SU1739507A1 - Nonlinear parametric acoustic receiver - Google Patents

Abstract

Use: for receiving four-wave sound waves in an acoustic resonator. The acoustic resonator is a round thin plate 1 made of solid material. In the center of the plate, a cylindrical emitter 2 of pumping longitudinal waves is installed coaxially to it. The plate is a combination frequency emitter. The radiation pattern of the radiator (plate) is formed in the wave zone, i.e. at the distance where the hydrophone receiver 3 is located. The rotation of the radiation pattern is carried out by synchronous rotation of the entire system, for example, around the center of the plate. 1 il.

Description

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This invention relates to underwater acoustics and can be used to receive sound waves propagating in a liquid.

A parametric hydrophone is known for receiving a low-frequency (LF) sound wave, which contains a high-frequency (HF) emitter and a receiver of sound waves located in an aqueous medium at a distance L from each other. In such a hydrophone, which is a traveling-wave antenna, nonlinear interaction of a low-frequency signal wave I and a high-frequency pumping wave occurs, resulting in the formation of combination-frequency waves a) ± O.

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

Known aperture parametric acoustic receiver containing consistently located on one

two high-frequency pump emitters, a plane-parallel layer of a nonlinear medium, whose impedance coincides with the impedance of the surrounding liquid, and a receiver spaced by R0 from the layer. The distance RO is determined by the distances eh, d2 between the pump emitters and the layer, as well as the frequencies (1) 1.0) 2 pump emitters and the frequency Q of the received low-frequency wave (Ro Oe (-) 1 where QO - - ftJ2 ± Q.)

The disadvantage of such a parametric receiver is the complexity of the design, due to the presence of two pump emitters and a nonlinear layer separated by a large distance.

The aim of the invention is to simplify the design.

The goal is achieved by the fact that in a nonlinear parametric acoustic receiver containing a coaxially mounted layer of a nonlinear medium and

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acoustic emitter pumping longitudinal waves and receiving hydrophone, a nonlinear medium layer made in the form of a circular plate made of solid material, in which a pump emitter in the form of a cylinder is installed coaxially, and the product of the density and velocity of longitudinal waves in the plate material differs from the product of density and sound speed in the environment and the radius R of the plate is determined by the ratio

R .l (t +3/4), (1)

where co is the excitation frequency of the pump emitter,

c, v is the velocity of the longitudinal waves and the Poisson’s ratio for the material of the plate,

m is an integer

plate thickness h is determined by the ratio

(2)

where D. is the wavelength of the low frequency QB environment;

/ C is the wavelength of the combination frequency “From 2 ° ± QB to the plate material;

n is an integer

the distance between the receiver and the plate D Russia, where RF is the Fraunhofer distance at the frequency (ik for the plate.

The invention is based on the use of four-wave interaction in an acoustic resonator for receiving sound waves. The acoustic resonator is a round thin plate made of a solid material whose impedance for longitudinal waves (i.e., the product of the material density and the velocity of the longitudinal waves in it) is different from the impedance of the surrounding medium (liquid). In the center of the plate, coaxially to it, there is a cylindrical pump radiator of longitudinal waves, the frequency w of which is chosen in accordance with relation (1). When a radiator is excited in a plate, a running cylindrical (diverging) wave with a wave vector K arises. Since the radiator is in the center of the resonator plate, a cylindrical wave running from the resonator edge toward the center (converging) with the same frequency also occurs in it. and and the wave vector -K. When a low-frequency wave with a frequency Q and a wave vector K falls on a plate, the three said waves interact due to the cubic nonlinearity of the plate material. The result of this interaction is the generation of a fourth wave with a frequency (Ds (i) + (i) ± QH) of the wave vector - - - S--.

Rum Kz K - K ± K ± K, which is emitted into the surrounding plate. Thus, the plate is a combination emitter of frequency% 2 ± Q. To efficiently emit a wave of the ultrasonic frequency to the plate, it is necessary to ensure the acoustic matching of the plate with the environment, for which the thickness h of the plate is chosen in accordance with relation (2). Radius r

the plate is determined by the required width of the 6b radiation pattern and is related to it by the ratio

20

R "A / 20b

(3)

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As is known, the pressure field of such a radiator is determined by the phase distribution of the sources of the combination frequency 0s over the aperture of the (flat) plate, which, in turn, is determined by the low-frequency wave (Q, K). With a normal incidence of a wave (Q, K) on a plate, the sources of the combinational frequency are common-phase aperture of the plate, and it creates a beam (Shz, Kb) along the acoustic axis. The radiation pattern of the radiator (plate) is formed in the wave zone, i.e. at a distance determined by the relation (3) where the receiver is located.

When the wave (O, K) is incident on the plate, the secondary sources of the frequency ufe appear on the plate aperture and it emits a wave (SW, Ks) at an angle to the acoustic axis, resulting in the amplitude of the signal received by the hydrophone. This is the mechanism for the formation of the DN of the proposed parametric hydrophone.

Since the device uses only one pump emitter, which is located in the solid-state plate (nonlinear layer) and represents one whole, the design of the proposed device is simpler than the known one

It should be noted that the parametric receiver is highly efficient due to both the strong acoustic nonlinearity of the plate material and the possibility of creating a more intense pump wave in a solid-state resonator plate than in water, where the pump intensity is limited by the cavitation threshold.

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

Nonlinear parametric acoustic receiver contains a round metal plate 1 of solid material. In a specific embodiment, plate 1 is made of copper (C 3.5-110 cm / s, 3). The plate radius R, its thickness h is chosen in accordance with ratios (1, 2) and equal, respectively, 25 and 2.3, see. In the center of plate 1, a cylindrical emitter 2 of rigid waves is rigidly fixed. The cylindrical emitter 2 is installed in the center of the plate 1 and is a solid cylinder. To ensure the effective interaction of the pump waves and the signal, it is necessary that the radius r of the radiators and the radius R of the plate satisfy the relation. In a specific embodiment, the radius g is 1.5 cm, its height h is 2.3 cm. The emitter frequency is selected in accordance with relation (1) and coincides with the resonant frequency of the fourth mode () of plate 1, equal to f a) / 2 TE 33 kHz. On the acoustic axis of the plate 1 at a distance D, selected in accordance with the ratio D D / Rf (in the concrete variant D 10 m), a hydrophone 3 is installed (for example, a hydrophone of type 8103, 8100 from Brühl and Kjерr).

Parametric receiver works as follows.

When a cylindrical emitter is excited at the indicated frequency in plate 1, resonant oscillations are excited at the same frequency. When a low-frequency wave propagating in water with a frequency F Q / 27T 10 kHz (L 15 cm) is incident on the plate 1, thickness oscillations are excited in the plate at the combination frequency fs Ok / 2 n 76 kHz. At this frequency, the wavelength AS in the copper plate is 4.6 cm. The plate thickness, as indicated above, is chosen to be 2.3 cm, i.e. half wavelength (). Thus, plate 1 emits an acoustic wave with a frequency of fs 76 kHz into the environment.

Claims (1)

The radiation pattern of plate 1, as an emitter, is formed at a distance Vf, where the hydrophone 3 is installed. The width of the Eb pattern of the parametric hydrophone is determined by the relation (3) and in a particular variant is 6b 15 °. Rotation of the radiation pattern is carried out by synchronous rotation of the entire system, for example, around the center of the plate 1. Formula of the invention A nonlinear parametric acoustic receiver containing coaxially mounted longitudinal wave pumping emitter, a nonlinear element and a receiving hydrophone differing from that. that, in order to simplify the design, the nonlinear element is made in the form of a circular plate of solid material, and the pump emitter is cylindrical and mounted coaxial to the plate, while the radius R of the plate is defined by the relation: R - l (t + 3/4) where o) is the excitation frequency of the pump emitter; c, V is the velocity of the longitudinal waves and the Poisson’s ratio for the material of the plate; m is an integer plate thickness h is defined by the relation: where L is the wavelength of low frequency Q in the environment; As is the wavelength of the combination frequency 2l ± QB of the plate material; n is an integer and the distance between the receiving hydrophone and the plate D 6f, where Rf is the Fraunhofer distance at frequency ah 5 for the plate. L