Phononic crystal-induced standing Lamb wave for the translation of subwavelength microparticles

Abstract

Phononic crystals (PCs) can modulate an incident acoustic wave to provide subwavelength microparticles with stable and flexible manipulation. However, fixed artificial structures of the PCs usually result in a steady acoustic field profile, thus limiting the dynamic manipulation of microparticles. This study proposes the construction of a phononic crystal plate (PCP) using a pair of periodic oppositely arranged gratings on a plate. Under the PCP's resonance frequency, a pair of nonleaky A0 mode traveling Lamb waves that intrinsically exist in a thin plate were excited and propagated. The pair of waves formed a highly localized standing Lamb wave field between the pair of periodic gratings. By adjusting the phase of the incident acoustic wave, the positions of pressure nodes of the PCP-induced standing Lamb wave were changed in a quantitatively tunable manner. Thus, polystyrene microparticles trapped and aligned at the pressure nodes via the acoustic radiation force could be moved to achieve the translation motion with a resolution of 2.2  μm, approximately 1/160 wavelength in water. The proposed methodology will lead to the fabrication of a disposable and easily operated tool for dynamically manipulating microparticles in subwavelength regions by engineering acoustic fields using acoustic metamaterials in microfluidic devices for cell sorting and drug delivery.