SU1516968A1 - Apparatus for contactless remote measuring of parameters of ultrasonic vibrations - Google Patents

Abstract

This invention relates to non-destructive testing by acoustic methods. The purpose of the invention is to improve the measurement accuracy of parameters of ultrasonic oscillations of objects with a variable reflection coefficient by eliminating errors associated with instability of the source radiation intensity and instability of the reflection coefficient of an object by automatically adjusting the intensity of the output signal of the measuring interferometer with negative feedback at a given frequency. The radiation source 1 generates a radiation flux, which, falling into the interferometer formed by the beam-splitting cube 4, the reflecting surface of the electromechanical transducer 5 and the surface 6 connected to the object, forms an interference pattern in the plane of the sensitive element of the photodetector 7. To compensate for instabilities, the optical length of the interferometer reference arm modulated by oscillations of the reflecting surface of an electromechanical transducer 5, which is excited through an adder 13 gene RATOR 12 at a given frequency. The signal of this frequency is extracted at the output of the interferometer using a band-pass filter 15 and serves to control the gain of the amplitude recovery unit 17 so that it passes a useful signal to the input of the recording unit 18 with an amplitude independent of the instabilities of the reflecting surface and the source of radiation 1.

Description

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signal of the measuring interferometer with negative feedback at a given frequency. The radiation source 1 generates a radiation flux, which, falling into the interferometer formed by the beam-splitting cube A, the reflecting surface of the electromechanical transducer 5 and the surface 6 connected to the object, forms an interference pattern in the plane of the photodetector sensing element 7. DP compensation and stability of the optical length of the reference arm interferr - the meter is modulated using a cole. The invention relates to non-destructive testing by acoustic methods and can be used to deflect protoscopy products in medicine,

The purpose of the invention is to improve the accuracy of measuring the parameters of ultrasonic vibrations of objects with a variable reflection coefficient by eliminating errors associated with the instability of the intensity of the source radiation and with the instability of the reflection coefficient obs. This is due to the automatic adjustment of the intensity of the output signal of the measuring interferometer using negative feedback at a given frequency.

Figure 1 shows the block diagram of the proposed device; Fig. 2 is a block diagram of one embodiment of an amplitude recovery unit;

The device contains an optic source 1, aperture 2, a long-focus lens 3, a measuring interferometer consisting of a beam-splitting cube 4, a reflecting surface of an electromechanical transducer 5 and a reflecting surface 6 (for example, an object), the first 7 and second B photodetectors, a differential amplifier 9 , the first low-pass filter 10, the auto-tuning amplifier 11, the generator 12, the adder 13, the beam splitter 1D, the band-pass filter 15, the second low-pass filter 16, the amplitude recovery unit 17 and the registration block 18.

The reflecting surface of the electromechanical transducer 5, which is excited through the adder 13 by the generator 12 at a given frequency. The signal of this frequency is extracted at the output of the interferometer using a band-pass filter 15 and serves to control the transmission coefficient of the amplitude recovery unit 17 so that it passes a useful signal to the input of the register unit 18 with an amplitude independent of the instability of the reflecting surface and the source 2 of the radiation 2 silt

The amplitude recovery unit 17 may be performed in a variant comprising an Envelope Detector 19, an analog-digital pre, C) transmitter 11

5 (ADC) 20, the permanent storage unit is: 1. representing a persistent storage device (ROM) and multiplying; digital-analog converter 22 (UTsP),

0 The device works as follows

Focused by a lens 3 from a pu-ray laser 1 is introduced into the beam-forming cube 4 formed, reflecting 5 the surface of the electromechanical transducer 5 and the surface 6 connected to the object, an interferometer.

The light intensity in the interference pattern of the photodetector 7 converts into an electrical signal, in which, along with useful components, carrying information about ultrasonic vibrations, there is interference, the sources of which are fluctuations of the intensity of the laser radiation 1 and the vibration of the optical elements of the installation together with the offset and by the vibration of the surface 6. When this signal passes through the differential amplifier 9, the signal fed to the second input of the differential amplifier 9 is subtracted from the output a second optical sensor 8, the recording laser emission fluctuations intensipnosti 1, which provides suppression of noise associated with intensity fluctuations of the laser radiation 1 1

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The signal from the output of the differential amplifier 9 through the low-pass filter 10, which delays the useful signal and passes the second component of the interference, is fed to the input of the auto-tuning amplifier 11, which drives the input signal to its level necessary to control the electromechanical converter 5 so that the offset its specularly reflecting surface under the action of this signal compensated for the phase shift arising due to uninformative displacements of the monitored surface 6, as well as due to vibration optical elements of the installation. The output signal of the differential amplifier 9 contains information only about the controlled ultrasonic oscillations and vibrations of the reflecting surface of the electromechanical transducer 5 under the action of the signal from the generator 12. These signals are modulated in amplitude due to a change in the transmission coefficient of the interferometer caused by the movement of the controlled surface 6 working point of the interferometer on the transfer characteristic. Therefore, to maintain a constant scale of converting the amplitude of ultrasonic vibrations into an electrical signal, the change in the transmission coefficient of the interferometer is compensated.

Since the reflecting surface of the electromechanical transducer 5 oscillates with a constant amplitude determined by the signal generated by the generator.12, the ratio of the amplitude recorded by the photoreceiver 7 and selected by the bandpass filter 15 of the control signal if the operating point of the interferometer is at the steepest part of the transmission signal characteristics, to the current value of the amplitude of the pilot signal, is the coefficient by which the amplitude of the signal must be multiplied, corresponding to the ultrasonic vibrations of the test surface 6, in order to keep unchanged the scale of the amplitude conversion of the ultrasonic vibrations into an electrical signal.

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displayed by block 18 of registration. The formation of the named coefficient and the multiplication of the information signal on it completes the signal amplitude recovery unit 17.

An embodiment of block 17 is implemented as follows.

Pilot signal allocated

The Q bandpass filter 15 is fed to the input of the envelope detector 19, the input of which is also the second input of the signal amplitude recovery unit 17. Detected

5, the signal is converted by the ADC 20 into a digital code, which is the address for the ROM 21, in which a pre-formed table of correction coefficients of the control UCAL 22 is stored,

20 to the input of the reference voltage of which, which is also the first input of the signal amplitude restoration unit 17, is supplied selected by the second filter.

16 bass information signal, which, multiplying in UCAP 22

the correction coefficient is brought to a predetermined scale of the conversion of the amplitude of ultrasonic vibrations into an electrical signal, 30 recorded by the recording unit 18 connected to the output of UCAP 22.

The correction factor table stored in the ROM 21 is formed so that when the amplitude recovery signal of the output of the bandpass filter 15 is connected to both inputs of the 17, the second low-pass filter 16 is disconnected from the block

17), and when the reflection coefficient of the test surface in the range characteristic of this class of surfaces changes, the measuring device 18 recorded a signal of constant amplitude.

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Claims (1)

Invention Formula A device for contactless remote sensing of ultrasonic oscillation parameters, containing a source of optical radiation, made in the form of a laser, a diaphragm, a long-focal lens, a measuring interferometer and a first photodetector, a second photodetector optically connected to the optical source radiation, electromechanical ps5 0 a diverter whose surface is a mirror of the reference channel of the measuring interferometer, a low-pass filter, a recording unit, a differential amplifier whose inputs are connected respectively to the outputs of the first and second photodetectors, and the output of the connection to the input of the lower-frequency filter, characterized in that improving the accuracy of measuring the parameters of ultrasonic oscillations of objects with a variable reflection coefficient, it is equipped with an auto-tuning amplifier, a generator, an accumulator, whose inputs are connected to s by the steps of the auto-tuning amplifier and the generator, and the output with the input of an electromechanical transducer, a band-pass filter, a second low-pass filter and an amplitude recovery unit. The first input is connected to the output of the second low-pass filter, the second input is connected to the output of the bandpass filter, and the output is connected to the input of the registration unit, the inputs of the second low-pass filter and the band-pass filter are connected to the output of the differential amplifier, the input of the self-tuning amplifier is connected to the output of the first lowpass filter frequencies. I .J Figg