A Self-Consistent Extrapolation Method for the Complex Permittivity and   Permeability Based on Finite Frequency Data
  We describe a method of extrapolation based on a "truncated" Kramers-Kronig relation for the complex permittivity ($\epsilon$) and permeability ($\mu$) parameters of a material, based on finite frequency data. Considering a few assumptions, such as the behavior of the loss tangent and the overall nature of corrections, the method is robust within a small relative error, if the assumed hypotheses hold at the extrapolated frequency range. 
Christine C. Dantas (AMR/IAE/DCTA-Brazil), Mirabel. C. Rezende   (AMR/IAE/DCTA-Brazil, ITA/DCTA-Brazil) and Simone S. Pinto ...
cond-mat.mtrl-sci