Broadband sound blocking from 0 to 850 Hz by merging negative density and negative compressibility ranges

This study presents a broadband single negative metamaterial that exhibits imaginary wavenumbers in the frequency range of 0–850 Hz. The unit cell of the metamaterial consists of two single negative metamaterials, a membrane-based metamaterial, and a Helmholtz resonator-based metamaterial. The membrane structure generates a negative effective density in the lower frequency range from 0 to 705 Hz. The Helmholtz resonator structure covers a high frequency range from 710 to 850 Hz using negative compressibility. The combined metamaterial structures are expected to provide both effective density and compressibility. The imaginary component of the wavenumber of the metamaterial composite continued from 0 to 850 Hz by merging the two single negative ranges. The experimental, theoretical, and numerical results demonstrate that it is possible to create the broadband single negative metamaterials, which enhances the practical applicability of broadband metamaterial silencers.