Trapping Force of Acoustical Bessel Beams on a Sphere and Stable Tractor Beams

Abstract

In noncontact particle manipulation by acoustic or optical beams, which is important for applications in the biological sciences and materials engineering, a $t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r$ $b\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}m$ can pull particles toward the beam's source, but long-range pulling is impossible without simultaneous trapping in the transverse direction. This study uses theory to gain insight into the parameters and conditions for simultaneous trapping and pulling of a spherical particle by an acoustic Bessel beam. Trapping at the pressure maximum of an axisymmetric Bessel beam in the Rayleigh regime is more flexible than the trapping by focused beams currently used for acoustic tweezers.