Time reversed wave propagation experiments in chaotic micro-structured cavities

Abstract

The elastic wave propagation in strongly scattering solid-state cavity consisting of a thin micro-patterned silicon wafer is studied experimentally. The chaotic behavior is induced by the irregular boundary of the cavity and/or by fabricating patterns of small holes in the wafer by laser machining. The pattern and hole size are designed with length scales matching the wavelength ⩽1 MHz and induce multiple scattering within the wafer bounds. Regular patterns of holes add phononic band like dispersion properties to the system. Elastic waves obey under very general conditions time reversal and reciprocity symmetry. In the cavity system the strong mode mixing in the wafer between shear and compression waves, the strong anisotropy of silicon, and even small dissipation is not destroying the time reversal and reciprocity symmetry in the system. We present a systematic study of the quality of the time-reversal signal as function of the chosen time interval and the position in the recorded signal. Also the influence of time dilatation, i.e. stretching and compressing the time scale of the re-emitted signal, is studied.