Some recent advances in electromagnetic, acoustic, and flexural wave scattering: CPAL and shape recognition

Abstract

In the first part of this webinar, I will present our recent contributions in the coherent perfect-absorber and laser (CPAL) for electromagnetic, elastodynamic, and acoustic waves. This intriguing effect is enabled by parity-time (PT)-symmetry breaking condition and leads to extremely precise rf sensors. In addition, the lasing operation of CPAL device is first observed theoretically and validated numerically (3D COMSOL full elasticity simulations) in elastic thin-plates. We further propose to accomplish ultra-sensitivity and robustness to noise by demonstrating a CPAL-locked sensor to detect extremely small-scale pressure perturbations. The results show that the sensitivity and resolvability of the CPAL-locked sensor may go well beyond the traditional acoustic sensors.In the second part, we propose a new approach for acoustic airborne waveguiding that relies on imposing spinning on a column of air, leading to high modified acoustic refractive indices for specific azimuthal modes, reminiscent of acoustic spinning fiber (ASF). The obtained effect is nonreciprocal and tunable via the spinning frequency. It may be seen as the counterpart of the “Zeeman effect”. The concept is shown in the realm of airborne acoustics, yet it can be extended to other wave types, e.g., optics or elastodynamics.Last but not least, I will shortly discuss a generative deep learning approach for shape recognition of an arbitrary object from its acoustic scattering amplitudes. The model exploits adversarial learning and variational inference to predict the unique shape of the object. The nonunique solution space is overcome by the multiangle and multifrequency phaseless far-field patterns.