JPH0446517B2 - - Google Patents

Description

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

(Background Art) Traditionally, piezoelectric ceramics, particularly lead titanium zirconate (PZT), are the most commonly used materials for both hydrophones and radiators. There is considerable flexibility in the design of the hydrophone as it can be made into a variety of shapes, such as shapes. Although ceramics can be made into a variety of shapes, there are practical constraints on the maximum size that can be assembled in one piece. 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 on ships and arrays with large openings 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 fabricated 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. Longer length hydrophones can reduce noise associated with turbulent boundary layer phenomena through a "spatial averaging" effect. In other words, by making the length of the hydrophone very long compared to the wavelength of the noise (the number of waves is large compared to the length of the hydrophone), the influence of noise on the hydrophone is averaged out (cancelled). decreases by 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. Similar to the present invention, large-aperture array hydrophones mounted on ships are susceptible to the effects of intermediate-wavenumber hull vibration noise (noise generated by hull vibrations, with wavelengths longer than turbulent boundary layer noise). It is also necessary to exclude.

Because of their light weight and mechanical flexibility, polymers are more resistant to impact than piezoceramics. The mechanical flexibility of polymers also allows the material to have irregular surfaces, enabling new types of hydrophone designs. Furthermore, the characteristic impedance of the polymer 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 difluoride, 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 hour. 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 comprised of a multilayer piezoelectric polyvinylidene difluoride (PVDF) hydrophone array consisting of multiple layers symmetrically disposed on either side of a central layer. The rigid structure provided by the central layer prevents bending modes in the operating frequency band. Attaching the arrays on both sides of the central layer provides an inertially balanced structure for acceleration cancellation.
That is, the polarity of the signal produced by the acceleration force on the array on one surface becomes opposite to the polarity of the signal produced on the array on the other surface, and is eliminated. The outermost layer of the multilayer array consists of a PVDF layer, and the middle layer is a PVDF layer.
Separate the layers 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 invention improves efficiency and simplifies construction. The salient features of the present invention are (1) placing multiple large area closely spaced hydrophone elements on a continuous sheet of PVDF to obtain the benefit of spatial averaging for noise reduction; (3) an intermediate layer between the outer PVDF array layers to provide separation between the outer signal sensing layer and the support layer and to improve the structure of the layer assembly; (4) provide an inertial balance structure for acceleration cancellation by appropriate electrical connections of the outermost PVDF layer; and (5) provide hydrostatic mode operation. be.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention is shown in FIG.
shown in a perspective view. Array assembly 10 has a central reinforcing and support layer 12 extending to each end to form a mounting support 11 at each end;
The support allows the assembly 10 to be secured to a support structure (not shown) and to a vibration absorbing mount (not shown). A method of attaching a transducer to a ship's hull with a vibration absorbing material or the like has been known in the art to prevent undesired vibrations from being transmitted to the transducer. The array structure 10 consists of composite layers 14', 14'' above and below a support layer 12, respectively. Electrodes 15' and layers 14',
A similar counterelectrode 15'' (not shown in FIG. 1) on the other side of 14'' forms a transducer element 16, which is connected by line 17 to the well-known beam forming Connected to circuit 18. 1st
Although only the electrically connected areas or electrodes 15' are shown on the outer surface of layer 14' in the figure,
A similar pattern of electrodes 15', 15'' is provided on the outer and inner surfaces of the other composite layer 14'', with the first
Not visible in the perspective view of the figure.

A cross-sectional view along line - of a modified embodiment of the array 10 of FIG. 1 is shown in FIG. This cross section is
The figures are vertically offset to clearly illustrate the invention. The embodiment of FIG. 2 shows three layers 21', 22', 26' forming composite layer 14'. Composite layer 1
4'' is the same as layer 14'. The central support layer 12 is
Provides a rigid structure that prevents bending modes in the operating frequency band of transducer array 10. Layer 12 also includes hydrophone array 10
and provides an inertial balance structure for acceleration cancellation. A suitable material for the support layer 12 is glass fiber reinforced resin, commercially available type G-
10 (manufactured by DuPont) is suitable. The high stiffness and low density of the glass fiber reinforced resin layer 12 are
This increases the array's resistance to bending stress and contributes to making the array lighter. However, other plastics and metals such as aluminum or steel having such properties may be used in other embodiments.

The outermost layers 21', 21'' consist of thick-film PVDF material and exhibit maximum sensitivity to stresses in the direction perpendicular to its plane.
It constitutes the main electromagnetically active layer of array 10. Electrodes 15', layers 21'' and corresponding electrodes 15'' on the inner surface of 21'' (shown on the inner surface of PVDF layer 21'' in FIG. 2), along with intermediate PVDF layers 21', 21'', A deducer element 50 is formed. Corresponding regions 15'' of layers 21', 21'' are connected in parallel and connected to a beam forming circuit as in known transducer arrays. Layers 21', 21'' The outermost electrodes 15' of are connected together by electrical conductor 152, and then by conductor 153.
is connected to ground by the inner electrode 15'', thereby forming a shield and preventing electrical noise from being picked up by the inner electrode 15''.In contrast, as shown in FIG. The electrodes 15' may be connected by separate wires 17 to the beamforming circuit 18, where they may be connected to ground.This wire 17 connection eliminates the crosstalk that sometimes occurs when a common ground wire is conventionally used. The signals provided by the electrodes 15'' of the array 10 are fed to the periphery of the array by lines 151, from which connections to well-known beamforming circuits are made. Electrodes 15', 15'' and connecting conductor 15
1,152,153 are formed by selective etching of commercially available metallized PVDF membranes used for layers 21', 21''. Therefore, PVDF
in a manner known to those skilled in the art, having the most sensitive axis of piezoelectricity in the direction intersecting the plane of each layer 21', 21'', the maximum axis exhibiting the greatest sensitivity to the normal application of the acoustic pressure to be sensed. thickness (0.04 inch (approximately 1 mm) currently available).

Thin film PVDF layers 22', 22'' are adhered to both the front and back sides of the support layer 12. Each PVDF layer 22', 22'' has a conductive film 23 on both sides thereof, to which electrical connections are made by wires 24. It will be done. thin film polymer layer 22',
22'' is stretched in the direction of arrow 25 and polarized in the thickness direction (in the direction perpendicular to the plane) to provide a membrane that produces a maximum output voltage for stress deformations along arrow 25.Thus, membranes 22', 22'' senses the strain (stress deformation) of the support layer 12 and generates a voltage proportional to the strain. layer 22', 2
2" are thin, typically about 1 mil (0.25 mm) thick, and are adhesively attached to the support layer 12 so that these layers are less sensitive to the mechanical stress of layer 12 than to the acoustic pressures normally encountered. Membranes stretched biaxially (in two orthogonal axes in the plane of the membrane) can also be used, with the layer 2
1', 21'', 22', 22'' can be replaced with uniaxially stretched membranes. The signal on line 24 is applied to an electrical circuit to which transducer element 50 is connected;
Transducer element 1 with PVDF layers 22', 22''
51 to cancel the same vibrational component of the undesired noise detected by each of them. Because the PVDF layers 22', 22'' are thin and polarized with maximum sensitivity in the plane of the layer, compressive stresses generated by varying water pressures do not produce a significant output voltage; It therefore does not act to reduce the signal generated by the transducer elements 50 of the layers 21', 21''. Thus, the noise sensing layers 22', 2
The output voltage on the 2'' line 24 will be proportional to the surface stress strain of the support layer 12.

Layers 26', 26'' are joined by glue or other suitable adhesive to outer layers 21', 21'' and to inner layers 22', 22'', respectively. Layers 26', 2
6" have two purposes. These layers electrically insulate the outer layer 21' from the inner layer 22', but primarily separate the hydrophone consisting of layers 21', 21" from the central support layer 12. have the purpose of Due to its large attenuation constant, polarized or unpolarized PVDF polymers are suitable materials for layers 26', 26''. The impedance of polarized or unpolarized PVDF is close to that of water, and the attenuation constant is Because it is large, transducer array 1
The impedance given by 0 will be close to the impedance of water. This impedance matching reduces scattering phenomena and forms a well-defined beam.

FIG. 3 is a perspective view of a transducer array 10' similar to array 10 of FIG. 1 in which the outer conductive film 30 is a continuous film and includes electrodes 15' as shown in FIG. The difference is that it is not patterned to form.

Transducer element 50 (not shown in FIG. 3) is defined by conductive electrode 15'' on the inner surface of outer PVDF layer 21', 21''. Third
The acoustic efficiency of the transducer array of FIG. 1 is comparable to that of the transducer array of FIG. is giving.

FIG. 4 is a cross-sectional view of the transducer array of FIG. 3, with the composite layers 14', 14'' having more components than the three layers shown in FIG.
In particular, instead of the single layer 26', 26'' of FIG.
PVDF layers 21', 21'' and inner PVDF layers 22', 2
2″ and N layers are provided respectively (total 2N layers).
layer). N layers [layers 1, 2...(N-1), N]
The outer PVDF can include a glue layer (adhesion mediating layer) if acoustically effective.
layer 2 is selected to provide damping between layers 21', 21'' and support layer 12, and in accordance with well-known impedance matching techniques using multilayer materials.
1'21'' and water. The N layers are arranged symmetrically with respect to the central support layer 12 with respect to layer thickness and layer properties. 1 to N may be isotropic or orthotropic and include a PVDF damping (or separation) layer. The cross-section in Figure 4 shows a continuous conductive film on the outer surface of the PVDF layer 21', 21''. It should be noted that

As previously mentioned, the metallization patterns 15', 15'' on the PVDF layers 21', 21'' of FIGS. 1 and 2 define an array arrangement, with a pair of opposing metallization surfaces 15', 15'', respectively. and their intermediate PVDF material constitute the hydrophone elements 16. Similar metallized patterns appear on both sides of the layers of the embodiment of FIGS. 1 and 2. The shape of each hydrophone element is Although optional, high packing density is desirable to obtain the noise reduction benefits of spatial averaging. To meet this requirement, square or rectangular patterns are used to reduce the unmetallized gaps between elements. It would be good to do so.
The size, quantity, and grouping of hydrophone elements are determined by well-known receive array design dimensions. Electrical connections are made by conductors 151 to the metallized surface of each hydrophone element.

Hydrophone array 10 includes a plastic or rubber coating (not shown) surrounding the array 10.
The electrical connections to the array are waterproofed by the Since both PVDF layers 21', 21'' are in contact with the acoustic field provided by the aqueous environment in which the array is used, the array 10 operates in hydrostatic mode, the sensitivity of which is determined by the piezoelectric constant gh. The sensitivity of each transducer element 151 will be the same since there is no bending mode due to the support layer 12, since the support layer 12 has the necessary stiffness to cancel 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. The corresponding layer can then be formed of an isotropic or orthotropic plate. Layer 21' has the same thickness and the same properties as layer 21''.
That is, layer N' has the same thickness and the same characteristics as layer N''.

Although the present invention has been described above with reference to embodiments, it will be apparent 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 the first
FIG. FIG. 3 is an isometric view of another embodiment of the invention. FIG. 4 is a sectional view taken along the line - in FIG. 3. (Explanation of symbols), 10: Array assembly, 1
2: Support layer, 14', 14'': Composite layer, 15', 1
5″: electrode, 21′, 21″: PVDF layer.

Claims (1)

[Scope of Claims] 1. A planar support layer; and a first piezoelectric polymer layer adhered on both sides of the support layer, each of the first piezoelectric layers being oriented in a direction parallel to the plane of the first layer. a first piezoelectric polymer layer that generates an electrical signal that is primarily generated by strain caused by the material; a second layer adhered to said first layer, each having a high acoustic attenuation constant; and said second layer. a third piezoelectric polymer layer adhered to the third piezoelectric polymer layer, the third piezoelectric polymer layer providing an electrical signal primarily in response to pressure applied in a direction perpendicular to the plane of the third layer; 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. 2. The transducer of claim 1, wherein the second layer is a polymer layer. 3. The transducer of claim 1, wherein the second layer is a PVDF layer. 4. The transducer of claim 1, wherein the planar support layer is a rigid layer resistant to bending. 5. The transducer of claim 1, wherein said support layer is a glass fiber reinforced resin layer having a thickness that provides sufficient rigidity for stable hydrophone response in the operating frequency band. 6. The conductive film of the third layer has at least one film patterned to provide an electrically isolated region on one surface of the layer, the region being a transducer of the third layer. 2. A transducer as claimed in claim 1, defining transducer elements comprising an array of elements. 7. The transducer of claim 1, wherein the first layer is a thin layer that is more sensitive to strain in the support layer than to acoustic signal pressure. 8. The transducer of claim 1, wherein said third layer is a thick layer that provides electrical signals from pressure applied primarily in a direction perpendicular to its plane.