RU2782354C2 - Apparatus for grading electroacoustic transducers - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to the field of acoustic measurements and hydroacoustics. Apparatus for grading electroacoustic transducers comprises an emitting path including a harmonic oscillation generator, a pulse modulator, a synchroniser, a power amplifier, a frequency meter, an emitting electroacoustic transducer, a receiving path including a reference receiving electroacoustic transducer and the graded one, an analogue key for switching the receiving electroacoustic transducers, an amplifier, a filter unit, a strobe unit, a control unit for the emitting and receiving paths, and a plugged pool for placing the electroacoustic transducers, containing a coordinate system for installing and moving the transducers. The novel feature of the invention consists in additionally including a second harmonic oscillation generator, an adder, an amplitude detector, a low-frequency filter, a matching amplifier and a band-rejection filter into the emitting path, wherein the outputs of both harmonic oscillation generators are connected with the two signal inputs of the adder, the first output whereof is connected via the pulse modulator, the matching amplifier, the power amplifier and the band-rejection filter with the input of the emitting electroacoustic transducer, the second output of the adder is connected via the amplitude detector and the low-frequency filter with the signal input of the frequency meter, and the outputs of the control unit are connected with the control inputs of both harmonic oscillation generators, the synchroniser, the frequency meter, and the analogue key.

EFFECT: apparatus for grading electroacoustic transducers has expanded operating capabilities of the apparatus and increases the accuracy and frequency range of measurements.

3 cl, 5 dwg

Description

The invention relates to the field of acoustic measurements and can be used to measure both the frequency dependence of the sensitivity in the mode of reception (radiation) and the directivity characteristic (CH) of an electroacoustic transducer in a given frequency range. The predominant area of use is acoustic measurements and hydroacoustics.

In hydroacoustic equipment for measuring sound pressure in the aquatic environment, hydrophones are used, previously calibrated using standard measuring instruments (see Ultrasound. Little Encyclopedia. Chief ed. I.P. Golyamin. - M .: "Sov. Encyclopedia", 1979, 400 pp. Hydrophone, pp. 85-86). With an increase in the number of hydroacoustic equipment produced, which include measuring hydrophones, the problem arises of developing new exemplary measuring instruments that allow calibration in a free field with a smaller error (less than 1 dB) with a higher confidence level (more than 0.68). In the practical implementation of these tasks in metrology, much attention is paid to reducing the size of equipment, increasing its productivity, as well as designing measuring instruments that have a radiating path with acoustic parameters that do not change much over a wide frequency band (see Blinova L.P., Kolesnikov A.E., Langans LB Acoustic measurements - M.: Publishing House of Standards, 1971. - 271 pp. Chapter 1. General issues of acoustic metrology, pp. 5 - 41). The main requirements for the measuring setup used both in the certification of hydrophones and in measuring the characteristic curves of hydroacoustic transducers in the free field are known: 2140 - 91 GSI Hydroacoustic measuring receivers (hydrophones. Requirements for the development of certification and verification methods http://normacs.ru/Doclist/doc/11BC1.html accessed 1.12.2019); 2) the size of the aperture of the electroacoustic transducer must ensure the conditions for carrying out measurements in the far field, and its design must not increase the reverberation time in the measuring pool; 3) the change in the frequency response of the radiator in the operating range should be monotonous without sharp drops and rises; 4) XH of the emitter should have a low level of the side field (about - 20 dB) with a little changing width of the main lobe (level - 3 dB in terms of sound pressure) in the entire operating frequency range; 5) the stability of the characteristics of the emitter over time under various climatic conditions (pressure, temperature, humidity). However, at present, measuring installations do not fully comply with a set of requirements, in particular, operability at discrete operating frequencies is ensured by using a set of interference electroacoustic transducers that have a significant unevenness of both frequency characteristics and the emerging ultrasonic field, which limits the operational capabilities of the devices.

A device is known for relative calibration by comparing electroacoustic transducers - sound emitters and sound pressure receivers (see Hydroacoustics Handbook. - L. "Shipbuilding", 1982, Chapter 7, § 7.3 Graduation of acoustic measuring paths, pp. 218-219), containing harmonic oscillation generator, pulse modulator, synchronizer, power amplifier, first amplitude meter, radiating electro-acoustic transducer, acoustically connected through a propagation medium with two receiving electro-acoustic transducers - a reference and a test one, a plugged-in pool equipped with a coordinate system for installing and moving transducers, an analog key for switching of receiving transducers, amplifier, band-pass filter, gated block, oscilloscope, recorder.

и неизвестной

соответственно, являются приемниками звукового давления, расположены рядом и без «затенения» на акустической оси излучающего электроакустического преобразователя в его дальней зонеThe device works as follows. In the radiating path, an electric radio pulse signal is formed with a given amplitude U1 and frequency ƒ _.i =ω _i /2π (i = 1, 2, ..., - the number of measurements, the frequencies are in the passband), which is fed to an electroacoustic transducer that emits ultrasonic impulse to the propagation medium. Exemplary and calibrated electro-acoustic transducers with sound pressure sensitivities - known

and unknown

respectively, they are sound pressure receivers, located side by side and without "shading" on the acoustic axis of the emitting electroacoustic transducer in its far zone

акустического пучка (D=2а - диаметр излучающего электроакустического преобразователя, ω_i - циклическая частота i-того возбуждающего сигнала, C₀ - равновесное значение скорости звука в среде). Необходимость выполнения условия (1) определяется тем, что поле излучения источника формируется в результате интерференции волновых процессов, приходящих в место расположения образцового и градуируемого электроакустических преобразователей от различных участков колеблющейся поверхности излучающего электроакустического преобразователя. В ближней прожекторной зоне (зоне Френеля) протяженностью

при равномерном (поршневом) амплитудном распределении поперек апертуры уровень звукового давления на акустической оси излучателя флюктуирует между минимальным и максимальным значениями (см. Кобяков Ю.С., Кудрявцев Н.Н., Тимошенко В.И. Конструирование гидроакустической рыбопоисковой аппаратуры. - Л. Судостроение, 1986, Глава 7 Параметры аппаратуры в режиме излучения, § 7.1 Характеристики направленности антенн, с. 92-93.). Образцовый и градуируемый электроакустический преобразователи преобразуют достигший их ультразвуковой импульс в электрические сигналы с амплитудами

и,

которые после усиления, фильтрации и стробирования фиксируются осциллографом и самописцем. Это позволит исследователю для необходимых спектральных составляющих (ƒi) частотного диапазона измерений рассчитать значения:those. at a distance greater than the length of the diffraction divergence

acoustic beam (D=2 and - the diameter of the radiating electro-acoustic transducer, ω _i - the cyclic frequency of the i-th exciting signal, C ₀ - 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 coming to the location of the exemplary and calibrated electroacoustic transducers from different parts of the oscillating surface of the radiating electroacoustic transducer. In the near searchlight zone (Fresnel zone) with a length

with a 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 (see Yu. Shipbuilding, 1986, Chapter 7 Equipment parameters in the radiation mode, § 7.1 Directional characteristics of antennas, pp. 92-93.). Exemplary and calibrated electro-acoustic transducers convert the ultrasonic pulse that has reached them into electrical signals with amplitudes

and,

which, after amplification, filtering and strobing, are recorded by an oscilloscope and a recorder. This will allow the researcher to calculate the values for the required spectral components (ƒi) of the measurement frequency range:

1) sound pressure sensitivity in the receiving mode for a calibrated electroacoustic transducer

2) the sensitivity of the electroacoustic transducer in the radiation mode

- величины звукового давления в точке приема, измеренные образцовым приемным преобразователем.where

- values of sound pressure at the point of reception, measured by the exemplary receiving transducer.

This device has disadvantages and limitations in use:

1) for measurements, an exemplary receiving electroacoustic transducer is required, and the measurement accuracy is limited by the error in performing the calibration of the exemplary electroacoustic transducer;

2) the operating frequency range of the device is limited by the operating ranges of both exemplary and radiating electro-acoustic transducers, and for the device to work in a wide frequency range, several exemplary electro-acoustic transducers are required;

3) when carrying out a relative calibration by the method of comparison, the unity of the measurement time is observed, because both electroacoustic receiving transducers are simultaneously exposed to ultrasound, but the condition of unity of their location is not met - this requires taking into account both the directional properties of the electroacoustic emitter and both receivers, and the influence of the reflecting surfaces of the pool, which reduces the measurement accuracy; 4) within an extended section of the near zone of diffraction of a radiating electroacoustic transducer, the use of the device gives a significant measurement error.

The above disadvantages limit the operational capabilities of the device, which reduces the accuracy and frequency range of measurements.

Features that coincide with the claimed object: a harmonic oscillation generator, a pulse modulator, a synchronizer, a power amplifier, an electro-acoustic radiating transducer, acoustically connected through a propagation medium with a receiving calibrated electro-acoustic transducer, a dead pool equipped with a coordinate system for installing and moving transducers, an analog key for switching receiving transducers, amplifier, bandpass filter, gated unit, oscilloscope, recorder.

A device for calibration based on the method of reciprocity of directional sound receivers is known (see Klyukin I.I., Kolesnikov A.E. Acoustic measurements in shipbuilding - L. Shipbuilding, 1966. S. 57-58), containing a generator of harmonic oscillations, a pulse modulator , synchronizer, power amplifier, transducers acoustically coupled through the propagation medium - auxiliary, reversible and tested, dead pool equipped with a coordinate system for installing and moving transducers, analog switch for switching receiving transducers, linear amplifier, logarithmic amplifier, reference resistance R, four-channel time selector, algebraic adder.

The device works as follows. The radiating path of the device, which includes a generator of harmonic oscillations, a pulse modulator, a synchronizer and a power amplifier connected in series, generates an electrical radio pulse signal with a given frequency ƒ _.i (where i = 1, 2, ... is the number of measurements in the total operating frequency band of the reversible converter , auxiliary emitter and sound receiver under test), which simultaneously enters directly to the input of the auxiliary emitter and through an analog switch for switching to the input of a reversible transducer, which synchronously emit acoustic pulses into the propagation medium, for example, into water. The device uses a "linear" mutual arrangement of the used electroacoustic transducers, i.e. they are installed on the same straight line connecting them - the acoustic axis of the calibrated directional sound pressure receiver, in such a way that the greatest distance (from the auxiliary emitter to the tested receiver) is 3r, and the distances from the reversible transducer to the auxiliary emitter and to the receiver under test are equal to 2r and r respectively. The reversible transducer is omnidirectional and has small dimensions in comparison with the length of the used acoustic wave, and, in order to avoid diffraction phenomena, its displacement from the acoustic axis by a distance equal to its diameter is permissible. The above spatial arrangement of electro-acoustic transducers allows to spread along the time axis pulsed electrical signals generated both by a calibrated receiver: U1 (- from a reversible transducer), U3 (- from an auxiliary emitter), and a reversible transducer: U2 (- from an auxiliary emitter). The digital numbering of the pulse signals corresponds to their location on the time axis, on which the voltage drop U4 at a small reference resistance R, connected in series with the reversible converter, is also indicated with the greatest delay. Taking into account the fact that the distances from the auxiliary emitter to the reversible transducer and sound receiver are not equal to each other, the expression for the 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 equal to

where r is the distance between the emission point and the reception point, m; λ is the wavelength of sound in the medium, m; ρ is the density of the medium, kg/m ³ s is the speed of sound in the medium, m/s; ƒ - frequency, Hz,

when emitting and receiving cylindrical waves, the reciprocity coefficient is equal to

where L is the length of the transducer,

when emitting and receiving plane waves

where S is the area of the emitter (see Klyukin I.I., Kolesnikov A.E. Acoustic measurements in shipbuilding - L .: Shipbuilding, 1966 Chapter 1 Elements of acoustic measuring paths. § 7 Graduation of electroacoustic transducers based on the principle of reciprocity, p. 51 , p. 90).

Pulsed electrical signals U1, U2, U3, U4 in the receiving path of the device, consisting of a series-connected analog key for switching receiving transducers, a linear amplifier, a logarithmic amplifier, a four-channel selector and an algebraic adder, are subjected to counting and decision processing, as a result of which they 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 V × 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) to carry out the calibration of directional ultrasound receivers based on the reciprocity method, additional transducers are required - reversible and auxiliary, which increases the length of the "linear" hydroacoustic channel of the pool and complicates the device;

2) for calibration, the overall dimensions of the anechoic pool equipped with a coordinate system for installing and moving transducers must exceed the minimum calibration distance (the length of the “linear” hydroacoustic channel) by 15–20 times, which creates difficulties in calibrating large transducers;

3) the minimum length of the “linear” hydroacoustic channel is determined by the total length of the sections of the near diffraction zones of the used electroacoustic transducers;

4) the operating frequency range of the device is limited by the operating ranges of electroacoustic transducers, and for the device to work in a wide frequency range, it is necessary to have several sets of electroacoustic transducers.

The above disadvantages limit the operational capabilities of the device, which reduces the accuracy and frequency range of measurements.

Signs that coincide with the claimed object: a harmonic oscillation generator, a power amplifier, an aquatic environment for the propagation of an acoustic signal, a calibrated electro-acoustic transducer, an anechoic pool equipped with a coordinate system for installing and moving transducers, an analog key for switching receiving transducers.

Closest to the claimed invention is a device for testing electro-acoustic transducers in the range of 0.001 - 100 kHz by the substitution method (see State special standard and all-Union verification scheme for sound pressure measuring instruments in the aquatic environment in the frequency range from 0.001 to 200 kHz. GOST 8.124 - 74. - M.: Publishing House of Standards, 1974. - 6 p.), containing a radiating path: a harmonic oscillation generator, a pulse modulator, a synchronizer, a power amplifier, a frequency meter, electro-acoustic transducers acoustically connected through an aqueous propagation medium - emitting and receiving: exemplary and test, plugged pool, equipped with a coordinate system for installing and moving transducers, which has a mechanical drive from the recorder; as well as the receiving path: an analog key for switching receiving converters, an amplifier, a filter unit, a strobe unit, an oscilloscope, a recorder, a control unit.

и неизвестной

соответственно, и являются приемниками звукового давления, расположены рядом и могут быть поочередно установлены (без «затенения») на акустической оси излучающего электроакустического преобразователя в его дальней зоне. Расстояние между излучателем и приемником должно превышать расстояние, необходимое для формирования их характеристик направленностиThe device works as follows. The radiating path of the device, which includes a generator of harmonic oscillations, a pulse modulator, a synchronizer and a power amplifier connected in series, generates an electric radio pulse signal with a given amplitude U1 and a frequency ƒ _.j (where i = 1, 2, ... is the number of measurements), which through an analog switch for switching emitters, controlled by a command from the control unit, is fed to the input of the required radiating electroacoustic transducer: 1 Electrodynamic LFI - frequency subrange (0.2 - 2.5) kHz with overall dimensions (500 × 300) mm; 2) piezoelectric RFID - frequency subrange (2.5 - 25) kHz with overall dimensions (200 × 150) mm; 3) piezoelectric RFID - frequency subrange (25 - 100) kHz with overall dimensions (100 × 40) mm. An electroacoustic transducer provides a double energy conversion: an electromechanical one, as a result of which part of the electrical energy supplied to the transducer is converted into the energy of vibrations of a certain mechanical system, and a mechanoacoustic one, in which a sound field is created in the medium due to vibrations of a mechanical system (see Ultrasound. Little Encyclopedia. Chapters I.P. Golyamin, edited by M.: Sov. Encyclopedia, 1979, 400 pp. Electroacoustic transducer, pp. 380-383). In particular, the basis for the design of an electrodynamic emitter (EDI) is a coil placed in a constant magnetic field, through which an alternating current flows. The variable force that arises in this case causes oscillations with the frequency of the current of the moving system of the electrodynamic radiator. The mobile system, in addition to the conductor with current, includes a radiating device associated with it in the form of a diaphragm. The unevenness of the frequency characteristics (up to 20%) and the amount of nonlinear distortion (harmonic coefficient up to 10%) created by the electrodynamic emitter are large, which cannot but affect the quality of measurements. The performance of piezoelectric RFIDs is based on the piezoelectric effect, and, if they are used in radiation mode, they are used in a narrow frequency range near the resonance of their mechanical system. Thus, the selected electroacoustic transducer in the required frequency range creates a sound field in the aquatic environment, which manifests itself in the occurrence of compression and rarefaction areas that propagate at the speed of sound in the direction of the receiving piezoelectric transducers: exemplary and calibrated. Exemplary and calibrated piezoelectric transducers have sound pressure sensitivities - known

and unknown

respectively, and are sound pressure receivers, located side by side and can be alternately installed (without "shading") on the acoustic axis of the emitting electro-acoustic transducer in its far zone. The distance between the transmitter and the receiver must exceed the distance necessary for the formation of their directivity characteristics

и

, которые через аналоговый ключ для коммутации приемных преобразователей по команде с блока управления поступают на вход приемного тракта, в котором после усиления, фильтрации и стробирования фиксируются осциллографом и самописцем. Это позволит исследователю для необходимых спектральных составляющих (ƒi) частотного диапазона измерений рассчитать значения чувствительности по звуковому давлению в режиме приема для градуируемого электроакустического преобразователяwhere D _izl and D _pr - the largest dimensions of the electroacoustic transducers - emitting and receiving, respectively, λ _i - the sound wave length corresponding to the cyclic frequency of the i-th excitation signal, i = 1, 2, ..., - the number of measurements taken, the frequencies are in the band emitter transmission. In accordance with the substitution method on the acoustic axis of a radiating electroacoustic transducer in the volume of a damped pool (see Klyukin I.I., Kolesnikov A.E. Acoustic measurements in shipbuilding - L. Shipbuilding, 1966 Chapter 111 Noise measurement. § 14 Measuring pools. Their characteristics, sound-absorbing coatings for pools, pp. 120-130, Handbook of hydroacoustics. - L. "Shipbuilding", 1982, Chapter 7, § 7.2 Measuring volumes. Hydroacoustic pipes and pools, pp. 208-213), equipped with a coordinate system for installation and movement of the transducers, first place the exemplary receiving transducer. When replacing the exemplary transducer with a calibrated transducer, the unity of place and the complete identity of the prototype equipment used are preserved, however, the unity of time is not preserved. This requires maintaining the invariance of the radiation regime, i.e. the stability of the operation of both the radiating path and the emitter, since it is unacceptable to separate the two indicated measurements for a significant period of time - external conditions may change, distorting the measurement results. The impact of the sound field on receiving: both exemplary and calibrated - transducers in accordance with the direct piezoelectric effect will lead to the appearance of an alternating electrical signal at their outputs. Thus, the exemplary and calibrated electroacoustic transducers alternately convert the ultrasonic pulses reaching them into electrical signals with amplitudes

and

, which, through an analog key for switching receiving converters, upon command from the control unit, enter the input of the receiving path, in which, after amplification, filtering and strobing, they are recorded by an oscilloscope and a recorder. This will allow the researcher for the required spectral components (ƒi) of the frequency range of measurements to calculate the sensitivity values for sound pressure in the receive mode for a calibrated electro-acoustic transducer

This device has disadvantages and limitations in use:

, где D_изл - максимальный размер источника. На более близком расстоянии от источника звуковое поле имеет сложный нерегулярный характер, что делает невозможным проведение достоверных акустических измерений в ВЧ диапазоне при используемом в прототипе объеме 1 м³ заглушенного бассейна с габаритными размерами (0,9×1,23×0,9) м. Например, для электродинамического НЧИ - поддиапазон частот (0,2 - 2,5) кГц с габаритными размерами (500 × 300) мм граница ближней зоны изменяется в диапазоне (0,07 - 0,83) м; для первого пьезокерамического ВЧИ - поддиапазон частот (2,5 - 25) кГц с габаритными размерами (200 × 150) мм - (0,07 - 0,7) м; для второго пьезокерамического ВЧИ - поддиапазон частот (25 - 100) кГц с габаритными размерами (100 × 40) мм - (0,33 - 1,33) м соответственно. Из указанного следует, что «измерительная» часть заглушенного бассейна имеет невысокую достоверность, что снижает и ограничивает как точность, так и частотный диапазон измерений;1) the formed directivity zone is formed at a distance from the installation signal emitter

, where D _izl is the maximum size of the source. At a closer distance from the source, the sound field has a complex irregular character, which makes it impossible to carry out reliable acoustic measurements in the HF range when used in the prototype volume of ¹ m For example, for electrodynamic LFI - frequency subrange (0.2 - 2.5) kHz with overall dimensions (500 × 300) mm, the boundary of the near zone varies in the range (0.07 - 0.83) m; for the first piezoceramic HFI - frequency subrange (2.5 - 25) kHz with overall dimensions (200 × 150) mm - (0.07 - 0.7) m; for the second piezoceramic HFI - frequency subrange (25 - 100) kHz with overall dimensions (100 × 40) mm - (0.33 - 1.33) m, respectively. It follows from the above that the "measuring" part of the anechoic pool has a low reliability, which reduces and limits both the accuracy and the frequency range of measurements;

2) assuming the sphericity of the emitters used in the prototype, we estimate the values of the diffraction constants: 98); for the first piezoceramic HFI - frequency subrange (2.5 - 25) kHz with an overall size of 200 mm - (0.7 - 0.1); for the second piezoceramic HFI - frequency subrange (25 - 100) kHz with an overall size of 100 mm - (0.2 - 0.048), respectively. It follows that the acoustic part of the radiating path of the prototype has a significant change in the diffraction constant, i.e. minimal distortion of the sound field is more consistent with the operation of only the electrodynamic LFO, which reduces and limits both the accuracy and the frequency range of measurements;

3) in the range (0.2-25) kHz, the functioning of the prototype in the required frequency band is due to the use of two standard electro-acoustic transducers: 2) piezoceramic HFI - frequency subrange (2.5 - 25) kHz with overall dimensions (200 × 150) mm (Fig. 2). As follows from FIG. 2, the sections of the frequency response of both LFI and RFI in the frequency subranges (0.2 - 2.5) kHz and (2.5 - 25) kHz have a significant indentation and non-monotonicity of the increment (dynamic range up to 48 dB, i.e. ~ 250 times): for LF - up to 18 dB (~ 8 times) and for HFI - up to 30 dB (~ 31 times). The implementation of measurements in the prototype with such sources is difficult, which limits the operational capabilities of the device, reducing the accuracy of measurements.

4) in the prototype, not for all emitters, the requirement of "the minimum number and levels of additional lobes in the directivity characteristic" is met. As follows from FIG. 5, the prototype fully complies with this criterion with the first RFID only at a frequency of 5 kHz.

The implementation of measurements in the prototype with such sources is difficult, which limits the operational capabilities of the device, reducing the accuracy of measurements.

The above disadvantages limit the operational capabilities of the device, which affects both the accuracy and the frequency range of measurements.

Signs that coincide with the claimed object: a harmonic oscillation generator, a pulse modulator, a synchronizer, a power amplifier, a frequency meter, electro-acoustic transducers acoustically connected through the aquatic propagation medium - emitting and receiving: exemplary and calibrated, muffled pool equipped with a coordinate system for installing and moving transducers, having a mechanical drive from the recorder, an analog key for switching receiving transducers, an amplifier, a filter unit, a strobe unit, an oscilloscope, a recorder, a control unit.

The objective of the invention is to create a device for calibrating electro-acoustic transducers with extended operational capabilities and high accuracy.

The technical result of the invention is to improve the accuracy of measurements and expand the frequency range of measurements through the use of an acoustic path with time-stable parameters in a wide frequency band.

The technical result is achieved by the fact that in a known device for calibrating electro-acoustic transducers, consisting of a radiating path, including a harmonic oscillation generator, a pulse modulator, a synchronizer, a power amplifier, a frequency meter, a radiating electro-acoustic transducer and a receiving path, including exemplary and calibrated electro-acoustic transducers, an analog switch for switching receiving electro-acoustic transducers, an amplifier, a filter unit, a strobe unit, a control unit for emitting and receiving paths, and a plugged pool for placing receiving electro-acoustic transducers and a coordinate system for installing and moving transducers, a second generator of harmonic oscillations, an adder are additionally introduced into the emitting path , an amplitude detector, a low-pass filter, a matching amplifier and a notch filter, with the outputs of both harmonic generators connected to two signals inputs of the adder, the first output of which is connected through a pulse modulator, a matching amplifier, a power amplifier and a notch filter to the input of a radiating electro-acoustic transducer, the second output of the adder is connected through an amplitude detector and a low-frequency filter to the signal input of the frequency meter, and the outputs of the control unit are connected to the control inputs both generators of harmonic oscillations, a synchronizer, a frequency meter, an analog key for alternately switching the outputs of the receiving transducers.

The radiating electro-acoustic transducer is made with a resonant frequency ƒ ₀ , and in its passband are the frequencies ƒ ₁ , ƒ ₂ harmonic oscillations of generators related by the ratio (ƒ ₁ +ƒ ₂ )/2=ƒ ₀ .

The device preferably comprises a recorder and an oscilloscope connected to a control unit.

The specified set of features is unknown from the prior art, therefore, the claimed device satisfies the condition of patentability "novelty". The set of essential features of the device for calibrating electroacoustic transducers makes it possible to expand the operational capabilities of the device through the use of the parametric radiation mode, in particular, the proposed device meets the set of requirements used both in the certification of hydrophones and in measuring the characteristic curve of hydroacoustic transducers in a free field. The parametric radiation mode in terms of quantitative measurements provides:

- increased directivity, which significantly reduces the effect of interference and improves accuracy;

- the absence of side lobes reduces the impact on the experiments of fasteners, reflective elements;

- independence of directivity characteristics from frequency allows to automate measurements;

- small transverse dimensions and mass of radiating electroacoustic transducers.

In FIG. 1 shows a block diagram of the proposed device;

in fig. 2 and FIG. 3 - experimental graphs for the range (0.2-25) kHz are presented, showing the dependences of the frequency characteristics of the sensitivities in the radiation mode for the prototype and the claimed device, respectively;

in fig. 4 and FIG. 5 in a rectangular coordinate system shows the experimental graphs of the angular dependence of the sound pressure developed in the radiation mode for the prototype (RF, three curves: 1 - 5 kHz, 2 - 20 kHz, 3 - 25 kHz) and the proposed device (four curves: 1 - 5 kHz, 2 - 20 kHz, 3 - 25 kHz, 4 - 100 kHz) respectively.

q, где а - размер апертуры электроакустического преобразователя 9, ω₀=2π׃₀ - циклическая частота, с₀ - равновесное значение скорости распространения звука в воде.The device for calibrating electro-acoustic transducers (Fig. 1) contains a radiating path: two generators 1, 2 harmonic oscillations with frequencies ƒ ₁ , ƒ ₂ , which are connected through a series-connected adder 3, a pulse modulator 4, a matching amplifier 6, a power amplifier 7, a notch filter 8 with a radiating electro-acoustic transducer 9, the operation of both a pulse modulator 4 through a synchronizer 5, and generators 1, 2 of harmonic oscillations is carried out through connections with a control unit 24, an additional output of the adder 3 is connected through a series-connected amplitude detector 21, a low-frequency filter 22 with signal input of the frequency counter 23, the control input of which is also connected to the control unit 24. The radiating electro-acoustic transducer 9 with a resonant frequency ƒ ₀ , in the passband of which there are frequencies ƒ ₁ , ƒ _{2 of} harmonic oscillations of both the first and second generators, are related by the relation (ƒ _one +ƒ ₂ )/2=ƒ ₀ , operating in the mode of parametric radiation (RPI), acoustically connected through the aquatic environment 10 propagation with electro-acoustic receiving transducers: exemplary 12 and test 13. The transducers 9, 12, 13 are located in the anechoic pool 11, equipped coordinate system 20 for their installation and movement, and the latter has a mechanical drive from the recorder 19. The receiving path of the device contains an analog key 14 connected in series for switching the outputs of the receiving transducers 12, 13 in turn through an amplifier 15, a filter unit 16, a strobe unit 17, the output of which connected to the inputs of both the oscilloscope 18 and the recorder 19, and the output of the latter is mechanically connected to the coordinate system 20. The operation of both the analog key 14 and the recording equipment - the oscilloscope 18 and the recorder 19 is carried out through connections with the control unit 24. The control inputs of the strobe block 17, oscilloscope 18 and recorder 19 with connected to the corresponding outputs of the synchronizer 5. The operation of the device for calibrating electroacoustic transducers (Fig. 1) occurs as follows. Generators 1 and 2 generate harmonic signals with frequencies ƒ ₁ , ƒ ₂ entering the two inputs of the adder 3, which is brought into operation by the operator on command from the control unit 24. From the first output of the adder 3, the received biharmonic electrical signal is fed through the amplitude detector 21, low-pass filter 22 to the input of the frequency meter 23 (control of the frequency value of the difference signal), and from the second output to the input of the pulse modulator 4, which is controlled by the operator on command from the control unit 24 through the synchronizer 5. As a result, at the output of the pulse modulator 4 we get a radio pulse with biharmonic filling, which through a matching amplifier 6, a power amplifier 7, a notch filter 8 enters the electroacoustic transducer 9. The performance of the electroacoustic transducer 9 is based on the piezoelectric effect, moreover, it is used in the passband, i. in the frequency range near the resonance of its mechanical system with a frequency (ƒ ₁ +ƒ ₂ )/2=ƒ ₀ =ω ₀ /2π. The electroacoustic transducer 9 in the required frequency range ƒ ₁ , ƒ ₂ creates a biharmonic sound field in the aquatic environment 10, which manifests itself in the occurrence of compression and rarefaction areas that propagate at the speed of sound in the direction of the receiving piezoelectric transducers: exemplary 12 and graduated 13. Since the aquatic environment 10 has a nonlinearity of its elastic characteristics, a nonlinear interaction of powerful waves with frequencies ƒ ₁ \u003d ω ₂ /2π, ƒ ₂ \u003d ω ₂ /2π in the propagation channel is carried out, the result of which is the generation of acoustic signals of the difference F \u003d ƒ ₂ -ƒ ₁ frequency, i.e. e. electroacoustic transducer 9 operates in the mode of parametric radiation. The nonlinear interaction of powerful waves during their propagation in water 10 makes it possible to separate in space the processes of converting electrical energy into acoustic energy (electroacoustic converter 9) and the formation of directional radiation (the volume of water 10, in which the spectral components of a powerful biharmonic wave interact and nonlinear sources of a difference frequency signal are distributed) . The amplitude of the sound pressure of the difference frequency signal on the acoustic axis of the electroacoustic transducer 9 gradually increases with distance from it, reaching a maximum at a distance commensurate with its boundary of the near zone

q, where a is the size of the aperture of the electroacoustic transducer 9, ω ₀ =2π׃ ₀ is the cyclic frequency, c ₀ is the equilibrium value of the speed of sound propagation in water.

и неизвестной

соответственно, и являются приемниками звукового давления, расположены рядом и могут быть поочередно установлены (без «затенения») на акустической оси излучающего электроакустического преобразователя 9. В соответствии с методом замещения на акустической оси излучающего электроакустического преобразователя 9 в объеме заглушенного бассейна 11, оборудованного координатной системой 20 для установки и перемещения преобразователей, сначала располагают образцовый приемный преобразователь 12. При замещении образцового преобразователя градуируемым 13 сохраняется единство места и полная идентичность используемой аппаратуры. Воздействие звукового поля на приемные: как образцовый 12, так и градуируемый 13 - преобразователи в соответствии с прямым пьезоэффектом приведет к появлению переменного электрического сигнала на их выходах. Таким образом, образцовый 12 и градуируемый 13 электроакустические преобразователи поочередно преобразуют достигающие их ультразвуковые импульсы в электрические сигналы с амплитудами

и

, которые через аналоговый ключ 14 для коммутации приемных преобразователей по команде с блока управления 24 поступают на вход приемного тракта, в котором после усиления (усилитель 15), фильтрации (блок фильтров 16) и стробирования (стробируемый блок 17) фиксируются осциллографом 18 и самописцем 19. Управляющие входы стробируемого блока 17, осциллографа 18 и самописца 19 соединены с дополнительным выходом синхронизатора 5, причем, предусмотрен механический привод от самописца 19 к координатной системе 20 бассейна 11. Данное устройство позволит исследователю для необходимых спектральных составляющих (ƒi) частотного диапазона измерений рассчитать значения чувствительности по звуковому давлению в режиме приема для градуируемого электроакустического преобразователя 13The distance from the electroacoustic transducer 9 to the maximum is called the saturation region: in it, the most intense transfer of the energy of the biharmonic wave to the difference frequency signal occurs, beyond the saturation region, absorption and diffraction weaken the process of nonlinear interaction of the spectral components of the biharmonic wave, and the amplitude of the sound pressure of the difference frequency signal also begins to gradually decrease . The angular divergence of the formed signal of the difference frequency practically coincides with that for the biharmonic wave (along the main lobe XH of the radiating electroacoustic transducer 9), and the level of lateral radiation is negligibly small due to the fact that for off-axis directions there is no nonlinear change in the elastic properties of water 10. As a result, with a small aperture of the electroacoustic transducer 9, it is possible to obtain the emission of low-frequency signals within small solid angles in the complete absence of a side field. A polyharmonic ultrasonic signal containing spectral components with frequencies ƒ ₁ , ƒ ₂ , F=ƒ ₂ -ƒ ₁ propagates in water 10, which fills a plugged pool 11, equipped with a coordinate system 20 for mounting and moving receiving piezoelectric transducers: exemplary 12 and graduated 13. Receiving piezoelectric transducers have sound pressure sensitivities - known

and unknown

respectively, and are sound pressure receivers, located side by side and can be alternately installed (without "shading") on the acoustic axis of the emitting electroacoustic transducer 9. 20 to install and move the transducers, first place the exemplary receiving transducer 12. When replacing the exemplary transducer calibrated 13, the unity of the place and the complete identity of the equipment used are preserved. The effect of the sound field on receiving: both exemplary 12 and graduated 13 - transducers in accordance with the direct piezoelectric effect will lead to the appearance of an alternating electrical signal at their outputs. Thus, the exemplary 12 and calibrated 13 electroacoustic transducers alternately convert the ultrasonic pulses reaching them into electrical signals with amplitudes

and

, which through the analog key 14 for switching the receiving transducers, upon command from the control unit 24, are fed to the input of the receiving path, in which, after amplification (amplifier 15), filtering (filter block 16) and gating (gated block 17), they are recorded by oscilloscope 18 and recorder 19 The control inputs of the gated block 17, the oscilloscope 18 and the recorder 19 are connected to the additional output of the synchronizer 5, and a mechanical drive from the recorder 19 to the coordinate system 20 of the pool 11 is provided. sensitivity to sound pressure in the receiving mode for a calibrated electro-acoustic transducer 13

Comparison of compliance with the criterion of "monotonicity of change" of the experimental graphs for the range (0.2-25) kHz, showing the dependence of the frequency characteristics of the sensitivities in the radiation mode for the prototype (Fig. 2) and the proposed device (Fig. 3) shows the following. For both graphs, on the vertical axis, the relative levels of the emerging sound pressure P/P ₀ are plotted in decibels (P ₀ =1 Pa), on the horizontal axis, a logarithmic scale is used for frequency values. In this range, the functioning of the prototype device in the required frequency band is due to the use of two standard electroacoustic transducers: 1 Electrodynamic LFI - frequency subrange (0.2 - 2.5) kHz with overall dimensions (500 × 300) mm; 2) piezoceramic HFI - frequency subrange (2.5 - 25) kHz with overall dimensions (200 × 150) mm (in Fig. 3, the boundaries of the subranges are marked with vertical dashed lines). It should be noted that the prototype also provides for the verification of the third standard electro-acoustic transducer - a piezoceramic RFID for the frequency subrange (25 - 100) kHz with overall dimensions (100 × 40) mm.

As follows from FIG. 2, the sections of the frequency response of both LFI and RFI in the frequency subranges (0.2 - 2.5) kHz and (2.5 - 25) kHz have a significant indentation and non-monotonicity of the increment (dynamic range up to 48 dB, i.e. ~ 250 times): for LF - up to 18 dB (~ 8 times) and for HFI - up to 30 dB (~ 31 times). The implementation of measurements in the technical solution of the prototype with such sources is difficult, which cannot but affect the quality of the calibration. For the proposed device, this criterion is satisfactorily met. From FIG. 4 it can be seen that the frequency response increases monotonically (dynamic range up to 30 dB, i.e. ~ 31 times), without sharp fluctuations, which is a significant advantage in comparison with the prototype, leading to an increase in measurement accuracy.

Let us compare the experimental graphs of the angular dependence of the sound pressure (in a rectangular coordinate system) developed in the radiation mode for the prototype (Fig. 4, RFID, three curves: 1 - 5 kHz, 2 - 20 kHz, 3 - 25 kHz) and the proposed device (Fig. 5, four curves: 1 - 5 kHz, 2 - 20 kHz, 3 - 25 kHz, 4 - 100 kHz). For graphs on the vertical axis, the relative levels of voltages U/U ₀ recorded by the hydrophone are plotted in decibels, and the values of the angle of deviation of the acoustic axis of the emitter from the direction to the hydrophone are plotted on the horizontal axis. As follows from FIG. 4, with an increase in the radiation frequency, the RF frequency gradually goes beyond the limits of compliance with this criterion: curve 1 - at a frequency of 5 kHz in the range (-150° ÷ +150°) radiation within the main lobe (dynamic range ~ 23 dB, angular width by level ( -3 dB) about 60°), there are no additional lobes, curve 2 - at a frequency of 20 kHz in the range (-45° ÷ +30°) radiation within the asymmetric main lobe (dynamic range ~ 23 dB, angular width by level (- 3 dB) about 20°), additional lobes appeared, moreover, the ultrasonic side field to the left and right of the acoustic axis is also asymmetrical, curve 3 - at a frequency of 25 kHz in the range (-45° ÷ +50°) radiation within the asymmetric main lobe (dynamic range ~ 45 dB, angular width (-3 dB) about 16°), additional lobes are significant (up to 30 dB), the ultrasonic side field to the left and right of the acoustic axis is significantly asymmetrical. Thus, the prototype fully complies with this criterion with RFID at a frequency of 5 kHz. As follows from FIG. 5, an increase in the frequency of radiation in the proposed device does not lead to going beyond the limits of compliance with this criterion: curves 1, 2, 3, 4 - at frequencies of 5 kHz. 20 kHz, 25 kHz, 100 kHz in the range (-60° ÷ +60°) radiation within the same main lobe (dynamic range ~ 30 dB, angular width in level (-3 dB) is also almost the same and is about 16°), additional lobes are absent at frequencies of 20 kHz, 25 kHz, 100 kHz (curves 2, 3, 4), insignificant symmetrical additional lobes with a level (-20 dB) are observed in the directions of 75° to the left and right relative to the acoustic axis . Thus, for the proposed device, this criterion is also satisfactorily met.

или в децибелах σ₀=20lg(1+σ/А_ср),For a practical assessment of the advantages discussed above, a test calibration of the hydrophone (∅50 mm, TsTS-19) was carried out in the frequency range (5 ÷ 25) kHz at discrete certified points of one-third octaves of the series using both the proposed device and the prototype device (see GOST 12090 - 80. Frequencies for acoustic measurements. Preferred series http://docs.cntd.ru/document/1200016367 accessed 1.12.2019). Metrological processing of the results of repeated measurements for each operating point consisted in calculating the root mean square error of measurement series

or in decibels σ ₀ \u003d 20lg (1 + σ / A _cf ),

- среднее значение измеряемой чувствительности гидрофона в режиме приема, A_i - чувствительность гидрофона в режиме приема при i-м измерении, n - число измерений. Оказалось, что использование заявляемого устройства в сравнении с прототипом позволило снизить среднюю квадратическую погрешность σ₀ многократных измерений: для прототипа она составила 0,6 дБ, а для заявляемого устройства - 0,4 дБ, т.е. удалось существенно увеличить точность измерений.where

- the average value of the measured sensitivity of the hydrophone in the receiving mode, A _i - the sensitivity of the hydrophone in the receiving mode at the i-th measurement, n - the number of measurements. It turned out that the use of the claimed device in comparison with the prototype made it possible to reduce the root-mean-square error σ ₀ of multiple measurements: for the prototype it was 0.6 dB, and for the claimed device - 0.4 dB, i.e. it was possible to significantly increase the accuracy of measurements.

Tests of the layout of the proposed device for calibrating electroacoustic transducers made it possible to establish the following technical characteristics:

range of operating signals of difference frequency - (2 ÷ 300) kHz;

reference sound pressure level 15 Pa at a distance of 1 m at a difference frequency of 5 kHz;

the width of the main lobe of the directional characteristic in the range of the above working signals of the difference frequency - (30±1) deg;

aperture parameters of the radiating electroacoustic transducer - resonant frequency 1.014 MHz, diameter 40 mm, slightly concave or resonant frequency 2.03 MHz, diameter 30 mm, slightly convex,

length of the diffraction zone - 5 cm or 4 cm;

spherical distribution zone - 0.5 m or 0.3 m;

operating mode - pulse; pulse duration - (0.06 ÷ 12) ms; pulse repetition rate - (0.5 ÷ 400) Hz; purpose - hydroacoustic measurements.

The proposed device for calibrating electroacoustic transducers can be widely used in the field of acoustic measurements and hydroacoustics.

Reference designations.

1, 2. Generators of harmonic oscillations,

3. Totalizer

4. Pulse modulator

5. Synchronizer

6. Matching amplifier

7. Power amplifier

8. Notch filter

9. Radiating electroacoustic transducer

10. Aquatic environment

11. Drowned pool

12. Exemplary electroacoustic receiving transducer

13. Graduated electroacoustic receiving transducer

14. Analog key of the receiving path

15. Receiving path amplifier

16. Filter block

17. Strobe block

18. Oscilloscope

19. Recorder

20. Coordinate system for installing and moving transducers,

21. Amplitude detector

22. Low pass filter

23. Frequency counter

24. Control unit

Claims (3)

1. A device for calibrating electroacoustic transducers, containing a radiating path, including a harmonic oscillation generator, a pulse modulator, a synchronizer, a power amplifier, a frequency meter, a radiating electroacoustic transducer, a receiving path, including exemplary and calibrated receiving electroacoustic transducers, an analog key for switching receiving electroacoustic transducers transducers, an amplifier, a filter unit, a strobe unit, a control unit for the radiating and receiving paths, and a muted pool for accommodating electroacoustic transducers, containing a coordinate system for installing and moving the transducers, characterized in that a second generator of harmonic oscillations, an adder, an amplitude detector, low-pass filter, matching amplifier and notch filter, and the outputs of both harmonic generators are connected to two signal inputs of the adder, not the first output of which is connected through a pulse modulator, a matching amplifier, a power amplifier and a notch filter to the input of a radiating electro-acoustic transducer, the second output of the adder is connected through an amplitude detector and a low-frequency filter to the signal input of a frequency meter, and the outputs of the control unit are connected to the control inputs of both harmonic oscillation generators , synchronizer, frequency meter and analog key. 2. A device for calibrating electro-acoustic transducers according to claim 1, characterized in that the radiating electro-acoustic transducer is made with a resonant frequency ƒ ₀ and in its passband there are frequencies ƒ ₁ , ƒ _{2 of} harmonic oscillations of generators related by the ratio (ƒ ₁ +ƒ ₂ ) /2=ƒ0 _. 3. The device according to claim. 1, characterized in that it additionally contains a recorder and an oscilloscope connected to the control unit.

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