Broadband quasi perfect absorption using chirped multi-layer porous   materials
  This work theoretically analyzes the sound absorption properties of a chirped multi-layer porous material including transmission, in particular showing the broadband unidirectional absorption properties of the system. Using the combination of the impedance matching condition and the balance between the leakage and the intrinsic losses, the system is designed to have broadband unidirectional and quasi perfect absorption. The transfer and scattering matrix formalism, together with numerical simulations based on the finite element method are used to demonstrate the results showing excellent agreement between them. The proposed system allows to construct broadband sound absorbers with improved absorption in the low frequency regime using less amount of material than the complete bulk porous layer. 
No\'e Jim\'enez, Vicent Romero-Garc\'ia, Alejandro Cebrecos, Rub\'en   Pic\'o, V\'ictor J. S\'anchez-Morcillo, Lluis M. Garc...
physics.class-ph