  Resistive-wall impedance usually constitutes a significant percentage of the
total beamcoupling impedance budget of an accelerator. Reduction techniques
often entail high electrical-conductivity coatings. This paper investigates the
use of negative-permittivity or negative-permeability materials for sensibly
reducing or theoretically nearly cancelling resistive-wall impedance. The
proposed approach is developed by means of an equivalent transmission-line
model. The effectiveness of such materials is benchmarked for the negative
permeability case with experimental measurements in two frequency bandwidths.
This first-stage study opens the possibility of considering metamaterials for
impedance mitigation.
