JPS6181000A - Piezo-electric type ultrasonic probe made of laminated polymer - Google Patents

Abstract

PURPOSE:To suppress fluctuation of characteristics by bending a piezo-electric polymer thin film so that polarization axes of both side cross orthogonally and laminating them, and slicing one part of electrode into multiple strips at specified interval and forming its lengthwise direction parallel to the bending line. CONSTITUTION:Common electrode 2 is formed on one surface of a piezo-electric poly mer thin film 3, and a specified number of stripped electrodes 1, 1' are formed on the other side. And an adhesive layer 4 is formed on the side of the stripped electrode 1, 1'. One unit element B is constituted with the common electrode 2 and each one stripped electrode 1, which are located opposite through the film 3. The stripped electrode 1, 1' opposing the inner bending surface of the film 3 is accurately positioned so that the bending line of the film 3 and the lengthwise direction of the stripped electrodes 1, 1' are paralleled each other. A copper plate 5 has a function of both sound reflecting plate and electrode part of common electrode 2. Supporting body 6 is made of acryl resin, epoxy resin, etc. This constitution prevents the beam scatter ing and electrical loss, controls the deviation between each element, and reduces the crosstalk between the elements.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a laminated polymer piezoelectric ultrasonic probe, and more specifically, the present invention relates to a laminated polymer piezoelectric ultrasonic probe. In a linear play type ultrasonic probe with electrodes, there is no electrical loss at the bending part or disturbance of the ultrasonic radiation beam, and there is a This invention relates to a laminated polymer piezoelectric ultrasonic probe with little variation in characteristics.

[Technical background of the invention and its problems]

For example, as a means of performing medical diagnosis using ultrasound,
Ultrasonic probes using a linear electronic scanning method, ie, linear array type ultrasound probes, have been put into practical use. Conventionally, such ultrasonic probes have been made using titanic acid, titanium, etc.
Turconic acid mf! , ceramic piezoelectric materials were used. These ceramic piezoelectric materials have a high elastic modulus, so
To create a linear array type, electrodes are installed in advance and pasted on a support at predetermined intervals, and the piezoelectric material is cut into strips to avoid undesirable interactions between adjacent elements. is commonly practiced.

However, these piezoceramic materials are hard and brittle, so they are prone to chipping and cracking during the cutting and dividing process as described above, and it is difficult to accurately form strip-shaped electrodes. Therefore, it lacks practicality in terms of manufacturing cost.

On the other hand, polyvinylidene fluoride (hereinafter referred to as PVF)
Organic synthetic polymers such as polyvinylidene fluoride/trifluoroethylene copolymer (hereinafter referred to as PVF, TrFE, or polyvinylidene cyanamide) have piezoelectric properties and It was discovered that it exhibits pyroelectricity.As a result, the organic synthetic polymer described above is attracting attention as a new piezoelectric material.

Such a polymeric piezoelectric material has electrodes provided on both sides in one polarization direction, and when a voltage is applied between the electrodes, thickness vibration is excited, so that applications to ultrasonic probes have recently been actively attempted.

Since the polymer piezoelectric material has a small elastic modulus, when it is applied to a linear array star probe, it has the advantage that there is no need for cutting time division unlike the above-mentioned ceramic piezoelectric material.

That is, it is sufficient to form a predetermined number of strip-shaped electrodes on one ceramic piezoelectric thin film. Moreover, since the specific acoustic impedance is close to that of a living body, the efficiency when applied to, for example, a clinical diagnostic device is extremely high.

However, on the other hand, the dielectric constant of polymer piezoelectric materials is generally about 10 orders of magnitude, which is much smaller than that of ceramic piezoelectric materials. When applied to an element with a small area υ, its electrical impedance becomes significantly high. Therefore, the commonly used 50Ω
Poor electrical compatibility with the system power supply (emitting/receiving circuit).

As a result, electrical loss of the ultrasound probe is caused.

In order to solve this problem, an ultrasonic probe having a laminated structure as shown in FIG. 3, for example, has been proposed. That is, electrodes 1 and 2ft are placed on both sides of the polymer piezoelectric thin film 3.
The formed product is one unit in total, and an appropriate number of layers are stacked so that the polarization direction axes of the polymer piezoelectric materials (indicated by arrows in the figure) face each other. It has a structure in which the electrodes are connected by a 1J- wire. In such a laminated ultrasonic probe, if the electrical impedance of a single layer thin film having a predetermined resonance frequency is t-Z0, then the electrical impedance 2 when the thin film is laminated in n layers is
is expressed as z=zO/n2. Therefore, in the case of a two-layer stack, the electrical impedance in the case of a single layer is the same as that in the case of a three-layer stack, and the electrical compatibility with the above-mentioned power supply is considerably improved.

However, in the laminated structure shown in FIG. 3, the connection between the electrodes of each layer and the lead wires is extremely complicated, so it cannot be said to be very practical.

Therefore, instead of stacking multiple thin films as described above, a single thin film with electrodes formed on both sides is folded so that their polarization axes face each other, as shown in Figure 4.
An ultrasonic probe with a layered structure has been proposed (
(Refer to Japanese Patent Application Laid-Open No. 56-47199). In this structure, electrodes 12 formed on both sides of the polymer piezoelectric thin film 3
For example, one of electrodes 1 and 2 is a strip-shaped electrode, and the strip-shaped electrode 1 is folded along a bending line that is perpendicular to the longitudinal direction of the strip-shaped electrode 1 to form a stacked WI structure. Namely.

In FIG. 4, a predetermined number of strip-shaped electrodes 1 are arranged in such a manner that the width direction is perpendicular to the plane of the paper.

By adopting the above structure, it is possible to reduce the electrical impedance, and at the same time, since the electrode 2 can be used as a common electrode, the connection of the lead wire is simple and the practicality is improved.

However, on the other hand, in the above-mentioned folded structure ultrasound probe, electrical loss and disturbance of the ultrasonic radiation beam occur near the folded part, which significantly impairs the function of the probe. There is a fact that. The causes of this are estimated and determined like arrows. First, when folding polymer piezoelectric thin films, in order to bond each layer and align the opposing strip electrodes, at least the surface on which the strip electrodes are formed is coated with epoxy resin, cyanoacrylic resin, etc. Generally, an adhesive such as a resin is applied, the laminate is folded, and then the laminate is uniformly pressed to make them stick together. However, at this time, as shown in Figure 1M3, the adhesive between the strip-shaped electrodes 1 that face each other tends to gather in the bent part A, and the gathered adhesive is compressed after bending (in the figure, It is thought that the adhesive layer inside the bent portion A is thicker and the bent portion A bulges out, resulting in an increase in electrical impedance.

Furthermore, in the case of an ultrasonic probe, in order to focus the ultrasonic radiation beam, piezoelectric bodies are laminated and then this laminated body is sometimes bent. In that case, for example, the fifth
An external force is applied from above to the central part of the laminate shown in the figure to form a curved shape as a whole. At this time, the aggregation of the adhesive described above becomes particularly noticeable, and the function of the probe is inhibited due to the scattering effect at the bulging bent portion A.

In order to solve this problem, a method can be considered in which the polymer piezoelectric material is coated with an adhesive T- and then folded, and then the laminate is uniformly pressed using a rotating roll or the like, but in this case, the rotating roll Not only is it difficult to maintain the gap accurately, but also slight irregularities in rotation may cause misalignment between the eyebrows of the laminate, resulting in inconveniences such as misalignment of the opposing strip-shaped electrodes. .

Furthermore, in the above-mentioned folded stacked ultrasonic probe, the adhesive layer between the opposing strip-shaped electrodes is not uniform, which tends to cause variations in characteristics between each element. Another problem is that it is difficult to accurately align the strip-shaped electrodes.

[Purpose of the invention]

The purpose of the present invention is to solve the above-mentioned conventional problems and to provide a laminated ultrasonic probe in which thin polymer piezoelectric films on which strip-shaped electrodes are formed are folded and laminated. There is no bulge in the area, therefore.

Radiation beam scattering and electrical losses at bends are prevented,
Moreover, it is an object of the present invention to provide a laminated polymer piezoelectric ultrasonic probe having a structure in which variations in characteristics between each element are small and the positioning of strip-shaped electrodes between each layer can be easily performed.

[Summary of the invention]

In the laminated polymer piezoelectric ultrasonic probe of the present invention, polymer piezoelectric thin films having electrodes on both sides are bent and laminated so that their polarization axes face each other, and adhesive is used between each layer. In a laminated polymer piezoelectric ultrasonic probe fixed by It is characterized by being parallel to the line.

The ultrasonic probe of the present invention has a structure in which both ends of each strip-shaped electrode are exposed on the end face of a folded laminate of polymeric piezoelectric thin films, so that when the layers are brought into close contact, there is no adhesion between the layers. The adhesive flows outward from both end faces, so that an appropriate amount of adhesive remains between the valleys and the eyebrows, and the bent portion does not bulge.

Next, the structure of the ultrasonic probe of the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of the laminated polymer piezoelectric ultrasonic probe of the present invention, in which a polymer piezoelectric thin film is folded once and laminated into two layers.

A common electrode 2 is formed on one surface of the polymer piezoelectric thin film 3, and a predetermined number of strip-shaped electrodes 1, 1' are formed on the other surface. An adhesive layer 4 is formed. The thin film 3 and the common electrode 2 facing each other with the thin film 3t interposed therebetween and one strip-shaped polarization l)
, one unit element B (area surrounded by a broken line in the figure) is constructed. The strip-shaped electrodes 1.11 facing each other on the inner bent surface of the thin film 3 need to be accurately aligned. In such a laminate, the bending line of the thin film 3 and the longitudinal direction of the strip-shaped electrodes 1, 1' are parallel to each other (in a direction perpendicular to the plane of the paper). Also, in FIG. 1, 5 is
This is a copper plate that serves both as an acoustic reflector and as an electrode part of the common electrode 2, and 1 is a support made of, for example, acrylic resin or epoxy resin.

The entire structure is covered with, for example, a polyester film 7.

In the above configuration, the polymer piezoelectric material is a so-called composite piezoelectric material in which a ceramic piezoelectric material powder such as PVFt, PVFt'TrFE, polyvinyrizo/anamide, titanate, titanium norconate, etc., as described above is mixed into a polymer resin. The thickness of the thin film is preferably set in the range of several μm to 100 μm.

On the other hand, the strip-shaped electrodes are made of gold and silver.

It is preferably formed using metal such as aluminum by vacuum evaporation, sputtering, plating, etc., and has a width of several hundred μm% a mrg, a length of several heads to several sides, and a distance of several tens of meters between adjacent electrodes. Appropriately set the range from μm to several groups.

Further, the number of strip-shaped electrodes, that is, the number of elements, is also selected appropriately. Furthermore, the adhesive used during lamination is not particularly limited, but epoxy resins, cyan acrylic resins, and the like are preferred, for example.

Such a laminated polymer piezoelectric ultrasonic probe is manufactured as follows.

First, a polar layer is formed on both sides of a thin film of a predetermined thickness by uniaxial stretching or casting of a polymeric piezoelectric material, for example, by vacuum evaporation, and then heated at a high temperature.
Polarization treatment is performed under a high electric field. Next, as shown in FIG. 2, the electrode layer 1 formed on one side of the thin film 3 thus obtained is patterned to form strip-shaped electrodes 1, 1' parallel to the uniaxial stretching direction of the thin film 3. do. After that, adhesive is applied to the surface on which the strip-shaped electrode 1.1' is formed, and the strip-shaped electrode is bent along a line parallel to the longitudinal direction of the strip-shaped electrode, that is, a bending line shown by a dashed line C in the figure. The opposing strip-shaped electrodes 1 and 1' are folded over one another while aligning their positions, and then fixed between the eyebrows, for example, by pressure pressing.

At this time, excess adhesive flows from the folded eyebrows onto both end surfaces of the laminate, and can be removed. In this way, bulging of the bent portion due to adhesive concentration does not occur, and moreover, the adhesive layer between the opposing strip-shaped electrodes becomes extremely uniform. Thereafter, lead wires are connected to the common electrode 2 and each strip-shaped electrode, respectively, and then the ultrasonic probe is completed with a structure as shown in FIG. 1.

[Embodiments of the invention]

Silver layers of approximately 0.5 μm in thickness were formed on both sides of the uniaxially stretched P'VF film with a thickness of 50 μm by vacuum evaporation, and the film was subjected to a polarization treatment at 100° C. and 6 KV for 1 hour. Next, the silver layer formed on one side was coated with 7 Otrenost (FPPRN11400 Fuji Pharmaceutical Co., Ltd.)
After patterning and etching, a strip-shaped electrode with a width of 0.9 m and a length of 131+III+ was
Sixty-four pieces were formed at regular intervals, resulting in 64 elements.

The silver layer on the other side becomes a common electrode in that state. After that, epoxy adhesive 301-2 (trade name; manufactured by Evotake Co., Ltd.) is applied on the film surface on which the strip-shaped electrodes are formed.
was applied to a thickness of about 50 to 100 μm, and then folded along the bending line parallel to the longitudinal direction of the strip-shaped electrode as described above, and then fixed using a pressure press. At this time, the adhesive cast from both end faces of the laminate was removed.

Furthermore, this entire laminate was placed on a copper plate fixed on a support as shown in Figure 1, and lead wires were connected to the common electrode and each strip-shaped electrode to complete an ultrasonic probe. .

It was confirmed that the electrical impedance of this ultrasonic probe was 520Ω on average per unit element, and the variation in electrical impedance between unit elements was within ±3%. Furthermore, when all eight elements of the probe were driven to perform electronic scanning, operation at a center frequency of 5 t was confirmed, and the influence of electrical crosstalk between unit elements was found to be extremely small. . In addition, in the sound field measurement of the probe, the electronically focused ultrasound beams are focused in 70 order, and the beam pattern exhibits a symmetrical sound field distribution as shown in Figure 6(a). It is clear that there is almost no disturbance in the ultrasonic waves.

For comparison, an ultrasonic probe was manufactured having the same materials, the same dimensions, and the same number of elements as those of the above-mentioned embodiments, except that it had a conventional structure. That is, this probe has a structure in which the strip-shaped electrodes are folded along a bending line perpendicular to the longitudinal direction. This ultrasonic probe has an average electrical impedance of 550Ω per unit element, and the variation in electrical impedance between unit elements is +20% (maximum 660Ω) to -10%.
% (minimum 500Ω), it was found that the variation in electrical impedance was significantly larger than that of the ultrasonic probe of the present invention. In addition, this ultrasound probe was found to have a bulge at the bent part, and in the sound field measurement, as shown in Figure 6(b), the ultrasound beam had poor left and right urinary sensitivity, and the ultrasound Beam disturbance was confirmed.

In this example, the PVF film was simply folded, but by providing micro holes or grooves in the folded parts and bending at these parts, the pattern of the opposing strip-shaped electrodes could be matched. can be made even easier.

〔Effect of the invention〕

As is clear from the above explanation, the laminated polymer pressure 'ilE type ultrasonic probe of the present invention avoids bulging of the folded part of the laminate due to adhesive concentration. Since scattering of the radiation beam and electrical loss do not occur, and variations in characteristics between each unit element are minimized, the effects of electrical crosstalk and acoustic coupling between adjacent elements can be minimized. It can be made smaller and its performance is significantly improved compared to conventional methods.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the laminated polymer piezoelectric ultrasonic probe of the present invention, FIG. 2 is a perspective view showing the relationship between the strip-shaped electrodes and the folding direction, and FIGS. 3 and 4 are A schematic cross-sectional view of the conventional 1-pi polymer piezoelectric ultrasonic transducer body part. Figure 5 is an enlarged view of the bent part in Figure 4. Figures 6 (a) and (b)
FIG. 2 is a diagram showing a focusing state of an ultrasonic beam. 1.1'...Strip electrode, 2...Common electrode, 3...
・Polymer piezoelectric thin film.

Claims (1)

[Claims] In a laminated polymer piezoelectric ultrasonic probe in which polymer piezoelectric thin films having electrodes on both sides are bent and laminated so that their polarization axes face each other, one electrode is formed at a predetermined interval. multiple strip-shaped electrodes,
Moreover, the laminated polymer piezoelectric ultrasonic probe is characterized in that the longitudinal direction of the strip-shaped electrode is parallel to the bending line.