Optimization of point spread function in ultrasound arrays

The design of aperture weightings in ultrasound arrays is a multi-objective optimization problem, involving parameters such as delays, aperture size, focal depth, operating frequency and beam properties. Besides, apodization causes the SNR in array output to be decreased. We introduce an analytic expression of the lateral point spread function and a model for SNR as nonlinear functions of weights, based on which, a new aperture design method is established, resulting in an optimal set of weights. These weights provide a point spread function having the predetermined peak sidelobe level, while the SNR in array output is optimized. Optimization results from a linear array with M=128 elements equally spaced at one wavelength, center frequency f0=3.5 MHz and 50% relative bandwidth, have shown that decreasing the peak sidelobe level, decreases the SNR. Therefore, an array designer can select a proper set of weights according to its application, using a SNR curve versus to the peak sidelobe level. In addition, the method can maintain the same beam properties over a long range with low variations in the SNR. Simulation results have shown only 1 dB variations in the SNR for depths from 20 mm to 120 mm, which is a longer range and better SNR performance than the conventional methods.