Time reversal of flexural waves in a beam at audible frequency

Abstract

There has been very limited work on the application of time reversal to the propagation of audible frequency waves in mechanical structures. The present work concentrates on the application of time reversal to the focusing of audible range, flexural waves in an infinite beam, and to the detection of local heterogeneity in such a beam. Practical applications of time reversal of flexural waves in structures include vibration energy focusing, detection of vibratory or acoustic sources, and detection of defects in mechanical structures. An analytical model of flexural wave propagation in the beam as well as sensing and emission using piezoelectric transducers is presented. Time reversal experiments are conducted and compared to the model results in either a homogeneous beam or a beam with point mass heterogeneities. In the various situations tested, it is shown that time reversal effectively compensates the spreading in time of the impulse due to the dispersive propagation of flexural waves. One interesting aspect of this property is the generation of large amplitude impulsive responses in the beam using remote actuators. Finally, the "Decomposition de l'Operateur de Retournement Temporel" approach is examined to detect and localize point mass scatterers in the beam.

A chirp excitation for focussing flexural waves

“…A similar problem was studied by Dion et al [6] who extracted the required input waveform from measured FRFs instead of time-reversal. Francoeur and Berry [7] implemented time reversal on an anechoic beam at audible frequencies, principally to identify and locate wave scatterers. They used an array of PVDF sensors and piezoelectric actuators to generate an impulsive acceleration at a remote position that was larger than at the source locations.…”

Laser-assisted See-through Technology for Locating Sound Sources Inside a Structure

“…If the line of sight is blocked, source localization cannot be done. Such a requirement has necessarily limited source localization to an obstacle-free space, regardless if it is an active source localization equipment such as radar 1,2,3 to detect an aircraft in air and sonar to catch a submarine underwater, 4,5,6 or a passive source localization approach using triangulation, 7,8,9 beamforming, 10,11,12 and time reversal 13,14,15 to locate sound sources in both air and underwater.…”