Rotating the directivity of sound radiation by acoustic meta-structures

Abstract

Radiation directivity is an important measure of sound fields radiated from acoustic sources. Manipulation of the directivity plays a significant role in many situations ranging from audio and auditorium acoustics to medical ultrasound applications. An acoustic meta-structure is presented here to rotate the directivity of sound radiation from sources surrounded by the meta-structure with an anisotropic acoustic property. The meta-structure consists of an array of platelets, regularly arranged in several concentric rings. The platelets’ orientation is determined from transformation acoustics model. Numerical simulations of sound fields with the structure reveal that the angle of sound directivity rotated by the structure is independent of sound frequency and source location. The rotation is verified through experimental measurements with the meta-structure fabricated by thermoplastics materials via 3D printing. The rotation angle varies over a broad range through tuning geometry parameters of the meta-structure. The meta-structure with its extreme performance can hence provide various applications in the effective control of radiation directivity in acoustic engineering.