Phase-based design method for meta-beam with achromatic wave focusing

Abstract

Owing to the various advances in artificial elastic surfaces, called metasurfaces, there have been growing demands on wave focusing devices in ultrasonic imaging, energy harvesting, etc. Nevertheless, previous approaches had suffered from critical limitation that it only works for a certain frequency, or it can be designed at only a small region. In this work, we propose a new metasurface design method for flexural wave focusing at various frequencies, i.e., achromatic metasurface, that can overcome the previous limitations and can be applied to any metasurface design. To this end, we newly investigated the theoretical requirements and design methods to achieve the achromatic metasurface. As a validation, the achromatic metasurface for wave focusing at various frequencies with the normal and obliquely incidence waves, which were impossible previously, are successfully designed. We expect the proposed achromatic design method can be applied in energy harvesting, wave control, and vibration control.