Spatiotemporal Binary Acoustic Metasurfaces

Over recent years, digital acoustic metasurfaces have been developed rapidly as a highly active research area owing to their unique and flexible manipulation of acoustic wavefronts. Nevertheless, nearly all recent attention in the acoustic community has been concentrated on space-encoded architectures, leaving the room free for benefiting from the unique features of spatiotemporally modulated metasurfaces. By entering the world of time, here, we propose a space-time-coding acoustic digital metasurface with exotic ability to dynamically transfer the energy of the carrier acoustic signal to a series of harmonic components, with equivalent magnitudes and phases that can be precisely and independently engineered. The transmission phases of the contributing elements are dynamically controlled in time by exploiting an elaborately designed electromechanical controller system. The study is supported by theoretical, numerical, and experimental verifications which are in excellent agreement. The results demonstrate that by distributing the coding sequences in both space and time dimensions, diverse scattering functionalities can be elaborately acquired for one or multiple harmonic frequencies in a programmable way. This paradigm of acoustic metasurfaces, without resorting to high-cost nonlinear components, opens up unprecedented potential for efficient harmonic control used in adaptive beamforming and acoustic imaging systems.