SU1415072A1 - Interference method and interference apparatus for measuring weak ultrasonic signals - Google Patents

Abstract

The invention relates to a measurement technique and can be used for high-precision measurements of the speed, attenuation and amplitude-time parameters of ultrasonic vibrations. The purpose of the invention is to increase the measurement accuracy by stabilizing the optical phase of the interferometer by changing the intensity of the optical radiation of the source by using as the reference signal the intensity level of the optical radiation of the source. A part of the radiation of the optical radiation source is transmitted through a dividing plate 5 to the photodetector 6, which generates an electrical signal fed further to one of the inputs of the differential amplifier 10. The other input of the differential amplifier 10 is fed a signal from the photodetector 9. A change in the radiation intensity leads to a simultaneous and common-mode change signals from photodetectors 6.9. Due to the large suppression of common-mode signals by the differential amplifier 10, the signal at the executive element 11 connected with one of the interferometer mirrors does not change. Thus, when the intensity of radiation of the laser 1 is changed, no change in the optical phase of the interferometer occurs, as a result of which an increase in the accuracy of measurement of small ultrasonic signals is achieved. 2 sec. f-ly, 1 ill. (L with

Description

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The invention relates to a measurement technique and can be used for high-frequency measurements of speed, attenuation and amplitude-time parameters of ultrasonic vibrations.

The purpose of the invention is to improve the measurement accuracy by stabilizing the optical phase of the interferometer when the intensity of the optical radiation of the source changes.

The essence of the method consists in comparing the intensity of the interference pattern with the reference signal, which uses the level and intensity of the optical radiation of the source, generating a feedback signal and determining the parameters of small ultrasonic signals.

The drawing shows an interference device implementing the method. .

The device contains a laser 1, which is a source of optical mono-chromatic coherent radiation for a two-beam interferometer (position 2 is the sample).

The interferometer consists of a beam-splitting element 3, a support mirror 4. A beam-splitting plate 5 and a photodetector 6 are installed on the path of the laser 1, a beam-splitting plate 7 is placed on the path of interfering beams, and a beam splitting beam 7 is reflected on the path of interfering beams - photodetectors 8 and 9, respectively. The signals from the photodetectors 6 and 9 are fed to the inputs of the differential amplifier 10, which controls the operation of the actuator II.

The method is carried out as follows.

A part of the radiation of laser 1 is transmitted via a beam-splitting plate 5 to a photodetector 6, which generates an electrical signal proportional to the intensity of the radiation of laser 1 fed further to one of the inputs of the differential amplifier 10.

This signal from the additional photodetector 6 does not depend on the optical phase of the interferometer. The second input of the differential amplifier 10 is supplied with a signal from the photodetector 9, the value of which is proportional to the intensity of the interfering rays.

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in reflected light. The change in the optical phase of the interferometer due to acoustic noise leads to a change in the signal of the photodetector 9, proportional to the detuning of the optical phase of the interferometer, which leads to the generation of a signal to the actuator 11, which compensates for acoustic noise. A change in the intensity of the radiation from laser 1 leads to a simultaneous and in-phase change in the signals from the photodetectors 6 and 9. Due to the large suppression of the in-phase signals by the differential amplifier 10, the signal on the actuator 11 does not change. When the intensity of the laser 1 is changed, there is no change in the optical phase of the interferometer.

Thus, the method and device provide the greatest degree of stabilization of the optical phase of the interferometer, which provides an increase in the accuracy of measuring small ultrasonic signals and, therefore, attenuation, speed and amplitude-time parameters of ultrasonic vibrations used in nondestructive quality control of materials and products.

Claims (2)

1. An interfacial method of measuring small ultrasound signals, which consists in comparing the intensity of an interference pattern with a reference signal, produces a feedback signal and determines the parameters of small ultrasonic signals, in order to increase the measurement accuracy, The intensity of the optical radiation of the source is used as a reference signal. 2. An interfacial device for measuring ultrasonic ultrasound signals, containing a sequentially installed optical radiation source and an interferometer, an actuator connected to one of the interferometer mirrors, a differential amplifier whose output is connected to an actuator, a beam-splitting plate mounted on the upper interferometer. 31415072 and two photodetectors, one of which, it is equipped with a second beamer mounted on the path of the rays passing through a plate mounted on through the beam-splitting plate, the optical radiation paths from the source are electrically connected to the entrance of the diffuser, and the third photodetector, the medium amplifier, and the second one, placed in the path of the beams reflected in the path of the rays reflected from the plate, from the second beam-splitting plastiote, characterized by the fact that they are usable, and electrically connected with the aim of increasing the accuracy by measuring the differential amplifier.