SU1753408A1 - Method for measuring velocity of ultrasonic oscillation propagation - Google Patents

Abstract

The invention relates to the field of mechanical testing, can be used for ultrasound studies of materials, mainly in obtaining the temperature dependences of their elastic constants near temperature phase transitions, invar effects and other nonlinear effects. The aim of the invention is to increase the reliability of measurements by equalizing the amplitudes of the reflected signals, which determine the propagation time of ultrasonic vibrations. By changing the amplitude of each second emitted ultrasound pulse so that the minimum amplitude of the third (fourth) period of high-frequency oscillations of the (n-1) -th reflected pulse is equal to the nominal amplitude of the minimum of the third (fourth) period of high-frequency oscillations of the first n-th reflected pulse of each first radiated ultrasound pulse, the errors associated with the dependence of the velocity of propagation of ultrasonic vibrations on the values of the amplitudes of the pressure of elastic waves in each point of the test sample. 2 Il C

Description

The invention relates to the field of mechanical testing, can be used for ultrasound studies of materials, mainly in obtaining the temperature dependences of their elastic constants near the temperature of phase transitions, invar effects and other nonlinear effects.

The known method consists in that ultrasound (US) pulses are emitted into the sample under study, receive reflected pulses, measure the time interval between the first half periods of successive reflections and

the measured time interval is determined by the propagation velocity of the ultrasound 1.

The closest to the proposed solution to the technical essence and the achieved result is a method of measuring the velocity of propagation of ultrasonic oscillations, which means that ultrasound pulses are emitted into the sample under study, receive reflected pulses, measure the time interval between the reflected pulses The time stamps and the measured time interval determine the speed

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propagation of ultrasonic vibrations 2.

The disadvantage of the above methods is the low accuracy of measuring the velocity of ultrasound propagation when conducting precision studies of single crystal materials with a coefficient of change of elastic constants less than 5-10 arbitrary units / degrees, in the area of phase transitions, invar effects and other nonlinear effects. This is due to the fact. that the propagation velocity of the ultrasound wave in the sample under study depends on the amplitude of the elastic wave pressure at each point, i.e., the propagation velocity of the first and subsequent reflected signals having different oscillation amplitudes due to attenuation processes are different. In addition, phase errors occur when amplifying the reflected signals of different amplitudes in the active elements of the measuring equipment.

The aim of the invention is to increase the reliability of measurements by equalizing the amplitudes of the reflected signals, which determine the time of propagation of ultrasonic vibrations.

The goal is achieved by the fact that in a known method of measuring the propagation speed of ultrasonic oscillations, namely, that ultrasound pulses are emitted into a sample, they receive reflected pulses, the time interval between the reflected pulses is measured by the calibration time marks coinciding with their vertices time determine the propagation velocity of the ultrasonic vibrations, according to the invention, change the amplitude of every second radiated ultrasound o pulse so that the minimum amplitude of the third (fourth) period of high-frequency oscillations of the (n-1) th reflected pulse is equal to the nominal minimum amplitude of the third (fourth) period of high-frequency oscillations of the n-th reflected pulse of each first emitted ultrasonic pulse, and the time interval measured between the minima of the third (fourth) period of high-frequency oscillations of the indicated reflected pulses.

FIG. 1 shows a block diagram of an installation that implements the proposed measurement method; figure 2 is a timing diagram of the reflection signals at the time of measurement.

The installation contains a series of electro-acoustically connected generator 1 of calibration markers, a divider 2 frequencies, a generator 3 of a probing signal, including a series-connected driver 4 adjustable

delays and a shock excitation generator 5 and an electronic switch 6, whose input is connected to an output of a variable delay driver 4, and an output to a second input of a shock excitation generator 5, an acoustic path including transceiver transducer 7, an acoustic conductor 8 and a test sample 9, an amplifier 10 and a two-beam oscilloscope 11, the second input of which is connected to the second

5 to the output of the generator 1 calibration time stamps, and the synchronous input - to the output of the divider 2 frequency.

Positions 12 and 13 (Fig. 2) denote calibration time stamps, 14 and 15 0 (p-1) - and p-echo signals.

Through the generator of calibration time stamps (FIG. 1), a series of pointed signals (pos. 12 and 13 of FIG. 2) are produced, the frequency of which

5 is determined by an adjustable precision generator-synthesizer (of the type GZ-110). This makes it possible to set the follow frequency of the time stamps 12 and 13 with an accuracy of no worse. Keenness

The 0 marks 12 and 13 of time (Fig. 2) should be comparable to the sharpness of the vertices of the fill signal (position 14 and 15 of Fig. 2). The ability to stably match signal waveforms

12 and 13 with reflections (Fig. 2) of the sonic ultrasonic signals is achieved by the general triggering of the synchronization signal of the two-beam oscilloscope 11 and the triggering of the generator 5 of the shock excitation. The generation of this trigger signal is achieved by dividing the frequency of the signal of the calibration time stamps by a fixed division factor in the frequency divider 2 (Fig. 2). The choice of the magnitude of the division factor is due to the processes of extinction in the acoustic path. A shock excitation generator 5 is used to generate a high frequency probing signal. The next start of the generator of shock excitation is after the complete attenuation of the signals of reflections from the previous start. This ensures the repetition of the initial phase of high-frequency signals on subsequent launches. When starting generator 5

5, an impact delay shaper 4 is provided for leveling the calibration marks 12 and

13 time (FIG. 2) and the reflected signals under study (14 and 15) on the oscilloscope screen 11.

The shock excitation generator 5 (Fig. 1) in the inventive device comprises an electronic switch 6 (Fig. 1), which makes it possible to reduce the amplitude of the produced signal to each value due to the corresponding smooth adjustment during each even (conditional) start. From the output of the generator 3 of the probing signal (figure 1) high-frequency signal is supplied to the piezoelectric transducer 7, mounted on the free end of the acoustic buffer sound conductors 8.

The acoustic signal, reflected from the second end of the Zvukovaya 8, returns to the transceiver transducer 7 (Fig. 1), represented the first reflection (pos. 14 Fig. 2). Part of the acoustic energy, having passed through the end-section - sound duct - sample 9, is reflected from the second sample face and through the buffer sound line 8 reaches the converter 7, being the second echo signal 15 (figure 2). The sound energy, reflected from the end face of sample 9, each time partially penetrates into the sound duct 8, thus forming the third, fourth, etc. n-th echo signal before complete attenuation. Audio echoes 14 and 15 (FIG. 2), reaching converter 7, are converted into electrical signals that are amplified by narrowband amplifier 10. By adjusting the oscillator frequency 1 of the calibration time stamps, the amplitudes of the first and second probe signals, and the delay of the time marks 12 and 13 (Fig. ) with respect to echoes 14 and 15, reach a position at which the amplitude of the third (fourth) minimum (n-1) -th echo signal is equal to the amplitude of the third (fourth) minimum of the n-th echo signal, and the time stamps coincide with the minima of the described periods , Because the period between the marks 12 and 13 times (Figure 2) driven by a master oscillator synthesizer, the last field of type-setting is determined Favored frequency - of the reciprocals of the intervals of time desired.

Thus, the increase in reliability is achieved by eliminating errors associated with the dependence of the propagation velocity of ultrasonic vibrations on the values of the amplitudes of the pressure of elastic waves at each point of the test sample, and using in the measurements of the upstream branch of echo signals. that is, the third (fourth) minimum of the reflected signals. In addition, the errors associated with different delays in the active elements of the measuring equipment when amplifying the EB from the signals of different amplitudes are eliminated.

Claims (1)

Claims The method of measuring the speed of propagation of ultrasonic vibrations, which consists in emitting ultrasonic pulses into a sample, receive reflected pulses, measure the time interval between reflected pulses by calibration time marks coinciding with their vertices and determine the speed of ultrasonic propagation oscillation, characterized in that, in order to increase the reliability of measurements, the amplitude of the ultrasonic pulse is changed so that so that the amplitude of the minimum of the third or fourth period of high-frequency oscillations of the (n-1) th reflected pulse is equal to the nominal minimum amplitude of the third or fourth period of high-frequency oscillations of the nth reflected pulse of each first emitted ultrasonic pulse, and the time interval is measured between the minima of the third or the fourth periods of high-frequency oscillations of the specified reflected pulses. rv or , N. N Vu & f Shig, 2