Design of a Directional Acoustic Sensing Device Based on Helical Metamaterials

Traditional directional acoustic sensing devices often rely on intricate internal circuit designs or multisensor complex algorithms to suppress ambient noise in a specific direction that improves the signal-to-noise ratio. However,these devices are large and difficult to adjust in terms of their directional characteristics,which can impact their effectiveness and universality in real-world situations. A new approach has been taken with the design of reconfigurable acoustic sensing devices based on helical metamaterials. This design enables a single-microphone acoustic system to have good directional sensing performance and frequency filtering characteristics,which achieved through the careful design of metaunits and the application of metastructures. By using single-blade helical metaunits,specific frequency and directional response characteristics can be attained. Drawing upon the theories of acoustic pathways and effective medium conversion,the acoustic transmissions of helical metamaterials exhibit periodic peak-valley frequency response characteristics. The pitch can be adjusted to design a metaunit with unique frequency characteristics within the fundamental and octave frequency bands,allowing control of the acoustic wavelength up to 15 times its own length. Through finite element simulations and a set of four sensor transmittance measurement systems,the frequency transmission characteristics of metaunits were studied and tested. The experimental results showed consistency with theoretical models regarding peak frequency processes. Furthermore,based on size modeling and sensitive angle analysis,a set of structural design schemes and implementation methods were proposed,leading to the creation of an octagonal columnar metastructure. An examination of the pressure variation at the central probe point,along with the internal and external pressure fields of the metastructure,revealed that replacing different metaunits with peak frequencies adjusts the sensitivity frequency of the whole metastructure. Additionally,rearranging the order of the metaunits allows for the reconfiguration of the metastructure directivity. The directivities of the metastructures were verified by an automated rotating experimental platform. The results indicated that the directional sensing is consistent with simulation results and capable of realizing different directional acoustic sensing devices through simple reconfigurations of the metaunit distribution. The design methods of metastructures offer a fresh perspective for the construction of adjustable directional acoustic acquisition devices with high signal-to-noise ratios. © 2024 Tianjin University. All rights reserved.