Anomalous refraction of acoustic waves using double layered acoustic grating

The paper proposes a double layered acoustic grating for fulfilling acoustic focusing in an anomalous direction. The acoustic grating consists of two layers of rigid panels with periodically perforated slits. By optimizing the positions of the slits on the two layers, both positive and negative refractive indices can be achieved with the phase shift tailored within [-π/2, π/2]. This allows acoustic energy of an obliquely incident plane wave to converge in a predefined focusing region in any direction. The paper predicts the wave propagation manipulated by the acoustic grating based on the surface coupling approach. Then, it discusses how to optimize the slits' positions to collimate the acoustic energy of an obliquely incident plane wave in a specific direction. Such acoustic grating has various potential applications, such as deflecting outdoor noise away from sensitive areas in building acoustics, enhancing acoustic energy in a target audience area in auditorium design, collimating acoustic surface waves, etc.