Broadband sound localization with gradient helical structure

Abstract

Acoustic sensors or microphones are essential equipments for the detection of sound signals. However, sound signal suffers from the inevitable attenuation due to many reasons, such as diffusion, damping, thermal, and viscous loss. To solve such a problem, we introduce a gradient acoustic metamaterial to magnify the sound signal before it can be coverted to the electrical signal by introducing a gradient refractive index along the sound propagating route. In this case, the acoustic signal can be magnified as the wave is compressed by the gradient increasing index. The helicoid metamaterial has the advantage to adjust acoustic parameters flexibility and continuity by changing the pitch of the blades. This design is of great significance to improve the working condition of signal detection and may contribute to the design of other sensors.