Scattering cancellation and radiation torque and forces via spinning media

When pressure acoustic waves interact with rotating scatterers, they undergo peculiar and intriguing characteristics. In this talk, we will discuss our recent findings on physics of acoustic propagation in spinning fluids. We will start with a brief review on the mathematical modeling of the scattering via spinning object using the Mie scattering theory. Then we will showcase two examples. In one example, we develop a generalized scattering cancellation theory (SCT) to cloak the spinning objects and hide them from static observers. This work extends the realm of SCT and brings it one step closer to its practical realization that involves moving objects. In another example, we study the torque and force a spinning object experiences in evanescent acoustic fields, and show that the resulting discontinuity can scatter sound in unusual ways, e.g., a negative radiation force, although it has no imaginary part (associated to intrinsic absorption) in its parameters.