High-dimensional multiplexed metamaterial for cross-media all-sound communication

Direct transmission of information-carrying sound waves across different states of matter holds significant implications for diverse disciplines. However, existing natural and artificial materials can modulate only one or a few dimensions of cross-media sound waves, imposing inherent bottlenecks on transmission rate and information density. Here, we propose a high-dimensional multiplexed (HDM) metamaterial capable of modulating all dimensions of cross-water-air sound waves including amplitude, phase, frequency, and orbital angular momentum in a passive, compact and efficient way. Thanks to this high-dimensional characteristic, the monolayered HDM metamaterial with subwavelength thickness enables simultaneously relaying and demodulating the spatial-spectral multiplexed signals from one medium to another, which significantly enhances channel capacity and spectral efficiency. We experimentally demonstrate an example of cross-water-air all-sound communication with the HDM metamaterial serving as a passive meta-repeater by transmitting a complex image encoded in both spatial and spectral domains through the metamaterial-based water-air communication link, showcasing real-time, high-speed, and postprocessing-free communication with a bit error rate near 1/10 of the forward error correction limit and strong robustness against background noise and fluctuating surface. This HDM metamaterial-based technique opens a new paradigm for sound wave control in complicated cross-media systems, with far-reaching implications in the Internet of Everything and beyond.