Phase aberration correction with ultrasonic time reversal mirrors

Abstract

Adaptive time delay focusing techniques allow an efficient correction of the effects due to an inhomogeneous layer close to the transducer array. We have developed in our laboratory a time reversal process able to compensate for all distortion effects in the transmit mode. This process has been extended by developing in the transmit-receive mode a spatiotemporally matched filter approach that focuses optimally on a reflective target whatever the distance between the layer and the transducer array. In this technique, a set of focusing signals perfectly matched to the reflector are built and stored. This set of signals is used to focus in both transmit and receive modes, yielding the maximal signal for the reflector location with a very low side lobe level. We present in this paper an extension of this technique to focus, not only on the reflector, but also around the reflector in order to image the surrounding zone. From the knowledge of the signals needed to focus on the initial reflector, we calculate the new signals matched to the new point of interest. The algorithm uses the concept of time reversal propagation