Finite element analysis of multilevel acoustic Fresnel lenses

摘要

Fresnel lenses have recently emerged as viable alternatives tonconventional spherical lenses for focusing ultrasonic waves in acousticnmicroscopy systems. Although these lenses are relatively straightforwardnto manufacture, their bulk represents a major handicap. A remedy to thisnproblem is to use multilevel acoustic Fresnel lenses. Multilevel lensesnare surface relief structures that can be fabricated very preciselynusing existing VLSI semiconductor technology. However, accurate toolsnfor designing lenses to achieve the desired efficiency and powernspecifications are not available. This paper presents a finite elementnstudy of multilevel acoustic Fresnel lenses. Results showing ultrasonicnwave propagation through such surface relief structures together withnthe resulting diffraction profiles are presented. The high efficiencynand focusing power of these lenses are also demonstrated. Simulationnresults together with a discussion on various multilevel lens designnissues are presented. These results confirm the advantages of suchnlenses, and suggest that the finite element model can serve as anvaluable tool for designing, simulating, and studying lens profilesnprior to their fabrication