The presence of the clutter of volume scattering and the echo return from rough interface hinders the detection of target in heterogeneous media. This work investigates the application of an iterative time reversal mirror to mitigate the difficulties. Numerical simulations based on pseudospectral finite-difference time-domain method are performed in one and two layered media. A wideband probe pulse is launched to initiate the process, and the time-reversed echo received at the same position is retransmitted as the renewed input signal for next iteration, and repeat the procedures iteratively. The results illustrate as the number of iteration increases, small volume clutter is eliminated, interface reverberation is suppressed relatively, and the echoes will converge to a time-harmonic waveform that corresponds to an object's dominant resonance mode. The detection of target is achieved by extracting this important acoustic signature.

The presence of echo returns from the rough interface of two layered medium, and the clutter of volume scattering hinders the detection of target buried in heterogeneous media. The situations are often raised in ultrasonic breast tumor diagnosis and underwater acoustic buried mine detection. This work investigates the application of monostatic single channel iterative time reversal in mitigating the difficulties with a numerical study. Simulations based on pseudospectral finite-difference time-domain method are performed with a sphere buried in the heterogeneous media of lower layer, a transmitter is situated at the upper homogeneous domain, and the interface position is normally distributed. A wideband signal is launched to initiate the process, and the time-reversed echo received at same position is emanated as renewed interrogation pulse for next iteration. Some field snapshots are taken and the echo is recorded in each iteration. The results illustrate as the number of iteration increases, small volume scattering is eliminated, and rough interface reverberation is suppressed relatively. The echoes will converge to a narrowband waveform corresponding to an object’s dominant resonance mode. The detection of target is achieved by exploiting this important acoustic signature. [Work supported by the CAS Innovation Fund.]