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, omega(SH) and omega(c). Our metamaterial is double negative and transparent for frequencies lower than omega(SH). For the frequencies omega(SH) < omega < omega(c), the medium is opaque and only the density is negative. For the frequencies above omega(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.''