A Numerical Study of Low-to-Moderately Focused Ultrasound Transducers (CNIB)
This work presents a numerical study of the linear focal shift effect and the length of the axial f ocus of low-to-moderately focused ultrasound transducers with a concave spherical geometry and a circular boundary. Single element and annular array transducers were studied. The impact of acoustic losses in the external medium was comparatively considered. In this scenario, it is shown that the linear focal shift effect depends on th e acoustic losses of the external medium, but the shift decreases more than the half for the arrays regarding the single e lement radiators, for a given geometrical focal gain in a linear acoustic context. Additionally, a significant r eduction of the length of the axial f ocus is obtained. Thes e general results can be a co ntribution for a proper planning of several mild-hyperthermia therapeutic applications currently used, where a geometrically focused ultrasound transducer is employed.