Selective focusing through inhomogeneous media: the DORT method

Abstract

The DORT method (Decomposition de l'Operateur de Retournement Temporel) applies to ultrasonic detection and focusing with arrays of transducers. It is a signal analysis method based on the invariance of ultrasonic propagation under time reversal. It requires the measurement of the inter element impulse responses of the the propagating medium for all pair of elements in the array. A hermitian matrix called the time reversal operator is deduced from these responses and diagonalized. The eigenvectors are then used to perform selective focusing. This method is applied here to phase aberration correction. Experiments with weakly and strongly aberrating medium are shown.