Acoustic Metamaterial with Controllable Directivity and Dispersion Characteristics

Current acoustic metamaterials are developed only with controllable directivity characteristics of wave propagation. The wave speed usually remains unaffected. This limits considerably the potential use of acoustic metamaterials in many critical military and civilian applications. In the present work, an attempt is presented for developing a class of acoustic metamaterials that have controllable directivity and dispersion characteristics. Such metamaterials are developed using a linear coordinate transformation of the acoustic domain to achieve the directivity control capabilities. The transformation is augmented with an additional degree of freedom to simultaneously control the dispersion characteristics. With such capabilities, the proposed acoustic metamaterials will be capable of controlling the wave propagation both in the spatial and spectral domains. The proposed control approach affects the density tensor of the acoustic metamaterials. The theory governing the design of this class of acoustic metamaterials is introduced and the parameters that control the tuning of the directivity and dispersion characteristics are presented in details. Several numerical examples are presented to illustrate the potential capabilities of this class of metmaterials. The proposed design approach of acoustic metamaterials with tunable wave propagation characteristics can be invaluable means for the design of many critical military and civilian applications.