Absorption enhancement by phase gradient metamaterial

This paper presents a design methodology to achieve enhanced absorption over a wide frequency and angle of incidence range by using conventional porous material. The obtained metamaterial structure is capable to form a phase gradient both on the reflected and transmitted surface. As indicated by the generalized Snell?s law, this circumstance leads to all higher orders of reflection and transmission becoming evanescent and thus substantially enhanced absorbing capability. Firstly, an analytical model for designing the phase response of reflection and transmission is set up and validated numerically, where a good match is found. Secondly, the aforementioned method is applied to derive a design, which is subsequently numerically and experimentally validated. A substantial absorption enhancement is found and a good match between simulation and experiment is observed. Lastly, an idealized numerical study is conducted to show how the phase gradient on reflected and transmitted surface influence the final pressure field.