Optimization of time delay laws for focusing with phased arrays

Abstract

Recently, phased arrays technology has been greatly improved and represents an efficient tool to focus an acoustic beam in various directions, just changing a time-delay law. Due to the extended dimension of the elements of the array, one major difficulty consists in the optimization of the desired time-delay law. In this paper, PASS (phased array simulation software, developed in the laboratory) is used to illustrate how classical algorithms (average, minimum value, center value) can significantly alter the resulting focal pattern. Then an optimization method based on time reversal is proposed. First, the focal point is replaced by a source and the array measures the resulting field. Then, each channel emits the time reversal of the received signals, thus generating an efficiently focused beam. Finally, a cross-correlation method allows to extract from these signals a time-delay law that is proved to be very efficient and adapted to the expected focal point. Various simulations will be presented to focus the beam through a plane interface separating a fluid and a solid, using two different arrays. It will be shown how classical algorithms fail, while the proposed method based on a time-reversal simulation yields very efficiently focused beams.