Transmission characteristics of double negativity acoustic metamaterials studied with fluid impedance theory.

Abstract

Input acoustic impedances and transmission coefficients of acoustic metamaterials composed of double negativity structures, i.e., periodic membranes (negative density) and side holes (negative modulus) set along pipes, are studied with the fluid impedance theory, by which the performances of the pipy metamaterials can be studied at any frequency, and the mechanisms of forbidden bands are presented with the theory of acoustic impedance match. In the type of pipy metamaterials, a forbidden band and a pass band successively occur from zero to the upper cut-off frequency of the double negativity. Then, another forbidden band occurs in the frequency range of the single negativity structure formed by the membranes or side holes. Meanwhile, it is found that the input acoustic resistance of the metamaterial is zero in the forbidden bands. Furthermore, other high-frequency forbidden bands caused by the Bragg scattering can be found. All the forbidden bands result from the acoustic impedance mismatch at the positions of the membranes and/or side holes. Finally, the influences of the structural parameters of the metamaterials on transmission coefficients, forbidden and pass band widths, fluctuations in pass bands, etc., are evaluated. [This work is supported by the National Natural Science Foundation of China Nos. 10904067 and 11074125, and Ph.D. Programs Foundation of Education Ministry of China No. 20090091120050.]