Acoustics with a spin: A new paradigm for acoustic metamaterials, scattering, and propagation of sound

Abstract

When pressure acoustic waves interact with rotating scatterers, they undergo peculiar and intriguing characteristics. In this talk, I will discuss our recent findings on the physics of acoustic scattering and propagation in spinning fluids.

First, I will show how a spinning column of fluid (air or water) in the same medium is endowed with intrinsic spin angular momentum. The radiation force and torque that are obtained will be analyzed and their peculiarities exposed, in particular when acoustic beams are employed. Next, I will propose to use the scattering cancellation technique to derive acoustic invisibility for rotating fluids. The acoustic waves in such media obey a modified governing equation as well as more complex boundary conditions, and new physics is expected from investigating scattering in such a scenario. I will show how to derive the physical properties of cloaking shells. In particular, I will demonstrate that a spinning shell with the same properties as the surrounding may cloak a rigid cylinder similar to a zero-density classical scheme. Last but not least, I will report a radically novel approach for acoustic waveguiding, which relies solely on spinning air, i.e., without material modulation. This proposal results in the acoustic analogue of optical fibers, that we coin acoustic spinning fiber (ASF). Our findings show that this ASF is not only tunable but also unidirectional, as spinning here acts as the counterpart of the Zeeman effect. This may lead to several applications in acoustic metamaterials and sound-based communication.

Brief Biography

Mohamed Farhat is currently a Research Scientist at KAUST, in the group of Prof. Ying Wu. He received his Ph.D. in Optics and Electromagnetism from Aix-Marseille University where he obtained as well his Master’s degree in Theoretical Physics. His Ph.D. dissertation was titled by “Metamaterials for Harmonic and Biharmonic Cloaking and Superlensing.” He has authored over 100 publications. His research lies in the fields of plasmonics and metamaterials with applications spanning optical and acoustical waves.