  Despite their self-reconstruction properties in heterogeneous media, Bessel
beams are known to degenerate when they are refracted from an isotropic to an
anisotropic medium. In this paper, we study the converse situation wherein an
anisotropic Bessel beam is refracted into an isotropic medium. It is shown that
these anisotropic Bessel beams also degenerate, leading to confined vortical
waves that may serve as localized particle trap for acoustical tweezers. The
linear nature of this degeneration allows the 3D control of this trap position
by wavefront correction. Theory is confronted to experiments performed in the
field of acoustics. A swirling surface acoustic wave is synthesized at the
surface of a piezoelectric crystal by a MEMS integrated system and radiated
inside a miniature liquid vessel. The wavefront correction is operated with
inverse filter technique. This work opens perspectives for contactless on-chip
manipulation devices.
