Broadband Muffler by Merging Negative Density and Negative Compressibility

We present a broadband muffler using a metamaterial consisting of a membrane structure and a Helmholtz resonator. The membrane structure with ventilation exhibited negative effective density in the 290-435 Hz frequency range. The Helmholtz resonator exhibited negative effective compressibility in the 440-600 Hz range. We connected the two frequency ranges to continue the negativity by matching the end frequency of the negative effective density and the start frequency of the negative effective compressibility. The metamaterial muffler showed a wide range of imaginary components of wavenumbers from 290 to 600 Hz. The muffler exhibits 10 dB transmission loss or 10 % power transmission in the frequency range 275-500 Hz. The realization of a metamaterial muffler with a broad and low-frequency performance range is unprecedented when considering the resonant properties of the metamaterial.(c) 2023 Elsevier Ltd. All rights reserved.