Pressure amplification and directional acoustic sensing based on a gradient metamaterial coupled with space-coiling structure

The detection and localization of weak sound sources are a topic of great interest in a wide range of applications, but generally require a pressure amplification and directivity acoustic system. Although acoustic technologies have been advanced in recent years, the realization of pressure amplification and directivity acoustic systems remains a slippery subject. Here, we propose a gradient acoustic metamaterial (GAM) coupled with space-coiling structure (GAM-SCS) for the detection and localization of weak sound sources. The GAM-SCS is evaluated both numerically and experimentally. Compared with the GAM without space-coiling structure, the GAM-SCS has a better pressure amplification performance which enables the sound signals to be pre-amplified. Meanwhile, the induced space-coiling structure, making use of subwavelength features, also enables the GAM-SCS to work in a lower frequency. Furthermore, the directivity of the GAM-SCS also shines lights on directional acoustic sensing to resist noise interference. We believe that this work opens up a new vista to realize the detection and localization of weak sound sources based on acoustic metamaterials.