Rupin et al., App. Phys. Lett. (2014)

From the measurements of ultrasounds (0.5 MHz) in a regular cylindrical shape water cavity (see Fig.1(a)), we perform focusing from a single emitter. For this purpose, the One Channel Time Reversal (OCTR) technique is a standard (see Fig.1(b)).

Due to the strong spatial symmetries of the cavity added to the directive radiation pattern of the piezoelectric transducers, strong coherents echos are visible on the time reversed impulse response e(t) in the top right panel in Fig.2. Thus, the OCTR is degraded as revealed by the spatio-temporal visualization of the focus spot given in Fig.2.

To overcome this limitation, we designed a single channel inverse technique based on the principle of the Spatio-Temporal Inverse Filter (STIF) technique. The key idea to transform the multi-channel STIF technique (MIMO) in a single channel one (SIMO) is to cut the impulse responses measured on plan of reception into J time windows. The latters being used as virtual sources by using the STIF process. As revealed by the results given in Fig. 3(a) (3 virtual sources) and (b) (20 virtual sources), the shape of the synthesized single signals of emission exhibit as many time windows as virtual sources used. This technique enables the optimal control of the temporal degrees of freedom available in a complex wavefield to enhance focusing in both space and time.