Comparison of balanced direct search and iterative angular spectrum approaches for designing acoustic holography structure

There are many pure phase methods for designing acoustical holography structures in the known literature. Different methods may have different characteristics and lead to different results, but few researchers put these methods together for comparison. So we have no idea which method should be taken when dealing with a specific optimization case. This paper investigated the characteristics of three different PM methods, one is the direct search method taking suitable objective function and another two are the conventional IASA methods but with different restricts in image plane, one called ISREL relaxes the whole background pressure constraints and one called ISRES restricts the whole background pressure to zero. We find that DS is a balanced method in terms of various metrics evaluating target pattern and background noise. Finally, the ability of particle manipulation of DS was verified experimentally by designing a holography structure projecting a circle with a non-uniform phase gradient. In a word, it provides a specific comparison between the two mainstream methods DS and IASA by two optimization cases. On one hand, it gives us a clear view of the characteristics of these methods in designing acoustic holography; On the other hand, we know that DS may be a preferred algoritm for most optimization cases owing to its balanced characteristic regardless of time costs.