RU1840780C - Magnetic induction type underwater sound transducer - Google Patents

Abstract

FIELD: instrument making.

SUBSTANCE: invention relates to field of hydroacoustic measurement technology. Technical result is achieved by means of that device contains case with located in it field magnet and conductor plate, adjoining to field magnet, which is rigidly connected to case.

EFFECT: design simplification of transformer of degradation of its electroacoustic characteristics.

2 dwg

Description

The present invention can be applied both in hydroacoustics and in geophysical surveys.

Known magneto-induction emitter (figure 1), containing the inductor 1, the housing 2, a movable conductive plate 3 connected to the housing using sealing elements 4, and return springs 5.

(See E.F. Dubrov. Sound geolocation, p. 56. "Subsoil", Leningrad. 1967).

In a magneto-induction emitter, when an alternating or pulsed current is passed through an inductor as a result of the interaction of the magnetic fields of the inductor current and the eddy currents induced in the plate, ponderomotive forces arise that repel the plate from the inductor. When the plate moves in a liquid adjacent to it, a shock wave arises, which can be considered as acoustic. The pressure amplitude in it depends on the amount of energy passed through the inductor coil and the resistance of the inductor.

In the known magneto-induction emitter, the plate acts like a piston. A design feature of the emitter is the mobility of the plate as a whole relative to the inductor. The plate is returned to its original position using special springs.

When a well-known magneto-induction emitter operates, two acoustic pulses are generated: the first is due to the initial repulsion of the plate from the inductor under the influence of induced currents, the second is due to the collapse of cavitation bubbles on the outside of the plate when it returns to its original position under the action of the springs (See Journal of Geophysicul Reseach , v.69, No. 14, 1964, pp. 3033-3041. HEEdgerton and GG Hayward, The ″ Boomer ″ Sonar Sourse for Seismic Profiling.). For sonar purposes, the first impulse is most important, as it has a certain directivity characteristic determined by the ratio of plate diameter to radiation wavelength and good reproducibility of parameters from cycle to cycle.

The disadvantages of the known device are:

1) short duration of the acoustic pulse,

2) the presence of return springs operating in hard dynamic mode, which dramatically reduces the reliability of the known emitter and complicates its design.

The short duration of the acoustic pulse is due to the design of the known emitter. Tests of its layout, conducted at our enterprise, showed that the conductive plate begins to move in the opposite direction from the inductor during the first quarter of the discharge current period, and for the remaining quarter of the first half-wave period, the plate passes a distance of about 10 mm. The gap formed between the inductor and the plate completely eliminates the effect of subsequent half-waves of a pulsed magnetic field on the plate. As a result, the duration of the pressure pulse is approximately half a millisecond.

In addition, in the known emitter, when the plate is removed from the inductor, the resistance of the electric discharge circuit increases and its oscillation frequency decreases, which makes it impossible to coordinate the electric and mechanical circuits of the emitter.

The purpose of the present invention was to increase the duration of the acoustic pulse, simplify the design of the emitter and increase the coefficient of conversion of electrical energy into acoustic.

In accordance with the invention, the goal is achieved by the fact that the conductive plate is made rigidly and hermetically fastened along the contour with the body of the inductor. Thanks to this design, the plate will not be able to move long distances under the action of ponderomotive forces and it will be possible to use the entire train of electrical vibrations, which will lead to an increase in the pulse duration. In addition, this will significantly simplify the design, increase reliability and improve the coordination of the electrical and mechanical circuits of the emitter. Better alignment of the circuits provides an increase in the coefficient of conversion of electrical energy into acoustic.

The essence of the invention is illustrated by the drawing, where figure 2 shows a General view of the emitter in section. The emitter (figure 2) consists of an inductor 1, a housing 2, a conductive plate 3 and sealing elements 4. The inductor 1 is made in the form of a flat spiral filled with an insulating mass, connected by current conductors to a power source and placed in the housing 2. A plate 3 made of conductive material, such as duralumin, is rigidly and hermetically connected around the perimeter with the housing 2.

When the emitter is operating, the discharge current, which has the character of a train of sinusoidal oscillations, excites a pulsed magnetic field in the inductor, which induces eddy currents in the surface layer of the conductive plate adjacent to the inductor. These eddy currents have their own secondary electromagnetic field. The interaction of these fields causes the appearance of bulk ponderomotive forces. These forces move the plate in the direction opposite to the inductor, and also create compressive stresses in the metal of the plate, propagating in the direction perpendicular to its surface, in the form of a compression wave. Due to the fact that the plate is rigidly bonded to the body and made strong enough so that its deformations under the action of ponderomotive forces remain in the elastic region, when the emitter is in operation, the energy of a pulsed damped periodic discharge is used more fully than in the known emitter, the coefficient of conversion of electrical energy into mechanical energy increases .

When the compression shock wave exits to the outer surface of the plate, part of the wave energy is transferred to the water, and part is reflected in the form of a tensile wave moving in the opposite direction. The tensile wave, having reached the free (facing the inductor) surface of the plate, is reflected with a variable sign, i.e. in the form of a compression wave moving in the original direction.

Further, the entire cycle is repeated. In this case, a damped sinusoidal current pulse during the second, third and subsequent half-waves additionally sways the oscillating plate. The resonant mode of plate oscillations is optimal when the shock pulse repetition rate equal to twice the frequency of the electric discharge circuit oscillations coincides with the natural frequency of the oscillations of the conductive plate fastened along the circuit to the housing.

It should be noted that the resonant mode of operation of the emitter can be ensured only in the proposed design, since in it the displacements of the plate relative to the inductor are negligible.

The operation of the proposed emitter was tested on an experimental sample in the pool, the diameter of the radiating surface was 200 mm The measurements were carried out in the far field.

When a capacitor bank is discharged (energy 10 kJ), a damped sinusoidal current flows with an oscillation period T = 2 × 10 ^-4 s. The acoustic signal received by a calibrated hydrophone and recorded by an oscilloscope had the form of a sine wave with a frequency of 10 kHz, which decays exponentially.

In this case, the maximum acoustic pressure reached 0.77 atmospheres, which corresponds to an energy of about 800 joules. If we take into account that the electric energy at the capacitors was 10,000 joules, then the electro-acoustic efficiency.

energy is about eight percent.

The pressure amplitude decreased two times in the interval of one millisecond duration and ten times in the interval of six milliseconds. Thus, compared with the known device, the pulse duration suitable for use in sonar has doubled and 12 times when used in sonar.

An important advantage of the proposed emitter is the sinusoidal nature of the pulse with a pronounced frequency. This allows the grouping of pulses in order to lengthen the signal and increase its acoustic power.

It should be noted that the proposed design is not limiting and the acoustic power of the emitter can be increased by increasing the amount of energy stored on the capacitors (theoretically unlimited).

Claims (1)

A magneto-induction hydroacoustic transducer comprising a housing with an inductor located in it and a conductive plate adjacent to the inductor, characterized in that, in order to simplify the design of the transducer without compromising its electro-acoustic parameters, the conductive plate is rigidly connected to the emitter housing.

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