Audible sound metamaterial

We fabricated a kind of 1D metamaterial which consists of periodic array of Helmholtz resonators and tested its acoustic transmission at audible sound frequency in air. The experimental results show that a transmission dip appears at the frequency range of 2.1-3.5 kHz. The transmission ratio simulated by acoustic transmission line method (ATLM) is in accordance with the experimental results. From the effective impedance calculated by ATLM, the transmission dip is ascribed to the backward wave reflection of HRs'resonance. Furthermore, the transmission pressure distribution measurement of the inner sample clearly demonstrates the resonance effect in the metamaterial, in which there is an out-of-phase response to the driving field. The value of effective modulus is calculated to be negative based on the resonant model mentioned before.