JPS60139100A - Transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

TECHNICAL FIELD This invention relates to hydrophone arrays, and more particularly to multilayer piezoelectric polymer (PVDF) hydrophone arrays.

(Background technology) Conventionally, piezoelectric ceramics, especially lead titanium zirconate (PZ
T) has been most commonly used for both hydrophones and radiators. Piezoelectric ceramics have shown considerable flexibility in the design of the itrophone.

The reason is that it can be formed into various shapes such as a cylinder, a ring, a plate, or a hemisphere.

Although ceramics can be made into various shapes,
- There are practical constraints on the maximum size that can be assembled in succession. This is due to the hard and brittle nature of piezoceramic materials. This limited maximum shape, the stiffness of ceramic and its high mass density (approximately equal to steel) make it useful in some applications, such as towed arrays used onboard ships and arrays with large apertures mounted on ships. is a drawback.

Piezoelectric polymers (PVDF) are a recently developed new transducer material that has overcome these limitations and developed lightweight, flexible hydrophones.

When used in the present invention, PVDF can be manufactured into long strips that are applied in towed arrays, or can be made into large flat sheets that are used in large aperture arrays. The low density and mechanical flexibility of polymers has proven advantageous when used in thin linear towed arrays, where the hydrophones must be long, thin, flexible, and lightweight. Long hydrophones are spatially averaged (5patial 4veragi)
ng) method to reduce noise associated with turbulent boundary layer phenomena. This method utilizes flow noise slower than the signal sound speed, which allows turbulent boundary layer noise (not the signal) to be discriminated. Large aperture array hydrophone elements also require large lateral dimensions, light weight, thinness, semi-flexibility, and ability to discriminate against high wave number turbulent boundary layer noise. A ship-mounted large aperture array hydrophone, as in the invention, must have the ability to discriminate against medium wavenumber ship vibration noise.

Because of their light weight and mechanical flexibility, polymers are more resistant to impact than piezoceramics. The mechanical flexibility of polymers allows the material to be shaped into irregular surfaces, allowing the design of new types of hydrophones.

Furthermore, the characteristic impedance of the pentapolymer closely matches that of water. Polymers also have the advantage of having large piezoelectric stress constants.

'Piezoelectric polymer membranes (layers) are currently made from polyvinylidene fluoride, often referred to as PVDF.

Polarization must be performed to make the polymer a useful piezoelectric material. This treatment is carried out by uniaxially stretching the membrane at elevated temperatures and returning it to its original length several times. One method of polarization is to metallize both sides of the membrane, apply a high DC electric field to the electrodes, and hold at 100° C. for about 1 h. It is then cooled to room temperature while an electric field is applied, resulting in permanent polarization.

SUMMARY OF THE INVENTION The present invention is a multilayer piezoelectric polyvinylidene fluoride polymer (PVD) consisting of a plurality of layers symmetrically arranged on either side of a central layer.
F) 14 hydrophone arrays are constructed. The rigid structure provided by the central layer prevents bending modes in the operating frequency band. Acceleration can be achieved by attaching the array to the central layer.
The initial equilibrium arrangement for cel Iing ) is obtained. The outermost layer of the multilayer play consists of a PVDF layer,
An intermediate layer separates the PVDF layer from the central support. The metallization pattern on the surface of the successive PVDF layers determines the shape and number of elements of the hydrophone array.

The present invention takes advantage of the unique properties of PVDF polymers and their ability to be made into large continuous sheets. The present invention
Improve efficiency and simplify structure. The salient features of the present invention are: (2) placement of large area, closely spaced hydrophone elements on a continuous sheet of PVDF to obtain the advantage of spatial averaging for noise reduction; A separate sensor layer is attached to the central support layer structure for noise cancellation (31) with an intermediate layer between the outer PVDF array layers to provide separation between the outer signal sensing layer and the support layer and to reduce the impedance of the layer assembly. (4) providing an initial equilibrium arrangement for acceleration cancellation by appropriate electrical connections of the outermost PVDF layer;
and (5) to perform hydrostatic mode operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the invention is illustrated in an isometric view of array 10 shown in FIG. Array assembly 10 has a central reinforcement and support layer 12 extending to each end and attached to each end to form a support 11 by which assembly 10 is provided with a support structure (Fig. (not shown) and can be fixed to a vibration absorbing mount (not shown). Methods of mounting to reduce structurally transmitted vibrations to transducers are well known. The array structure 10 consists of composite layers 14', 14' above and below the support layer 12, respectively. electrode 15' and layer 14';
A similar counterelectrode 15'' (not shown in FIG. 1) on the other side of the transducer element 1
6 and the element 16 is connected by a line 17 to a known beam forming circuit 18.

Although only the electrically connected areas or electrodes 15' are shown on the outer surface of layer '14' in FIG. 1, a similar pattern of electrodes 15', 15' can be seen on the other composite layer 14'
and are not visible in the isometric view of FIG.

A cross-sectional view along line ll--H of a modified embodiment of the array 10 of FIG. 1 is shown in FIG. This cross section is offset longitudinally to clearly illustrate the invention.

The embodiment of FIG. 2 includes three layers 2 forming a composite layer 14'.
1-・221 shows a male. Composite layer 14'' is identical to layer 14'. Central support layer 12 provides a rigid structure that prevents bending modes in the operating frequency band of transducer array 10. Layer 12 also The attachment of array 10 provides structure and provides an initial equilibrium arrangement for acceleration cancellation.

A suitable material for the support layer 12 is glass fiber reinforced resin, commercially available type G-10 being suitable. Glass fiber reinforced II
The high stiffness and low stiffness of the MJl layer 12 increase the array's resistance to bending stress and contribute to reducing the weight of the array. However, what other plastics, aluminum or steel, etc., that have such properties? I
- Can be used in other embodiments.

The outermost layers 21', 21'' are made of thick film PVDF material and exhibit the greatest sensitivity to stresses in the transverse plane.
constitutes the main electromagnetically active layer of D. Electrode 151, layer 2
1″ and corresponding electrodes 15′ on the inner surfaces of 21′,
(FIG. 2 (1) Shown on the inner surface of the PVDF layer 21'; b)
21' and 71z (10 transducer elements 5
form 0. Corresponding area 15# of layer 211°21'
are connected in parallel and connected to a beamforming circuit as in one well-known transducer e-array. layer 21
The outermost electrode 15' of ', 21' is an electrical conductor 15'.
2, let's join together on one bank
Rank k”F is fractured, thereby forming a shield,
This prevents electrical noise from being picked up by the inner electrode 15'. Unlike this, as shown in FIG. 17 to the beam forming circuit 18, where it may be connected to ground. This connection by line 17 minimizes the roughness during crosstalk that sometimes occurs when a common ground line is conventionally used. The signals provided by electrodes 15# of array 10 are fed to the periphery of the array by lines 151, from which connections are made to well-known beamforming circuits. Electrodes 15', 15'' and connecting conductors 151, 152, 1
53 is the commercially available metallized PV used for layers 21-21#
It is formed by selective etching of the DF layer. PVDF
Layer 21'.

Since the 21# is sensitive to pressure changes applied to the external surface, the PVDF is applied to each layer 21', 2 in a manner known to those skilled in the art.
A maximum thickness of 0.04 inch (approximately 1 xya) is currently available, with the most sensitive axis of the piezoelectricity in the direction intersecting the plane of the available).

Thin PVDF layers 22', 2g are adhered to respective opposite sides of support layer 12. Each PVDF layer 22', 22' has a conductive film 23 on both sides thereof, and #! Electrical connections are made by 24. Thin film polymer layer 221° 22# is stretched in the direction of arrow 25 and polarized in the thickness direction (transverse to the plane) to provide a membrane that produces a maximum output voltage for stress deformation along arrow 25. In this way, thin film 2
2' and 22' sense the strain (stress deformation) of the support layer 12 and generate a voltage proportional to the strain. layer 22
', 22' is thin (typically about 1 mil (0,25
mm) and are glued to the support layer 12, so that these layers are usually sensitive to mechanical vibrations of the layer 12 rather than to luminous acoustic pressure. Biaxially stretched membranes can also be utilized with 5 layers 21', 2
1″, 22′.

It can be replaced with 2g uniaxial membrane. The signal on line 24 is applied to the electrical circuit to which the transducer elements 50 are connected to cancel the same vibrational component of unwanted noise sensed by each of the transducer elements 151 of the PVDF layers 22', 22''. do.

Since the PVDF layers 22', 22' are thin and polarized with maximum sensitivity in the plane of the layers, compressive stresses generated by varying water pressures do not produce a significant output voltage and therefore the layer 21' , 21'' does not act to reduce the signal generated by the transducer elements 50 of the noise sensing layers 22', 22'.
The output voltage on line 24 will be proportional to the surface stress strain of support layer 12.

The layers 26', 26'' are attached to the outer layers 21', 21'' and to the inner layers 22', 22' by K glue or other suitable adhesive.
The layers 26' and 26'', respectively joined to the outer layer 21' and the inner layer 22', have two purposes.
', but mainly the layers 21', 21'
The purpose of separating the hydrophone from the central support layer 12 is as follows. Due to its large attenuation constant, polarized or unpolarized PVDF polymers
It is a suitable material for Polarized or non-polarized PVD
The impedance of F is close to that of water, and the attenuation gate is large, so transducer array 1
The impedance given by o will be close to the impedance of water. This impedance matching reduces dispersion effects and forms a narrow beam.

FIG. 3 is an isometric view of a trough array 10' similar to array 1o of FIG. Transducer element 50 (not shown in Figure 3), except that it is not patterned to form electrode 15' as shown.
c. defined by conductive electrodes 15'' on the inner surfaces of the outer PVDF layers 21', 21'. The acoustic efficiency of the transducer array of FIG. 6 is that of the transducer array of FIG. FIG. 4 shows the lines rv- of the transducer reference array of FIG.
In the cross-sectional view from the rv, the composite layer 14', 14'' has more components than the six layers shown in FIG. PVDFl@21
N layers are provided between each of the inner PVDF layers 22' and 21' (2N layers in total). N layers [
Layers 1, 2... (N-1), N) can include a glue layer (adhesion mediating layer) if acoustically effective, and the outer PVDF layer 21'.

21' is selected to provide damping between layer 21' and support layer 12, and is selected to provide impedance matching between layer 21' and water in accordance with well-known impedance matching techniques using multilayer materials. . The N layers are arranged symmetrically with respect to the central support layer 12 with respect to layer thickness and layer properties.

Layers 1-N may be isotropic or orthotropic and include PVDF damping (or separation) layers. The cross section in Figure 4 is PVDF.
It should be noted that a continuous electrically conductive film is shown on the outer surface of layers 21', 21'.

As mentioned above, the PVDF layer 21' of FIGS. 1 and 2
, 2f' define an array distribution and a pair of opposing metallization surfaces 15', 15' respectively.
° and those 17) in rMIPVT) 1;'h keba, r
1. The same metallization pattern appears on both sides of the layers of the embodiments of FIGS. 1 and 2. Although the shape of each hydrophone element is arbitrary, A dense packing factor is desirable to obtain the benefit of noise reduction through spatial averaging. To meet this requirement, square or rectangular patterns are used with unmetallized gaps between elements. It would be better to reduce the size of the hydrophone element.

Quantities and groupings are determined by well-known receive array designs. Electrical connections are made by conductors 151 to the metallized surface of each hydrophone element.

Hydrophone array 10 surrounds said array 10 (
A plastic or rubber coating (not shown) is made waterproof to provide waterproofing of the electrical connections to the array. PVD
Since both F layers 21', 21' are in contact with the sound field provided by the aqueous environment in which the array is used, the array 1
0 operates in hydrostatic mode and its sensitivity is determined by the piezoelectric constant g
Each transducer element 15 determined by h
The sensitivity of No. 1 is the same since there is no bending motor degree due to the support Ji12.

This is because the support layer 12 has the necessary rigidity to eliminate bending resonance in the operating frequency band. It should be noted that the layers making up the array 10 are arranged symmetrically with respect to the support layer 12 with respect to layer thickness and layer properties. and,
The corresponding layers can be formed from isotropic or orthotropic plates. Layer 21' has the same thickness and the same properties as layer 21'. That is, layer N' has the same thickness and characteristics as layer G.

Although the present invention has been described above according to embodiments, it is obvious to those skilled in the art that other embodiments utilizing the idea of the present invention are possible.

[Brief explanation of the drawing]

FIG. 1 is an isometric view of a transducer array constructed in accordance with the present invention. Figure 2 is a sectional view taken along line II--II in Figure 1. FIG. 3 is an isometric view of another embodiment of the invention. FIG. 4 is a sectional view taken along line IV--IV in FIG. 3. (Explanation of symbols) 10 Near array assembly 12: Support layer 14/, 14': Composite layer 15', 15': Electrode 21', 21'': PVDF layer M Applicant: Raytheon Company (5 others)

Claims (1)

[Scope of Claims] 11) a planar support layer; and a first piezoelectric polymer layer adhered on each side of the support layer, each of the first piezoelectric layers being predominately affected by a planar strain of the 1i1 layer. a first piezoelectric polymer layer that generates an electrical signal generated by a piezoelectric material; a second piezoelectric layer adhered to said first layer, each having a high acoustic attenuation constant; and a third piezoelectric polymer layer adhered to said second layer. It's a polymer layer,
a third piezoelectric polymer layer that provides an electrical signal primarily in response to pressure intersecting the plane of the three body layers; wherein the first and third piezoelectric layers have conductive films on both sides of each layer and supply the electrical signal in response to strain between the layers. (22 Claim 1 in which the second layer is a polymer layer)
Transducer as described in section. (3) The transducer according to claim 1, wherein the second layer is a PVDF layer. (4) The transducer according to claim 1, wherein the planar support layer is a rigid layer that is resistant to bending. (5) The transducer according to claim 1, wherein the support layer is a glass fiber-reinforced resin layer, the thickness of which provides sufficient stiffness so that the hydrophone response is uniform in the operating frequency band. Yusa. (6) the conductive film of the third layer has at least one film patterned to provide an electrically insulated region on one surface of the layer; A transducer according to claim 1, characterized in that the transducer elements comprise an array of transducer elements. 7. The transducer of claim 1, wherein said layer force ζ is a thin layer that is more sensitive to strain in said support layer than to acoustic signal pressure. (8) The transducer of claim 1, wherein the sixth layer is a thick layer that provides electrical signals primarily from pressure in a direction intersecting the plane of the sixth layer.