Acoustically driven rapid flow through microporous media

Porous media provides numerous useful capabilities, including absorption, filtration, separation, and large surface areas for reactions and diagnostics. Acoustofluidic techniques have been tentatively explored to enhance flow in such media, but the majority of such work has problems, including flows that bypass the medium, irregular pores, slow or opposing flows, and non-directional random flow. Of particular interest is the porous material's significant acoustic losses; therefore, attenuation is greater when pore dimensions are small and non-directional. In this work, we drive fluids through randomly oriented pores as small as 12 micrometers. Acoustic streaming phenomena generated by the attenuation of traveling surface acoustic waves in the medium are used to pump the fluid. The media is carefully laminated with the sides sealed to facilitate flow solely through the media. The flow rates generated by a unique floating electrode unidirectional transducer (FEUDT) are compared with a typical interdigital transducer. Because the FEUDT is specifically designed to continuously generate unidirectional acoustic waves, we show that the flow is 3 times faster than the diffusion rate. Furthermore, we reveal new evidence of homogeneous mixing caused by acoustic streaming inside the porous media.