking direction. An ultrasound probe comprising an acoustic matching layer formed on one vertical surface.