Design of Metamaterial Surfaces with Broad-band Absorbance
  A simple design paradigm for making broad-band ultra-thin plasmonic absorbers is introduced. The absorber's unit cell is composed of sub-units of various sizes, resulting in nearly 100% absorbance at multiple adjacent frequencies and high absorbance over a broad frequency range. A simple theoretical model for designing broad-band absorbers is presented. It uses a single-resonance model to describe the optical response of each sub-unit and employs the series circuit model to predict the overall response. Validity of the circuit model relies on short propagation lengths of the surface plasmons. 
Chihhui Wu and Gennady Shvets
physics.optics