Finite Element Method Modeling for Extended Depth of Focus Acoustic Transducer

Abstract

Extended depth of focus (DOF) with high lateral resolution is the primary requirement of the transducer in scanning acoustic microscopy to generate high-resolution images of the three-dimensional sample over a large depth. Traditionally, focused ultrasonic spherical transducers are used to tightly focus the acoustic waves generated from a piezoelectric material for a wide range of applications in industrial, medical, and other fields. Such transducers have a problem of narrow DOF which restricts the imaging range in depth. In the present work, we propose three different transducer designs such as single axicon, central flat axicon, and double axicon, which enable the possibilities of high transverse resolution imaging over greater depths due to the significant increase in DOF. Finite element modeling (FEM) in comsol of a spherical, single axicon, central flat axicon, and double axicon transducer is systematically performed and compared in terms of transverse resolution, DOF, and acoustic pressure in the central lobe. In addition, the single axicon and double axicon transducer modeling is done for different apex angles. It is observed that the central flat axicon transducer allows customizable DOF and the double axicon transducer provides high lateral resolution and reduced pressure in the side lobes compared to a single axicon lens.