Time reversal in heterogeneous flexural beams

Abstract

Time reversal of acoustic and structure-borne waves has been explored in recent years mostly for ultrasound and for nondispersive propagation, that is under frequency-independent wave velocity. In contrast, the case of time reversal in flexural beams presented here involves dispersive propagation, and is carried for frequencies below 5 kHz. The study has been started with analytical time reversal simulations in infinite homogeneous or heterogeneous beams (comprising point-mass scatterers). Experiments have also been realized on a 5 m beam with anechoic terminations and under transverse impact excitation. The time-reversal mirror was made of several thin piezoceramic elements bonded on the beam to sense the impulse response of the structure and re-emit its time-reversed image. The experimental results are in good agreement with the analytical results, and show that time spreading due to dispersive propagation of bending waves is successfully compensated by the time reversal operation. The presentation will illustrate the main results of the simulations and a comparison with the experiments.