JPH0142034Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an ultrasonic probe, and particularly an array type ultrasonic probe using an ultrasonic transmitting/receiving piezoelectric element made of a polymeric piezoelectric material. Regarding.

[Prior Art] In various ultrasonic devices that perform diagnosis, flaw detection, measurement, etc. using ultrasonic waves, array-type ultrasonic probes are used, which consist of a plurality of vibrators arranged with electrodes on both sides of a piezoelectric body. child is used. This type of ultrasonic probe utilizes the electroacoustic transduction effect of a piezoelectric material, and conventionally, a piezoelectric element made of ceramics has been used as the piezoelectric material.

However, although ceramic piezoelectric elements have high sensitivity, their acoustic impedance is approximately 30
×10 ⁶ Kgf/m ² s, the acoustic matching with the human body and water (acoustic impedance approximately 1.5 × 10 ⁶ Kgf/m ² s) is poor, and the minimum thickness of one sheet is about 200 μm. Since the shape ratio (width/thickness at the smallest cross section when formed into a rectangular parallelepiped shape) cannot be made sufficiently small compared to the wavelength, it is virtually impossible to make the arrangement pitch sufficiently small. Therefore, ceramic piezoelectric elements can only be arranged in a low density and can only be used in the low frequency range of about 5 MHz or less, while the high frequency range of about 5 to 20 MHz, which is increasingly required for applications to the human body and water, can only be used. The drawback was that it was not suitable for phased arrays.

For this reason, piezoelectric bodies formed from polymeric piezoelectric materials have recently attracted attention. for example
Piezoelectric bodies made of polymeric piezoelectric materials such as PVDF have broadband characteristics, and have an acoustic impedance of about 3 to 4 × 10 ⁶ Kgf/m ² s, so they have a higher impedance than the ceramic piezoelectric elements mentioned above. The acoustic impedance is close to that of the human body or water, so it has good acoustic matching and excellent resolution on scanner images.

In addition, since the polymer piezoelectric material has a thickness of about 9 to 30 μm and can be arranged in high density, it is suitable for application to the frequency range of about 5 to 20 MHz.
It has the advantage of being easily obtainable with a diameter of 200 to 50 μm.

Conventionally, as a vibrator using such a polymeric piezoelectric material, one constructed as illustrated in FIG. 1 has been used. That is, 1... is a polymer piezoelectric element, and these polymer piezoelectric elements 1... are made by polymerizing a plurality of pieces (three in the figure) in the thickness direction, that is, in the polarization direction (Y), and bonding them together integrally. Thus, a piezoelectric body 2 is formed. Pairs of electrodes 3 facing each other in the thickness direction are arranged on the piezoelectric body 2 at a predetermined arrangement pitch along the width direction, that is, along the stretching axis direction (X) of the polymer piezoelectric element 1. There is. In addition, in the figure, 4 is a front plate, and 5 is a back plate.

However, since the vibrator with the above configuration utilizes the vibration mode in the polarization direction (Y) of the polymer piezoelectric element 1 (thickness mode = direction crossing the stretching axis direction), the acoustic impedance is approximately 4. ×
10 ⁶ Kgf/m ² s, which is still a difference in the acoustic matching method compared to the acoustic impedance of the human body, water, etc., which is approximately 1.5×10 ⁶ Kgf/m ² s.

In addition, in the above-mentioned vibrator, the piezoelectric body 2 is formed by laminating and integrally bonding a plurality of polymer piezoelectric elements 1, so the electroacoustic mutual conversion efficiency is low, and the piezoelectric body 2 is Since the piezoelectric d-constant is small, there is also the drawback that the electrical to acoustic conversion efficiency is poor.

For this reason, the present inventors focused on utilizing the vibration mode in the direction of the stretching axis of the polymer piezoelectric material. The acoustic impedance of the vibration mode in the stretching axis direction of the polymer piezoelectric element is approximately 3×10 ₆ Kgf/m ² s.
Therefore, compared to the case of using the vibration mode in the thickness direction as shown in Figure 1 above, the acoustic impedance of the human body, water, etc. is closer to approximately 1.5 × 10 ⁶ Kgf/m ² s, and therefore the acoustic consistency is improved. Since the image quality is further improved, there is an advantage that the scanner image becomes even clearer.

By the way, the inventors of the present invention have researched and developed a vibrator having the configuration shown in FIG. 2 as a vibrator that utilizes the vibration mode in the direction of the stretching axis of a polymeric piezoelectric material.

In FIG. 2, the vibrator 10 is, for example, a PVDF
It is equipped with a piezoelectric body 11 made of a polymeric piezoelectric material such as and electrodes 12, 12. The polymer piezoelectric material 11 is
The electrode 1 is formed into a rectangular parallelepiped shape having a length l in the direction of the stretching axis (X) and a thickness t in the polarization direction (Y).
2 and 12 are formed of a suitable conductive material in the form of thin films and are attached to both sides of the piezoelectric polymer 11 in the polarization direction (Y) by, for example, vapor deposition or adhesion.

Such vibrators 10 are arranged at a predetermined array pitch in the polarization direction, and front plates 13 are provided at both ends in the stretching direction.
and a back plate 14 are provided, respectively, and a gap 15 is formed between adjacent vibrators 10, 10. The front plate 13 is configured to function as a protective layer, an acoustic matching layer, or an acoustic lens for the transducers 10, and the back plate 14 serves as a backing layer and an acoustic absorption layer for the transducers 10. and an acoustic matching layer.

The gap 15 is filled with an electrically insulating material (eg, air).

And each electrode 1 for each vibrator 10...
By appropriately controlling the phase and amplitude of the potential difference Ei between 2 and 12, it is configured to operate as a phased array utilizing the vibration mode in the stretching axis direction (X).

According to such a configuration, since the vibration mode in the stretching axis direction (X) of the polymer piezoelectric material 11 is utilized,
The acoustic impedance is approximately 3×10 ⁶ Kgf/m ² s, and the acoustic impedance of the human body, water, etc. is approximately 1.5×10 ⁶ Kgf, compared to the case where the vibration mode in the thickness direction is used as in the configuration shown in Figure 1 above. /m ² s. Therefore, acoustic consistency is further improved,
Scanner images become even clearer.

In addition, this product utilizes the vibration mode in the stretching axis direction (X), so the polymer piezoelectric material 1
The length l in the vibration direction of 1 can be easily formed to match the desired frequency by simply cutting the material, thereby covering a practically preferable frequency band (approximately 5 to 20 MHz). I can do it.

Furthermore, since the vibration mode in the stretching axis direction (X) is used as described above, the polymer piezoelectric material 1
The thickness t in the polarization direction of the oscillators 10 can be made sufficiently thin, and the arrangement pitch of the oscillators 10 can therefore be made sufficiently small compared to the conventional method, making it easy to achieve high density, and making it easier for the human body and the like. This is advantageous for high-frequency phased arrays suitable for water and the like.

[Problems to be solved by the invention] However, in the structure shown in FIG. , electrodes 12, 12 arranged on both sides in the polarization direction (Y)
and a polymer piezoelectric material 1 facing the subject.
There is a problem in that the end face thickness t of No. 1 is small, that is, the wave transmitting/receiving area is small.

If the thickness t of the polymer piezoelectric material 11 is increased in an attempt to increase the wave transmitting/receiving area, it is possible to increase the sensitivity due to the increase in the wave transmitting/receiving area. There is a problem in that the mechanical coupling coefficient decreases, resulting in a decrease in sensitivity, and as a result, no improvement in overall sensitivity can be expected.

In addition, in the case of piezoelectric materials made of polymeric materials, the thickness t can only be about 9 to 30 μm, and the maximum thickness of a single sheet is about 30 μm.
Even if we try to increase the area for transmitting and receiving waves, there is a limit.

The present invention was developed based on the above circumstances, and its purpose is to expand the wave transmitting and receiving area and improve the electromechanical coupling coefficient in a device that utilizes the vibration mode in the stretching axis direction of a polymer piezoelectric material. The present invention aims to provide an array-type ultrasonic probe that has good acoustic matching to the human body, water, etc., and is suitable as a high-frequency phased array.

[Means for Solving the Problems] In the present invention, in an array type ultrasonic probe in which a plurality of vibrators are arranged, each of which has electrodes on both sides of a piezoelectric body formed from a piezoelectric polymer material, the distance between the electrodes is The piezoelectric body is formed by laminating a plurality of polymer piezoelectric elements, and these polymer piezoelectric elements are polarized in the direction crossing the stretching axis in order to utilize the vibration mode in the stretching axis direction of the polymer piezoelectric material. The above-mentioned electrodes are arranged in the piezoelectric device, and these polymer piezoelectric elements are stacked so as to vibrate independently of each other.

[Function] According to this configuration, the piezoelectric body is formed by laminating a plurality of polymer piezoelectric elements that utilize the vibration mode in the stretching axis direction of the polymer piezoelectric material, so the overall thickness increases and the wave transmission/reception area increases. The sensitivity increases due to the expansion of As a result,
Overall sensitivity is improved.

[Example] The present invention will be described below based on an example shown in FIG.

In addition, in FIG. 3, the vibrator 20 is a piezoelectric body 21.
and electrodes 22, 22. The piezoelectric body 21 is
For example, it is constructed by laminating a plurality of thin film elements 23 (three in the illustrated example) made of a polymeric piezoelectric material such as PVDF. These polymer piezoelectric elements 23 are stacked in the thickness direction in order to utilize the vibration mode in the direction of the stretching axis (X), as in the case of FIG. 2. And each of these polymer piezoelectric elements 2
3...An oily thin film (not shown) such as silicone oil is inserted between each polymer piezoelectric element 23.
... are stuck together by the surface tension of this oily thin film. However, in this case, the polymer piezoelectric elements 23 are kept in a non-bonded state with each other so that they can vibrate independently.

The electrodes 22, 22 are laminated in the polarization direction (Y) of the laminated polymer piezoelectric elements 23, 23 on both sides via an oily thin film such as the silicone oil.

Such a vibrator 20 is arranged at a predetermined arrangement pitch in the polarization direction, and a front plate 13 and a back plate 14 similar to those shown in FIG. A gap 25 is formed between the children 20, 20. and gap 25
is filled with an electrically insulating material (such as air).

According to the above configuration, the piezoelectric body 21 is formed by laminating a plurality of polymer piezoelectric elements 23 that utilize the vibration mode in the stretching axis direction of the polymer piezoelectric material.
Sensitivity increases by increasing the overall thickness and expanding the area for transmitting and receiving waves. Moreover, a plurality of polymer piezoelectric elements 23
... can vibrate independently in a thin state, so a large electromechanical coupling coefficient of the longitudinal vibration mode of the thin plate in the direction of the stretching axis can be used.

In other words, the smaller the thickness t of the polymer piezoelectric element, the more efficiently the electromechanical coupling coefficient (the rate at which applied electrical energy is converted into mechanical sound wave energy) is converted into the vibration mode in the stretching axis direction without being affected by the thickness. can do. Therefore, when a plurality of polymer piezoelectric elements 23 are stacked, the electromechanical coupling coefficient is improved compared to when a single polymer piezoelectric element having the same wave transmitting/receiving area is used. As a result, the vibration mode in the stretching axis direction can be used more effectively, and the overall sensitivity is improved.

Moreover, since the thickness t of each of the plurality of polymer piezoelectric elements 23 can be reduced, it is possible to reduce the coarse modes (spurious) other than the vibration mode in the stretching axis direction (for example, the vibration mode in the thickness direction). Because noise waves are reduced, scanner images become clearer.

Note that since an oily thin film such as silicone oil was inserted between each polymer piezoelectric element 23 and between the polymer piezoelectric element and the electrodes 22, 22, each polymer piezoelectric element 23...
And the electrodes 22, 22 are attached to each other by the surface tension of this oily thin film, which not only facilitates assembly, but also allows each polymer piezoelectric element 23... and the electrodes 22, 22 to vibrate independently. are buffered from each other so that

That is, the polymer piezoelectric elements 23... vibrate also in the thickness direction, and if an oily thin film exists between the adjacent polymer piezoelectric elements 23... and the electrodes 22, 22, the vibrations in the thickness direction will cause appropriate viscosity. The vibration mode can be absorbed by the thin film, the influence on neighboring components can be alleviated, and the vibration mode in the stretching axis direction (X) can be effectively extracted.

It should be noted that the present invention is not limited to the above-mentioned embodiment. For example, as shown in FIG. Alternatively, a vibrator 30 may be provided. The probe configured in this manner can be used as a broadband probe in the same way as conventional probes used for nondestructive testing, flow measurement, and the like.

Furthermore, even in the case of the embodiment shown in FIG.
An oily thin film such as silicone oil may be inserted between the electrode 32 and the electrode 32 .

However, the present invention is not limited to inserting an oily thin film such as silicone oil,
The polymer piezoelectric elements and the piezoelectric elements and the electrodes may simply be brought into contact.

[Effects of the invention] As explained above, according to the invention, the piezoelectric body is formed by laminating a plurality of polymer piezoelectric elements that utilize the vibration mode in the stretching axis direction of the polymer piezoelectric material. In addition, the multiple polymer piezoelectric elements can vibrate independently in their thin state, which increases the electromechanical coupling coefficient of the vibration mode in the direction of the stretching axis. This can be effectively utilized, resulting in improved overall sensitivity. Therefore, it is possible to provide an array-type ultrasonic probe that has good acoustic matching to the human body, water, etc., and is suitable as a high-frequency phased array.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional example, Fig. 2 is a sectional view showing the background art of the invention, Fig. 3 is a sectional view showing one embodiment of the invention, and Fig. 4 is another embodiment of the invention. FIG. 20, 30... Vibrator, 21, 31... Piezoelectric body, 22, 32... Electrode, 23, 33... High molecular piezoelectric element, X... Extension axis direction, Y... Polarization direction.

Claims (1)

[Claims for Utility Model Registration] (1) In an array type ultrasonic probe in which a plurality of vibrators are arranged, each of which has electrodes on both sides of a piezoelectric body formed of a piezoelectric polymer material, a piezoelectric body between the electrodes is arranged. is formed by laminating a plurality of polymer piezoelectric elements, and these polymer piezoelectric elements have the above-mentioned electrodes in a polarization direction that intersects with the stretching axis direction in order to utilize the vibration mode in the stretching axis direction of the polymer piezoelectric material. What is claimed is: 1. An array type ultrasonic probe, characterized in that the polymer piezoelectric elements are stacked so as to vibrate independently of each other. (2) A thin oil film is interposed between the polymer piezoelectric elements and between the polymer piezoelectric element and the electrode, and each polymer piezoelectric element is maintained to vibrate independently by the oil thin film. An array type ultrasonic probe according to claim 1 of the utility model registration claim.