Study on focusing properties of acoustic beams in solid

Focusing and scanning of acoustic beams in solids have a strong potential in applications. But they have not been exactly analysed yet. In this paper we systematically investigated the beam focusing and scanning with the frequency produced by one-dimensional Fresnel arrays on the surface of isotropic media. The past work in this aspect is little and almost all used scalar theory to deal with such vector field problems. Obviously that is imperfect. We used the exact vector diffraction theory of surface source excitation to calculate the wave field distribution along the symmetrical axis and the line perpendicular to the axis on the +1 order focus as well as on the whole plane. We found that the foci can scan along the axis when the frequency changes. The numerical analogue of convergent beams and divergent beams was also clearly shown on a CRT monitor with its pixel brightness modulated by the sound intensity. These investigations not only included the longitudinal wave (P wave) but also the transversal wave (SV wave) which can not be dealt with by the conventional scalar theory. The comparisons between the results of the exact theory and those of the scalar theory are also given