RU121113U1 - ACOUSTIC CONVERTER SELF-GRADING DEVICE - Google Patents

Abstract

A device for absolute self-calibration of an electroacoustic transducer containing a continuous oscillator, a power amplifier, a reference resistance, a decibel divider, an amplifier, an oscilloscope, a pool, a reflecting surface and a reversible calibrated transducer acoustically connected to it through the propagation medium, characterized in that a chronizer is additionally introduced into it -modulator, receiving electroacoustic transducer, preamplifier, analog switch, calculating and deciding unit and control unit; the generator of continuous oscillations through the chronizer-modulator is connected to the input of the power amplifier, the additional input of the chronizer-modulator is connected through a preamplifier to the output of the receiving electro-acoustic transducer, and the additional output is connected to the third input of the analog switch, the first and second inputs of the analog switch are connected to the output of the reference resistance and output of a reversible calibrated converter (in the reflected signal reception mode), respectively, the output of the amplifier is connected to the input of the calculating unit, the control inputs of the continuous oscillator, the chronizer-modulator, the analog switch, the decibel divider, the amplifier, the oscilloscope and the calculating unit are connected to the corresponding outputs of the control unit, and the receiving electroacoustic transducer is located on the acoustic axis of the transducer to be calibrated and can be moved along the vertical, which makes it possible to sequentially measure the levels of acoustic signals catches at a reflective interface as in water, that

Description

The utility model relates to the field of acoustic measurements and can be used to increase the accuracy of absolute self-calibration of reversible electro-acoustic transducers in the working frequency band based on the reciprocity method by taking into account the acoustic transparency of the reflecting boundary, in particular, the water-air interface. The preferred area of use is sonar.

A device for relative graduation by comparing the electro-acoustic transducers of sound emitters and sound pressure receivers (see the Guide to hydroacoustics. - L. "Sudostroenie", 1982, S. 218-219), containing a continuous oscillator, pulse modulator, power amplifier, the first amplitude meter, emitting transducer, acoustically connected through the propagation medium with two receiving transducers - a model and a test one, a pool, an input switch, a preamplifier, a polo Owl filter, time selector, second amplitude meter, recorder.

The device operates as follows. An electro-acoustic transducer receives an electric radio-pulse signal with a given amplitude U1 and frequency f _.i = ω _i / 2π (i = 1, 2, ..., is the number of measurements taken in its passband), which is emitted as an acoustic pulse into the propagation medium. Exemplary and graduated transducers having pressure sensitivities - known M _{0 (fi)} and unknown M _{X (fi),} respectively, are sound pressure receivers located nearby on the acoustic axis of the radiating transducer in its far zone

those. at a distance greater than the length of the diffraction divergence l _{D of the} acoustic beam (D = 2 a is the diameter of the emitting transducer, ω _i is the cyclic frequency of the i-th exciting signal, c ₀ is the equilibrium value of the speed of sound in the medium). The need to fulfill condition (1) is determined by the fact that the radiation field of the source is formed as a result of the interference of wave processes arriving at the location of the model and graduated transducers from different parts of the oscillating surface of the emitter, moreover, in the near projection zone (Fresnel zone) of length l _Di with uniform (piston) amplitude distribution across the aperture the sound pressure level on the acoustic axis of the emitter fluctuates between the minimum and maximum values (s m.Kobyakov Yu.S., Kudryavtsev N.N., Timoshenko V.I. Construction of hydroacoustic fish-finding equipment. - L.: Shipbuilding, 1986. - p. 92-93.). The exemplary and graduated transducers convert the acoustic impulse that reaches them into electric signals with amplitudes U _{0 (fi)} and U _{X (fi)} , which, after gating, filtering, and amplification, are recorded by a second amplitude meter and recorder. This will allow the researcher to calculate the values for the necessary spectral components (fi) of the frequency range of measurements:

1) pressure sensitivity in receive mode for graduated transducer

2) transducer sensitivity in radiation mode

where P _(fi) = U _{0 (fi)} / M _{0 (fi)} are the sound pressure values at the receiving point, measured by the model receiving transducer.

This device has disadvantages and limitations in use:

1) to carry out measurements, an exemplary receiving transducer is required, moreover, the accuracy of measurements is limited by the accuracy of the calibration of the exemplary transducer;

2) the pressure sensitivity in the reception mode of the reference transducer is unstable in time, which requires the implementation of its verification using absolute methods;

3) the operating frequency range of the device is limited to the operating ranges of both the model and emitting transducers, moreover, for the operability of the device in a wide frequency range, several model transducers are needed;

4) when carrying out relative calibration by the method of comparison, the unity of the measurement time is observed, because both receivers are simultaneously exposed to sound, but the condition for the unity of their location is not fulfilled - this requires taking into account both the directed properties of the emitter and receivers, and the influence of reflective surfaces, which reduces the accuracy of measurements;

5) within the extended section of the near diffraction zone of the radiating transducer, the use of the device gives a significant measurement error.

The reasons that impede the achievement of the claimed technical result are the limited operational capabilities of the device due to the need to use an exemplary receiving transducer.

Signs that coincide with the claimed object: continuous oscillator, power amplifier, graduated transducer, acoustic wave propagation medium, pool, recorder.

A device for graduation based on the reciprocity method of directional sound receivers (see Klyukin II, Kolesnikov AE Acoustic measurements in shipbuilding - L .: Sudostroenie, 1966. p.57-58), containing a continuous oscillation generator, pulse modulator, power amplifier, transducers acoustically connected through the propagation medium — auxiliary, reversible, and test, pool, input commutator, linear amplifier, logarithmic amplifier, four-channel time selector, algebraic adder.

The device operates as follows. The emitting path of the device, which includes a continuous oscillator, a pulse modulator and a power amplifier, generates an electric radio pulse signal with a given frequency f _.i (i = 1, 2, ... is the number of measurements in the total working frequency band of a reversible converter, auxiliary radiator and a test sound receiver), which simultaneously arrives directly at the input of the auxiliary emitter and through the switch to the input of the reversible transducer, which synchronously emit acoustic pulses are emitted into the propagation medium, for example, into water. The device uses a “linear” relative arrangement of the used electro-acoustic transducers, i.e. they are mounted on one straight line connecting them — the acoustic axis of the graduated directional sound pressure receiver, so that the greatest distance (from the auxiliary emitter to the test receiver) is 3r, and the distances from the reversible transducer to the auxiliary emitter and to the test receiver are 2r and r respectively. A reversible transducer is omnidirectional and has a small size in comparison with the length of the used acoustic wave, moreover, it is permissible to avoid diffraction phenomena its displacement from the acoustic axis by a distance equal to its diameter. The spatial arrangement of the electro-acoustic transducers indicated above makes it possible to distinguish along the time axis pulsed electrical signals generated by both a calibrated receiver: U1 (- from a reversible transducer), U3 (- from an auxiliary transducer), and a reversible transducer: U2 (- from an auxiliary transducer). The digital numbering of the pulse signals corresponds to their location on the time axis, on which the voltage drop U4 at the small reference resistance R, connected in series with the reversible converter, is also indicated with the greatest delay. Given that the distances from the auxiliary emitter to the reversible transducer and the sound receiver are not equal, the expression for sensitivity takes the form

where H is the reciprocity coefficient for a reversible transducer, which is determined by the conditions of radiation, reception and the nature of the generated acoustic field. When emitting and receiving spherical waves, the reciprocity coefficient for a reversible transducer is

where r is the distance between the radiation point and the receiving point, m; λ is the wavelength of sound in the medium, m; ρ is the density of the medium, kg / m ³ , c is the speed of sound in the medium, m / s; f is the frequency, Hz,

when emitting and receiving cylindrical waves, the reciprocity coefficient is

where L is the length of the Converter

when emitting and receiving plane waves

where S is the area of the emitter (see Klyukin II, Kolesnikov AE Acoustic measurements in shipbuilding - L .: Shipbuilding, 1966. p.51, p.90).

Pulse electrical signals U1, U2, U3, U4 in the receiving path of the device, consisting of a series-connected input switch, a linear amplifier, a logarithmic amplifier, a four-channel selector and an algebraic adder, are subjected to counting-decoding processing, as a result of which are expressed in decibels:

where on the left side of the equality the sensitivity of the calibrated sound receiver is expressed in decibels relative to 1 in × m ² / n, R - in decibels relative to 1 Ohm, H - in decibels relative to 1 m ⁴ s / kg.

This device has disadvantages and limitations in use:

1) for the calibration of directional sound receivers based on the reciprocity method, additional transducers are needed - reversible and auxiliary, which increases the length of the "linear" sonar channel of the pool and complicates the device;

2) for the calibration, the overall dimensions of the non-damped measuring pool must exceed the minimum calibration distance (length of the "linear" sonar channel) by 15-20 times, which creates difficulties when calibrating large-sized transducers;

3) the minimum length of the "linear" sonar channel is determined by the total length of the sections of the near diffraction zones of the used electro-acoustic transducers.

4) the calibration of large-sized transducers in full-scale conditions of a natural pool-water reservoir is complicated by the fulfillment of the condition of a “linear” mutual arrangement of the used directional electro-acoustic transducers, i.e. their location on one straight line - the common acoustic axis.

The reason that impedes the achievement of the claimed technical result is the limited operational ability of the device due to the need to use additional transducers - reversible and auxiliary, which increases the length of the "linear" sonar channel of the pool and complicates the measurement process.

Signs that coincide with the claimed object: a continuous oscillator, a power amplifier, an acoustic signal propagation medium, a graduated transducer, a pool, a reference impedance.

A device for self-calibration based on the reciprocity method was selected as a prototype (see Klyukin II, Kolesnikov AE Acoustic measurements in shipbuilding - L .: Sudostroenie, 1966. p. 59-60), containing a continuous oscillation generator, pulse modulator, power amplifier, reference impedance, input switch, decibel divider, amplifier, oscilloscope, pool, reflective surface and a reversible transducer acoustically connected through the propagation medium.

The device operates as follows. A calibrated electro-acoustic reversible transducer receives an electric radio-pulse signal with a given amplitude, produced by a series-connected continuous oscillator (frequency values f _.i = 1, 2, ... are determined by the required measurement accuracy and the passband of the converter), a pulse modulator and a power amplifier. The value of the current strength I, exciting the calibrated electro-acoustic reversible transducer, is determined by measuring the voltage U4 at a small reference resistance R (its value is much less than the total electrical resistance of the transducer in the entire range of calibration frequencies), included in series with the specified transducer, moreover, the reading of the voltage U4 is carried out from the screen of the cathode-ray tube of the oscilloscope, which is connected at the time of radiation to the resistance through the input ne switch decibel divider and amplifier. The electro-acoustic transducer emits an acoustic impulse into the aqueous propagation medium towards a reflective surface located at a distance r / 2 from it, which is used as the “water-air” interface. It is known that if an object with different acoustic properties is located on the path of propagation of acoustic vibrations in some medium, then part of the sound energy is reflected from the interface and propagates in the opposite direction in the form of a reflected wave, moreover, in case of significant dimensions (in comparison with the wavelength) Radiation theory is applicable to the description of both “irradiated” boundaries to describe both reflected and refracted wave processes (see Kudryavtsev V.I. Industrial hydroacoustic and fishing. M: Food industry, 1 978.- 22-25 s). For a quantitative description of the passage through the interface of sound energy, it is customary to use reflection coefficients both in pressure V _P = P _sp / P _pad and in intensity (ratio of sound pressures or intensities in the reflected _Neg P, I and falling _{Neg pad} P, I _pad waves respectively), values of which are determined by the values of densities ρ _1,2 and c _1,2 sound velocities in adjacent environments, as well as the angle of incidence α _pad primary sound wave (relative to the normal to the boundary). The calculated values of the reflection coefficients V _P and transparency W _P by pressure are determined by the relations

where m = ρ ₂ / ρ ₁ ; n = c ₁ / c ₂ . From relation (9) it follows that the reflection coefficient in pressure will be, the greater, the greater the difference in acoustic impedances of adjacent media. For example, since for water (ρ ₁ c ₁ ) there is approximately 3,500 times more (ρ ₂ · c ₂ ) air (m = 0,0013; ), as a result of the normal incidence of an acoustic wave on a flat interface from water to air, the maximum transparency coefficient (α _pad = 0) can be written as W _P = (2m / n) · cosα _pad and has a value of ≈5.7 × 10 ^-4 , and the reflection coefficient is V _P ≈ (-1). Thus, the sound pressure during the transition of a wave from water to air is weakened by about 2000 times, and the transmitted acoustic energy is only 10 ^-3 of the incident, i.e. we can assume that the acoustic energy emitted by the transducer is almost completely reflected and does not transfer to another medium. This allows, instead of the auxiliary emitter, to introduce an imaginary source located in the air at a distance of r / 2 from the water-air interface, which is a mirror image of the electro-acoustic transducer in a flat water-air surface. Thus, the sound pulse is completely reflected in the opposite direction and propagates to the transducer operating in the reception mode. The electro-acoustic transducer transforms the reflected pulse of sound pressure, generating a pulsed electrical signal, which through the input switch, decibel divider, amplifier is fed to the deflecting plates of the cathode-ray tube of the oscilloscope, from the screen of which the voltage value U3, corresponding to that reflected from the water-air interface, is counted »Signal. The sensitivity of the graduated electro-acoustic reversible transducer is determined by the ratio

where the value of the reciprocity coefficient H is indicated above (see relations (5) - (7)).

This device has disadvantages and limitations in use:

1) using the method of imaginary sources, we consider the propagation of sound vibrations from an imaginary emitter 5 'to a graduated electro-acoustic transducer 5 in the receiving mode, separated by a reflective screen or a flat section 7 (Fig. 1). As follows from the condition of the necessity of separating the emitted and received pulses, the distance between the converters must satisfy the inequality r '> Δt × c, Δt is the pulse duration, s, c is the speed of sound in the medium, m / s. The sizes of the transducers D, the reflecting screen R _e and the value of r 'are related by the relations (see the Reference for hydroacoustics / A.P. Evtyutov, A.P. Lyalykov, V. B. Mitko, V. I. Ponomarenko, A. L. Prostakov , G.M.Sverdlin, M.D.Smaryshev, Yu.F. Tarasyuk, A.E. Kolesnikov - L .: Shipbuilding, 1982. - p.215)

where λ is the sound wavelength in the medium. Thus, the device under consideration for self-calibration based on the reciprocity method has a limitation on the lower boundary of the frequency range (from 15 kHz to 200 kHz) - the lower the frequency, the larger the screen size and the distance to it (for example, if 10 kHz - r '> 0.9 m, R _e > 0.37 m, then for 1 kHz -r'> 9 m, R _e > 3.7 m). So, for a radiator with a size of 1 m operating in water at a frequency of 10 kHz (λ = 0.15 m), the generated acoustic field will be located no closer than 6 m from the radiator. It should be borne in mind that modern sonar antenna systems, consisting of a set of separate electro-acoustic transducers, differ in both large sizes, reaching (8-12) m, and low operating frequencies, which requires very large volumes of water to be measured and the use of bulky expensive equipment (see Prostakov A.L. Hydroacoustic and ship - L .: Shipbuilding, 1967, pp. 18-26, 32-45, 91-102; Mitko V.B., Evtyutov A.P., Gushchin S.E. Hydroacoustic communication and observation means - L .: Shipbuilding, 1982, pp. 74-119).

2) the use of an imaginary source instead of an auxiliary emitter located in air at a distance of r '/ 2 from the water-air interface, which is a mirror image of a graduated electro-acoustic transducer, is not fully valid, since in accordance with radiation theory this boundary possesses some opacity: sound pressure wave is attenuated at about 2000 times (- 66 dB), and passed acoustic energy is about 10 ^-3 of the incident (- 30 dB), which is not considered during calc comrade and increases the accuracy of indirect measurement sensitivity in the operating frequency range;

3) the structural diagram of the device under consideration for self-calibration based on the reciprocity method does not contain blocks and connections that allow in the working frequency range to carry out a procedure that establishes the correspondence of the characteristics of the "radiating path" of the imaginary emitter 5 '(Fig. 1) to its real parameters, i.e. calibration by experimental measurement of the existing acoustic transparency of the reflecting interface;

4) a theoretical study of the transparency of the “water-air” interface (see O. Godin. Passage of low-frequency sound from water to air. Acoust. Journal, vol. 53. 2007. - No. 3. - S.353-361) gives it is reasonable to assume that in the low-frequency range there is an anomalous increase in the transmission of inhomogeneous sound waves generated by the source, provided that the interface is removed from it by distances comparable to the radiation wavelength. The experiments carried out gave a positive result (see Voloshchenko V.Yu., Voloshchenko A.P., Tarasov S.P. An experimental study of acoustic transparency of the water-air interface for sound frequencies // Materials of the 12th international scientific-practical. seminar “PRACTICE AND PROSPECTS FOR THE DEVELOPMENT OF PARTNERSHIP IN THE HIGHER SCHOOL”, April 12-14, 2011, Donetsk, volume 2, p.29-32): for example, when the interface is irradiated using a separate excited section of a cylindrical antenna (D≈ ( 0.1 × 0.1) m, λ = 0.19 m, D ² / λ≈0.05 m, ν = 8 kHz) a decrease in the depth (from 2 m to 0.1 m) yielded the increase in the transmission coefficient from (- 65 dB) to (- 45 dB) (figure 2).

The reason that impedes the achievement of the claimed technical result is the limited operational capabilities of the device for self-calibration due to the lack of consideration of the acoustic transparency of the water-air interface, which reduces the accuracy of the acoustic measurements.

Signs that coincide with the claimed object: a generator of continuous oscillations, a power amplifier, a reference impedance, a decibel divider, an amplifier, an oscilloscope, a pool, a reflecting surface and a reversible calibrated transducer acoustically connected to it through a propagation medium.

The objective of the utility model is to expand the operational capabilities of the device by taking into account the influence of acoustic transparency of the reflecting water-air interface on the measurement results in the working frequency band, which will allow absolute self-calibration of the electro-acoustic transducer with increased accuracy.

The technical result of the utility model is to increase the accuracy of absolute self-calibration of acoustic transducers by taking into account the influence of acoustic transparency of the reflecting water-air interface.

The technical result is achieved by the fact that in the device for absolute self-calibration of acoustic transducers containing a continuous oscillator, power amplifier, reference impedance, decibel divider, amplifier, oscilloscope, pool, reflective surface and a reversible graduated transducer acoustically connected through it through the propagation medium, are additionally introduced chronizer-modulator, receiving electro-acoustic transducer, pre-amplifier, analogue key, counting unit and control unit; a continuous oscillator through a chrono-modulator is connected to the input of the power amplifier, an additional input of the chrono-modulator is connected through a pre-amplifier to the output of the receiving electro-acoustic transducer, and an additional output is connected to the third input of the analog key, the first and second inputs of the analog key are connected to the output of the reference resistance and the output of the reversible calibrated transducer (in the mode of receiving the reflected signal), respectively, the output of the amplifier is connected to the input of the The deciding unit, the control inputs of the continuous oscillator, chronizer-modulator, analogue key, decibel divider, amplifier, oscilloscope and counting-decisive unit are connected to the corresponding outputs of the control unit, and the receiving electro-acoustic transducer is located on the acoustic axis of the graduated transducer and can move along the vertical , which allows you to consistently measure the levels of acoustic signals at a reflecting interface both in water and in the air media for measuring its acoustic transparency.

The introduced units together with the described connections will allow expanding the operational capabilities of the device by experimentally measuring the acoustic transparency of the reflecting water-air interface at each frequency of the working calibration range, thereby increasing the accuracy of the absolute self-calibration of the electro-acoustic transducer.

In figure 1. a diagram is presented explaining the functioning of the calibration path of a device for calibrating a reversible acoustic transducer based on self-reciprocity (5 - calibrated electro-acoustic transducer, 7 - reflecting interface, 5 ′, 5 ″ - imaginary radiator - upper position when transparency is not taken into account, lower - when anomalous transparency is taken into account ), Fig. 2 - graphs of changes in the acoustic transparency (transmission) coefficients W _P (1 - experiment, 2 - “ray” theory) versus the normalized depth depth h / λ of the qi section a linear antenna at a radiation frequency of 8 kHz, figure 3 is a structural diagram of a device for absolute self-calibration of an electro-acoustic transducer.

A device for absolute self-calibration of the electro-acoustic transducer (figure 3) functionally combines the paths:

1) radiation - a continuous oscillation generator 1 is connected through a series-connected chroniser-modulator 2 (pulse modulator channel) and a power amplifier 3 with a graduated electro-acoustic transducer 5, which is in acoustic contact with the water-air interface 7 of the filled pool 6 and located so that the axis of the main lobe of the directivity characteristic is normal relative to the above boundary;

2) calibration - the receiving electro-acoustic transducer 8 through the pre-amplifier 9 and the chrono-modulator 2 (the sampling channel in the receiving) is connected to the third input of the analog switch 10, and the receiving electro-acoustic transducer 8 is located both on the axis of the main lobe of the graduated transducer 5 and near of the reflecting boundary 7, moreover, it can move along the vertical, which allows sequential registration of the levels of acoustic signals at the reflecting interface both in water and in air to measure its acoustic transparency, i.e. assessment of its reflectivity;

3) reception - the analog switch 10 through the decibel divider 11, the amplifier 12 is connected to the inputs of the oscilloscope 13 and the computing unit 14, and the first, second and third inputs of the analog switch 10 are connected to the outputs of the graduated electro-acoustic transducer 5 in the reception mode, the reference small resistance 4 by the value of R and the gating channel in the reception of the chroniser-modulator 2, respectively;

4) control the functioning of the units of the device - the outputs of the control unit 15 are connected to the corresponding control inputs of the continuous oscillator 1, the chroniser-modulator 2, the analog key 10, the decibel divider 11, the amplifier 12, the oscilloscope 13 and the computing unit 14

The operation of the device for absolute self-calibration of the acoustic transducer is as follows. The continuous oscillation generator 1 in the radiating path of the device generates an electric signal with a frequency f _.i (the value of the frequency f _.i , i = 1, 2, ... is determined by the required measurement accuracy, the passband of the converter and, when further measurements are taken, can be synchronously tuned with a given change step by command from the control unit 15), received at the input of the channel of the pulse modulator in the chronizer-modulator 2, which is brought into operation by the command from the control unit 15, as a result of which we obtain radio pulse with harmonic RF filling. Chronizer-modulator 2 is designed to operate as both a pulse modulator (first channel) and a receiving gating device (second channel) when conducting acoustic measurements in a pulsed mode in laboratory and field conditions, developed at the Department of Electro-Acoustics and Ultrasound Engineering of the Taganrog Radio Engineering Institute ( see T.N. Gorovaya, V.V. Grivtsov, M.S. Rybachek. “Chronizer-modulator for acoustic measurements”, international collection “Applied Acoustics”, issue VI, Taganrog, TRTI, 1978, P.136 -142). The output of the first channel of the modulator 2 through the power amplifier 3 is connected to the inputs of both the graduated transducer 5, which emits an acoustic pulse into the water environment of the pool 6, and to the second input of the analog switch 10, which is closed for a while by the command from the control unit 15. At the time of radiation, the first input of the analog switch 10 is connected to the output of a small reference resistance 4, connected in series with the converter 5, which is necessary to determine the value of the current I of its excitation by means of rhenium in the receiving path (11 - decibel divider, 12 - amplifier, 13 - oscilloscope) voltage drop U4 = I × R at this resistance 4 of value R. The calibrated electro-acoustic transducer 5 is located so that the axis of the main lobe of the directivity is normal to the boundary Section 7 "water-air" of the filled pool 6, which allows for acoustic contact with the surface and minimize unwanted reflections. To achieve a technical result - to increase the accuracy of self-calibration by evaluating the acoustic transparency of the water-air interface - the calibration path of the proposed device should be used, which allows sequentially recording the levels of electrical signals (U _pad , U _pr at the reflecting interface of section 7 generated by the receiving electro-acoustic transducer 8, which correspond to acoustic signals both in water (P _pad ) and in air (P _ol ) media from a graduated transducer 5. These electrical signals from the output of the receiving electro-acoustic transducer 8 through the preamplifier 9 and the gating channel in the reception of the chrono-modulator 2 are fed to the third input of the analog switch 10, the output of which is connected to the remaining blocks of the receiving path (11 - decibel divider, 12 - amplifier, 13 - oscilloscope) and the input of the computing unit 14, the control inputs of which are connected to the corresponding outputs of the control unit 15. Using the calibration path of the proposed device, it is necessary on the working part It is necessary to experimentally measure the value of acoustic transparency of the border 7 of the “water-air” section, on the basis of which correction factors should be calculated (counting-decisive block 14). Recall that the operability of the device under consideration as a means of measurement is based on the fact that the emitted pulse after reflection is received by the same calibrated transducer 5, which corresponds to the third measurement step in the universal method of three transducers based on the reciprocity principle (measured: I is the excitation current of the reversible transducer, U ₃ is the electrical voltage at the output of the graduated transducer and the distance r between the reversible and graduated transducers), as well as the assumption that the water-air interface is considered to be a completely reflective surface. However, it is known that the sound pressure during the transition of a wave from water to air is weakened by about 2000 times, i.e. the transmitted acoustic signal (P _CR ) is ~ 0.0005 times or 0.05% of the incident P _pad (1 or 100%), as a result of which the reflected acoustic signal (P _neg ) is insignificant but smaller (0.9995 or 99, 95%) compared to falling. An increase in the level of the reflected (P _neg ) acoustic signal before equalization with the incident (P _pad ) can be achieved by approaching the location of the imaginary source (for example, from 5 ′ to 5 ″ that are distant from the calibrated transducer 5 by distances r ′ and r ″ (respectively), i.e., decreasing the distance r, the value of which is included in the reciprocity coefficient (5) - (6), which eliminates the overestimation of the calculated value of the desired sensitivity of the graduated transducer 5. We give the estimated calculations of the correction coefficients µ, pos olyayuschih determine the true value of sensitivity for the calibrated converter 5, the radiating and receiving spherical wave. In the above-described "classic" case W _P transmittance pressure ≈0,05% and μ = 0,99975, increase the acoustic transparency of the reflective interface 20 dB (10 times), 30 dB (31.6 times), 40 dB (100 times) specify the range of correction factor µ from 0.9977 to 0.9747, which corresponds to an increase in the difference Δr = r′-r ″ from 0.0021 × r ′ to 0.026 × r ′, i.e. the convergence of the graduated transducer 5 and the imaginary source. Electro-acoustic transducer 5 transforms the reflected pulse of sound pressure By generating a pulsed electrical signal U3 ', which through the third input of the analog switch 10, the decibel divider 11, the amplifier 12 is fed to the deflecting plates of the cathode ray tube of the oscilloscope 13, from the screen of which the voltage U3 corresponding to the one reflected from the “water- air ”to the signal. The sensitivity of the graduated electro-acoustic reversible transducer 5 is determined by the ratio (counting-decisive block 14)

where, in the value of the reciprocity coefficient H, the measured distance r ′ between the reversible and graduated transducers is multiplied by the correction coefficient µ obtained above, i.e. became equal to r ″. For the values of increase in acoustic transparency: by 20 dB, 30 dB, 40 dB - the accuracy of indirect measurements of the sensitivity of the calibrated transducer 5 will be increased by 1.0023, 1.0076 and 1.026 times, respectively

The problem of increasing the accuracy of the method is quite relevant. So, for the calibration by the method of self-reciprocity of electro-acoustic transducers used in medical echolocation systems, for operating frequencies of 1 MHz and 2 MHz in continuous and pulsed modes, the "traditional" installation provided an error of ~ 30% and 20%, respectively (see Reid JM Self-reciprocity Calibration of Echo-Ranging Transducers. JASA, 1974, vol. 55, No. 4, p. 862-868). The description is known (see RB Patterson. Using the Ocean Surface on a Reflector for the Self-Reciprocity Calibration of a Transducer. - JASA, 167, vol. 36, p. 1557) of the results of using the self-reciprocity method for calibration (accuracy ~ ± 20 dB ) an electro-acoustic transducer with an operating frequency of 1.78 kHz (wavelength 10 m) under ocean conditions, and its depth was ~ 360 m. The introduction of large antennas into the practice of sonar created the need for special methods for calibrating them at short distances, which resulted in Two complex and expensive solutions to the problem of near field librations. The first method uses a hydrophone probe to measure the amplitude and phase of the pressure in the aquatic environment at many points in the near field of the antenna, which then allows you to calculate sound pressure in the far field (see DRL - DDBaker method. Determination of Far-Field Characteristics of Large Underwater Sound Transducers from Near-Field Measurements. - JASA, 1962, vol. 34, p. 1737). The second (see Trott grating - WJTrott. Underwater Sound Transducer Calibration from Nearfield Data. - JASA, 1964, vol. 36, p. 1557) is based on the use of a flat antenna array consisting of small sound sources (the distance between them is ~ 0, 8λ, the maximum dimensions should not exceed 0.1λ), in the near field of which there is a region of homogeneous plane traveling waves into which the calibrated antenna is placed, and, on the principle of reciprocity, it is possible to perform measurements in which the Trott grating serves as a receiver for determining the sensitivity large antenna in radiating mode i.

Claims (1)

A device for absolute self-calibration of an electro-acoustic transducer containing a continuous oscillator, power amplifier, reference impedance, decibel divider, amplifier, oscilloscope, pool, reflective surface and a reversible calibrated transducer acoustically connected through it through the propagation medium, characterized in that a chronizer is additionally introduced into it -modulator, receiving electro-acoustic transducer, pre-amplifier, analog key, computing unit and bl ok management; a continuous oscillator through a chrono-modulator is connected to the input of the power amplifier, an additional input of the chrono-modulator is connected through a pre-amplifier to the output of the receiving electro-acoustic transducer, and an additional output is connected to the third input of the analog key, the first and second inputs of the analog key are connected to the output of the reference resistance and the output of the reversible calibrated transducer (in the mode of receiving the reflected signal), respectively, the output of the amplifier is connected to the input of the the deciding unit, the control inputs of the continuous oscillator, chronizer-modulator, analog key, decibel divider, amplifier, oscilloscope and counting-decisive unit are connected to the corresponding outputs of the control unit, and the receiving electro-acoustic transducer is located on the acoustic axis of the graduated transducer and can move along the vertical, which makes it possible to sequentially measure the levels of acoustic signals at a reflecting interface both in water and in air media for measuring its acoustic transparency.