Résumé:
To focus ultrasonic waves in an unknown heterogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. (In most applications of ultrasounds, medical imaging, medical therapy , non-destructive testing, the first step consists in focusing a broad band ultrasound beam deeply inside the medium to be investigated.) Focusing in a homogeneous medium simply requires to compensate for the varying focus-array elements geometrical distances. Nevertheless, heterogeneities in the medium, in terms of speed of sound, density or absorption, may strongly degrade the focusing. Different techniques have been developed in order to correct such aberrations induced by heterogeneous media (Time Reversal, Speckle Brightness, for example). In the companion to this paper, we investigated a new broadband focusing technique: the spatio-temporal inverse filter. We present here experimental results obtained in various media, such as reverberating and absorbing media. In particular, intra-plate echoes suppression and high quality focusing through a human skull as well as hyper-resolution in a reverberating medium will be shown. It is important to notice that all these experiments were performed with fully programmable multichannel electronics whose use is required to fully exploit the spatio temporal technique.

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