RU2568070C1 - Method of measuring complex frequency dependence of transfer impedance of radiator-receiver pair in free field - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method includes placing a radiator and a receiver in a basin, the receiver being situated at a certain distance from the radiator; measuring the time delay of the signals of the radiator reflected by boundaries of the medium relative to the forward signal of the radiator; exciting the radiator with noise in a frequency band whose width is determined based on the values of the time delay of the reflected signals; measuring the radiator current power spectrum and the cross-spectrum of the radiator current and the receiver output voltage, relative to which the complex frequency dependence of the transfer impedance of the radiator-receiver pair is determined; determining the complex frequency dependence of the transfer impedance of the radiator-receiver pair in a free field by sliding complex weighted averaging in a set frequency window of the complex frequency dependence of the transfer impedance of the pair in a reverberation field of a medium with reflecting boundaries using a weight function, which is obtained based on the values of the time delays of the reflected signals.

EFFECT: high measurement accuracy.

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Description

The invention relates to acoustic measurements and can be used to calibrate acoustic transducers over a field in a reverberation field arising from the continuous emission of noise in an environment with reflecting boundaries (reverberation chamber, sonar pool).

The term "calibration of the acoustic transducer by field" means the determination of the sensitivity of the transducer to receive / radiation by voltage / current in the free field of a traveling sound wave [1]. A free sound field is understood to mean a sound field in a homogeneous isotropic medium, the boundaries of which have a negligible effect on sound waves [1]. In practice, it is impossible to implement such conditions, therefore, graduating a transducer over a field is almost always complicated by the need to combat reflections.

A known method for determining the transfer impedance of a pair of emitter-receiver by field in an unmuffled measuring pool [2, 3], in which the direct signal of the emitter and the signals reflected by the boundary surfaces of the pool are separated by the method of temporary selection. In this case, a tone-pulse signal is used as a radiation signal.

The disadvantages of this method are distortion of the shape of the tonal pulse by transients in a narrow-band measuring path, a decrease in the efficiency of temporal selection with a decrease in the frequency and, as a result, a limitation of the lower frequency of graduation over the field, a long measurement time for a detailed frequency response, the need for coherent accumulation of tonal pulses at the reception to increase the ratio signal / noise.

There is a method of determining the transmit impedance of a pair of emitter-receiver by field in the conditions of continuous emission of a linear-frequency-modulated (LFM) signal with known parameters in an unmuffled pool with frequency separation of direct and reflected signals [4].

The second analogue consists in the location in the pool with the reflecting boundaries of the emitter and the receiver with a known distance between the emitter and the receiver, determining the time delays of the emitter signals reflected by the boundaries relative to the direct signal of the emitter, exciting the emitter with a chirp signal with known parameters, measuring the emitter current and the receiver output voltage suppressing reflected signals in the output voltage using an intermediate frequency filter, the passband of which is adjusted based from the parameters of the LFM signal and the time delays of the reflected signals, determining the frequency dependence of the transfer impedance of the emitter-receiver pair in a free field from the frequency dependences of the emitter current and voltage at the output of the intermediate frequency filter.

This analogue is called the method of spectrometry of time delays (SVZ). The disadvantages of the SVZ are large errors in determining the frequency dependence of the transfer impedance of the emitter-receiver pair over the field, due to insufficient suppression of the reflected signals and distortions of the desired frequency dependence by averaging over the frequency in the intermediate frequency filter.

For the prototype adopted a method for a similar purpose [5]. The prototype consists in arranging an emitter-receiver pair in a medium with reflecting boundaries at a known distance between the emitter and the receiver, determining the time delays of the emitter signals reflected by the medium boundaries relative to the direct emitter signal, exciting the emitter with a signal with power distributed in the frequency band, and measuring the receiver output voltage and the emitter current, determining the complex frequency dependence of the transfer impedance of the emitter-receiver pair in a medium with reflecting boundaries , determining the complex frequency dependence of the transfer impedance of the emitter-receiver pair over the field by moving complex weighted averaging (SLE) of the complex frequency dependence of the transfer impedance in the reverberation field of the medium with reflecting boundaries using the weighting function, which is obtained based on the values of the time delays of the reflected signals.

As a signal with power distributed in the frequency band in the prototype, a linear frequency-modulated (LFM) signal is used. This leads to the following disadvantages of the prototype.

The use of the LFM signal does not exclude the influence of the transient process, as a result of which the error in determining the transfer impedance of the emitter-receiver pair in the field increases. The chirp signal is not used when testing resonant transducers. The accuracy of the measurement result to a large extent depends on the parameters of the chirp signal. Due to the difference in the arrival times of the direct and reflected LFM signals at the receiving point, their instantaneous frequencies never coincide. This property of the LFM signal, useful for the SVZ method, causes errors during processing of the SLE.

1) Error due to the non-stationary influence of reflections

The difference between the instantaneous frequencies of the direct and reflected chirp signals causes the non-stationary distortion of the experimental frequency dependence of the reflections.

2) Error due to mismatch in the amplitude modulation of the direct and reflected waves

Due to the difference in the arrival times of the direct and reflected LFM waves, the reflected signal is modulated in amplitude not according to the law of modulation of the direct wave. The mismatch of the amplitude modulation of the direct and reflected waves reduces the efficiency of editing the experimental frequency dependence [6].

The technical result obtained from the implementation of the invention is to increase the accuracy of determining the transfer impedance of the emitter-receiver in the field by eliminating the above disadvantages.

This technical result is achieved due to the fact that in the known method, consisting in the location in a medium with reflecting boundaries of the pair of emitter-receiver at a known distance between the emitter and the receiver, determining the time delays of the emitter signals reflected by the boundaries of the medium relative to the direct signal of the emitter, excitation of the emitter a signal with power distributed in the frequency band, measuring the output voltage of the receiver and the emitter current, determining the frequency dependence of the transfer impedance emitter-receiver pairs in a medium with reflecting boundaries, determining the frequency dependence of the transfer impedance of the emitter-receiver pair over the field by moving complex weighted averaging in the established frequency window of the obtained complex frequency dependence of the transmission impedance in the reverberation field of the medium with reflecting boundaries using the weighting function, which is obtained on the basis of from the values of the time delays of the reflected signals, as a signal with power distributed in the frequency band for the emitter’s excitations use a noise signal whose frequency bandwidth is determined based on the values of the time delays of the reflected signals, while measuring the power spectrum of the emitter’s current and the mutual spectrum of the emitter’s current and the receiver’s output voltage, and the complex frequency dependence of the transfer impedance of the emitter-receiver pair in the reverberation field of the medium with reflecting boundaries is defined as the ratio of the mutual spectrum to the power spectrum.

The invention is illustrated in the drawing, which shows a diagram of the implementation of the method and shows:

PC - a personal computer that performs the functions of noise generation and signal processing and is equipped for this purpose:

DAC-converter digital - analog signal,

ADC-converter analog signal - digital,

SPO-specialized software, including software modules:

1 - the formation of a random numerical sequence with a given spectrum,

2 - direct and inverse Fourier transforms,

3 - calculation of the power spectrum and the mutual spectrum, including the accumulation function,

4 - calculation of the ratio of the spectra,

5 - moving complex weighted averaging of the frequency dependence;

UM - power amplifier;

VU - input amplifier;

R is the calibrated resistance in the emitter circuit for measuring current;

And - emitter;

P is the receiver.

The essence of the method for obtaining the frequency dependence of the transfer impedance of a pair of emitter-receiver over a field in the frequency range [f ₀ -Δf / 2, f ₀ + Δf / 2] using SLE processing using acoustic noise is as follows.

A pair of emitter-receiver is located in the measuring pool with a known distance between the emitter And and the receiver P.

The frequency averaging interval Δf _{wa is} determined. To do this, the emitter is excited with a short pulse, the direct emitter signal is received and the signals reflected by the pool boundaries, the time delays τ ₁ , τ ₂ , ..., τ _{n of the} first significant reflections relative to the direct emitter signal are determined. Based on the obtained time delays, the frequency interval of the moving complex weighted averaging is determined Δf _wa = 1 / τ ₁ + 1 / τ ₂ + ... + 1 / τ _n (usually n does not exceed three) [7, 8].

Form a radiation signal. To do this, using a random number generator form random numerical sequences x _0i (t) with a uniform spectrum in the frequency band [f ₀ - (Δf-Δf _wa ) / 2, f ₀ + (Δf + Δf _wa ) / 2] [7, 8]. Random numerical sequences with a given spectrum shape are obtained, for example, by the formula:

x _i (t) = ℑ ^-1 {V _w (f) · ℑ {x _0i (t)}},

where V _w (f) is the weighting function that defines the shape of the spectrum in the frequency band [f ₀ - (Δf-Δf _wa ) / 2, f ₀ + (Δf + Δf _wa ) / 2], ℑ {...} and ℑ ^-1 {...} mean, respectively, the direct and inverse Fourier transform.

. Усиленными шумовыми сигналами

возбуждают излучатель И, создавая, таким образом, в измерительном бассейне реверберационное поле шумовой акустической волны.An acoustic noise signal is emitted. For this, random numerical sequences x _i (t) are fed to the DAC and receive analog noise radiation signals

. Amplified Noise Signals

excite the emitter And, thus creating, in the measuring pool, the reverberation field of the noise acoustic wave.

ток

через резистор R и выходное напряжение приемника

усиливают и преобразуют в цифровые случайные последовательности тока излучателя i_i(t) и выходного напряжения приемника u_i(t). Вычисляют текущие спектры напряжения U_i(f)=ℑ{u_i(t)} и тока I_i(f)=ℑ{i_i(t)}, спектры мощности тока

и взаимные спектры тока и напряжения

. Текущие спектры накапливают и получают спектр мощности тока излучателя II(f)=<II_i(f)> и взаимный спектр тока излучателя и выходного напряжения приемника UI(f)=<UI_i(f)> (<…> - обозначает операцию накопления спектров).Form signals at the reception. For each noise signal

current

through resistor R and receiver output voltage

amplify and transform into digital random sequences of the emitter current i _i (t) and the receiver output voltage u _i (t). The current voltage spectra U _i (f) = ℑ {u _i (t)} and current I _i (f) = ℑ {i _i (t)} are calculated, the current power spectra

and mutual spectra of current and voltage

. The current spectra accumulate and receive the power spectrum of the emitter current II (f) = <II _i (f)> and the mutual spectrum of the emitter current and the receiver output voltage UI (f) = <UI _i (f)>(<...> - denotes the accumulation operation spectra).

получают как отношение взаимного спектра к спектру мощности:The complex frequency dependence of the transfer impedance of a pair of emitter-receiver in a reverberation field

get as the ratio of the mutual spectrum to the power spectrum:

.

.

в частотном диапазоне [f₀-(Δf-Δf_wa)/2, f₀+(Δf+Δf_wa)/2]:The complex frequency dependence of the transfer impedance of the emitter-receiver pair over the field Z _PH (f, Δf _wa ) in the frequency range [f ₀ -Δf / 2, f ₀ + Δf / 2] is obtained by moving complex weighted averaging (SLE) in the frequency range Δf _wa frequency dependence

in the frequency range [f ₀ - (Δf-Δf _wa ) / 2, f ₀ + (Δf + Δf _wa ) / 2]:

[6, 7].where W _SKVU (f) is the weighting function obtained by the convolution of rectangular functions with bases of width

[6, 7].

. Влияние отражений устраняют последовательными скользящими усреднениями в частотных интервалах Δf_i, соответствующих запаздываниям отражений, либо одним взвешенным скользящим усреднением в частотном окне

по формуле (1).Simplified essence of the SLE method can be represented as follows. The distortion of the frequency dependence caused by the reflection delayed at the receiving point relative to the direct signal of the emitter by the time τ _ref is eliminated by moving averaging the dependence in the frequency interval of width 1 / τ _ref . If there are several reflections, for each suppressed reflection with number i use their own averaging interval

. The influence of reflections is eliminated by successive moving averages in the frequency intervals Δf _i corresponding to the delay of the reflections, or by one weighted moving averaging in the frequency window

by the formula (1).

Thus, the disadvantages of the prototype are eliminated, the accuracy of determining the transfer impedance of the emitter-receiver in the field is increased, and the set technical result is achieved.

Literature

1. International standard IEC 50 (801), International Electrotechnical Vocabulary. Chapter 801: Acoustics and electroacoustics, (International Electrotechnical Dictionary. Chapter 801: Acoustics and Electroacoustics, 1994-07).

2. Bobber R.J. Hydroacoustic measurements. / Per. from English under the editorship of A.N. Golenkova. - M .: World. - 1974., CEI / IEC 60565: 2006.

3. Underwater acoustics - hydrophones - calibration in the frequency range 0.01 Hz to 1 MHz. International Electrotechnical Commission. Geneva. Switzerland - 2006.

4. Peder S. Pedersen, Peter A. Lewin, Leif Bjørnø, Application of time-delay spectrometry for calibration of ultrasonic transducers / IEEE transaction on ultrasonics, ferroelectric and frequency control. - March, 1988. - Vol. 35, No. 2. - P. 185-205.

5. RF patent No. 2390968 C2. Cl. H04R 29/00, published 05/27/2010 in BI No. 15, adopted as a prototype.

6. Isaev A.E., Matveev A.N., Nekrich G.S., Polikarpov A.M. Integrated graduation of a pressure gradient receiver using the reciprocity method procedure // Acoustic Journal. 2014.V. 60. No. 1. S. 48-55

7. Isaev A.E., Matveev A.N. Graduation of hydrophones in a field with continuous radiation in a reverberant pool // Acoustic Journal. 2009. Volume 55. No. 6. S. 727-736.

8. Isaev A.E. Accurate graduation of sound pressure receivers in an aqueous medium under free field conditions. - Mendeleevo: FSUE VNIIFTRI. 2008.369 s.

Claims (1)

A method for determining the complex frequency dependence of the transfer impedance of a pair of emitter-receiver over a field, consisting in arranging in a medium with reflecting boundaries of a pair of emitter-receiver at a known distance between the emitter and receiver, determining the time delays of the emitter signals reflected by the boundaries of the medium relative to the direct signal of the emitter, excitation a radiator with a signal with power distributed in the frequency band, measuring the receiver output voltage and the radiator current, determining the frequency the dependence of the transfer impedance of a pair of emitter-receiver in a medium with reflecting boundaries, determining the frequency dependence of the transfer impedance of a pair of emitter-receiver over a field by moving a complex weighted average of the obtained complex frequency dependence of the transfer impedance in a reverberation field of a medium with reflecting boundaries using a weighting function that is obtained from values of time delays of reflected signals, characterized in that as a signal distributed in the floor All frequencies with a power to excite the emitter use a noise signal whose frequency bandwidth is determined based on the values of the time delays of the reflected signals, while measuring the power spectrum of the emitter current and the mutual spectrum of the emitter current and the output voltage of the receiver, and the complex frequency dependence of the transfer impedance of the emitter-receiver pair in a reverberation field, a medium with reflecting boundaries is defined as the ratio of the mutual spectrum to the power spectrum.