The Feasibility and Design of Multifrequency Acoustic Traps

Single frequency acoustic traps are widely applied to microparticle trapping, filtering, sorting and manipulation. This work considers how additional frequencies can be used to achieve better trapping. The acoustic radiation force on a small (sub-wavelength) particle in a rigid walled cavity vibrating at multiple harmonic frequencies is calculated analytically and applied to developing a trap with large regions of near constant force and a stiff local trap at the cavity center. A 1D transmission line model is used to demonstrate that these multi-frequency traps should be realizable in a straight forward acoustic system and that the trap stiffness can be increased more than 2.5 ×compared to a single frequency trap without increasing power requirements or the acoustic intensity in the chamber.