SU1231411A1 - Optoelectron apparatus for measuring amplitudes of surface acoustic vibrations - Google Patents

Abstract

The invention relates to a measurement technique and can be used in the interference measurements of acoustic fields. The purpose of the invention is to improve the measurement accuracy by narrowing the signal spectrum. An optoelectronic device for measuring the amplitudes of the acoustic oscillations of a surface contains a laser interferometer that converts the surface displacement of the object under study, the movable mirror of the interferometer into an interference signal at the photodetector. The second generator excites acoustic oscillations in the object under study. An object mounted on a piezo-modulator makes vertical oscillations under the action of generator voltage. As a result, two interference signals are observed at the photodetector output. An attenuator controlled by the voltage from the elements is installed to eliminate parasitic modulation. From the preselector, the signal goes to the mixer, which controls the voltage that is generated by the frequency divider. From the mixer signal passes to the amplifier. The signal from the attenuator passes to the detector. The constant component of the signal is extracted by the amplifier and fed to the recorder. The subject table gives the translational displacement of the object under study. Information on the linear movement of the object table from the meter is input to the recorder input, as a result of which the plot of the oscillation amplitude distribution is obtained. 1 il. WITH/)

Description

I 1

The invention relates to a measurement technique and can be used in interference measurements of acoustic fields.

The aim of the invention is to improve the measurement accuracy by narrowing the spectral signal.

The drawing shows a block diagram of the device.

A device for measuring the amplitudes of the acoustic oscillations of a surface contains a laser interferometer 1 whose movable mirror is the object under study, a photodetector 2 installed at the output of the interferometer, a piezomodulator 3, a generator 4 connected to a piezomodulator 3, a recorder 5, a second generator 6 and a subject table 7 with a displacement meter 8 connected to the input of the recorder 5, the preselector 9 connected in series, the input connected to the output of the photoreceiver 2, the mixer 10, the amplifier 11, the detector 12, two attenuators 13.14 The second amplifier 15, the second detector 16 and the filter 17, output connected to the input of the second attenuator 1A, the third amplifier 18 connected between the second output of the attenuator 13 and the second input of the recorder 5, divider 19 connected between the second-i generator 6 and the second input of the mixer 10, and the second input of the second attenuator 14 is connected to the output of the photoreceiver 2.

The optoelectronic device for measuring the amplitudes of the acoustic oscillations of a surface operates as follows.

The laser interferometer converts the oscillatory displacements of the surface of the object under study of the movable mirror of the interferometer, which are normal parallel to the laser beam, into an interference signal at the photodetector 2.

The object under study, for example, a quartz resonator, is located at the focal point of the interferometer lens. The second generator 6 excites high-frequency surface oscillations in the object under study (acoustic field)

A (x, y, t.) A (x, y) sin 2 frft,

where x, y are the rectangular coordinates in the plane of the object under study;

314M, g

f is the excitation frequency of the object; l 0.01-100 MHz; А (х, у) - amplitude distribution

in the object to 5 swan on the surface

A (x, y) "- |,

The object of research is installed on a piezomodulator 3, which, under the action of generator 10, makes vertical piston olebani

B (t) (v + ZITFt), t "i F J & 10 - 50 Hz, where the database -3 (2-4);

; 0.6 g, 2 microns;

Vj, is a value characterizing

the average position of the surface of the piezoelectric modulator 3 and. determines the working point of the interferometer,

j As a result, two interference signals are observed simultaneously at the output of the photodetector 2: a high-frequency (informative) U and a VENTURING signal from the reflection coefficient

low-frequency auxiliary IU sn

(Respectively, at the excitation frequencies of the sample f and piezo table F), whose ratios determine the amplitude of the surface oscillations under study.

 When scanning a diffuse surface, parasitic modulation appears deeply and, due to the chaotic nature of the modulation, the measurements are practically not feasible.

To eliminate this drawback, a controlled attenuator 13 is installed in the main signal path, which: is controlled by the voltage generated in the ring of the functional

 automatic gain control with elements 14-17. This ring operates on a low-frequency interference signal and / and an adjustable attenuator 14 is identical to the 0 eMONsy attenuator 13 of the main path. At the output of the amplifier 15 of the ring, opfla and the same c1 amplitude of the signal U are automatically maintained regardless of the signal U – d, therefore the coefficient

55 transmission attenuators 14 and 13 has the form

15 KU - o

40

those. will be inversely proportional to the low-frequency interference signal and. This achieves an automatic calibration of the informative signal by the level of the coefficient of light reflection from the object. Increasing the sensitivity of the device to subangently. Oscillations of the object surface are achieved by accumulating a weak electrical signal U.j at the output of the photodetector. After preselector 9, the pre-filtered signal Ur is fed to the input of the mixer 10, controlled by the voltage, coherent excitation voltage of the sample. The control voltage of the mixer 0 is generated by a divider 19. frequency by two. Observed at the output of the mixer 10 zero beats and. in the form of a low-frequency voltage of small amplitude, they are fed to a low-noise amplifier 11. The polarity of the signal U is determined by the position of the operating point of the interferometer and, due to the low-frequency piston oscillations of the entire sample, constantly changing sign. In connection with this, the signal U after the passage of HI or the controlled attenuator 13 is fed to the detector 12, after which

information about the value of Ux, (and slit dovetetelno and amplitude of oscillations)

turns out to be enclosed in a constant

component of the high signal

U4 K., and,

I 1 t I

 and -1-Ы1.

 and.

  Qi. The constant component of the informative signal is allocated by the third integrating amplifier 18. As a result of the operation of the entire device, the effective bandwidth (and threshold sensitivity) is determined by the time constant of the third integrated amplifier ISt. Then the signal goes to the recorder 5, which is a two-coordinate recorder. To obtain a plot of the amplitude distribution A (x, y) in a certain section of the object under study

2314114

(for example, along the axis ox), the subject table 7 gives a translational displacement of the object under study (along the x axis), information about the linear displacement of which is transmitted from the meter 8 to the linear movement of the subject table (for example, a linear potentiometer) is input to the recorder 5. As a result On the recorder 5, a plot 10 of the distribution of the amplitudes of oscillations in the section x0 A (x) is obtained. To obtain. topograms of the acoustic field A (x, y) must be sequentially scanned in a number of sections of the object under study and reconstruct the entire topogram from the diagrams obtained.

20

25

0

five

0

five

Form

An optoelectronic device for measuring the amplitudes of the acoustic oscillations of a surface, comprising a laser interferometer, a photodetector mounted at the output of the interferometer, a piezoelectric modulator, a generator connected to the piezoelectric modulator, a recorder, a second generator connected to the object, a subject table with a displacement meter connected to recorder input, characterized in that, in order to improve the measurement accuracy, it is equipped with a successively connected preselector, an input connected to the photodetector output a, a mixer, an amplifier, a detector, an attenuator — a second amplifier whose output is connected to the second input of the recorder, as well as serially connected by a second attenuator, a third amplifier, a second detector and a filter, the output of which is connected to the control inputs of the first and second attenuators, divider connected between the second generator and the second input of the mixer, and the input of the second attenuator is connected to the output of the photodetector.

Order 2557/47 Circulation 507Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Rastiskal nab. 4/5

Production and printing company, Uzhgorod, Projecto st., 4

Claims (1)

Claim An optical-electronic device for measuring the amplitudes of acoustic vibrations of a surface, comprising a laser interferometer, a photodetector installed at the output of the interferometer, a piezomodulator, a generator connected to the piezoelectric modulator, a recorder, a second generator connected to the object, an object table with a displacement meter associated with the input of the recorder, characterized in that, in order to improve the accuracy of measurements, it provides a component of the rectified signal ^U 4 = ^K p ' ^and 1 = H · * neither ¹⁵ 1 nor 11114 "* The constant component of the information signal is extracted by the third integrating amplifier 18. As a result of the operation of the entire device, the effective bandwidth (and threshold sensitivity) are determined by the time constant of the third integrating amplifier 18 £. Next, the signal goes to the recorder 5, which is a two-coordinate recorder. To obtain a plot of the distribution of amplitudes A (x, y) in a certain section of the test object, the wife is connected in series by a preselector, an input connected to the output of the photodetector, a mixer, an amplifier, a detector, an attenuator, a second amplifier, the output of which is connected to the second input of the recorder, and connected in series by a second attenuator, a third amplifier, a second detector and a filter, the output of which is connected to the control inputs of the first and second attenuators, a divider connected between the second generator at the input and the second input of the mixer, and the input of the second attenuator is connected to the output of the photodetector.