Time Reversal Of Signals Research Articles

Specific Features of Applying Signal Time Reversal in a Nonstationary Waveguide

Specific Features of Applying Signal Time Reversal in a Nonstationary Waveguide

Multi-sensor network for industrial metal plate structure monitoring via time reversal ultrasonic guided wave

Active ultrasonic guided wave is considered to be the most effective and important on-line damage monitoring method for industrial steel plates structure health monitoring. Aiming at the problem of poor practicability of extracting damage scattering signal from baseline signal, a baseline-free time reversal probabilistic imaging algorithm (BFTRPI algorithm) is proposed in this paper based on ultrasound guided waves time reversal theory and probability statistics principle. Firstly, the time reversal of signal and the adaptive focusing mechanism of wave source are used to eliminate the dispersion effect of Lamb wave by the multi-sensor network. Secondly, the energy characteristic difference coefficient between the reconstructed Lamb wave signal and the original excitation signal, is taken as the damage factor. Finally, the relative distance between the damage and the direct path of the sensor-actuator channel is used to adjust the weight distribution function. The weighted probabilistic values of each sensor path in the sensor network are mapped to the discrete coordinates in the detection area, and the probabilistic imaging of the damage appearing on these discrete coordinates is constructed for multiple damages imaging and location. Experiments on aluminium sheets show that the method can clearly separate the damage scattering signals without baseline signals, achieve the focus of the original excitation signal, and obtain the damage probability images of structure. Compared to traditional probability distribution function method, it has better imaging accuracy and imaging quality. The positioning accuracy of the BFTRPI algorithm is obviously higher than that of traditional algorithm. The estimated position by BFTRPI algorithm is more close to the actual damage position. The location area of damage and artifact for traditional algorithm are both higher than that of BFTRPI algorithm. This method can accurately identify and locate multiple damages in aluminium sheet, which verifies the validity of this method and has certain engineering application value.

Spatiotemporal coupled-mode theory in dispersive media under a dynamic modulation

A simple and general formalism for mode coupling by a spatial, temporal or spatiotemporal perturbation in dispersive materials is developed. This formalism can be used for studying various linear and non-linear optical interactions involving a dynamic modulation of the interaction parameters such as non-reciprocal phenomena, time reversal of signals and spatiotemporal quasi-phase matching.

Classical problems of nonlinear acoustics and wave theory

Focusing of a vibration field in finite sized elastic systems using time reversal of signals from a point’s wideband source is theoretically analyzed. It is shown that the result of space and time focusing for a classical reversal algorithm in limited systems with small losses depends of the positional relationship of the source and the signal receiver. A focusing algorithm eliminating this dependence and increasing the efficiency of the focusing of the vibration field is proposed. Theoretical estimates are confirmed with the results of numerical experiments with the models of elastic bodies.