Comment on "Propagation and Negative Refraction" [Backscatter]

Hunter et al. in the above-named article (ibid., vol. 13, no. 5, pp. 58-65, July/Aug. 2012) have recently presented a confusing interpretation of the phenomenon of negative refraction in metamaterials. In the first part of their article, the authors make bold and general claims that negative refraction is not possible at a single interface due to causality issues. They attempt to explain the decade-old experimental and numerical evidence of negative refraction with a couple of paragraphs on the premise that this is only possible in the case of a finite-thickness slab based on modal interference. To support their claim, the authors continue by proposing an even/odd mode analysis, which would presumably explain all the observed negative refraction phenomena. They then go on applying this theory to lumped-circuit networks and to specific metamaterial geometries that have successfully reported negative refraction based on a variety of different phenomena. In this comment, we would like to clarify and rectify several misleading statements appearing in their article and straighten the physical meaning and underlying phenomena behind negative-refraction and negative index metamaterials.