RU2003237C1 - Nonlinear parametric acoustic receiver - Google Patents

Abstract

The invention relates to hydroacoustics and can be used to receive sound waves propagating in a liquid. The invention is aimed at increasing the conversion coefficient. The parametric receiver contains a nonlinear element made in the form of a rotation paraboloid, at the top of which a pump emitter 1 il

Description

The invention relates to hydroacoustics and can be used to receive sound waves propagating in a liquid,

A parametric hydrophone for receiving a low-frequency (LF) wave is known, comprising high-frequency (HF) emitter and receiver of sound waves located in the aquatic environment at a distance L from each other. In such a hydrophone, which is a traveling wave antenna, a nonlinear interaction of the low-frequency signal wave QH of the high-frequency pump wave occurs, and as a result, the waves of combination frequencies o) ± QL

The disadvantage of such a hydrophone is low efficiency due to the small value of the parameter of acoustic nonlinearity of water.

Technical solutions are known that are free from this drawback, for example, an aperture parametric receiver, which contains two high-frequency pump emitters arranged in series on the same axis, a plane-parallel layer of a nonlinear medium, the impedance of which coincides with the impedance of the surrounding liquid, and located at a distance D from hydrophone layer. The distance D is determined by the distances cH, d2 between the pump emitters and the layer, as well as the frequencies ol, (ao, pump emitters and the frequency L of the received low-frequency wave DQ (W2 / d2-wi / di) 1, where co -ca ± Q.

A disadvantage of such a parametric receiver is the design complexity associated with the presence of two pump emitters and a nonlinear layer spaced apart a large distance.

A non-linear parametric acoustic receiver is known, which contains a cylindrical-shaped longitudinal longitudinal acoustic pump emitter mounted in the center of a round plate made of solid material, coaxial. A receiving hydrophone is installed at a distance D from the plate (D R $, where Нф is the Frauigofer distance for the plate at a frequency ± Q. The radius of the plate R0 and its thickness h are determined, respectively, by the relations

Ro. 3C (m + 3 / n

(At VI - 1G

h p “L (2)

where ft) is the excitation frequency of the pump emitter;

C, v is the longitudinal wave velocity and Poisson's ratio for the plate material;

m, n 1, 2, 3 ... are integers;

L-wavelength of low frequency Q in the environment;

As is the wavelength of the Raman frequency cos.

The disadvantage of such a receiver is the low conversion factor due to the need to position the hydrophone at a large distance D from the plate, where the radiation pattern of the plate is formed, such as emitters.

The aim of the invention is to increase the conversion coefficient.

This goal is achieved by the fact that in a nonlinear parametric acoustic receiver containing an axially symmetric nonlinear element of solid material, in which is aligned with it, a pump emitter in the form of a cylinder, as well as mounted on one

axes with them are a receiving hydrophone, a nonlinear element is made in the form of a rotation paraboloid, and a pump emitter is installed at its top, and the opening radius of the paraboloid is determined according to

the ratio

, lC (t + 3 / n),.,

HOR -1 /

35

-iHm ± 3 /; f -p. about)

z L wpv-i -v7 J

where C, v is the longitudinal wave velocity and Poisson's ratio for the paraboloid material;

(i is the pump excitation frequency;

t 1,2,3 ...

P is the focal parameter of the paraboloid, and the receiving hydrophone is located at a distance from the top of the paraboloid

D p

Qx

/ 1 + Щ

 Oh)

where ± Q, q 1, 2, 3, ...

Q is the frequency of the received sound wave.

55 The inventive idea is to

focusing the rf wave generated by the interaction of acoustic waves in the cavity. In this case, both the conversion of the frequency of the low-frequency signal and the focusing of the resulting high-frequency combination wave are performed with

with the help of one structural element - a rotation paraboloid made in a certain way, which is an acoustic resonator. The radius of the opening of the paraboloid is selected in accordance with relation (3) (the radius of the opening of the paraboloid is the radius of the circle formed when the paraboloid is cut by a plane perpendicular to its axis and drawn on

distance H / Xe / 2p from its peak). Therefore, upon excitation of a pump emitter located at the top of the paraboloid (its acoustic center) at its resonant frequency CD, waves traveling from the center and to the center of the cylindrical wave form a standing cylindrical wave in the bulk of the paraboloid. When an LF wave with a frequency of O is incident on a paraboloid, due to the odd nonlinearity of the paraboloid material, these waves (pump and signal) interact. The result of this interaction is the creation of a wave with a combination frequency .a q ± Q (q 1, 2, 3 ...), which is emitted into the environment. Thus, the paraboloid is a Raman wave emitter ws 2ш q ± Y. The pressure field of such a radiator is determined by the phase distribution of the Raman frequency sources (as according to its aperture, which, in turn, is determined by the LF wave. When the LF wave is incident along the axis of the paraboloid, the sources of Raman frequency will be distributed over the surface of the nonlinear element according to a parabolic law, therefore, at a point on the axis of the paraboloid (from the side of its concave surface) located at a distance, With the help of relation (4), the wave will be focused (see the mathematical application). As a result of focusing the cos wave, the pressure Ps at this point where the hydrophone is located increases significantly, which ensures an increase in the conversion coefficient (see mathematical application).

When the LF wave is incident on the layer at an angle to its axis, the out-of-phase of the secondary sources appears along the aperture of the paraboloid; as a result, its amplitude of the signal received by the hydrophone decreases. This is a mechanism for shaping the bottom line of the proposed receiver; the width # about its bottom (as aperture type antennas) is determined by the radius p0 of the paraboloid opening and is associated with it by the ratio

, and L / 2 / 9o

(5)

An undoubted advantage of the proposed device is its small, compared with the prototype, dimensions. This is ensured by a closer position of the receiving hydrophone to the non-linear element. It should be noted that the traditional (without pumping) use of a single paraboloid as a focusing device will not lead to an increase in the conversion coefficient, because: firstly, the low-frequency wave passes through a thin layer () almost without reflection, and, in secondly, focusing of the LF wave (due to the long wavelength A) is ineffective 5 on.

In the proposed device, first

in the volume of the parabolic layer occurs

frequency conversion up (Q,

after which the focus is

0 high frequency cos.

The drawing shows a block diagram of one of the variants of the proposed device.

The non-linear parametric acoustic receiver 5 contains a non-linear element of solid material made in the form of a paraboloid 1 of revolution. In a specific embodiment, the paraboloid

0 1 is made of copper (C 3,5 105,, 3).

The thickness h and the radius of the opening of paraboloid 1 are selected in accordance with the relations (2, 3) and are equal to 1.15 cm and 24 cm, respectively, in a particular embodiment. The focal parameter of the paraboloid is 1 P 1 m.

At the top of the paraboloid 1, a radiator 2 of longitudinal waves, made in the form of a continuous cylinder, is coaxially mounted to it. To ensure effective

In the interaction of the pump and signal waves, it is necessary that the radius r of the emitter and the radius of the opening of the paraboloid satisfy the relation. In a specific embodiment, the radius of the emitter g is 1

5 cm, its height coincides with the thickness h and is equal to 1.15 cm. The frequency of the emitter is selected in accordance with relation (3). In a particular embodiment, it coincides with the resonant frequency of the eighth mode (m 8) and is equal to f (L / 2l: 70 kHz.

On the acoustic axis of a nonlinear parametric receiver, at a distance D from the top of the paraboloid, selected in accordance with relation (4) from the side

5 of its concave surface (in a specific embodiment, D 1.14 m) a hydrophone 3 is installed (for example, a hydrophone of type 8103, 8100 from Bruhl and Kier).

The parametric receiver operates as follows.

When the emitter 2 is excited at the resonant frequency of a paraboloid in its volume, a stagnation wave is excited at the same frequency. When an LF wave propagating in water with a frequency F ЈУ27Г 10 kHz is incident on paraboloid 1, these waves interact in its volume, as a result of which thick vibrations are excited in it at the combination frequency fs rr

150 kHz. At this frequency, the wavelength in copper is As 2.3 cm. The thickness of the paraboloid, as indicated above, is chosen to be 1.15 cm, i.e. half wavelength (n 1). Thus, paraboloid 1 emits into the environment an acoustic wave with a frequency f s 150 kHz, which focuses at the point where the receiving hydrophone 3 is located. The width Or, the DM of the parametric receiver is determined by the relation (5), and

in a particular embodiment, is $ 0 ± i150. The rotation of the beam is carried out by synchronous rotation of the entire system, for example, around the apex of a paraboloid. Note that in the prototype device, the distance between the pump emitter and the hydrophone was

it would be HF § § в в 20 m (A ;; 1 cm is the wavelength with a frequency fs 150 kHz in water), and the floor level at the hydrophone would be PF / D. 20 / 1.14 17.5 times less than in the proposed device, i.e. the conversion coefficient of the proposed receiver (with equal aperture) high / e conversion coefficient of the receiver-prototype of 17.5

time,

(56) Copyright certificate of the USSR

No. 422197, class 06 V 1/00.

Nazarov V.E., Sutin A.M. Theory of a parametric sound receiver with a nonlinear layer. Acoustic Journal, 1989, vol. 35, No. 5.0.877-881.

Formula a inventions

A NONLINEAR PARAMETRIC ACOUSTIC RECEIVER containing an axially symmetric nonlinear element of solid material and mounted in parallel with it a pump emitter in the form of a cylinder and a receiving hydrophone, characterized in that the nonlinear element is made in the form of a rotation paraboloid, and the pump emitter is installed at its apex, while the radius the opening pQ of paraboloid rotation is determined by the ratio

 l with (ggn- -y) PQ

7T

1 1 p c- (IT. 2 aJFvT T

"

where c, v are the longitudinal wave velocity and Poisson's ratio for the paraboloid material, respectively;

a) is the excitation frequency of the pump emitter;

m is an integer;

P is the focal parameter of the paraboloid

rotation

and the receiving hydrophone is located at a distance from the top of the paraboloid

(1 ± Ј (

where ws 2wq ± Q; q 1,2,3, ...;

fi is the frequency of the received sound wave.