JPS5997299A - Ultrasonic wave probe - Google Patents

Abstract

PURPOSE:To reduce electric impedance and to attain ease of matching with a power supply by laminating at least >=2 polymer piezoelectric film stretched uniaxially and making parallel the electrode split direction and the stretched direction of the piezoelectric film. CONSTITUTION:Silver is vapor-deposited on both sides of a PVF2 (polyvinylidenefluoride) stretched uniaxially, the deposited film is polarized at a high temperature under an electric field, and the film is quenched rapidly to form a PVF2 piezoelectric film. Then, a narrow paper-tablet electrode 2 is formed by etching so as to be parallel to the uniaxial direction of the piezoelectric film. The opposite side 3 of the electrode 2 is patternized for a whole surface or partly as required. The PVF2 piezoelectric film 1 is folded and laminated. This is adhered onto a printed board 5 so that the narrow paper-tablet electrode 2 and a copper plate in common use of the sound reflecting plate and the electrode are overlapped with each other. Leads are led out from common electrode leads 3 to a common electrode section 6 of the printed board 5 by using silver-epoxyd- tight paint 7.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an ultrasonic probe in which a multilayer piezoelectric membrane is laminated with electrodes provided on both sides of a polymeric piezoelectric material, and the d pole is divided. It's about children.

[Prior art and its problems]

Polyvinylidene fluoride (hereinafter abbreviated as pVF), P
Synthetic polymers such as copolymers containing VF2, polyacrylonitrile, and polyvinylidene chloride are known to exhibit piezoelectricity when polarized at high temperatures and high electric fields. Ultrasonic probes that utilize the thickness vibration of piezoelectric polymers have recently been significantly developed.

In particular, ultrasonic probes used in electronic scanning methods are conventionally made of ceramics such as lead titanate and lead titanium zirconate.
An array type is used, in which the body is cut into strips and separated. However, since ceramic piezoelectric materials are hard and brittle, there is a high risk of chipping or cracking during cutting and separation, and it is extremely difficult to precisely form a multi-magnetic pole structure. Furthermore, in order to prevent acoustic and electrical coupling and crosstalk between adjacent piezoelectric bodies, it is necessary to insert an insulating elastic body with a certain width between the piezoelectric bodies that are cut into strips and separated. From this point of view as well, it has become difficult to achieve uniformity, homogeneity, yield, large area, etc. of ultrasonic probes, and the manufacture of ultrasonic probes has inevitably become complicated and expensive.

In contrast, ultrasonic probes using polymer piezoelectric materials
The acoustic impedance is close to that of a living body, the attenuation of ultrasonic waves in a polymer piezoelectric material is much greater than that of a ceramic piezoelectric material, and the piezoelectricity in the plane direction can be made different. It is often assumed that there is no need to cut and separate them into sections. However, the frequency of ultrasonic probes used in ultrasonic flaw detection equipment, non-destructive testing, testing equipment, ultrasonic flaw detection equipment, etc. is approximately 1 to 10 RI.
This is within the range of approximately IHz, and with the desirable film thickness of the polymer piezoelectric material driven at this frequency, a problem arises in that the electrical matching between the electric circuit and the receiving circuit deteriorates. For example, a PVF 2 film with a thickness of 150 μm can excite an ultrasonic wave of about 4 ME (z), but the area ICI It has an electrical impedance of about IKΩ, which does not match the normal 50Ω power supply, and the ultrasonic detection The loss of the contactor is significantly reduced.In order to avoid such a drawback, it is useful to use a laminated piezoelectric film that can maintain the desired frequency and reduce the electrical impedance by laminating a plurality of relatively thin polymer piezoelectric films as appropriate. gender is being considered.

[Purpose of the invention]

The present invention has been made to address the above-mentioned problems, and is characterized in that at least two or more axially stretched polymer piezoelectric films are laminated, and the direction in which the electrodes are divided is parallel to the direction in which the piezoelectric films are stretched. The object of the present invention is to provide an ultrasonic probe with extremely low acoustic and electrical coupling and crosstalk, low electrical impedance, and easy electrical matching with a power source.

[Summary of the invention]

Ceramic piezoelectric materials such as lead titanate and titanium/lead zirconate have almost uniform piezoelectricity in all directions, and as a result, ultrasonic waves generated at one point propagate uniformly, causing acoustic coupling and Invites electrical crosstalk. On the other hand, in the -axis stretched polymer piezoelectric film, the piezoelectric constant d31 in the stretching direction is 10 to several tens of times larger than the piezoelectric constant d32 in the direction perpendicular to this, and the piezoelectric constant in the thickness direction is It is said to be approximately equal to d33. Therefore, in an array-type ultrasonic probe that has a strip shape, acoustic coupling and electrical crosstalk can be minimized by making the dividing direction of the array almost parallel to the stretching direction of the uniaxially stretched polymer piezoelectric film. It becomes possible to However, since the surface of the arrayed probes may be a curved surface, this effect will not be significantly reduced even if the dividing direction intersects with the -axis stretching direction within the range of -45° to +45°. do not have.

Next, in a method of laminating a polymer piezoelectric film, for example, two polymer piezoelectric films having a film thickness t are bonded and laminated with an intermediate electrode sandwiched therebetween so that the directions of polarization are opposite to each other. When a back reflector is installed on either side of the laminated piezoelectric film obtained in this way, and the four poles in the same polarization direction are connected, an ultraviolet light that matches the fundamental mode of λ/4 = 2t (λ = 8t) is produced. It becomes possible to excite sound waves. In other words, compared to the case where a single piece of polymer piezoelectric film with a film thickness of 2 tons is made, the driving voltage is halved, the capacitance of the piezoelectric film is four times as large, and the electrical impedance is therefore 1/4. Improves electrical matching.

The method of laminating polymer piezoelectric films is to alternately reverse the direction of polarization and stack them in a basis weight. It is also possible to laminate different thicknesses.

〔Effect of the invention〕

As explained in the above-mentioned invention summary, by making the stretching direction of the -axis-stretched polymer piezoelectric material substantially parallel to the electrode dividing direction, each strip-shaped unit can be adjusted to reduce the acoustic noise of adjacent elements. It is extremely unlikely to be affected by physical/electrical coupling or crosstalk. Therefore, since ultrasonic waves with less noise can be emitted or received, an ultrasonic probe capable of obtaining ultrasonic images with extremely high resolution can be obtained.

Further, by layering the preloaded electric film, an ultrasonic probe having a large capacitance and a low electrical impedance can be obtained, and as a result, electrical matching with a power source is easily achieved.

[Embodiments of the invention]

Examples of the present invention will be described below.

Silver was deposited to a thickness of about 700X by vacuum evaporation on both sides of a 55 μm thick uniaxially stretched P■゛2 film at a temperature of 10
A PVF2 piezoelectric film was produced by polarizing at 0°C for 1 hour under an electric field of 6 KV and rapidly cooling to room temperature. Next, as shown in Fig. 1, a rectangular strip was formed so that the unit element had a width Q of 9 mm, a length of 13ηlηL, and a unit element spacing of 0.1 mm, parallel to the uniaxial stretching direction of the PVF2 piezoelectric film. 'Id pole (2
) were formed into 64 elements by etching. In this case, the surface on which the strip-shaped electrode (2) is formed and the reflective electrode surface (3) are formed entirely or patterned as necessary. Thereafter, as shown in FIG. 2, the two PVF'' piezoelectric films (1) were stacked (three layers) in a folded manner.

Regarding the lamination of PVF 2-pressure direct membrane, the strip-shaped pole (2)
Care must be taken to ensure that they overlap vertically. This laminated PV
The F2 pressure release membrane is attached to a printed circuit board (5) as shown in Figure 3 in advance.
), the thickness of the strip-shaped electrode (2) and the acoustic reflector/electrode is 300 mm.
Copper plates (rectangular shape) (4) of .mu.m were bonded together so as to overlap each other. In addition, from the common electrode lead part (3) in the figure, the button-epoxide-tight paint (manufactured by Fujikura Kasei) -75
3> According to (q), the lead was taken out to the common electrode part (6) of the printed circuit board (5).

Finally, a polyester film with a thickness of 12 μm was adhered to the 6-pole portion using epoxy resin to provide insulation between the poles and to provide water resistance, thereby obtaining an ultrasonic probe. When a voltage was applied between the eight strip-shaped d-pole elements and the common electrode, it was confirmed that this ultrasonic probe operated efficiently at 3.5 ME (z).

Furthermore, in the operating state of the ultrasonic probe, there is no acoustic coupling or electrical crosstalk in the strip-shaped polarized portion of the non-voltage applied portion adjacent to the eight elements of the strip-shaped electrode (2). confirmed.

In the ultrasonic probe of the present invention exemplified above, each strip-shaped unit element is extremely unlikely to be affected by acoustic or electrical coupling or crosstalk between adjacent elements. -Thus, ultrasonic waves with less noise can be emitted or received, so ultrasonic effects with extremely high resolution can be obtained. By laminating the trenched polymer piezoelectric films, an ultrasonic probe having a large capacitance and a low electrical impedance can be obtained, and as a result, it is easy to electrically match the drive power source.

[Brief explanation of drawings]

1 to 3 are perspective views showing the structure of an ultrasound probe according to the present invention. 1... Municipal piezoelectric film 2... Strip-like electrode 3... Common i-pole 4... Acoustic reflector/electrode 5... Printed circuit board base 6... Common i-pole lead portion 7 ... Dotite Paint Agent Patent Attorney Kensuke Chika (and 1 other person) Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an ultrasonic probe in which at least two piezoelectric films each having electrodes provided on both sides of a molecular piezoelectric material are laminated, and the electrode on at least one surface of the piezoelectric film is divided into a plurality of strip-shaped electrodes, the above-mentioned An ultrasonic probe characterized in that the piezoelectric film is uniaxially stretched, and the electrode division direction of the piezoelectric film is parallel to the stretching direction of the piezoelectric film.