Composite Acoustic Medium with Simultaneously Negative Density and Modulus

We fabricated an acoustic composite structure consisting of a periodic array of interspaced membranes and side holes. Experimental data on the transmission, effective density, and phase velocity are presented. The system exhibits two critical frequencies, ω_SH and ω_c. Our metamaterial is double negative and transparent for frequencies lower than ω_SH. For the frequencies ω_SH<ω<ω_c, the medium is opaque and only the density is negative. For the frequencies above ω_c, the system is double positive and transparent. The present medium exhibits a very wide double negative spectral range that opens the possibility of the application of metamaterials for “white lights.”