Acoustically coupled reflectors for multiplexed wavefront engineering

Acoustic standing wave fields, with stable pressure nodes and antinodes, are valuable in biology, medicine, chemistry, and engineering due to their noninvasive nature. While standing waves from high-impedance boundaries have been used, these boundaries typically exceed transducer size. The coupling effect between acoustic waves and objects with sizes above the wavelength of the acoustic field on particle/cell manipulation remains unexplored. We combined theoretical analysis with experimental investigation to study reflector effects on acoustic fields for particle manipulation. Our research shows that in the aqueous phase, objects whose dimensions exceed the wavelength scale (∼1λ), with impedances greater than 6 MRayl, can modulate the angular threshold of the acoustic standing wave pattern formation maximum to 55°. This method enables controlled particle and cell patterning with spacing variation conforming to a secant relationship d=λ sec θ. Object size determines the angle range of standing wave control and can locally modify both angle and wavelength. Multiple boundary coupling creates various biocompatible acoustic field modes. This method offers a reliable approach for local acoustic field control with implications for lab-on-a-chip technologies.