Ultrafast Rayleigh-like streaming in a sub-wavelength slit between two phononic crystal plates

Abstract

We demonstrate a type of boundary-driven streaming in a subwavelength slit (the slit width is smaller than the acoustic wavelength) between two phononic crystal plates (PCPs) by using the limiting velocity method. It is found that this streaming has the characteristics of four-quadrant streaming similar to classical Rayleigh streaming, and the smaller the slit width, the larger is the maximum velocity of streaming. The maximum velocity of the demonstrated streaming is approximately four orders of magnitude higher than that of classical Rayleigh streaming in two rigid plates with the same slit width of 15 μm. In addition, in the case of this streaming, the vortex sizes are related to the lattice constant of the PCPs, which can be much smaller than those realized in Rayleigh streaming. These effects originate from the strong antiphase coupling of the nonleaky zero-order antisymmetric A0 Lamb modes intrinsic to these thin plates. We denote this streaming as ultrafast Rayleigh-like streaming, which can find potential application in acoustofluidic devices for particle manipulation, rapid mixing and chemical reactions, etc.