Dual‐Band Fano Resonance of Low‐Frequency Sound Based on Artificial Mie Resonances

It is reported both experimentally and numerically that dual‐band acoustic Fano resonances (AFRs) of low‐frequency sound are realized by a compound unit array composed of two types of multiple‐cavity unit cells with different inner radii. Eigenmode analyses show that two types of monopolar Mie resonance (MMR) modes can be observed below 650 Hz, which arise from the coupling resonance of the overall structure and the Helmholtz resonance of each resonance cavity, respectively. Based on the MMRs with the out‐of‐phase characteristic induced by the mutual coupling of the two types of unit cells, the dual‐band AFRs, in which the quality factor of the AFR II can exceed 600 when the ratio of the inner radii is closed to 1.0, can be observed. More interestingly, the application of the dual‐band AFRs in sound encryption communication is further discussed. The proposed multiple‐cavity unit cell and its associated dual‐band AFRs provide diverse routes to design multiband sound devices with versatile applications, such as filtering, sensing, and communication.