Acoustic Metasurface for Space-time Reflection Manipulation

Recently, space-time modulation has revolutionized the wave engineering technologies, providing unprecedented opportunities beyond traditional static systems. This advancement is crucial across diverse fields, ranging from non-reciprocal transmission to wireless communication. However, the current approaches to sound modulation require bulky artificial structures and are limited in achieving space-time-variable sound-matter interactions. Here, a prototype of space-time acoustic metasurface (STAM) is proposed and implemented, consisting of a reflective piezoelectric array controlled by a field-programmable gate array. Leveraging the spatiotemporally programmable phases of the STAM, this is experimentally achieved Doppler-like chirp modulation and space-time modulation with deterministic frequency and momentum shifts of waterborne acoustic waves. Furthermore, based on this flexible and efficient modulation strategy, a stochastic space-time modulation method is introduced, showcasing its applications in single-channel direction-of-arrival estimation. The proposed STAM extends the frontier of wave control and thereby lays the foundation for versatile space-time applications involving sound.