Finite Element Modeling of Binary Acoustic Fresnel Lenses
Binary acoustic Fresnel lenses (BAFLs) have recently emerged as possible replacements for spherical lenses for applications in acoustic microscopy. BAFLs are surface relief structures that are relatively easy to manufacture compared to conventional spherical lenses. While the latter requires careful grinding and polishing, the former can be easily fabricated to sub-micron dimension accuracy using existing VLSI etching technology. The term binary arises from the fact that each masking step during the lens production creates two phase levels. Therefore, a total of 2 n phase levels are created in n masking etching steps. A special case is when n = 1 (2 phase levels), which corresponds to the conventional Fresnel lens (zone plate).