JPH07136164A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To avoid the absolute decrease in sensitivity caused by miniaturization of a piezoelectric element by constituting the piezoelectric element so as to oscillate it under different mode on transmitting and receiving in an ultrasonic probe consisting of an acoustic matching layer or an acoustic lens, the piezoelectric element and a back face loading material. CONSTITUTION:An ultrasonic transducer 1 used for this ultrasonic probe consists of a piezoelectric element 2, an acoustic matching layer 9 and a back face loading material 10. The piezoelectric element 2 is formed by providing the first and the second electrodes 3 and 5 respectively on the surface and the rear face of the main plane of a sheet-like piezoelectric ceramic 6 and the third electrode 4 on the side face part and is polarized in the diameter direction by the electrodes 3 and 5. The first electrode 3 is to be a common GND electrode for the electrodes 5 and 4 and the second electrode 5 is to be a plus electrode for transmission and the third electrode 4 is to be a plus electrode for receiving. The back face loading material 10 is arranged on the second electrode 5 side and an insulating layer 11 is formed on the bottom part of the back face loading material 10. In addition, the mechanical quality coefficient Qm of this piezoelectric element 2 is at least 300.

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 ultrasonic endoscopes used for medical purposes,
More specifically, the present invention relates to an ultrasonic probe having a piezoelectric element of an ultrasonic transducer.

[0002]

2. Description of the Related Art In recent years, ultrasonic probes have shown rapid growth in demand as ultrasonic diagnostic devices for medical use in addition to nondestructive inspection devices. A probe such as an ultrasonic endoscope emits high-frequency acoustic vibrations from an ultrasonic transducer into a living body, receives the reflected ultrasonic waves, and receives the ultrasonic waves with a slight difference in interface characteristics. By processing different information, it is possible to obtain a cross-sectional image of the inside of the living body.

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 uses an electrode formed on the surface of the piezoelectric element to apply a high-frequency voltage pulse to the piezoelectric element to cause the piezoelectric element to resonate and rapidly deform, thereby generating an ultrasonic pulse. . However, in the case of an ultrasonic probe for blood vessels that requires higher frequencies and a smaller size, the shape of the piezoelectric element becomes smaller, making it extremely difficult to obtain absolute sensitivity.

Conventionally, there is known an ultrasonic probe using a transducer integrated with transmission and reception as disclosed in Japanese Patent Laid-Open No. 58-62554. This ultrasonic probe is shown in FIGS.
6, the resonance frequencies are different (thickness t ₁ ,
t ₂ ) Two or more piezoelectric elements 41a and 41b are provided. Electrodes 42a and 42b and electrodes 43a and 43b are formed on the front and back of the principal plane of the piezoelectric elements 41a and 41b, respectively, and the piezoelectric elements 41a and 41b are polarized in the thickness direction. Acoustic matching layers 44a and 44b corresponding to the resonance frequencies are provided on the surfaces of the piezoelectric elements 41a and 41b, respectively. On the acoustic matching layers 44a and 44b, an acoustic lens 45 that converges each ultrasonic wave at one point. Is provided. Also, on the back surfaces of the piezoelectric elements 43a and 43b,
The back load material 46 is joined.

[0005]

Problems to be Solved by the Invention JP-A-58-6255
In the transducer having the configuration as disclosed in Japanese Patent No. 4 publication, if the shape is not limited, a good sensitivity can be obtained to some extent from the near field to the far field. However, miniaturization is required,
Moreover, in the case of a transducer that is a transmission / reception-integrated type adopting a mirror type capable of observing a near field, a conventional transducer cannot obtain a necessary sensitivity. Generally, it is said that the sensitivity decreases in proportion to the square of the area of the piezoelectric element. Therefore, in the ultrasonic probe of the conventional example, if the area of the piezoelectric element is made smaller according to the diameter of the ultrasonic probe, the S / N ratio becomes smaller and a clear image cannot be obtained. There was a problem.

The present invention was developed in view of the above-mentioned problems of the prior art, and the absolute sensitivity decrease due to the miniaturization of the piezoelectric element is improved by changing the structure of the transducer, and the sensitivity is high even with a small diameter, and the image accuracy is high. The purpose is to provide a good ultrasonic probe.

[0007]

In order to solve the above problems, the present invention provides an ultrasonic probe including at least one or more acoustic matching layers or acoustic lenses, a piezoelectric element, and a back load material. In the tentacle, the piezoelectric element was configured to vibrate in different modes during transmission and reception. And
The piezoelectric element is provided with at least three electrodes and is formed into a plate shape, and is polarized in the thickness direction between a pair of first and second electrodes formed on the main plane of the piezoelectric ceramic, and at the same time, the first or second electrode is formed. The second electrode or the fourth electrode provided on the main plane and the third electrode formed on the side surface of the piezoelectric ceramic are polarized in the radial direction. Also,
In the ultrasonic probe, the mechanical quality factor Qm of the piezoelectric element is set to 300 or more. Further, in the ultrasonic probe, the distance between the electrodes used during reception is longer than the distance between the electrodes used during transmission. In the ultrasonic probe, a load mass is applied to the third electrode section.

[0008]

According to the above construction, at the time of transmitting and receiving ultrasonic waves, different electrodes are used for at least one of them, and vibrations of different modes can be utilized for transmission and reception. Then, at the time of transmission, a voltage pulse is applied between the first and second electrodes, vibration in the thickness direction of the piezoelectric element is used, and at the time of reception,
Using the third electrode and the first or second electrode, lateral bending vibration is converted into an electrical signal. Also, for the piezoelectric element,
When a material having a high electromechanical quality factor Qm and a large electromechanical coupling factor (Kt, K ₃₁ ) in the thickness direction and the radial direction is used, a highly sensitive ultrasonic probe can be obtained. Further, if the distance between the electrodes used during reception is longer than the distance used between the electrodes during transmission, the voltage generated between the reception electrodes becomes high, and an image with high resolution can be obtained. Further, when the load mass is applied to the third electrode portion, the flexural vibration at the time of reception increases, and the sensitivity improves.

[0009]

[Embodiment 1] An ultrasonic probe of the present embodiment will be described with reference to FIGS. 1 is a side view showing an ultrasonic transducer of an ultrasonic probe of the present embodiment, FIG. 2 is a plan view showing a piezoelectric element, FIG. 3 is a side view showing a manufacturing process of the piezoelectric element, FIG.
Is a side view showing a state in which lead wires are connected to the ultrasonic transducer used in the ultrasonic probe of the first embodiment, and FIG. 5 is a tip of the ultrasonic probe of the present embodiment in which the ultrasonic transducer is mounted. It is a side view which shows a part.

In FIG. 1, reference numeral 1 denotes an ultrasonic transducer, which is composed of a piezoelectric element 2, an acoustic matching layer 9 and a back load material 10.
The piezoelectric element 2 is provided with a first electrode 3, a second electrode 5 and a third electrode 4, and the first electrode 3 is a common GND electrode of the second electrode 5 and the third electrode 4. The second electrode 5 is a plus electrode for transmission, and the third electrode 4 is a plus electrode for reception. The acoustic matching layer 9 is arranged on the first electrode 3 side. The back load material 10 is the second electrode 5
An insulating layer 7 is formed on the bottom of the back load material 6 on the side.

The piezoelectric element 2 is shown in FIGS. 2 and 3 (d).
As shown in FIG. 2, a pair of first and second electrodes 3 and 5 are formed on the front and back sides of the main surface of the plate-shaped piezoelectric ceramic 6, and as shown in the figure, the first and second pair of electrodes 3 and 5 are formed on the side surface portion where the electrodes are not formed It is manufactured by forming three electrodes 4.

[0012] Specifically, in order to obtain a high polarization efficiency, a block-shaped piezoelectric ceramics 6 as shown in FIG. 3A is produced, and a pair of silver baking electrodes 4 provided on the side surfaces of the piezoelectric ceramics 6. , 23 were formed, and polarization was performed in the polarization direction (radial direction) indicated by the arrow 7. After that, the piezoelectric ceramics 6 is cut and lap-polished and processed to have a thickness of a predetermined frequency. As shown in FIG.
The electrode 4 (second electrode 4) was formed on the side surface of the. Next, in a temperature range lower than the Curie point Tc, silver electrodes 1 and 3 are formed on the main surface of the piezoelectric ceramics 6 by a vapor deposition method as shown in FIG. Directional polarization was performed. As a result, the piezoelectric element 2 having the first, second, and third electrodes 3, 5, and 4 provided on the piezoelectric ceramic 6 and polarized in the radial direction and the thickness direction is shown in FIGS. 2 and 3D. Was prepared as shown in.

This piezoelectric element 2 has an electromechanical quality factor Qm.
Was as high as 1500, and a hard diameter PZT having a large electromechanical coupling coefficient (Kt, K ₃₁ ) in the thickness direction and the radial direction was used. The piezoelectric element 2 manufactured as a trial has a size of width W = 0.6 mm, length L = 1.5 mm, and thickness t =
The distance was 0.1 mm (resonance frequency 20 MHz), and the distance between electrodes for radial vibration was a = 0.3 mm.

Using the piezoelectric element 2, the ultrasonic transducer 1 shown in FIG. 1 was manufactured by the following method. First,
The acoustic matching layer 9 was provided on the first electrode 3 (GND) side of the piezoelectric element 2. The acoustic matching layer 9 is made of epoxy resin except for a part of the electrode 3 in the direction opposite to the third electrode 4 so that the electrode 3 can be connected later. Formed by

On the other hand, a convex back load material 10 in which an epoxy resin is mixed with a tungsten filler is prepared, and an insulating layer 11 made of an epoxy resin layer is provided on the bottom (the side opposite to the convex).
Is formed in advance, and next to the formation of the acoustic matching layer 9, the back load material 10 with the insulating layer 11 is formed on the second electrode 5 side of the piezoelectric element 2 with the acoustic matching layer 9 formed earlier. The upper surface of the convex portion of the back load material 10 and the piezoelectric element 2 were pressure-bonded to each other using an anaerobic adhesive (not shown). At this time, the positional relationship between the back load material 10 and the piezoelectric element 2 was such that the point P, which is the bonding end, was bonded to the third electrode 4 of the piezoelectric element 2 at a distance of 0.2 mm. Further, the back load material 10 is arranged so that a part of the electrode 5 in the opposite direction to the third electrode 4 is exposed so that the second electrode 5 can be connected later. Then, the silicone resin 12 was filled between the third electrode 4 and the back load material 10 to manufacture the transducer 1 shown in FIG.

Next, lead wires 13a, 13b and 1 are respectively attached to the three electrodes 3, 4 and 5 of the transducer 1.
3c is connected with solder 14a, 14b, 14c, and the epoxy-based encapsulating resin 15 that also serves as reinforcement and insulation protects the exposed electrodes 3 and 5 of the main plane, and the third electrode 4 is It was sealed with silicone resin 16 and manufactured as shown in FIG.

Then, the flexible shaft 19 is brazed to the housing 18 in which the metal pipe is processed, and the housing 18 shown in FIG.
The transducer 1 of is fixed with an adhesive and for reinforcement,
The ultrasonic probe 2 shown in FIG. 6 is fixed with silicone resin 17.
0 was produced.

The ultrasonic probe 20 having the above-described structure applies a high-frequency voltage pulse between the first electrode 3 and the second electrode 5 provided on the front and back sides of the main surface of the piezoelectric ceramic 6 during transmission, The piezoelectric element 2 is resonated in the thickness direction to generate an ultrasonic wave pulse, and the ultrasonic wave is radiated to the subject (for example, a living body) via the acoustic matching layer 9.

On the other hand, the echo returning to the subject and subjecting it to pressure deforms the piezoelectric element 2. At this time, the transducer 1 causes bending resonance with point P in FIG. 1 as a fulcrum, and the third electrode 4 which is a signal electrode for reception,
A voltage is generated between the first electrode 3 which is a GND electrode common for transmission and reception. The generated voltage is taken as a signal for reception into an image processing device (not shown) to image the subject.

Further, the receiving electrode 3 in the piezoelectric element 2,
In order to increase the flexural vibration between the four electrodes and obtain a high voltage, a flexible silicone resin is used as a reinforcing and insulating sealing material near the third electrode 4. The piezoelectric element 2 has an electromechanical coupling coefficient (K
A material having a large t, K ₃₁ ) and a large mechanical quality factor Qm is suitable. Among them, if the mechanical quality factor Qm is 300 or less, the reception voltage is lowered and the effect cannot be expected.

In the ultrasonic probe 20 having the above-mentioned structure, the voltage generated between the electrodes 3 and 4 at the time of reception is higher than the voltage between the electrodes 3 and 5 in the thickness direction because the voltage is higher. Therefore, even with a small transducer, the S / N ratio is improved,
When imaged by an image processing device (not shown), a high-resolution image can be obtained.

In this embodiment, the distance between the electrodes 3 and 4 was set to a = 0.3 mm (see FIG. 2) as described above, but a = 0.2.
The same effect can be obtained if it is at least mm. Further, although the solder 11 is used for connecting the electrodes 3, 4, 5 and the lead wires 13a, 13b, 13c, the same effect can be naturally obtained even if a wire bonder or a conductive resin is used. To be Furthermore, the method of applying the electrode may be sputtering other than vapor deposition, and when performing the polarization step after applying the electrode,
The electrode may be formed by baking or plating, and the same effect can be obtained as long as the electrode material is silver, gold, copper, or an alloy containing them.

[0023]

[Embodiment 2] FIG. 5 is a side view showing a configuration of a transducer portion of an ultrasonic probe according to Embodiment 2 of the present invention. The basic configuration of the present embodiment is the same as that of the first embodiment, and the same components are designated by the same reference numerals and only different points will be described.

In this embodiment, the metal block 21 made of copper, which is not shown in the drawing, is attached to the receiving positive electrode 4 of the piezoelectric element 2 having the thickness resonance frequency of 12 MHz and the thickness t = 200 μm as shown in FIGS. It is configured to be adhesively fixed using an adhesive. Furthermore, the acoustic lens 2 is provided above the transmission electrodes 3 and 5 of the piezoelectric element to which the metal block 21 is adhered.
2 is formed. An acoustic matching layer 10 is formed near the metal block 21 and the receiving signal electrode 4.

In this embodiment, after the metal block 21, the acoustic lens 22, and the acoustic matching layer 9 are provided, the back load material 10 with the insulating layer 11 is adhered to the piezoelectric element 2 as in the first embodiment. Sealing was performed with the silicone resin 16 so as to cover the metal block 21, and the transducer part was produced.

Then, as in the first embodiment, the transducer section is mounted on the housing 18 with the flexible shaft 19 as shown in FIG. 5, and the three lead wires 13a, 13b, 13c are respectively connected. On this occasion,
The connection between the reception signal electrode 4 and the lead wire 13b was performed by soldering the lead wire 13b and the metal block 21 to form the ultrasonic probe of this example.

In the ultrasonic probe having the above-mentioned structure, since the metal block 21 is adhered to the signal electrode 4 for reception, when the pressure of the echo wave is applied and the bending vibration is generated around the point P as a fulcrum, the metal block 21 is used. 21 acts as a load mass and a large vibration is generated. Further, although the reception signal electrode 4 has a small area, the transducer of the present embodiment can be electrically connected via the metal block 21. Furthermore, in order to transmit ultrasonic waves through the acoustic lens 22 during transmission,
The ultrasonic beam is focused and the lateral resolution is improved.

According to this embodiment, since the metal block 21 is applied to the receiving electrode 4 of the piezoelectric element 2 as the load mass to form the transducer, a large amplitude can be obtained even if the pressure due to the echo wave is the same. As a result, the output voltage also increases, and an ultrasonic probe with high sensitivity can be obtained. Further, since ultrasonic waves are transmitted through the acoustic lens 22 during transmission and ultrasonic waves are received through the acoustic matching layer 9 having the most efficient thickness during reception, the lateral resolution can be improved without lowering sensitivity. Since the receiving signal electrode 4 and the metal block 21 are joined with a conductive adhesive, the lead wire 13b is connected to the metal block 21.
The wiring can be done easily, and the reliability is improved.

In this embodiment and the first embodiment, as shown in FIG.
The piezoelectric element 2 provided with the three planar electrodes 3, 4, and 5 as shown in FIG. 3 was used, and the perspective view of FIG.
A disk-shaped piezoelectric ceramics 6a as shown in the sectional view of (b) is used, transmission electrodes 3a, 5a are provided in the central portions of the main planes on the front and back sides of the piezoelectric ceramics 6a, and reception signal electrodes 4a are provided on the side surfaces. The same effect can be obtained by using the piezoelectric element 2a provided and configured.

As shown in the perspective view of FIG. 8 (a) and the sectional view of FIG. 8 (b), a hole 24 is formed in the central portion of the piezoelectric element 2a of FIG. 7 to facilitate wiring. Piezoelectric element 2
The same effect can be obtained by using b.

Further, as shown in the perspective view of FIG. 9, the piezoelectric element 2 in which the electrodes 3c and 5c used at the time of transmission are wound around the side surface of the piezoelectric ceramics 6c to facilitate the wiring.
The same effect can be obtained with c. In addition, the common GND of FIG.
The same effect can be obtained even in the piezoelectric element 2d configured by dividing the electrode 3c into the transmitting GND electrode 25 and the receiving GND electrode 26 serving as the fourth electrode as shown in FIG.

[0032]

[Third Embodiment] FIG. 11 is a perspective view showing an ultrasonic transducer of an ultrasonic probe of the present embodiment, FIG. 12 shows a piezoelectric element used in the ultrasonic probe of the present embodiment, and FIG. ) Is a plan view, FIG. 12B is a perspective view, and FIG. 13 is a perspective view showing the tip end portion of the ultrasonic probe of the present embodiment mounted with an ultrasonic transducer.

The basic structure of this embodiment is the same as that of the first embodiment, and the same reference numerals are given to the same components and only the differences will be described. As shown in FIG. 12, the piezoelectric element 2d used in this embodiment has a common GND electrode (first electrode) 3d for transmission and reception and a transmission electrode (first electrode) at the center of the main surface on the front and back sides of the disk-shaped piezoelectric ceramics 6d. The second electrode) 5d is formed, and the connecting portions of the electrodes 3d and 5d are shifted by 45 degrees so as to be easily connected to the lead wire and are extendedly arranged on the side surface portions of the piezoelectric ceramics 6d. On the other hand, a signal electrode for reception (third electrode) 4d
Is formed on the side surface portion of the piezoelectric ceramics 6d, and is disposed on substantially the half circumference of the side surface portion of the piezoelectric ceramics 6d so that both ends thereof are displaced from the connecting portions of the electrodes 1d and 3d by 45 degrees. There is.

Then, an acoustic matching layer 9 having a thickness of (1/4) λ made of epoxy resin containing alumina filler is provided on the transmitting / receiving signal electrode 3d side of the piezoelectric element 6d. The acoustic lens 22 is formed on the upper surface of the acoustic lens 22 with an epoxy resin. Next, each electrode 3
d, 4d, 5d connection parts and lead wires 13a, 13b, 1
3c and solder 14a, 14b, 14 as shown in FIG.
Connect with c. Then, the center of the back load material (not shown) having a diameter smaller than that of the piezoelectric element 2d and the center of the piezoelectric ceramics 6d are aligned, and the back load material is adhesively bonded to the transmitting signal electrode 3d side.

Next, in order to insulate the electrodes 3d, 4d and 5d and to reinforce the connection portion, the periphery of the back load material is sealed with the silicone resin 16 together with the lead wires 13a, 13b and 13c, and the periphery of the piezoelectric element 2d is also coated. Then, the transducer 29 shown in FIG. 11 is manufactured.

The transducer 28 is replaced with the flexible shaft 19 and the SUS reflection mirror 29.
An ultrasonic probe 30 shown in FIG. 13 was manufactured by vertically fixing it to a housing 18 marked with an adhesive.

The ultrasonic probe 30 having the above-described structure can be electrically connected from the three electrodes 3d, 4d, 5d on the side surface of the piezoelectric element. The operation principle of transmission and reception is the same as that of the above-described embodiment, and at the time of transmission, a voltage pulse is applied between the electrodes 3d and 5d provided on the main plane to generate ultrasonic waves by resonance in the thickness direction. At the time of reception, bending vibration occurs with the boundary between the back load material and the silicone resin 16 as a fulcrum. This vibration is converted into a voltage generated in the electrodes 3d and 4d and imaged through an image processing device.

According to this embodiment, it is possible to manufacture a mirror-type small-diameter ultrasonic probe capable of observing at an extremely short distance, which has good sensitivity. In this embodiment, the two-layer structure of the acoustic matching layer 9 and the acoustic lens 22 is shown, but the same effect can be obtained if at least one of the acoustic matching layer and the acoustic lens is provided.

[0039]

As described above, according to the ultrasonic probe of the present invention, at the time of transmitting and receiving ultrasonic waves, at least one of the electrodes uses different electrodes, and different modes vibrate during transmission and reception. By using, it is possible to manufacture an ultrasonic probe having high sensitivity even if it is downsized.

[Brief description of drawings]

FIG. 1 is a side view showing an ultrasonic transducer used in an ultrasonic probe according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a piezoelectric element according to Example 1 of the present invention.

FIG. 3 is a side view showing a manufacturing process of the piezoelectric element according to the first embodiment of the present invention.

FIG. 4 is a side view showing a state in which lead wires are connected to the ultrasonic transducer used in the ultrasonic probe according to the first embodiment of the present invention.

FIG. 5 is a side view showing a tip portion of the ultrasonic probe according to the first embodiment of the present invention in which the ultrasonic transducer is mounted.

FIG. 6 is a side view showing a transducer in the ultrasonic probe according to the second embodiment of the present invention.

7A and 7B show modified examples of the piezoelectric element according to Examples 1 and 2 of the present invention, in which FIG. 7A is a perspective view and FIG.

8A and 8B show modifications of the piezoelectric element according to Examples 1 and 2 of the present invention, in which FIG. 8A is a perspective view and FIG.

FIG. 9 is a perspective view showing a modified example of the piezoelectric element in Examples 1 and 2 of the present invention.

FIG. 10 is a perspective view showing a modified example of the piezoelectric element in Examples 1 and 2 of the present invention.

FIG. 11 is a perspective view showing an ultrasonic transducer in an ultrasonic probe according to a third embodiment of the present invention.

FIG. 12 shows a piezoelectric element according to Example 3 of the present invention,
(A) is a plan view and (b) is a perspective view.

FIG. 13 is a perspective view showing a tip end portion of an ultrasonic probe according to a third embodiment of the present invention in which an ultrasonic transducer is mounted.

FIG. 14 is a front view showing a conventional ultrasonic probe.

FIG. 15 is a left side view showing a conventional ultrasonic probe.

FIG. 16 is a right side view showing a conventional ultrasonic probe.

[Explanation of symbols]

 1 29 Ultrasonic Transducer 2 Piezoelectric Element 3 First Electrode 4 Third Electrode 5 Second Electrode 6 Piezoelectric Ceramics 9 Acoustic Matching Layer 10 Back Load Material 20 30 Ultrasonic Probe 21 Metal Block 22 Acoustic Lens

Claims (5)

[Claims] 1. An ultrasonic probe comprising at least one acoustic matching layer or acoustic lens, a piezoelectric element, and a back load material, wherein the piezoelectric element vibrates in different modes during transmission and reception. An ultrasonic probe characterized by being configured as described above. 2. The ultrasonic probe according to claim 1, wherein:
The piezoelectric element is formed in a plate shape by providing at least three electrodes on a piezoelectric ceramic, and is polarized in the thickness direction between a pair of first and second electrodes formed on the main plane of the piezoelectric ceramic. An ultrasonic probe characterized by being radially polarized between one or a second electrode or a fourth electrode provided on the main plane and a third electrode formed on a side surface portion of the piezoelectric ceramics. Tentacles. 3. The ultrasonic probe according to claim 1, wherein the mechanical quality factor Qm of the piezoelectric element is 300 or more. 4. The ultrasonic probe according to claim 1, wherein the distance between the electrodes used during reception is longer than the distance between the electrodes used during transmission. Tentacles. 5. The ultrasonic probe according to claim 1, 2, 3 or 4, wherein a load mass is applied to the third electrode portion.