In the dissertation, scientific research was conducted that aimed at reducing the measurement error.
A mathematical model of LDV signal in the optoelectronic path has been developed. The model is based on the theory of Mie scattering.
The signal model takes into account the effect of matching the scattered radiation on the intensity and state of polarization.
In addition to these parameters of scattered radiation, the degree of phase matching of the "elementary" Doppler signals is also affects the modulation depth and the signal-to-noise ratio.
The depth of modulation of the Doppler signal is determined by the product of the coefficients of the amplitude, polarization and phase matching. These coefficients can vary from 0 to 1.
The studies that were carried out in the work showed the following.
Reduction of the degree of scattered radiation phase, polarization and intensity inconsistency can be achieved by using a filter that must be installed instead of the receiving diaphragm. This will improve visibility, signal-to-noise ratio and accuracy of flow rate measurement.
The optical parts of the experimental LDA were developed and manufactured using a high-power laser diode with a low degree of radiation coherence.
An optoelectronic converter has been developed to convert low-intensity frequency modulated radiation. It uses an avalanche photodiode and a sensitive broadband photocurrent amplifier.
The effect of scattered radiation intensity on the modulation depth of the Doppler signal was experimentally investigated.
The method for increasing modulation depth of the Doppler signal by matching the intensity of the scattered radiation is experimentally confirmed.
In the thesis the following new scientific results are obtained:
- it is first proposed to increase the modulation depth of the Doppler signal, SNR and the accuracy of the laser Doppler velocimeter (LDV) by filtering scattered radiation, which has a low degree of intensity matching;
- it is first proposed to increase the modulation depth of the Doppler signal, SNR and the accuracy of the LDV by filtering scattered radiation, which has a low degree of polarization matching;
- for the first time, it is proposed to increase the modulation depth of the Doppler signal, SNR and the accuracy of the LDV by filtering scattered radiation, which results in the output of the photodetector signals in counter-phase;
The practical significance of the thesis results are:
- a technique has been developed to determine the shape of the filter. The use of such a filter in LDV with the reception of forward scattered radiation increases the intensity coordination degree of radiation, the modulation depth of the Doppler signal, SNR and measurement accuracy of the flow velocity;
- a technique has been developed to determine the shape of a filter. Using such a filter in the LDV with back scattering radiation increases the degree of polarization of the radiation, the modulation depth of the Doppler signal, the signal-to-noise ratio, and the accuracy of the flow velocity measurement;
- a technique was developed to determine the shape of the filter. The use of such a filter in increasing the degree of harmonization of "elementary" Doppler signals by phase, the modulation depth of the Doppler signal, the signal-to-noise ratio and the accuracy of flow velocity measurement;
- two and three component laser Doppler velocity meters, the structures of which have been developed in the work, are intended to measure the flow velocity according to the specifics of the measurement;
- laser Doppler velocity and length meter, the structure of which is designed in the work, is intended for use in those technological processes where it is necessary to measure the speed of solid surfaces and their length. For example, wire during its wiring, electrical cables, rolling in metallurgical production and other production processes;
- laser Doppler aerosol counter, the structure of which is designed in the work, is intended for use in those technological processes where it is necessary to determine the quantitative distribution of aerosols by size. For example, to control the state of the air in industrial premises of the electronics and pharmaceutical industries;
- laser Doppler meter of two components of vibration velocity, the structure of which is developed in the work is intended for the study of the nature of vibration during bench tests of aircraft engines, as well as during the study of vibration of power equipment units, automobile engines and other equipment;
- laser Doppler meter of two components true airspeed of unmanned aerial vehicle the structures was developed.
Keywords: measurement, velocity, aero/hydrodynamic flow, laser, Doppler, error, modulation depth, signal/noise ratio, intensity, polarization, phase, scattering.
