Study on a gradient structure acoustic metamaterial for underwater sound sensing enhancements

Exploitation in improving the performance of underwater acoustic detection is endless. Acoustic metamaterials (AMMs), which have been rapidly emerging in recent years, can improve underwater acoustic detection performance through extraordinary acoustic wave manipulation to adapt to the ever-increasing new demands and challenges of water acoustic detection, such as the growing sophisticated, long-range, and high efficiency. In this paper, a gradient subwavelength structure is proposed inspired by similar structure AMMs in air; Simulations and experiments are carried out to study its feasibility and basic mechanism in underwater application. This type of AMM can trap a specific frequency of acoustic waves at a particular location, while achieving the amplification of acoustic signals. This work opens up new prospects for the development of acoustic sensors based on metamaterials underwater.