SU1384961A1 - Device for measuring velocity of ultrasound waves - Google Patents

Abstract

This invention relates to the field of materials research and is intended to measure the speed of ultrasonic waves in environments with high attenuation. The purpose of the invention is to improve the accuracy of measuring the velocity of ultrasonic waves by increasing the signal-to-noise ratio. In the device, in addition to measuring the velocity over the time interval between the maxima of the envelope of the transformed signal, corresponding to the resonances of the emitted frequency-modulated ultrasonic waves, in the measuring chamber with the material under study, the velocity is measured by the propagation delay of ultrasonic waves, coherent accumulation of realizations of the transformed signal, quantized in amplitude and time, the signal-to-noise ratio as well as the spectral analysis of the averaged realization are transformed th signal using fast Fourier transform algorithm. 2 Il. i (Л С

Description

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The invention relates to the field of materials research using ultrasonic vibrations and can be applied to measure the speed of acoustic waves in environments with high attenuation.

The purpose of the invention is to improve the accuracy of measuring the velocity of propagation of ultrasonic waves in Q media with high attenuation due to an increase in the signal-to-noise ratio.

FIG. 1 shows a block diagram of the proposed device; in fig. 2 shows voltage plots and laws 15 of signal frequency variations explaining device operation.

The device contains serially connected modulator 1, high-frequency oscillator 2 of tuned 20 frequency, power amplifier 3, radiating converter 4, measuring chamber 5, receiving converter 6, voltage amplifier 7, mixer 8, low-pass filter 9, 25 analog-digital The converter 10, calculator 11 and indicator 12. The output of the high-frequency generator 2 of the tunable frequency is connected to a full range of the operating mode of the mixer 8, fed to the second input of the mixer 8 to the first input of which a signal is output from High Frequency Generator 2 Tunable Frequency. Frequency of the useful signal component

(f and f. in Fig. 2a), present at the second input of the mixer 8, and vary according to the same law as the frequency of the emitted signal (f, in Fig. 2a), present at the first input of the mixer 8, however, the useful component the signal present at the second input of the mixer 8 is delayed by the value of c (Fig. 2a)

about a signal present n

the first input of the mixer 8. As a result of multiplying these signals at the output of the mixer 8, a conversion signal is produced, the frequency of which is fg. | fp-fc / (Fig. 26) is proportional to the value of T,. Different times of propagation of acoustic waves will correspond to different values of the frequencies fj-. The amplitude of the transformed signal increases with the resonance in the test substance, which occurs in the case when

the input input of the mixer is 8, and the second input 30 is the length of the measuring chamber;

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In this mode, the operation mode of the mixer 8 is fed to the second input of the mixer 8, to the first input of which a signal is output from the high-frequency generator 2 of a tunable frequency. Frequency of the useful signal component

(f and f. in Fig. 2a), present at the second input of the mixer 8, changes according to the same law as the frequency of the emitted signal (f, in Fig. 2a), present at the first input of the mixer 8, however, the useful signal component present at the second input of the mixer 8 is delayed by the value of c (Fig. 2a) relative to the signal present at

the first input of the mixer 8. As a result of multiplying these signals at the output of the mixer 8 a conversion signal is formed, the frequency of which is fg. | fp-fc / (Fig. 26) is proportional to the value of T,. Different wave propagation times will correspond to different signs. The frequencies fj-. The amplitude of the transformed signal increases at resonance in the substance under study, which occurs in the case when

analog-to-digital converter 10 is connected to the second output of the modulator 1.

The device works as follows.

In the modulator 1, an analog sawtooth signal is generated, which arrives at the high frequency generator 2 of a tunable frequency and changes its frequency according to the law of an asymmetric saw (fp in Fig. 2a). ... An electrical signal from the output of a high-frequency generator 2 of tunable frequency, amplified by a power amplifier 3, is fed to a radiating transducer 4 installed in the measuring chamber 5. Emitting transducer 4 Converts an electrical signal to an acoustic signal that propagates in the test substance and acts on the receiving one transducer 6. At the output of transducer 6, there is an electrical signal representing an additive mixture of noise and useful components. The output signal of the receiving transducer 6, amplifying the amplifier 7 voltage to the required value, providing a linear am5

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with a test substance, an integer number of ultrasonic half-waves of the probing signal is placed. The signal generated at the output of the mixer 8 (Fig. 2c - the case of low attenuation of acoustic waves, Fig. 2d - the case of large attenuation of acoustic waves), is filtered by a low-pass filter 9, the band of which is chosen so as to skip the converted signal with a wide range fJ. (which corresponds to a wide range of velocities of the longitudinal waves of the studied substances), not distorted in amplitude, and not to transmit signals with frequencies f, f, f f and other combinational components. From the output of the low-pass filter 9, the converted signal (Figs. 2b and 2d) is fed to the analog-to-digital converter 10, the second input of which receives clock pulses from the second output of the modulator 1 (Fig. 2e), which discretize the converted signal over time . At the moment of action of the clock pulses, the transformed signal amplitude quantizes (Fig. 2e). Signal counts

Digitally transferred to the calculator 11. In the calculator 11, digital processing of the realizations of the converted beat signal is carried out, the results of which are displayed on the screen of the indicator 12.

Digital processing is carried out as follows. At the first stage, a coherent accumulation of the realizations of the transformed signal is made over the modulation periods to increase the signal-to-noise ratio to a level that ensures the specified measurement accuracy. At the second stage, longitudinal waves are measured over a time interval between adjacent envelopes of the quantized transformed signal, which correspond to adjacent acoustic resonances of longitudinal waves in the substance under study. The resulting velocity estimate is then used to identify the spectral component that corresponds to the longitudinal wave that arrived through the test substance. At the third stage, the averaged transformed signal quantized in time and in amplitude is subjected to spectral analysis using the Fast Fourier Transform algorithm in order to increase the accuracy of the estimation of the velocity of longitudinal waves. The processing results are displayed on the indicator 12.

The measurement of the additional information parameter — the delay in propagation of elastic waves — is carried out in conjunction with the coherent processing of realizations of the transformed signal, which increases the signal-to-noise ratio, and, consequently, the accuracy of measurements. In addition, a measurement is made of the velocity of the longitudinal wave at the neighboring maxima of the envelope of the transformed signal with the corresponding resonances of the longitudinal wave in the substance or rock under study. This velocity estimate is used to identify the informative spectral component in the spectral analysis of the converted signal, which ensures high accuracy of measurements.

The measurement of the additional information parameter leads to the fact that the instability of the gain factors and phase characteristics of the blocks (nodes) do not affect the accuracy of measurements.

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rhenium, since the information parameter is related to the frequency of the converted signal.

The frequency of the converted signal fJ is related to the velocity V of acoustic waves in the substance under study by the relation

(one)

where u

uFi

 the slope of the change in the frequency of the emitted signal; geometrical length, distance between receiving and radiating converters; frequency deviation

five

T u

the steering signal, & F,

one

M

period of modulation of the probing signal.

The potential accuracy of determining the velocity of acoustic waves (5 "from (U) using an additional information parameter - time T, the delay of propagation of elastic oscillations, with a large modulation index is determined by the ratio

c .. (v) v2

. (fr) 4- “nor p-ITF Tq

(2)

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where is sweat and (r

Sweat

Crg)

(ff)

- according to the accuracy of determining the frequency of the converted signal and the delay Ci. It follows from (2) that the accuracy is higher, the greater the signal-to-noise ratio and the frequency band of the emitted signal (with a large modulation index, the band of the linear-frequency modulated signal is equal to its deviation). The magnitude of the LU is limited by the bandwidth of the piezo transducers. Therefore, in the device, high accuracy of the velocity measurement is provided along with the use of the widest piezo transducers by increasing the signal-to-noise ratio. For this, a coherent accumulation of realizations of the converted signal with a duration of one period of modulation of the emitted signal is carried out. The realization of the signal at the output of the mixer 8 (the large attenuation of the elastic oscillations in Fig. 2d) is the additive sum of the useful component of the transformed signal, repeated in each modulation period and the noise component, the sources of which are its own thermal reception path noise (voltage amplifier 7 and mixer 8) and acoustic noise of the medium under study. Intra-noise noise is known to be stationary normal white noise. Regarding acoustic noise, it is known that its spectrum occupies a range of frequencies from units of hertz to units of megahertz. The bandwidth on the level of 0.707 receiving transducer 6, which, together with the radiating transducer 4, is the most narrow-band link in the path of the formation and reception of the high-frequency frequency-modulated signal, has a value of 500 kHz in the device. Thus, acoustic noise can be considered stationary normal white noise with zero average. Under such conditions, an efficient accumulation of the converted signal is ensured. An increase in the signal-to-noise ratio is directly proportional to the number of averages of the converted beat signal over modulation periods. Accumulation can be performed due to the fact that the phase structure of the transformed signal is rigidly synchronized with the bursts of clock pulses, sent from the modulator 1 to the analog-to-digital converter 10.

In the implementation of the transformed signal, averaged over the periods of modulation, the algorithm finds two adjacent envelope maxima. The speed of the longitudinal acoustic waves is determined from these maxima, corresponding to the resonances of the acoustic waves in the substance under study. The calculation is carried out according to the formula

, (3)

where T is the time interval between the maxima of the transformed signal, defined by the formula At,

where N is the number of points between the maxima of the envelope of the transformed signal;

ut is the time sampling between samples of the converted signal realization (determined by the frequency of the clock pulses).

e -

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Produced in this way a rough estimate of the velocity of longitudinal waves, then the converted signal is subjected to

with spectral analysis using the fast Fourier transform algorithm, as a result of which a line spectrum of the transformed signal realization is obtained. At the same time, the real frequencies are 10 fy; the spectral components of the transformed signal are related to the normalized frequencies fj of the spectra by

f5; fi / & t. (4)

15 In order to provide high frequency accuracy with the help of the fast Fourier transform, the number of points in the analyzed implementation of the transformed signal is increased due to

20 zero calculations, which results in interpolated estimates of the spectral components and, in addition, the sampling time interval & t of the converted signal

25 to analog-to-digital converter 10.

Since the transformed signal is multicomponent due to the fact that oscillations of various types propagate in the test medium.

30 (longitudinal, transverse, and other), a spectral analysis yields a set of estimates for the propagation delays of elastic waves:

f. --Y- (5)

 I - P T1 H- /

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At the next stage, an estimate of the velocity of the longitudinal wave, obtained from the analysis of the temporal position of the resonant maxima of the magnifying transformed signal, is used to identify the spectral component associated with the longitudinal elastic oscillations. In the case of a sharply inhomogeneous medium (which is typical of rocks), the fact that the longitudinal wave has the highest speed is taken into account, which means, in the spectrum of the transformed signal, as the first spectral peak.

by- ,

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maximum at frequency f. By calculating with the power of relations (4) and (5) the delay corresponding to a given frequency ff, the velocity of the longitudinal wave was determined by the formula

,, (6)

where P is the distance between the emitting and receiving transducers, is considered known.

The beat signal spectrum also contains information about the speed of ultrasound waves of other types, the identification of these waves is associated with a particular test substance.

The results are displayed on the indicator device in the form of a graphic image of the spectrum of the transformed signal and numerical data corresponding to the measured values of the longitudinal velocity.

Claims (1)

Invention Formula A device for measuring the speed of ultrasonic waves, containing a measuring chamber, a high-frequency tunable frequency generator, emitters and receiving transducers installed in the measuring chamber, a voltage amplifier whose input is connected to the output receiver five 0 Converter, and indicator, characterized in that, in order to improve measurement accuracy for environments with high attenuation, it is equipped with a modulator, a power amplifier connected in series with a mixer, low pass filter, analog-to-digital converter and calculator, the output of a high-frequency tunable frequency generator connected to the first input of the mixer and to the input of the power amplifier, the output of which is connected to the input of the radiating converter, the first output of the modulator is connected to the input of the high-frequency gene Ator my tunable frequency, the second output - to a second input of the analog-digital converter, the output calculator connected to the input of the indicator, and the output voltage of the amplifier - a second input of the mixer. - 7 eleven 12 1