Extraordinary Acoustic Transmission in a Helmholtz Resonance Cavity-Constructed Acoustic Grating

We investigate both experimentally and numerically a complex structure, where 'face-to-face' Helmholtz resonance cavities (HRCs) are introduced to construct a one-dimensional acoustic grating. In this system, pairs of HRCs can intensely couple with each other in two forms: a bonding state and an anti-bonding state, analogous to the character of hydrogen molecule with two atoms due to the interference of wave functions of sound among the acoustic local-resonating structures. The bonding state is a 'bright' state that interferes with the Fabry-Perot resonance mode, thereby causing this state to break up into two modes as the splitting of the extraordinary acoustic transmission peak. On the contrary, the anti-bonding state is a 'dark' state in which the resonance mode remains entirely localized within the HRCs, and has no contribution to the acoustic transmission.