Topology optimization of the kerf fillings in linear phased arrays for therapy

Cross talk in ultrasonic arrays is an important problem that affects the array performance. For therapy arrays, cross talk decreases the acoustic power efficiency and array steering capabilities. Since arrays used for therapy are generally air-backed, structure-borne cross talk from the kerf fillings that connect the elements is predominant. In this paper, design strategies are developed to reduce the cross talk in linear phased arrays by optimizing the topology of kerf fillings. Two topology optimization schemes, an element-by-element design and layer-by-layer design, are developed. Sequential linear programming is used to solve the nonlinear optimization problem. Using an array subset technique as the basis for the design, an objective function based on maximizing the normal velocity response of the wet surface of an electrically driven element is shown to improve both the power output and steering of the array.