Ultralow Frequency, Subwavelength Scale, Tunable Resonance Double Panels as Extraordinary Function Metamaterials

Absorbing ultralow-frequency noise less than 150 Hz is nearly impossible for conventional sound barriers. Here, we propose the metamaterial double panels with periodic resonance blocks. The band structures of flexural waves are calculated by using the finite element method and its bandgap frequency regions are the agreement with the operating frequencies of negative dynamic mass density, deriving local resonance mechanism. Numerical results show the ultralow-frequency bandgap existence in the frequency ranges 96 Hz-131 Hz and 121 Hz-148 Hz for the different block thicknesses, confirmed double-panel dimension 7mm (approximately λ / 397) at the subwavelength scale. Moreover, sound transmission loss by utilizing the multiple reflection theory delineates favorably that the tunable resonance bandgaps can control the ultralow-frequency noise. Our designed metamaterial double panels could pave an original path for noise reduction applications.