Controlling spatial and rotational movement of small, acoustically levitated particles by phasing and rotating piezoelectric transducer arrays

Acoustic levitation is a technique that utilizes sound waves to hold particles in a levitated state within fluids. An ultrasonic array of transducers creates standing waves in an enclosed domain, giving rise to nonlinear effect, holding the particles at designated locations, that are potential wells. To move the levitated particles in a designated trajectory in 3D space, previous works controlled the relative phase of the transducers in a pre-computed manner such that the acoustic field deforms, and particles move to new equilibrium points. The latter is slow and hard to implement. An alternative approach that manipulates the position of a reflector in front the transducer array was suggested. It is shown that by tilting and moving the reflecting plate, one can deform the acoustic field and move the levitated particles quickly and effectively. To verify and illustrate the method, a simulation using Boundary elements was carried out in COMSOL, relating displacements of the levitated particle to motion of the reflector. The latter continuously moved the potential wells. The effect of moving the reflector is verified in an experiment using a Schlieren imaging system with which the deformation of the acoustic field is visible.