JPH07194517A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To provide an ultrasonic probe of good picture accuracy which can provide high sensitivity although of a small diameter and be driven with low- voltage pulses by remodeling the construction of a transducer for improvement as to the absolute sensitivity degradation of the probe due to miniaturization of a piezoelectric element. CONSTITUTION:In this ultrasonic probe comprising a piezoelectric element made up of a stack of plates of piezoelectric ceramics, an acoustic matching layer or acoustic lens, and a back load material, the piezoelectric element is provided with at least three or more electrodes 1-3, and during transmission of ultrasonic waves, a pulse voltage is applied between the electrodes 1, 2 to cause vibration along the thickness of the element, and a flexing vibration caused by an echo wave is detected between the electrodes 1, 3 during reception of the ultrasonic waves.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe used in an ultrasonic endoscope for medical use, and more particularly to the structure of a piezoelectric element of the ultrasonic probe.

[0002]

2. Description of the Related Art Recently, ultrasonic probes have been used for nondestructive inspection,
Demand for ultrasonic diagnostic equipment for medical use is growing rapidly. The probe of the ultrasonic endoscope emits high-frequency acoustic vibration from the ultrasonic transducer into the living body, receives the reflected ultrasonic wave and returns it to the ultrasonic transducer.
A cross-sectional image of the inside of a living body is obtained by processing different information due to slight differences in interface characteristics.

The vibrator of the ultrasonic transducer is roughly divided into a piezoelectric element, an acoustic matching layer, and a back load material. The ultrasonic transducer applies a high-frequency pulse voltage to the piezoelectric element via an electrode formed on the surface of the piezoelectric element, causes the piezoelectric element to resonate, and causes a sudden deformation to generate an ultrasonic pulse.

However, in the case of ultrasonic probe for blood vessels which requires higher frequency and smaller size, it becomes very difficult to obtain absolute sensitivity because the shape of the piezoelectric element becomes small. .

Conventionally, as this type of ultrasonic probe, for example, an ultrasonic probe using a transducer integrated with transmission and reception as disclosed in JP-A-58-62554 is known. As shown in FIG. 11, this is because electrodes 26a to 26d are formed on the front and back of the main plane and are polarized in the thickness direction.
Acoustic matching layers 10a and 10b corresponding to the resonance frequencies are provided on the surfaces of two or more piezoelectric elements 4a and 4b having different resonance frequencies (thicknesses t1 and t2), and one ultrasonic wave is applied to each acoustic matching layer. Acoustic lens 15 to focus on
Is provided and joined to the backside load member 8. According to this ultrasonic probe, since two frequencies are used, good sensitivity can be obtained from the near field to the far field.

[0006]

However, in the above-mentioned conventional device, when the shape is not restricted, a certain level of good sensitivity can be obtained from the near field to the far field, but due to the demand for downsizing. If the area of the piezoelectric element is limited,
There is a problem that sufficient sensitivity cannot be obtained. Since it is said that the sensitivity changes in proportion to the square of the area of the piezoelectric element, in such a probe, if the area of the piezoelectric element is reduced according to the diameter of the ultrasonic probe, S The / N ratio deteriorates, and a clear image cannot be obtained.

Further, even in the case of a mirror type ultrasonic probe of integrated transmission / reception type capable of observing a near field, if it is manufactured by a conventional transducer structure, the area of the piezoelectric element is further reduced and the required sensitivity is required. Couldn't get

The present invention has been made in view of the above-mentioned problems, and an absolute reduction in sensitivity due to miniaturization of the piezoelectric element is improved by changing the structure of the transducer, and the sensitivity is high even with a small diameter.
It is an object of the present invention to provide an ultrasonic probe with good image accuracy, which can be driven by a low voltage pulse.

[0009]

To achieve the above object, in an ultrasonic probe of the present invention, a piezoelectric element composed of a laminated body of plate-shaped piezoelectric ceramics, an acoustic matching layer or an acoustic lens, and a back load material. In the ultrasonic probe consisting of
It is characterized in that the piezoelectric element has at least three or more electrodes, at least one of the electrodes is different when transmitting and receiving ultrasonic waves, and vibrations of different modes are used during transmission and reception.

In this case, the gap between the first electrode and the second electrode formed on the principal plane of the plate-like piezoelectric ceramic is polarized in the thickness direction, and the third electrode and the other electrode paired therewith are polarized. It is preferable to polarize in the radial direction.

A load mass may be applied to the third electrode portion.

[0012]

In the ultrasonic probe of the present invention having the above structure,
At the time of transmission, a pulse voltage is applied between the first and second electrodes of the laminated body to utilize the vibration of the piezoelectric element in the thickness direction.
Then, at the time of reception, the third electrode and another electrode paired with the third electrode (one of the first electrode and the second electrode may be used, or a separately provided fourth electrode may be used). ) And are used to convert lateral bending vibrations into electrical signals.
Since the laminated body is used for the piezoelectric element, it can be driven at a low voltage. Further, a highly sensitive ultrasonic probe can be obtained by using a material having a large electromechanical coupling coefficient (Kt, K33) in the thickness direction and the radial direction. Further, when a load mass is applied to the third electrode portion, flexural vibration at the time of reception becomes large, and the sensitivity is further improved.

Embodiments of an ultrasonic probe according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

[0014]

First Embodiment First, an ultrasonic probe according to a first embodiment of the present invention will be described in the order of its manufacturing steps.

As shown in FIGS. 1 and 2, a pair of first and second electrodes 1 and 2 are formed on the main plane of the plate-shaped piezoelectric ceramic 4, and the side surfaces where no electrodes are formed on the main plane are formed. Is the third
The electrode 3 is formed and the piezoelectric element 6 is manufactured. In this embodiment, the first electrode 1 is also used as the GND side electrode,
The third electrode 3 is used as a pair with the first electrode. This piezoelectric element 6 includes a pair of electrodes 1 and 2 provided on the front and back of the main plane.
Is polarized in the thickness direction as shown by the arrow 5a,
The space between the third electrode 3 and the first electrode is polarized in the radial direction as indicated by arrow 5b.

The piezoelectric element 6 of this embodiment was produced by using a hard PZT having a high electromechanical quality factor Qm of 1500 and a large electromechanical coupling factor (Kt, K33) in the thickness direction and the radial direction. In order to obtain highly efficient polarization, a block-shaped piezoelectric element was produced, a pair of silver baking electrodes including side electrodes were formed, and first radial polarization was performed, followed by lapping. After processing to a thickness of a predetermined frequency, silver electrodes 1 and 2 were formed on the main plane by vapor deposition in a temperature range lower than the Curie point Tc, and polarization in the thickness direction was performed. The size of this prototype piezoelectric element 6 has a width W = 0.
6 mm, length L = 1.5 mm, thickness t = 0.1 mm (resonance frequency 20 MHz). Also, the electrodes for radial vibration 1,
During 3 periods, a = 0.3 mm.

Next, the piezoelectric element 6 thus manufactured is
As shown in FIG. 3, a plurality of sheets are prepared and bonded with an epoxy adhesive 23 so that the polarization directions of the main planes are reversed and the electrode 1 on the GND side is the surface, and the piezoelectric laminate as shown in FIG. 24
To get

Next, using this piezoelectric laminate 24, as shown in FIG.
An ultrasonic transducer part as shown in is prepared.

First, the acoustic matching layer 10 made of epoxy resin
Is formed on the upper surface of the piezoelectric laminate 24 with a thickness of ¼λ.
At this time, a part of the electrode 1 is removed so that connection can be made later. Next, the convex back load material 8 in which the filler of tungsten is mixed with the epoxy resin is manufactured. Back load material 8
An epoxy resin layer is formed as the insulating layer 9 on the bottom surface of the. Then, the back load material 8 with the insulating layer 9 and the piezoelectric laminate 24 with the acoustic matching layer 10 are pressure-bonded with an anaerobic adhesive (not shown). At this time, the back load material 8 and the piezoelectric laminate 24 were bonded so that the point P at the bonding end was 0.2 mm from the third electrode 3. Next, a silicone resin 7a was filled between the third electrode 3 and the back load material 8. The acoustic lens 15 is adhesively laminated on the acoustic matching layer 10 of this laminated body, and after curing, cut into a desired width with a precision cutting machine.

Lead wires 12a to 12d are respectively connected to the three electrodes 1 to 3 of the transducer by solders 11a to 11d, and exposed on the main plane side by an epoxy type sealing resin 13 which also serves as reinforcement and insulation. The transducer 21 is obtained by protecting the electrode portion and sealing the peripheral portion of the third electrode 3 with the silicone resin 7b.

The transducer 21 manufactured as described above is bonded to the housing 18 to which the flexible shaft 19 has been brazed in advance, and is fixed with the sealing resin 13 for reinforcement, and the ultrasonic probe as shown in FIG. Obtain the tentacle 20.

When using the ultrasonic probe 20 of the embodiment thus constructed, a high frequency pulse voltage is applied between the electrodes 1 and 2 provided on the front and back sides of the main plane during transmission, and the piezoelectric element 6 is used. Are resonated in the thickness direction to generate ultrasonic pulses, and ultrasonic waves are radiated through the acoustic matching layer 10 and the acoustic lens 15.

On the other hand, the echo wave returned upon hitting the subject deforms by applying pressure to the piezoelectric element 6, so that the transducer 21 causes bending resonance with the point P in FIG. 5 as a fulcrum, and the third electrode A voltage is generated between the receiving signal electrode 3 and the first electrode, which is the common GND electrode 1 for transmission and reception. This voltage is taken as a received signal into an image processing device (not shown) to form an image. In addition, increasing the bending vibration between the receiving electrodes 1 and 3,
In order to obtain a high voltage, a flexible silicon resin was used as a reinforcing and insulating sealing material near the third electrode 3.

According to the ultrasonic probe 20 having the above structure,
Since the piezoelectric elements are laminated, good transmission is possible even when the input pulse has a low voltage. Further, the voltage generated between the electrodes 1 and 3 at the time of reception is higher than the voltage between the electrodes 1 and 3 in the thickness direction, and thus is a high voltage. Therefore, the S / N ratio is improved even with a small transducer, and an image with high resolution can be obtained when the image is processed by the image processing device.

In this embodiment, the two-layer structure of the acoustic matching layer 10 and the acoustic lens 15 is shown, but the same effect can be obtained if at least one acoustic matching layer or acoustic lens is provided. Further, in the present embodiment, the distance between the electrodes 1 and 3 is set to a = 0.3 mm, but even if it is more than this, the same effect can be obtained if vibration in an appropriate mode is obtained. Furthermore, the electrode may be applied by sputtering instead of vapor deposition. When the polarization step is performed after applying the electrode, the electrode may be formed by baking or plating. In addition to silver, the same effect can be obtained as long as the material of the electrode is conductive, such as gold, copper and alloys containing these. Although the solder 11 is used for the connection, the same effect can be obtained by using a wire bonder or a conductive resin. Then, the piezoelectric laminated body was produced by bonding the piezoelectric element, but it may be produced by printing the internal electrodes on the green sheet and firing.

[0026]

Second Embodiment Next, a second embodiment of the present invention will be described. Figure 7
FIG. 4 is a side view showing a transducer portion of this embodiment.
As shown, in this embodiment, as shown in FIG. 4, a laminated body having a structure in which two piezoelectric elements 6 having a thickness resonance frequency of 12 MHz and a thickness t = 200 μm are laminated is printed with an internal electrode 17 on a green sheet. The external electrode 16 for facilitating the connection from the internal electrode 17
And, the signal electrode 3 for reception was baked to prepare. A metal block 14 made of copper is formed on the positive electrode 3 for reception of the piezoelectric laminate.
Were bonded with a conductive adhesive to prepare the transducer section 21.

An acoustic lens 15 is provided above the transmitting electrodes 1 and 2 of the piezoelectric laminate to which the metal block 14 is adhered.
The acoustic matching layer 10 is formed in the vicinity of the metal block 14 and the receiving signal electrode 3, and the back load material 8 with the insulating layer 9 is adhered thereto as in the first embodiment, and sealing is performed. The transducer portion 21 is performed so as to cover the metal block 14.
Was produced.

This transducer section 21 is used in the first embodiment.
Similarly, housing 1 with flexible shaft 19
8 and the four lead wires 12a to 12d are respectively connected. At this time, the reception signal electrode 3 and the lead wire 12e were connected to the metal block 14 by soldering.

In this embodiment, a metal block 14 is bonded to the receiving signal electrode 3. This metal block 14
Receives the pressure of the echo wave and acts as a load mass when causing flexural vibration about the point P as a fulcrum, and generates a large vibration. Further, although the reception signal electrode 3 has a small area, the transducer of this embodiment can be electrically connected through the metal block 14. Furthermore, since ultrasonic waves are transmitted through the acoustic lens 15 during transmission, the ultrasonic beams are focused and the lateral resolution is improved.

According to this embodiment, since the metal block 14 is applied to the receiving electrode 3 of the piezoelectric laminate as the load mass, a large amplitude can be obtained even if the pressure due to the echo wave is the same, and the output is obtained. The applied voltage also increases, and a highly sensitive ultrasonic probe can be obtained. Moreover, since ultrasonic waves are transmitted through the acoustic lens 15 at the time of transmission and received through the acoustic matching layer 10 having the most efficient thickness at the time of reception, the lateral resolution can be improved without lowering the sensitivity. . Since the receiving signal electrode 3 and the metal block 14 are joined by a conductive adhesive, the lead wire 12e may be connected to the metal block 14, and the lead wire 12e can be easily connected and the reliability is improved. Also, the provision of the external electrode 16 facilitates connection to the signal electrode for transmission.

[0031]

Third Embodiment Next, a third embodiment of the present invention will be described. In this embodiment, the piezoelectric laminate 24 having a four-layer structure as shown in FIG.
To use. This piezoelectric laminate 24 is a laminate of four sheets produced by the green sheet method, and the electrode configuration of each layer is the same as in FIGS. In this embodiment, the vitreous insulating material 2 is provided every other layer on the side surface of the laminated body internal electrode 17.
5 is deposited, and then silver electrodes are baked as the external electrodes 16a and 16c. After that, the positive electrode 3 for reception is applied and polarization treatment is performed to obtain the piezoelectric laminate 24.

Next, as shown in FIG. 9, an epoxy resin having a thickness of 1 is used as the acoustic matching layer 10 on one side of the piezoelectric laminate 24.
Then, the lens 15 is formed by printing so as to have a length of / 4λ, and the mold is pressed against the upper portion of the transmitting electrode before the resin is cured. Next, the back load material 8 is bonded with an anaerobic adhesive (for example, LI-504 manufactured by Loctite Co., Ltd.). Then, the two external electrodes 16a, 16c and the receiving positive electrode 3 are connected to the lead wires 12a, 12b, 12c by the solder 11, and the periphery of the back load material is surrounded by the silicon resin 7 for the insulation of the electrode portion and the reinforcement of the connection portion. The whole lead wire is sealed and the transducer section 21 is manufactured.

The transducer portion 21 is vertically fixed to the housing 18 having the flexible shaft 19 and the SUS reflection mirror 22 with an insulating adhesive,
An ultrasonic probe 20 as shown in FIG. 10 is obtained.

In the ultrasonic probe 20 of this embodiment, since it is multi-layered at the time of transmission, it is driven at a low voltage, and at the time of reception, bending vibration occurs with the boundary between the back load material and the silicone resin 7 as a fulcrum. Since there is an electrode gap, a high signal voltage can be obtained. The voltage converted from this vibration is taken into the image processing device to form an image.

According to the present embodiment, it is possible to obtain a mirror-type small-diameter ultrasonic probe capable of observing an ultra-near field with good sensitivity. Further, since the piezoelectric laminated body is used, it is driven at a low voltage, and the safety when used on the human body is improved. In addition, when forming the external electrodes by vapor deposition, if they are extended not only to the side surface of the piezoelectric laminate but also to the back load material, the subsequent connection becomes easy.

In each of the above embodiments, two or four piezoelectric laminated bodies were used, but the same effect can be obtained if two or more piezoelectric laminated bodies are used.

[0037]

As described above, according to the ultrasonic probe of the present invention, the absolute sensitivity decrease due to the miniaturization is improved by changing the structure of the transducer, the sensitivity is high even with a small diameter, and the laminated body is used. It is possible to obtain an ultrasonic probe that can be driven with a low-voltage pulse and has good image accuracy.

[Brief description of drawings]

FIG. 1 is a side view showing a piezoelectric element used in an ultrasonic probe of Example 1.

2 is a top view showing a piezoelectric element used for the ultrasonic probe of Example 1. FIG.

FIG. 3 is a diagram for explaining how a piezoelectric layered body is manufactured by stacking piezoelectric elements.

FIG. 4 is a side view showing a piezoelectric laminate used in the ultrasonic probe of Example 1.

5 is a side view showing an ultrasonic transducer used in the ultrasonic probe of Example 1. FIG.

FIG. 6 is a side view showing the distal end portion of the ultrasonic probe according to the first embodiment of the present invention.

7 is a side view showing an ultrasonic transducer used in the ultrasonic probe of Example 2. FIG.

FIG. 8 is a side view showing a piezoelectric laminate used in the ultrasonic probe of Example 3;

FIG. 9 is a side view showing an ultrasonic transducer used in the ultrasonic probe of Example 3;

FIG. 10 is a side view showing a distal end portion of an ultrasonic probe according to a third embodiment of the present invention.

11A and 11B are a front view and left and right side views illustrating a conventional ultrasonic probe.

[Explanation of symbols]

 1 1st electrode 2 2nd electrode 3 3rd electrode 4 Piezoelectric ceramics 5 Polarization direction 6 Piezoelectric element 7 Resin 8 Back load material 9 Insulation layer 10 Acoustic matching layer 11 Solder 12 Lead wire 13 Sealing resin 14 Metal block 15 Acoustic lens 16 External electrode 17 Internal electrode 18 Housing 19 Flexible shaft 20 Ultrasonic probe 21 Transducer 22 Reflective mirror 23 Adhesive 24 Piezoelectric laminate 25 Insulator 26 Surface electrode

Claims (3)

[Claims] 1. An ultrasonic probe comprising a piezoelectric element made of a laminate of plate-shaped piezoelectric ceramics, an acoustic matching layer or an acoustic lens, and a back load material, wherein the piezoelectric element has at least three or more electrodes. An ultrasonic probe characterized by having different electrodes for at least one of transmission and reception of ultrasonic waves and utilizing vibrations of different modes for transmission and reception. 2. The ultrasonic probe according to claim 1, wherein:
The first electrode and the second electrode formed on the principal plane of the plate-shaped piezoelectric ceramic are polarized in the thickness direction, and the third electrode and the other electrode paired with the third electrode are polarized in the radial direction. An ultrasonic probe characterized by being polarized into. 3. The ultrasonic probe according to claim 1, wherein a load mass is applied to the third electrode portion.