Fig. 1.

Schematic diagram of acoustic trapping (Lee et al. 2010a). A sphere is interrogated by two incident rays (denoted as a and b) in Gaussian intensity profile. A series of scattering events around the sphere occurs both internally and externally. As the incident rays propagate through the sphere, due to the momentum transfer, the outgoing rays induce the pressures of P_a (a thick arrow) and P_b (a thin arrow), respectively. Because P_a may be higher than P_b, the net pressure P may direct the sphere toward the beam axis