Multifunctional reflected lenses based on aperiodic acoustic metagratings

Acoustic metagratings (AMs) have provided diverse routes for sound modulations based on high-efficiency diffractions created by periodic supercell structures. The emergence of the extension of the generalized Snell's law (GSL), covering both acoustic diffractions and phase modulations, has promoted the design of the AMs with aperiodic phase profiles, which have a great potential in designing high-performance multifunctional devices. However, the realization of reflected aperiodic AMs and its associated multifunctional devices remain a challenge. To overcome this, we here theoretically design and experimentally demonstrate a class of reflected aperiodic AMs and multifunctional acoustic lenses. By using the extension of the GSL, we can overcome the limitations of the GSL (such as the phase gradient and the incident critical angle) and experimentally demonstrate theoretical predictions of sound reflections created by the aperiodic AMs with arbitrary phase gradients under a full-angle incidence. Additionally, we experimentally design a multifunctional reflected lens composed of two selected aperiodic AMs. Interestingly, by simply adjusting the incident angle of sound, we can realize the transformation between the beam splitting and the Bessel-like beam without changing the structure of the lens. Our work paves a way for modulating sound reflections and designing reflected multifunctional devices with promising applications.