Metamaterial-Assisted Single Hydrophone Underwater DOA Estimation in Multipath Environments

The challenging problem of single-hydrophone underwater acoustic (UWA) direction of arrival (DOA) estimation draws significant attention from diverse underwater drone applications due to its small size requirement and low hardware overhead, addressing which from the perspective of acoustic metamaterial retains a frontier. In this article, an acoustic metamaterial shell with multiple pore-cavity structure is randomly designed to generate anisotropic direction-dependent frequency modulation (DDFM) effect, which enables single-hydrophone collaborative DOA estimation by exploring the sparsity of spatial target distribution and the preknown DDFM pattern. To mitigate the deterioration of the DDFM effect caused by a multipath UWA channel, a metamaterial-assisted multipath-decoupling (MAMD) sparse recovery method is further developed. Specifically, the contribution of the multipath channel response is decomposed into time delay and amplitude components, which are then recombined with preknown DDFM pattern matrix and a sparse direction vector, respectively, to achieve DOA estimation via a sparse recovery algorithm. Numerical simulations and lake experiments onboard an autonomous underwater vehicle (AUV) demonstrate that the proposed method reduces the root mean square error (RMSE) by approximately 7.8296° and improves the estimated success rate (SR) by about 7.4% compared to traditional array-based techniques.