JPS5946338B2 - ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a flexible ultrasonic probe that can closely contact an object of any shape (or a part of the human body, etc.), easily send ultrasonic waves, and receive reflected waves. It is related to.

Ultrasonic devices have come to be widely used as acyclic inspection devices to check for defects in substances such as nuclear reactor materials, and as diagnostic devices to check the structure inside the eyeball.

In order to further improve the resolution, the frequency of the ultrasonic waves used has recently come to range from 10 to 20 MHz. The characteristics desired for a probe used in the above ultrasonic frequency range are (1) easy construction of a mechanical resonance system of 10 to 20 MHz, and (2) low dielectric constant and electrical resistance. (3) The mechanical Q value is sufficiently low, making it easy to transmit and receive short ultrasonic pulses; (4) It is flexible and can be easily attached directly to objects with arbitrary shapes. For example, it is possible to send ultrasonic waves to and receive the reflected waves.

Conventionally, inorganic piezoelectric materials such as piezoelectric ceramics and quartz crystals have been used in the 1 to 5 MHz region, but in the above-mentioned high frequency region, piezoelectric ceramics and the like are generally not used, but quartz crystals are used.

The reason is that piezoelectric ceramics have a resonant frequency of 10MHz.
2, the thickness must be approximately 200 μm, making it extremely difficult to create such a vibrator, and the relative dielectric constant is close to 2000, which places an extremely heavy load on the electrical drive system. It is. However, even in conventional probes using quartz crystal, measures must be taken to lower the mechanical Q value, and since quartz crystal is not flexible, it cannot be directly attached to objects of arbitrary shapes. For this reason, in order to eliminate this drawback in conventional probes using inorganic piezoelectric materials, contact methods as shown in FIGS. 1, 2, and 3 are used.

In FIG. 1, a probe 2 having a piezoelectric body 1 and an object 3 are both placed in a water tank 4 and immersed in a liquid 5. In FIG. 2, a flexible container 6 is attached to the probe 2, and a piezoelectric material 1 is attached to the liquid 5.
After making sure that the object is completely submerged, place the flexible container on the object. At this time, if the liquid 5 is dropped between the outer wall of the container and the object, the adhesion will be increased. In FIG. 3, a probe 2 uses a piezoelectric body 7 processed into a shape that matches the shape of an object 3, and a liquid 5 is dripped between the piezoelectric body and the object to obtain adhesion. 1st
The method shown in the figure is not suitable for inspecting objects that cannot be immersed in liquid or for diagnosing eyeballs.

The method shown in Figure 2 improves on the drawbacks of the method shown in Figure 1.
Since it can come into contact with an object of any shape, it is used when diagnosing the eyeball 8 as shown in Figure 4, but the wave reflected at the contact surface between the container wall and the eyeball (referred to as front reflection, also used below) may prevent diagnosis. Furthermore, with the method shown in FIG. 2, it is not easy to converge the ultrasonic beam within an arbitrarily shaped object. In the method shown in Figure 3, there is no adverse effect due to front reflection as in the case of Figure 2, and it is possible to connect the ultrasonic beam to a focused point, but since the shape of the piezoelectric body is constant, it cannot be used against various objects. Although it is necessary to create a piezoelectric body that matches each shape, it is extremely difficult and expensive. The present invention solves the drawback of the conventional ultrasonic probe using an inorganic piezoelectric material, which is the difficulty of making close contact between the piezoelectric material and an object, and provides an ultrasonic probe that has excellent responsiveness. The purpose is to provide children.

In order to achieve the above object, the present invention fills a container with a flexible polymeric piezoelectric film as part of the wall with a liquid or gas, or a highly elastic solid such as polyurethane, By pressing the piezoelectric film as a contact surface against an object of any shape and bringing it into close contact, ultrasonic waves are sent and received at the container wall that is in contact with the object, and the ultrasonic waves are automatically focused. The polymer piezoelectric material mentioned above is polyvinylidene fluoride (hereinafter referred to as PVDF).
A piezoelectric polymer film such as an electret, which has metal thin film electrodes on both sides to electrically drive ultrasonic waves.
Preferably, at least the electrode on the side of the contact surface with the object is coated and insulated with a polymer film or the like.

For example, in the case of PVDF5 electret, the thickness is 25
~100 Itm, has flat frequency characteristics around 10 MHz, and has an electromechanical coupling coefficient of 0.12 or more, which exceeds that of quartz crystal. PVDF has a dielectric constant of 55 to 6.0 at room temperature and a frequency of 8 to 20 MHz.
5, there is no difficulty in electrical drive as in the case of piezoelectric ceramics, and the mechanical Q value is 9 to 9 at room temperature.
Since it is as small as 10, unlike the case of crystal, the mechanical Q value of the entire probe can be easily lowered, so that reflected waves do not overlap. In addition to the above-mentioned PVDF, we also experimented with polyvinyl fluoride as a piezoelectric material, but PVDF
It was not possible to obtain such characteristics.

As described above, by using an ultrasonic contactor constructed of a flexible container with a polymeric piezoelectric material as the contact surface, it can be brought into close contact with an object of any shape and directly send ultrasound without any pre-reflection.
The reflected waves can be observed.

At this time, due to the flat frequency characteristics of the polymer piezoelectric material,
Observations can be made with good temporal resolution, and since the piezoelectric material itself deforms according to the shape of the object, ultrasound can be automatically focused. Note that there are known examples of devices using polymeric piezoelectric materials as described above, such as Japanese Patent Publication No. 51-23439, but even after being formed into a probe, the surface of the piezoelectric material deforms according to the arbitrary shape of the object. No husband has been made to do so. EXAMPLES Hereinafter, the present invention will be explained in detail with reference to examples.

Example 1 FIG. 5 shows a flexible container and support 1 using a polymer piezoelectric film 9.
0 is an embodiment of the present invention.

In the figure, the wall 11 facing the polymer membrane of the container is made of a flexible material such as rubber that absorbs ultrasonic waves.
A water tank 7 and two pots 12 are attached to adjust the amount of water. When the water volume is adjusted by pushing the water bag, the water overflowing from the upper pot passes through a conduit 13 and drips to the outside of the piezoelectric membrane. In this way, liquid can be added to increase the adhesion between the object and the piezoelectric film at the same time as the volume of the container is adjusted. The layered structure of the polymer piezoelectric film 9 is shown in FIG.

The polymer piezoelectric material 14 itself has a thickness of 25 to 100 μm, and metal electrodes 15 such as gold or aluminum are formed on both sides by vacuum evaporation. After dissolving small polymer powder in an organic solvent, a coating layer 16 is formed on the electrode surface. The insulating coating on the surface of the electrode, which is the contact surface between the outer wall of the container and the object, is essential when probing electrically conductive objects such as metals, and it is also necessary when probing insulators. It is often formed to prevent conductivity caused by water used to increase the conductivity, and it is also desirable to form a coating on the electrode inside the container wall, but it is not necessarily necessary when putting polyurethane etc. inside the container. . It is desirable that the coating film be as uniform and thin as possible. A portion where the piezoelectric film 9 is attached to the support 10 is shown in FIG.

Electrical leads 17 are attached to electrodes 15 with conductive room temperature silver paste. The material of the support body 10 is highly insulating plastic, and the material of the screw 19 holding the piezoelectric film is Teflon. Connect the probe described above to a high-frequency oscillator, press the contact surface against a cylindrical rod, and observe the echo using the pulse method. A clear echo could be observed from what appeared to be. In addition, when observing the reflected waves from the end face using a flat sample, it was found that a piezoelectric film with a thickness of 95 μm and an electromechanical coupling coefficient of 0.123 was coated with an aluminum electrode deposited on a PVDF polymer. Is it enough to use the probe by hand? When pressed against the material, the loss within the center is approximately 23 dB/? It was hot. Example 2 Figure 8 shows that when the surface of the container facing the piezoelectric film is made of aluminum metal, etc., which is not flexible and does not absorb ultrasonic waves sufficiently, rubber or the like is pasted on the inside of the container. 5
An example is shown that has the same effect as the rubber wall in the case shown in the figure.

As shown in the figure, since the piezoelectric membrane itself deforms, the ultrasonic waves generated on the membrane surface travel in the direction of the arrow shown in the figure and automatically focus. In this example as well, pulse echoes comparable to those in Example 1 could be observed. As explained above,
According to the present invention, it is possible to adhere extremely well to an object of any shape, and to directly transmit ultrasonic waves around 10 to 20 MHz.
It is possible to provide a probe that can be sent without pre-reflection and can receive the reflected wave, making a great contribution to the industry.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are diagrams showing a method of contacting an arbitrary-shaped object with a conventional ultrasound probe, and Figure 4 shows a case where the method of Figure 2 is applied to an eyeball. It is a diagram.

Claims (1)

[Claims] 1. Flexible ultrasound characterized by comprising a container having a flexible polymeric piezoelectric film as a part and having a variable shape and volume and its support, the piezoelectric film serving as a contact surface. probe.