  Selective single beam tweezers open tremendous perspectives in microfluidics
and microbiology for the micromanipulation, assembly and mechanical properties
testing of microparticles, cells and microorganisms. In optics, single beam
optical tweezers rely on tightly focused laser beams, generating a
three-dimensional (3D) trap at the focal point. In acoustics, 3D traps have
so-far only been reported experimentally with specific wavefields called
acoustical vortices. Indeed, many types of particles are expelled (not
attracted to) the center of a focused beam. Yet the trapping capabilities of
focused beams have so-far only been partially explored. In this paper, we
explore numerically with an angular spectrum code the trapping capabilities of
focused beams on a wide range of parameters (size over wavelength ratio and
type of particles). We demonstrate (i) that 3D trapping of particles, droplets
and microorganisms more compressible than the surrounding fluid is possible in
and beyond Rayleigh regime (e.g. polydimethylsiloxane, olive oil, benzene, and
lipid sphere) and (ii) that 2D trapping (without axial trap) of particles with
positive contrast factor can be achieved by using the particles resonances.
