JPS5919680B2 - Variable curvature sound wave transmitter/receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound wave device, and more particularly to a sound wave transmitting/receiving device capable of arbitrarily changing the curvature of a sound wave transmission and/or reception surface.

For example, in ultrasound detection, ultrasound therapy, etc., it is extremely desirable to be able to arbitrarily change the curvature of the ultrasound transmitting/receiving surface. The only option was to combine them and control their orientation.

When a large number of devices are used by such means, a plurality of control devices are also used for control, and a simple device cannot be expected.

The present invention further includes at least one piezoelectric material layer, one or more sets of electrode layers arranged on both sides of the piezoelectric material layer (in this specification, arrangement does not necessarily mean adjacent arrangement). Then, one piece of the piezoelectric material layer or at least one other material layer disposed on both sides of the piezoelectric material layer has an electrode layer or/and another material layer on both sides of the piezoelectric material layer. electrical wiring for changing the curvature of the structure by changing the voltage applied between at least one pair of the electrodes; A sound wave transmitting/receiving device in which the piezoelectric layer of a variable curvature structure made of a voltage-controllable DC power source serves as a sound wave transmission or reception surface,
Therefore, at least one pair of the electrodes of the piezoelectric layer is connected to an electrical circuit for transmitting and/or receiving sound waves (hereinafter referred to as a transmitting/receiving electrical circuit), that is, a "signal circuit", together with or separately from the above-mentioned DC power source. It is.

In the present invention, the sound waves include ultrasonic waves above the audible frequency and infrasound below the audible frequency.

A so-called bimorph piezoelectric element, in which two piezoelectric material layers are symmetrically joined via an electrode layer, and electrode layers are also provided on the surfaces of the piezoelectric material layers on both sides, can be bent by changing the applied voltage. Although this has been well known for a long time, this bimorph element can be considered to have an asymmetric structure when viewed from the center of one piezoelectric material layer.

In addition, a multilayer body made asymmetric by varying the thickness or structure of the electrode layer or (and) another material layer deposited on the organic piezoelectric material layer can also become a piezoelectric element that bends by changing the applied voltage. Yoshikawa et al. published JP-A No. 48-52487 (
This was proposed in Special Publication No. 52-37356.

The change in curvature of the transmitting/receiving surface of the acoustic wave device of the present invention is caused by the same principle as either the bimorph piezoelectric body or the asymmetric structure having a single piezoelectric element layer as disclosed in Japanese Patent Application Laid-Open No. 48-52487.

A variable curvature mirror having a multilayer structure with a piezoelectric element layer having only one layer was proposed in Japanese Patent Laid-Open No. 135346/1983.

In JP-A-53-135346, a bimorph type inorganic piezoelectric layer is mainly used as the piezoelectric layer.

In addition, Sato et al. confirmed that a laminate of a piezoelectric polymer film and a non-piezoelectric rigid body such as glass can change the curvature more effectively, and proposed a mirror with variable curvature. The variable curvature mechanism applied to these mirrors is further applied to a single-sound wave transmitting/receiving device.

The present invention uses such a laminate with variable curvature as a surface for transmitting and/or receiving sound waves. It is in C4.

First of all, it is known that the curvature of the piezoelectric structure serving as the base of the sound wave transmitting/receiving device of the present invention can be arbitrarily changed depending on the voltage, for example, in Japanese Patent Laid-Open No. 53
It is clear from the mirror example in the specification of -135346,
A general case where the piezoelectric layer proposed by Sato et al. is a single layer will be described next.

In the following description, an ultrasonic transmitter/receiver will be described as an example, but the present invention is not limited thereto.

In Fig. 1, 1 is a piezoelectric structure that serves as the base of the ultrasonic transmitter/receiver, and electrodes 3 and 3' are attached to both sides of a layer 2 of a piezoelectric material film such as piezoelectric ceramic or piezoelectric polymer. , furthermore, on this one electrode 3', for example, metal, glass,
The stress interference body layer 4 made of ceramic, synthetic resin, paper, wood, or other arbitrary material is laminated.

In this case, if the stress interference layer 4 is a conductor such as metal or carbon, the electrode 3' may be omitted and the electrode 4 may be used as one electrode.

As shown in Fig. 2, it is assumed that the electrodes 3 and 3' are extremely thin ((electrodes are omitted in the opening of Fig. 2) and the force required for bending them is negligible. ) has a strong piezoelectric constant d31 only in one direction (indicated by H), and the stress interference layer 4 has no piezoelectricity (hereinafter referred to as a piezo layer).

The width of the piezo layer 2 in the direction perpendicular to the piezo axis direction is Wl,
Let the thickness be tl and have a Young's modulus E1, and the similar width, thickness and Young's modulus of the non-piezo layer 4 be W2, t2 and E2, respectively, for example a voltage amplifier 5DA.
A DC voltage V is supplied from a controllable DC power supply device 8 consisting of a combination of a converter 6 and a microcomputer 7.
is applied between both electrodes.

Consider a sheet with if, W1=W2=W.

When a bending moment is applied to this sheet, the radius of curvature ρ
When bending with , the center of the bend, the neutral plane, will be eccentric toward the material with a higher Young's modulus.

If the distance from the surface of the non-piezo layer to the neutral plane is a, then the elastic bending moment M around this neutral plane is the elongation when a voltage V is applied to the piezo layer, and the tensile force of contraction. P is given by, and if it is bent by this P, the moment derived from P should balance the bending moment M in equation (2), so the radius of curvature ρ is given by equations (2), (3) and the piezo The stress of expansion and contraction that occurs in the piezoelectric material over a distance from the center layer of the layer to the neutral plane changes into bending stress due to interference stress originating from the structure of the piezo layer and the non-piezo layer, and the structure deforms.

Since equation (4) is an equation inversely proportional to the voltage V, it can be written as
The piezoelectric constant of the piezo layer 4 is determined by the material and thickness of the piezo layer 4 and the structure of the piezoelectric structure 1, so the radius of curvature of the piezoelectric structure, which is a fixed layered structure, can be changed arbitrarily by changing the voltage V. It turns out that it can be done.

In addition, the piezoelectric structure as a laminate has a ratio of 1/ρ in advance.

If it has a curvature of

Next, consider the case where the width W1 of the piezo layer 2 and the width W2 of the non-piezo layer 4 are different.

Neutral axis position a. and the radius of curvature ρ, are expressed by the following equation.

When 玖IE21 jt + t21d3□ and V are constant, W1/W2=b, and the equation 8) can be written as.

Therefore, if you want to change the curvature in the length direction l, for example, as shown in Figures 3 and 4,
This can be achieved by changing 1/W2.

3 and 4 are examples in which W2 is kept constant and Wl is varied, but it is also possible to keep Wl constant and vary W2, or to vary both.

Equations (4) and (8) only take into account the piezoelectric constant d3□, that is, the case where d3□ is extremely small compared to dat of the piezo layer, but a piezo layer in which d32 cannot be ignored is also used. In this case, equations (4) and (8) are also applied in the width direction, and in particular, when aat and d32 are approximately equal, a change in curvature close to that of a spherical surface should theoretically be obtained.

(However, when creating a quadratic curved surface, folds are generated on the inner surface and hinder the curve, so if you want to curve with a large curvature, it is necessary to provide notches here and there.

) However, when comparing the piezoelectric constants of piezoelectric polymer films obtained by polarizing uniaxially stretched polymer films and biaxially stretched polymer films obtained using current technology, it is found that d31 of the biaxially stretched polymer film and Even if the sum of d32 (which can be thought of as the total piezoelectric force of this film) is the largest, it is smaller than the value of d3□ alone in a normal uniaxially stretched polymer film, and d3□ and d3□ are equal. Moreover, since the production of a highly sophisticated biaxially stretched piezoelectric polymer film requires extremely advanced technology, it is advantageous to use a uniaxially stretched film in which d31 is higher than d3□ if possible.

A method of changing the curvature in the width direction using a piezo film with only a large d3□ is, for example, as shown in Fig. 5 or 6, in which the piezo layer 2 or electrode 3 (only the electrode in the figure) is perpendicular to the piezo axis. The electrode may be divided into a plurality of electrodes in the direction, and a low voltage may be applied to the central electrode, and a higher voltage may be applied toward both ends.

In this case, it is cumbersome to have to apply a different voltage to each electrode, but it is possible to change the curvature in the width direction by appropriately changing the ratio of the voltages applied to each electrode. .

Further, if both d3□ and d3° are large and the piezoelectric structure has a spherical surface from the beginning, it is also possible to use the structure shown in FIG. 7 or 8.

One specific example of the ultrasonic transmitter/receiver according to the present invention uses the piezo layer of the variable curvature piezoelectric structure shown in FIGS. 1 to 8 as an ultrasonic transmitter or receiver element, as shown in FIG. 9. A controllable DC power supply circuit 8, a high frequency oscillation circuit 9 as an oscillation circuit, and/or a reception circuit 10 are coupled between the electrodes 3 and 3' of the piezo layer 2.

In addition, 11 is a transmitting/receiving switch, 12 is an impedance conversion FET, and 13 is a capacitor.

When a DC voltage is applied to this piezoelectric structure 1, the curvature of the piezoelectric structure curves according to the voltage as described above.

Since the surface of the piezo layer is similarly curved, for example, in an ultrasonic transmitter that uses this curved piezo surface as the transmission surface, it is possible to arbitrarily adjust the distance to the point or line (center of curvature) where the ultrasonic waves are focused. can.

Similarly, in the receiving device, the receiving surface can be freely bent.

The piezo layer serving as the sound wave transmitting or receiving surface of the device of the present invention is, for example, a thin plate of piezoelectric ceramic such as lead titanate or lead zirconate, or a vapor-deposited film of cholera, vinylidene fluoride, vinyl fluoride, fluorochloro, Any thin film layer such as a polymer obtained by polymerizing or copolymerizing a polar monomer such as vinylidene as a main component can be used.

In addition, the layers laminated with these piezo layers are metal, glass,
Any material such as ceramic, synthetic resin, paper, leather, wood, etc. can be used as one or more composite layers.

As shown in FIGS. 5 to 8, there may be a plurality of pairs of electrodes on both sides of the piezo layer of the device of the present invention; For example, if two or more electrically independent anodes are combined with a common cathode on the back side, each anode and cathode combination is considered to be a different pair. ) All sets of electrodes are not necessarily connected to the DC power supply circuit and the transmitting/receiving electric circuit, for example, the high frequency electric circuit, at the same time.

In the case where there are a plurality of electrodes, the following circuit combinations are possible, for example, in an ultrasonic transmitting/receiving device.

(1) Direct current and transmitting/receiving electric circuits (
This includes all cases in which the transmitting high-frequency circuit and/or the receiving circuit sequentially switch each electrode pair or alternately switch between transmitting and receiving;

(2) A DC circuit is coupled to all pairs of electrodes, and some of the pairs are further coupled to a transmitting/receiving electric circuit.

(3) a DC circuit is coupled to at least one of the electrode pairs;
A transmitting and receiving electrical circuit is coupled to another pair of electrodes.

(4) There is at least one electrode pair to which only a DC circuit is coupled, at least one electrode pair to which only a transmitting/receiving electric circuit is coupled, and at least one electrode pair to which both a DC circuit and a transmitting/receiving electric circuit are coupled.

(5) Transmitting/receiving electric circuits are coupled to all electrode pairs, and at least one of the electrode pairs is coupled to a DC circuit.

If the DC circuit and the transmitting/receiving electric circuit are connected using different wiring, for example, the transmitting/receiving electrode can be provided by sandwiching only the piezo layer, and one pole of the DC electrode can be provided by sandwiching a thin insulating film. It is.

In addition, when a DC power supply circuit or a high frequency oscillation circuit is connected to multiple electrodes, the DC or high frequency power supplies do not necessarily have to be the same, and the voltages of each power supply can be different. It is also possible to have different frequencies for each.

The sound wave transmitting/receiving device of the present invention is useful when it is desired to radiate sound waves in parallel, when it is desired to concentrate sound waves, or when it is desired to change the direction of sound waves. It is used in a wide variety of applications, including ultrasound diagnostic equipment and ultrasound treatment equipment.

Furthermore, when applied to a sound collection microphone or a speaker, one with variable directional characteristics can be obtained.

Next, a design example of a variable curvature piezoelectric structure portion of an ultrasonic transmitting/receiving device as an example of the present invention will be shown, but it is clear from Sato et al. As shown in the proposed embodiment.

Design example 1 A piezoelectric polymer film with aluminum evaporated electrodes on both sides, thickness t1=o, o 3mm, d3□=2. OX
1 10 m/V, Young's modulus E, = 3.0 x 109 N/
d using a polarized film of uniaxially stretched polyvinylidene fluoride, and a Young's modulus E2=7.6×101 as a non-piezoelectric sheet.
°N/rr? The radius of curvature of piezoelectric structures as laminated plates for variable curvature ultrasonic transmitter/receiver devices of various designs was calculated using a glass plate.

First, one piezoelectric polymer film is used as a piezo layer, and glass plates of different thicknesses are bonded to this layer. Figure 10 shows the change in the radius of curvature ρ when a voltage of 100 V is applied to both poles of the piezo layer of each sample. This is as shown by curve a.

Next, when only the thickness of the piezoelectric polymer film is changed to 60μ, glass plates of different thicknesses are bonded to this, and the same voltage of <1oov is applied between both poles of the piezo film, the 10th
The curve is as shown in the figure.

This time, we bonded two 30μ piezoelectric polymer films with different piezoelectricity surfaces to create a bimorph structure laminate, used this bimorph laminate as a piezo layer, and bonded glass plates with different thicknesses to this. , the case where a voltage of 100 V is applied to each bimorph piezo layer of each sample is as shown in FIG. 10C.

As a result, polyvinylidene fluoride was used as the piezo layer,
Furthermore, when the non-piezo layer is made of a material with a high Young's modulus such as glass, it is known that the bimorph structure piezo layer is disadvantageous.

Design Example 2 A two-layer piezoelectric structure is designed using the same piezoelectric polyvinylidene fluoride film used in Design Example 1 as the piezo layer and a non-polarized polyvinylidene fluoride film as the non-piezo layer.

100 when El = E2 and t2 is varied variously
The calculated value of the curvature when v is applied is shown in FIG.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view of a piezoelectric structure as a variable curvature laminate of the device of the present invention, and FIGS. 2 to 8 are explanatory views of various examples of the piezoelectric structure as a variable curvature laminate. Figure 2 A shows a longitudinal cross section, Figure 2 opening shows a plane, Figure 2 C shows a white cross section, Figures 3 to 8 each show a plane, and Figure 9 shows the present invention. An explanatory diagram of the entire device, and Figures 10 and 11 are explanatory diagrams of changes in curvature at a constant voltage when the thickness of the non-piezo layer (glass plate or PVDF plate) is changed with respect to the piezo layer (PVDF film layer). It is. 1... Piezoelectric structure, 2... Piezoelectric material layer, 3, 3...
- Electrode, 4... Stress interference layer, 5... Voltage amplifier,
6...DA conversion i, 7...microcomputer,
8... Variable DC power supply, 9... High frequency oscillation circuit, 10
... Receiving circuit, 11... Selector switch.

Claims (1)

[Scope of Claims] 1. A piezoelectric material layer and first and second electrode layers disposed on both sides of the piezoelectric material layer and forming a pair with each other, the first electrode layer and the second electrode layer Alternatively, another material layer disposed on the second electrode layer and the second electrode layer are asymmetrical with respect to the piezoelectric material layer, and at least one set of the first and second electrode layers A voltage controllable DC power supply device is connected between the electrode layers, and a signal circuit is connected between at least one set of electrode layers of the first and second electrode layers, including a set of electrode layers to which the DC power supply device is connected. A variable curvature acoustic wave transmitting/receiving device, characterized in that the curvature of the piezoelectric material layer is changed by the output voltage of the DC power supply device. 2 At least one of the other material layers is another piezoelectric material layer, a third electrode layer is disposed on the other piezoelectric material layer, and the first to third electrode layers are connected in a bimorph type. A variable curvature acoustic wave transmitting/receiving device according to claim 1, characterized in that: 3. The variable curvature acoustic wave transmitting/receiving device according to claim 1, wherein the other material layer is a material layer that does not have piezoelectricity. 4. The variable curvature sound wave transmitting/receiving device according to any one of claims 1 to 3, wherein the piezoelectric material layer is a piezoelectric organic polymer film. 5. The piezoelectric material layer is a piezoelectric organic polymer film, and at least one of the other material layers is a material layer that does not have piezoelectricity and has a higher Young's modulus than the piezoelectric polymer film. A variable curvature sound wave transmitting/receiving device according to claim 1, 3, or 4. 6. Claims 1, 3, or 4, characterized in that the piezoelectric material layer is a piezoelectric organic polymer film, and the other material layer is an organic polymer material that does not have piezoelectricity. The variable curvature sound wave transmitting/receiving device according to any one of the above. 7. A variable curvature=a(S=: signal device) according to any one of claims 1 to 6, characterized in that the signal circuit is a transmitting circuit. 8. The signal circuit is a receiving circuit. A variable curvature sound wave receiving device according to any one of claims 1 to 6, characterized in that: 9. A patent characterized in that the signal circuit has a transmitting circuit and a receiving circuit that are mutually switchable. A variable curvature liquid transmitting/receiving device according to any one of claims 1 to 6. 10. A DC power supply device and a signal circuit are connected between all sets of electrode layers of the first and second electrode layers. , the variable curvature sound wave transmitting/receiving device according to any one of claims 1 to 9, characterized in that the signal circuit is a transmitting/receiving circuit.11 Among the first and second electrode layers. A DC power supply device is connected between some of the sets of electrode layers, and a signal circuit is connected between the other sets of the first and second electrode layers, and the signal circuit is a transmitting/receiving circuit. A variable curvature sound wave transmitting/receiving device according to any one of claims 1 to 9, characterized in that: 12. A set of electrode layers to which only a DC power supply is connected and only a signal circuit are connected. At least one set of electrode layers and a set of electrode layers to which the DC power supply device and the signal circuit are connected are included in the first and second electrode layers, respectively, and the signal circuit is configured to transmit and receive signals. The variable curvature sound wave transmitting/receiving device according to any one of claims 1 to 9, characterized in that it is a circuit.13 Direct current between all sets of the first and second electrode layers. A power supply device is connected, and a signal circuit is connected between some pairs of the first and second electrode layers, and the signal circuit is a transmitting/receiving circuit. A variable curvature sound wave transmitting/receiving device according to any one of items 1 to 9.14 A signal circuit is connected between all sets of the first and second electrode layers, and the signal circuit is connected between the first and second electrode layers. A DC power supply device is connected between some sets of electrode layers of the electrode layers, and the signal circuit is a transmitting/receiving circuit. The variable curvature sound wave transmitting/receiving device described in .