<title>Perspectives of fiber sensors based on optical reflectometry for nondestructive evaluation</title>

Theory of symmetrical two-frequency signals and key aspects of its application

“…From (4) follows that the first item in square brackets defines spectrum of Fourier series indexes (3), and the second and the third items describes suppression influence at its components. The level of suppression depends on modulation index m. If we take E 3 = 0, we will receive the optimal modulation index m opt = 5/9, and the resulting oscillation will be almost…”

“…We consider the set of the analysis and synthesis problems which should be solved by development of the theory and technical equipment of optical reflectometers for fiber optical structures (FOS) monitoring in optical two frequency domain (OTFDR) [3][4][5][7][8] . Based upon this technique, the synthesis of two frequency symmetrical probing radiation (TFSPR), various photonic sensing of fiber optic structures and optical information-processing applications have been developed [9][10][11][12][13][14][15] .…”

Fiber-optic system for checking the acoustical parameters of gas-turbine engine flow-through passages

“…Distributions of pressure and velocity throughout the cantilever obtained at conditions of channel flow action are calculated by using the finite-element method; the background noises are in this case ignored; as a result, it made it possible to determine the non-uniformities of the noise structure of reactive gas flow at the nozzle section more exactly [10][11][12][13][14] . At the same time, it is possible to determine the presence of typical or uncertain defects by using as the base the deviations of frequency levels of acoustic pressure from the reference ones.…”