An extended view for acoustofluidic particle manipulation: Scenarios for actuation modes and device resonance phenomenon for bulk-acoustic-wave devices.

For the manipulation of microparticles, ultrasonic devices, which employ acoustophoretic forces, have become an essential tool. There exists a widely used analytical expression in the literature which does not account for the effect of the geometry and acoustic properties of the chip material to calculate the acoustophoretic force and resonance frequencies. In this study, we propose an analytical relationship that includes the effect of the chip material on the resonance frequencies of an acoustophoretic chip. Similar to the analytical equation in the literature, this approach also assumes plane wave propagation. The relationship is simplified to a form which introduces a correction term to the acoustophoretic force equation for the presence of the chip material. The proposed equations reveal that the effect of the chip material on the resonance frequency is significant-and is called the device resonance-for acoustically soft materials. The relationship between the actuation modes of the piezoelectric actuator(s) and position of the nodal lines inside the channel are discussed. Finite element simulations are performed to verify the proposed equations. Simulations showed that even if some of the assumptions in the derivations are removed, the general conclusions about the motion of the microparticles are still valid.