JP2552362B2 - Underwater acoustic receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an underwater acoustic wave receiver, and more particularly to an underwater acoustic wave receiver used for measurement of underwater sound and the like.

[Prior Art] Conventionally, an underwater acoustic wave receiver (hereinafter referred to as an organic piezoelectric material wave receiver) used for underwater sound measurement or the like is disclosed in the following document as an example.

References; Journal of the Acoustical Society of America, {Journal of Acoustical
Society of America, 80 , [2], (August 1986),
(US), P.375-381: Mark B. Moffett et al, “A ρh”
ydrophone "} The organic piezoelectric material wave receiver disclosed in the above reference is a flat plate made of a polymer material having viscoelasticity and piezoelectricity for measuring underwater sound. Is characterized by a density close to that of water and a speed of sound close to that of water, which makes this organic piezoelectric material more than the acoustic impedance of previous ceramic receivers. Since the wave receiver has a value that is closer to the acoustic impedance of water, it is a wave receiver with good acoustic characteristics that has acoustic transparency up to a high-frequency region when receiving underwater sound waves. This organic piezoelectric material receiver, which is not attached to a housing or the like, that is, placed in a free sound field, is made of a polymer material having viscoelastic properties. The sharpness of resonance is small compared to
Moreover, it had excellent characteristics that a flat wave receiving sensitivity characteristic was obtained even in the vicinity of resonance.

[Problems to be Solved by the Invention] However, in the conventional organic piezoelectric material wave receiver as described above, an integrated wave receiver in which organic material piezoelectric electrons are molded with a viscoelastic material is formed, and, for example, natural vibration or other When mounted on a case or the like that vibrates by virtue of this, when the vibrating case flexibly vibrates, the organic piezoelectric material receiver undergoes bending deformation or extension deformation. Further, if the vibrating housing undergoes translational vibration, translational vibration based on this vibration is produced. In this case, stress due to bending deformation, extensional deformation, or stress due to translational motion (called acceleration noise) is induced in the organic material piezoelectric electrons, and stress due to the sound wave signal arriving at the receiver is generated. As a result, the desired wave-reception sensitivity characteristic of the wave receiver is deteriorated. Further, it is possible to use an extremely soft material as the molding material so as not to receive the sound of these deformations, but in this case, there is a problem that the strength of the wave receiver cannot be maintained.

The present invention relates to a wave receiver in which organic material piezoelectric electrons are molded. In the wave receiver, stress caused by the above-mentioned bending deformation, extension deformation, and translational motion deteriorates the wave receiving sensitivity, and a soft mold for removing the stress. This was done to eliminate the drawback that the strength of the wave receiver cannot be maintained when using a material, and its purpose is to provide an underwater acoustic wave receiver with excellent sound wave reception sensitivity characteristics. is there.

[Means for Solving the Problems] In the underwater acoustic receiver according to the present invention, organic material piezoelectric electrons are bonded to both surfaces of a rectangular thin metal flat plate having acoustic transparency in water, and electrodes are provided on the outside thereof. Organic piezoelectric material receiver with sandwich plate structure (hereinafter referred to as composite piezoelectric plate)
A first mold body obtained by molding the composite piezoelectric plate into a thin plate shape with a viscoelastic material that is soft and has good acoustic transparency (for example, urethane rubber having low hardness), and the first mold body is opposed to the first mold body. The first mold body is formed into a plate shape with a viscoelastic material (for example, high hardness urethane rubber or the like) that is hard and has good acoustic transparency, while leaving a pair of side surfaces (for example, long side surfaces of a rectangle) among the side surfaces to be formed. It is composed of a second molded body.

[Operation] In the present invention, first, the composite piezoelectric board having a heavy structure in which the organic piezoelectric board is attached to the metal plate having good sound permeability in water is molded with the soft viscoelastic material. The resonance frequency of translational vibration determined by the mass and the stiffness of the molding material (first molding body) is reduced to the target frequency or lower.

Furthermore, in this case, the electrodes attached to the organic material piezoelectric plate bonded to the metal plate also have a thickness in the range of good acoustic transparency, and the composite piezoelectric plate formed of a rigid metal plate has a second moment of area related to bending deformation. Since it becomes large, the bending vibration and extension vibration of the piezoelectric plate are raised above the target frequency.

In addition, since the first mold body for molding the composite piezoelectric electronic plate is made of a soft viscoelastic material to reduce its stiffness, when the vibration displacement is transmitted to the composite electronic plate through this molding material, the target frequency is reduced. In the range, the vibration noise of the compound piezoelectric plate vibrating housing is reduced by refraction vibration and extension vibration based on bending vibration and acceleration noise based on translational vibration of the vibrating housing, and the stress due to the above vibration displacement is removed.

Further, a two-stage molding method in which the first mold body molded with the composite piezoelectric electronic plate is molded with a hard viscoelastic material while leaving a pair of opposite side surfaces of the mold body to form a second mold body. Since the first mold body has a low stiffness, the deformation of the mold material in the thickness direction is freely transmitted in the lateral direction, and the longitudinal elastic modulus of a value smaller than the bulk elastic modulus in the thickness direction. It is possible to realize a soft molding material structure applicable to.

[Embodiment] FIG. 1 is a structural schematic view of an organic piezoelectric material wave receiver constituting an underwater acoustic wave receiver according to an embodiment of the present invention. 1A is a plan view and FIG. 1B is a sectional view taken along the line AA shown in FIG.

In the figure, reference numeral 6 denotes a composite piezoelectric plate which constitutes an acoustic sensor of an organic piezoelectric material wave receiver, in which a plate-shaped organic material piezoelectric plate 3 is joined to the upper and lower surfaces of a metal plate 4, and the organic material piezoelectric The electrodes 2 are attached to both surfaces of the plate 3. Reference numeral 7 denotes a first molded body obtained by molding the composite piezoelectric panel 6, which is a first molded body of the composite piezoelectric panel 6 using a soft viscoelastic molding material, for example, a low hardness urethane rubber molding material I1. The molded body of FIG. Further, the first mold body 7 is made of a hard molding material having viscoelasticity, for example, a molding material of high hardness urethane rubber.
The second mold body is formed by molding using II5.
Constitutes the molded body of. In this case, the second mold body 8 is formed with the side surface 9 of the first mold body 7 left, that is, only the side surface 9 is not covered with the mold material II5, and the organic piezoelectric material wave receiver according to the present invention is formed. It is what constitutes.

When this wave receiver is mounted as an underwater acoustic wave receiver, the lower surface 10 of the second molded body 8 is bonded to a housing or the like that generally vibrates due to natural vibration or the like. When the wave receiver is put to practical use, the surface of the second molded body 8 other than the lower surface 10 is covered with fluid (water). The side surface 9 of the first molded body 7 is not molded with the molding material II5, so that it contacts the fluid in the same manner.

Next, the operation will be described. When a sound wave signal of, for example, an underwater sound arrives at the underwater acoustic receiver (hereinafter referred to as a receiver) from a distance through a fluid, the incoming sound wave is generated by the molding material I1,
Since the mold material II5 and the organic material piezoelectric plate 3 each have a value close to the acoustic impedance of the fluid, and the electrode 2 and the metal plate 4 are thin, the mold material II5 does not reflect within the target frequency range. , The molding material I1, the electrode 2, the organic material piezoelectric plate 3, and the metal plate 4. Then, the organic material piezoelectric plate 3 responds to the pressure of the incoming sound wave (sound pressure) by the electrode 2
In between, a voltage is induced and a sound wave is received. On the other hand, since the lower surface 10 of the second molded body is mounted on a vibrating casing or the like, the vibration displacement of the casing is transmitted to the first molded body 7. Then, the vibration displacement is transmitted from the first mold body 7 to the composite piezoelectric plate 6.

In the above configuration, when the vibration displacement is transmitted to the composite piezoelectric plate 6 via the molding material I1, in order to remove the stress due to the vibration displacement, that is, in the target frequency range, the composite pressure based on the bending vibration of the vibrating casing is used. In order to reduce the flexural vibration and extension vibration of the electronic plate 6 and the translational vibration based on the translational vibration of the vibrating housing, the stiffness of the molding material I1 of the first molding body is reduced. The explanation of the concrete measures for reducing the stiffness will be described later.

In addition, the organic material piezoelectric plate 3 is attached to the metal plate 4 having an appropriate thickness (see Table 1) within a range having acoustic transparency to form a heavy composite piezoelectric plate 6, thereby The resonance frequency of the translational vibration determined by the mass of the electronic plate 3 and the stiffness of the molding material I1 is lowered below the target frequency.

Further, the organic material piezoelectric plate 3 attached to the metal plate 4
By forming a composite piezoelectric plate 6 by using a rigid metal plate 4 having an appropriate thickness (see Table 1) in both upper and lower sides of the electrode 2 of FIG. The second moment is increased so that the bending vibration and the extension vibration of the organic material piezoelectric plate 3 are increased to the target frequency or higher.

Here, a concrete measure devised in the present invention and its effect in order to reduce the stiffness of the molding material I1 will be described.

The stability of the molding material I1 is obtained by molding the first molding body 7 with the hard molding material II5 and by molding with the molding material II5 while leaving a pair of side surfaces 9 among the opposite side surfaces of the plate of the first molding body 7. I made it lower. That is, for example, when the entire first mold body 7 is aged with a hard mold material II5, the bulk modulus of elasticity of the first mold body 7 shows a large value. When the molding material II5 is used to mold a pair of side surfaces that face each other (that is, the side surface 9 is not covered with the molding material II5), the deformation in the thickness direction of the molding material I1 is freely transmitted to the side surface 9 direction. It is possible to realize a soft molding material to which a longitudinal elastic modulus smaller than the bulk elastic modulus can be applied in the thickness direction.

In this structure, since the side surface 9 of the first mold body is in contact with the fluid, a deformation that tends to displace the fluid occurs on the side surface, so that the fluid receives a load. This load is on the side 9
Is determined by the radiation impedance (resistance that makes it difficult for sound waves to effectively propagate) that is a function of the size of and the wave number of the fluid, but in the present invention, the side surface shape of the first mold body 7 is a very elongated rectangle (the beam shape in Table 1). The radiation impedance is made extremely small to the extent that it can be ignored by setting the length to 1) and selecting a smaller area. By adopting such dimensions, the molding material I1 can freely extend in the direction of the side surface 9 of the first molding body 7.

Therefore, although the wave receiver of the present invention having the above structure has a strong structure in which the second mold body 8 forms the outer side, the outer side of the composite piezoelectric plate 6 is molded with the soft molding material I1. Therefore, it is possible to obtain an underwater acoustic wave receiver having excellent characteristics that the surface of the organic material piezoelectric plate 3 is not subjected to unnecessary shearing force.

Next, an example obtained based on specific numerical values based on the configuration of the organic piezoelectric material wave receiver of the present invention as described above will be described using calculation results. The numerical values shown below are examples and do not limit the present invention.

FIG. 2 is a schematic diagram showing a vibration system model used for explaining an embodiment of the organic piezoelectric material wave receiver according to the present invention. 2 (a) is a plan view of the wave receiver, FIG. 2 (b) is a sectional view,
2 (d) is a side view, and FIG. 2 (c) is an enlarged view of a portion B shown in (d). 1 to 10 are the same reference numerals used for the portions corresponding to the reference numerals used in the description of the embodiment of FIG.

In FIG. 2, as an example of a simple model, the part of the second mold body 8 is a rigid body, and the lower surface 10 sine-oscillates with a uniform amplitude x _I (where ω is an angular frequency). . The composite piezoelectric plate 6 having a layered structure is considered to be a beam having a long length and a short width. Further, the first mold body 7 is assumed to be composed of a viscoelastic material having structural damping independent of ω, and its complex longitudinal elastic coefficient is E ₁ ^* = E ₁ (1 + j
θ). Where E ₁ is the storage Young's modulus, θ is the loss tangent, j
Is an imaginary unit. The viscoelastic support thickness of the first mold body 7 is h ₁ as shown in FIG. 2B, the width of the beam having the layer structure is b ₁ as shown in FIG. As shown in FIG. 2 (c), the thickness of the electrode 2 is h ₃ , the organic piezoelectric plate 3
Is h ₄ , the thickness of the metal plate 4 is h _5, and the length of the beam is l. Further, the density of the organic material piezoelectric plate 3 is ρ ₂ , the Young's modulus is E ₂ , the density ρ ₁ and Young's modulus of the electrode 2 are E _1, and the density ρ ₀ and Young's modulus of the metal plate 4 are E ₀ . . The beam amplitude is represented by x _II . Then, the target frequency range is set to f ₀ to 10f ₀ (where f ₀ is the lower limit frequency).

Table 1 shows the dimensions and physical constants of the members forming the molding material I1 and the beams. The elastic modulus (Young's modulus) was selected with reference to the elastic modulus of rubber or the like that actually exists.

As shown in Table 1, the storage Young's modulus E ₁ of the first mold body is 5 × 10 ⁷ N / m ² , 5 × 10 ⁶ N / m ² , 5 × 10 ⁵ N / m ² , 10 ⁵ N /
Four model samples each No.1 of m ^2, No.2, No.3,
It was set as No. 4.

FIG. 3 is a diagram showing the frequency response characteristics of the beam of each sample obtained by calculation under the parameter conditions of Table 1. In the figure, the horizontal axis is the normalized frequency. The vertical axis represents the normalized vibration displacement transmissibility (also referred to as acceleration transmissibility), which is shown by the maximum amplitude x _{II max} of the beam amplitude normalized by the vibration x _I of the lower surface 10 of the second mold body 8. It is a thing.

As can be seen from FIG. 3, when a hard viscoelastic material such as sample No. 1 is used, the vibration displacement transmissibility is 1 or more in the target frequency range, and the vibration damping effect cannot be realized. In addition, Sample No. 2 and No. 3 are cases where a viscoelastic material softer than No. 1 is used, but in the target frequency range, translational vibration resonance of the beam appears, and the amplitude at the resonance point is about It has been enlarged 2.3 times. However, when a soft viscoelastic material such as Sample No. 4 is used, the translational vibration resonance of the beam is reduced to about 0.43f ₀ , and the vibration transmissibility is attenuated to 0.3 or less in the target frequency range. There is.

As described above in detail regarding the examination result of FIG. 3,
Vibration is damped by selecting a small elastic modulus of the viscoelastic material of the molding material I1, that is, a storage Young's modulus E ₁ , and selecting a large mass of the composite piezoelectric plate 6 having a layered structure by using the metal plate 4 and the electrode 2. However, the acceleration noise due to the translational vibration is reduced, and the sound wave receiving sensitivity characteristic is improved.

FIG. 4 is a diagram showing the vibration modes of the beam at f ₀ of sample No. 4. The horizontal axis represents the position coordinates of the beam in the x direction shown in FIG. 2B, and the vertical axis represents the beam amplitude. As can be seen in the figure, the amplitude of the beam is almost irrelevant to the position coordinates of the beam and is constant, so that the first bending vibration mode does not appear significantly. Further, it can be seen that the displacement is attenuated because the vibration mode at f ₀ is 1 or less.

Further, FIG. 5 is a diagram showing the vibration mode of the beam in 10f ₀ of sample No. 4. The horizontal axis and the vertical axis are the same as those in FIG. Even in the case of 10f ₀ in FIG. 5, it does not appear in the first bending vibration mode as in FIG. 4, and the beam amplitude is smaller than that in the case of f ₀ in FIG. Indicates that it is greatly attenuated. This is because the rigidity of the beam is increased by adopting the structure in which the metal plate is attached to the organic material piezoelectric plate as described in the embodiment.
This shows the effect of increasing the resonance of bending vibration to 10f ₀ or higher (range greater than the target frequency).

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained by adopting the configurations shown in the following items.

1) The whole underwater acoustic wave receiver has a strong structure because the integral wave receiver including the composite piezoelectric plate molded by the soft viscoelastic material is further molded by the harder viscoelastic material.

2) Since the outer side of the composite piezoelectric panel is molded with a soft molding material, unnecessary shear force is not applied to the surface of the organic piezoelectric panel.

3) Since the viscoelastic material used for molding is selected so as to have almost the same acoustic impedance as that of water, it has good permeability of underwater sound waves.

4) Since the specific gravity of the molding material is selected to be approximately the same as the specific gravity of water, the underwater weight of the receiver is light.

5) The organic material piezoelectric wave receiver has a laminated structure of an organic material piezoelectric plate and a metal plate, and since it has a large bending rigidity, the flexural vibration mode does not appear in the target frequency range, and therefore, the underwater acoustic wave receiver has good reception sensitivity. A wave instrument is obtained.

[Brief description of drawings]

FIG. 1 is a schematic structural view of an underwater acoustic receiver showing an embodiment of the present invention, FIG. 1 (a) is a plan view thereof, and FIG. 1 (b) is A- shown in (a). A sectional view, FIG. 2 is a vibration system model diagram used for explaining an embodiment of the underwater acoustic receiver according to the present invention, FIG. 2 (a) is a plan view, FIG. 2 (b) is a sectional view, 2 (c) is an enlarged view of the portion B of (b), FIG. 2 (d) is a side view, and FIG. 3 is the frequency response characteristics of the beam of each sample calculated under the parameter conditions of Table 1. Diagram showing,
FIG. 4 is a diagram showing the vibration mode of the beam at f ₀ of sample No. 4, and FIG. 5 is a diagram showing the vibration mode of the beam at 10 f ₀ of sample No. 4. In FIG. 1, 1 is a mold material I, 2 is an electrode, 3 is an organic material piezoelectric plate, 4 is a metal plate, 5 is a mold material II, 6 is a composite piezoelectric plate, 7 is a first mold body, and 8 is The second mold body, 9 is a side surface, and 10 is a lower surface.

Claims (1)

(57) [Claims] 1. An organic piezoelectric material wave receiver having electrodes on an organic piezoelectric material bonded to both sides of a rectangular metal plate, and a rectangular plate-shaped first plate formed by molding the organic piezoelectric material wave receiver with a soft viscoelastic material. And a second mold body formed outside the first mold body and molded with a viscoelastic material that is harder than the viscoelastic material while leaving a pair of opposite side surfaces of the first mold body. Underwater acoustic receiver characterized by consisting of.