A crossed T-gradient metamaterial for enhanced acoustic sensing

Detecting weak acoustic signals within a strong background noise environment is of significant importance across various research fields. However, conventional detection sensors for sound source are constrained by the minimal detectable pressure, making them unable to extract sound signals that are contaminated by strong background noise. Although metamaterial devices based on gradient refractive index have been used to realize weak signal detection, the current structures are mainly focused on two-dimensional planes and are not capable of acoustic sensing in three dimensions. In this study, a three-dimensional Crossed T-gradient metamaterial device (CTGM) for acoustically enhanced sensing is proposed by utilizing the strong wave compression effect and the equivalent medium mechanism. The superior amplification signal amplitude capability and frequency selectivity of the CTGM structure is verified by numerical simulations. Compared with conventional gradient metamaterial without a T-shape (GAM) and gradient structure without protrusion (GWPM), CTGM could reduce the operating frequency without any change in volume. It has a stronger ability to control acoustic signals at larger wavelengths. The experimental test results show that CTGM has higher acoustic enhancement capability and frequency selectivity in the detection of acoustic signals with Gaussian pulses. This study demonstrates the potential of the designed acoustic metamaterials for enhancing the subtle fault signals detection in acoustic sensing, providing a pathway to enhance the cost-effectiveness of fault diagnostic techniques.