JP3353962B2 - Ultrasonic probe manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe utilizing an ultrasonic echo.

[0002]

2. Description of the Related Art Ultrasonic probes are rapidly increasing in use as medical ultrasonic diagnostic equipment in addition to nondestructive inspection equipment. For example, a probe such as an ultrasonic endoscope radiates high-frequency acoustic vibration from the ultrasonic transducer into a living body, receives the reflected ultrasonic wave by the ultrasonic transducer, and detects a slight difference in interface characteristics. By processing different information, a cross-sectional image of the inside of a living body is obtained.
The transducer section of the ultrasonic probe is configured by sequentially stacking an acoustic matching layer, a piezoelectric element, and a back load material. This ultrasonic probe applies a high-frequency voltage pulse to the piezoelectric element from the electrode formed on its surface, causes the piezoelectric element to resonate and rapidly deforms, and this piezoelectric element transmits and receives ultrasonic echoes and Is obtained, and this is image-processed and observed. In general, such a piezoelectric element of an ultrasonic probe is manufactured through a polarization step after a pair of opposed electrodes are provided.

FIG. 21 to FIG.
No. 98 discloses a piezoelectric element used for a conventional ultrasonic probe. This piezoelectric element is a piezoelectric ceramic 1
The electrodes are formed on both sides of FIG.
As shown in FIG. 2, the entire surface is an electrode 110, and the electrode on the other surface is a divided electrode 120 divided concentrically into a plurality as shown in FIG. In the piezoelectric element having such a structure, the intensity of spontaneous polarization of the piezoelectric ceramics 100 immediately below the split electrode 120 decreases stepwise from the center to the outer periphery as shown by arrows in FIG. Side lobes near the lobes can be reduced.

[0004]

However, in the above prior art, since it is necessary to divide the electrode of the piezoelectric element concentrically into a plurality of electrodes, it is necessary to prevent leakage to an adjacent electrode during polarization when a high voltage is applied. A divided electrode must be manufactured with high precision without bleeding or the like. Therefore, there is a problem that the production becomes troublesome and an ultrasonic probe having no characteristic due to a wide gap between the electrodes. Further, since the piezoelectric element of the conventional ultrasonic probe has the divided electrodes, a high voltage pulse is repeatedly applied instantaneously, so that a stress acts on the electrode boundary and strain is accumulated. For this reason, there is also a problem that the fatigue destruction of the piezoelectric ceramic occurs and the life of the ultrasonic probe is shortened.

The present invention has been made in view of the above circumstances, and uses a piezoelectric element which can be polarized without using a divided electrode and which does not break down the piezoelectric ceramics even when a voltage is applied. It is an object to provide an ultrasonic probe.

[0006]

Means for Solving the Problems and Actions The method for manufacturing an ultrasonic probe according to the present invention comprises the steps of:
The first electrode which is made to adhere to the electrode made of
Polarization step, and the piezoelectric ceramic is different from the electrode
An electrode made of conductive rubber having a shape
At least a second polarization step of performing polarization by the
From the center of the piezoelectric ceramic toward the outer periphery,
A polarization process in which the polarization is gradually changed
On both sides of the piezoelectric ceramics polarized by the polarization process
A step of producing a piezoelectric element by attaching electrodes over the entire surface;
Laminate back load material and acoustic matching layer on both sides of the piezoelectric element,
Attaching the laminate to a housing.
It is characterized by that.

As described above, the polarization step is divided into a plurality of times.
By doing so, the spontaneous polarization gradually decreases from the center to the outer periphery.
Variously changed piezoelectric elements are manufactured.

[0008]

[0009]

[0010]

Embodiment 1 FIGS. 1 and 2 show a piezoelectric element 1 used in an ultrasonic probe according to Embodiment 1 of the present invention. This piezoelectric element 1 is formed by forming full-surface electrodes 2 and 3 on both surfaces of a disk-shaped piezoelectric ceramic 15. The piezoelectric ceramic 15 has been subjected to a polarization treatment before the formation of the full-surface electrodes 2 and 3, whereby the spontaneous polarization gradually changes from the center to the outer periphery. In this embodiment, FIG.
As shown by the arrow, the polarization at the center is the strongest, and gradually becomes weaker toward the periphery.

FIGS. 3 to 6 show this piezoelectric ceramic 1.
5 shows a polarization treatment step. The piezoelectric ceramics 15 is manufactured by forming and firing a lead zirconate titanate (PZT) -based ceramic material, and then grinding the disk to form a disk having a diameter of 25 mm and a thickness of 0.5 mm, followed by lapping of # 3000. I do. This PZT-based material has V1 = 0.7
By applying a DC voltage of kV / mm, the coupling coefficient Kt = 3
0%, and similarly for V2 = 1.6 kV / mm, the coupling coefficient Kt = 45% and V3 = 3.5 kV / mm
Has a polarization characteristic of a coupling coefficient Kt = 62%.

First, as shown in FIG. 3, a pair of electrodes 16 of substantially the same diameter, made of conductive rubber, are tightly sandwiched between both surfaces of a piezoelectric ceramic 15 before the electrodes are formed.
7 to apply a DC voltage of V1 = 0.7 kV / mm to perform the first-stage polarization. Next, as shown in FIG. 4, an electrode 16 made of a conductive rubber having a reduced diameter sandwiches a portion of the piezoelectric ceramics 15 excluding an outer peripheral portion, and V = 1.6 kV / m.
The second-stage polarization is performed by applying a DC voltage of m. Then, as shown in FIG. 5, the inner peripheral portion of the piezoelectric ceramics 15 is sandwiched between electrodes 16 made of conductive rubber having a further reduced diameter, and a DC voltage of V3 = 3.5 kv / mm is applied to perform third-stage polarization. I do. By this polarization processing, the polarization of the piezoelectric ceramics 15 gradually decreases from the central portion toward the outer peripheral portion. After this polarization treatment, the piezoelectric ceramics 15 is sputtered, and as shown in FIG. In FIG. 6, an arrow 4 indicates the intensity of polarization by a vector.

FIG. 7 shows an ultrasonic probe 18 using such a piezoelectric element 1. One electrode of the piezoelectric element 1 is connected to the positive lead wire 9 of the coaxial cable 13, and the other electrode serving as a GND electrode is connected to the housing 8 made of a conductive metal with a wire 11. Further, the GND lead wire 10 of the coaxial cable 13 is connected to the housing 8. In this state, the piezoelectric element is laminated on the back load member 7 and sealed in the housing 8, and the acoustic matching layers 5a and 5b are laminated and bonded. As the acoustic matching layers 5a and 5b, machinable ceramics and epoxy resin can be used after being adjusted to a thickness of λλ.

In the ultrasonic probe 18 having such a configuration, the piezoelectric characteristics are weakened toward the outer peripheral portion of the piezoelectric element 1, so that the amplitude continuously decreases toward the outer peripheral portion. Therefore, the ultrasonic probe 18 having a small ratio of the side lobe to the main lobe can be obtained. Accordingly, in this embodiment, the ultrasonic probe 18 having a small ratio of the side lobe to the main lobe can be easily obtained only by changing the polarization method of the piezoelectric element 1, and can be manufactured in the same manner as the conventional assembling method. That is, the ultrasonic probe 18 with improved resolution in the angular direction and improved image accuracy can be easily manufactured. In addition, since the piezoelectric element 1 does not have the divided electrodes, an ultrasonic probe that is efficient and hardly causes fatigue failure and has high reliability is obtained. In this embodiment, the polarization of the piezoelectric ceramic is performed in three stages, but the same effect can be obtained if the polarization is performed in two or more stages.

[0015]

Second Embodiment FIGS. 8 to 11 show the polarization processing of a piezoelectric element in an ultrasonic probe according to a second embodiment of the present invention. The same elements as those in the first embodiment are denoted by the same reference numerals and correspond to each other. is there.
In the present embodiment, first, as shown in FIG. 8, a pair of electrodes 16 made of conductive rubber are brought into close contact with the piezoelectric ceramics 15 to perform first-stage polarization. Next, as shown in FIG. 9, a pair of electrodes 16 formed in a ring shape
The second-stage polarization is performed with the portion excluding the central portion of the 挟. Then, as shown in FIG. 10, third-stage polarization is performed with the outer periphery of the piezoelectric ceramics 15 interposed between the ring-shaped electrodes 16. The polarization is performed by gradually increasing the polarization voltage from the first stage to the third stage. This makes it possible to produce a piezoelectric ceramic in which the polarization becomes stronger from the center toward the outer periphery. After this polarization, as shown in FIG. 11, silver is vapor-deposited on both surfaces of the piezoelectric ceramics 15 to form electrodes 2 and 3 on the entire surface. An arrow 4 in the figure is a vector indicating the intensity of polarization.

FIG. 12 shows an ultrasonic probe in which a back load member 7 is joined to one surface of the piezoelectric element 1 and an acoustic matching layer 5 is joined to the other surface. Here, an epoxy resin mixed with a tungsten filler can be used as the back load member 7, and an epoxy resin having a thickness of ４λ can be used as the acoustic matching layer 5.

In the ultrasonic probe according to the present embodiment having the above-described structure, the outer periphery of the piezoelectric element 1 is radiated at the moment when a pulse is applied, as shown in FIG. The ultrasound beam 14 may be slightly focused. FIGS. 14 and 15 show the intensity (relationship between distance and sensitivity) of an ultrasonic probe using a piezoelectric element in which the entire surface of the piezoelectric element is uniformly polarized, and the ultrasonic probe of this embodiment with respect to the distance of the ultrasonic beam. Is a characteristic diagram measured using a hydrophone. Although the sensitivity of the ultrasonic probe of this embodiment is slightly inferior in the near field as shown in FIG. 14, the same sensitivity can be obtained in the far field because the ultrasonic beam does not diverge and tends to focus. There are benefits.

In the ultrasonic probe of this embodiment, the divergence of the ultrasonic beam can be prevented and the resolution in the angular direction can be greatly improved without forming an acoustic lens which is difficult to manufacture or performing spherical processing on the piezoelectric element. Can be higher. Further, since the acoustic matching layer 5 can have a high transmission efficiency of 1 / 4λ at any part, the reflection at the boundary surface during the transmission and reception of the ultrasonic waves is small, and the ultrasonic probe of the conventional piezoelectric element which is uniformly polarized over the entire surface. Sensitivity and
The sensitivity is as good as in the near field, and higher in the far field than before.

Since the electrodes used for polarization only change the range of polarization, if only one of them is formed in a ring shape, the other electrode can be polarized almost equally even in a shape in contact with the whole piezoelectric ceramic.

[0020]

Third Embodiment FIG. 16 shows the polarization of the piezoelectric element 1 in the ultrasonic probe according to the third embodiment of the present invention. Electrode 1 of this embodiment
One of the electrodes in 6 is a conductive rubber molded body 16a, and an insulator 19 such as a substantially semi-cylindrical silicon rubber fitted on the surface of the molded body 16a facing the piezoelectric ceramics 15 so as to be flush with the molded body. It consists of When the piezoelectric ceramics 15 is polarized using the electrodes 16, the voltage applied to the piezoelectric ceramics 15 decreases according to the thickness of the insulator 19. Therefore, the spontaneous polarization of the piezoelectric ceramics 15 after the polarization process changes only in the width direction as shown by the arrow 4 in FIG.

The silver wraparound electrode 22 is not depolarized on the polarized piezoelectric ceramics 15 by vapor deposition.
The piezoelectric element 1 shown in FIG.
Then, using the piezoelectric element manufactured by this method, a thickness of about 20
An ultrasonic probe having 0 μm and a resonance frequency of 12 MHz is manufactured.

More specifically, 1 / 4λ is used as the acoustic matching layer 5.
Epoxy resin of thickness and insulating resin layer 20 for short circuit prevention
Is bonded to both surfaces of the piezoelectric element 1 with an anaerobic adhesive 21. Thus, the transducer shown in FIG. 19 is manufactured. This is cut in the length direction as shown by the broken line using a precision cutting machine to produce a transducer for an ultrasonic probe.

Then, this transducer is mounted on a housing 8 produced by processing a metal pipe, and an ultrasonic probe shown in FIG. 20 is produced. Specifically, first, the housing 8 is soldered using the flexible shaft 25 and the silver solder 24. Then, the coaxial cable 13 is connected to the shaft 25.
Then, the ground side lead wire 9 and the housing 8 are connected using the conductive paste 23, and the positive side lead wire 10 is directly connected to the electrode of the piezoelectric element 1 using the conductive paste 23. Then, in order to secure insulation, sealing is performed with an insulating resin 26.

In the ultrasonic probe having the above structure, at the moment when the pulse is applied, the piezoelectric element 1 is deformed more in the length direction toward the end than at the center, and the emitted ultrasonic wave is increased. The beam 14 can be slightly but focused along the length of the piezoelectric element.

In this embodiment, in consideration of productivity, there is a difference in the intensity of spontaneous polarization in only one direction. In this case, too, the divergence of the ultrasonic beam can be prevented and the resolution in the angular direction can be increased. . In addition, since the acoustic matching layer can have a high transmission efficiency of 1 / 4λ in any portion, there is little reflection at the boundary surface when transmitting and receiving ultrasonic waves, and the ultrasonic probe of the conventional piezoelectric element uniformly polarized over the entire surface. The sensitivity in the near field is comparable to the sensitivity of the child, and the sensitivity in the far field can be made higher than before. Note that the same effect can be obtained by combining an insulating material and a conductive material in a stepwise manner, instead of using a combination of an insulated insulating material and a conductive material.

[0026]

As described above, according to the present invention, the size of the spontaneous polarization is generated in the same element by performing the polarization operation before applying the electrode without having the divided electrode as the piezoelectric element. By using such an ultrasonic probe, it is possible to disperse the strain intensively applied to the electrode boundary portion and to provide an ultrasonic probe having a low rate of occurrence of discharge breakdown and fatigue breakdown.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a piezoelectric element according to a first embodiment of the present invention.

FIG. 2 is a front view of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a polarization process of a piezoelectric element.

FIG. 4 is a cross-sectional view showing the polarization processing of the piezoelectric element.

FIG. 5 is a cross-sectional view showing the polarization processing of the piezoelectric element.

FIG. 6 is a sectional view of a piezoelectric element.

FIG. 7 is a cross-sectional view of the ultrasonic probe according to the first embodiment.

FIG. 8 is a cross-sectional view illustrating a polarization process according to the second embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a polarization process according to the second embodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating a polarization process according to the second embodiment of the present invention.

FIG. 11 is a sectional view of a piezoelectric element according to a second embodiment.

FIG. 12 is a cross-sectional view of the ultrasonic probe according to the second embodiment.

FIG. 13 is a cross-sectional view of the operation of the ultrasonic probe.

FIG. 14 is a characteristic diagram showing the intensity of the ultrasonic beam of the ultrasonic probe.

FIG. 15 is a characteristic diagram showing the intensity of the ultrasonic beam of the ultrasonic probe.

FIG. 16 is a perspective view of a polarization process according to the third embodiment.

FIG. 17 is a sectional view of a piezoelectric element according to a third embodiment.

FIG. 18 is an exploded side view of the transducer according to the third embodiment.

FIG. 19 is a perspective view of a transducer according to a third embodiment.

FIG. 20 is a cross-sectional view of the ultrasonic probe according to the third embodiment.

FIG. 21 is a sectional view of a piezoelectric element used for a conventional ultrasonic probe.

FIG. 22 is a left side view of FIG. 21.

FIG. 23 is a right side view of FIG. 21.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2, 3 Full surface electrode 5a, 5b Acoustic matching layer 7 Back load material 8 Housing

Continuation of the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 8/00-8/15 H04R 1/32 H04R 17/00 H01L 41/22

Claims (1)

(57) [Claims] 1. A laminated body in which a back load member, a piezoelectric element provided with full-surface electrodes on both sides, and an acoustic matching layer are sequentially laminated, and a housing to which the laminated body is attached. An ultrasonic probe characterized in that spontaneous polarization gradually changes toward a part.