Bandgaps and cloaks with soft and hard surfaces

Soft and hard surfaces for electromagnetic waves were defined in 1988. Here we will explain the similarity between the anisotropic soft surface, and the last decade´s isotropic artificial magnetic conductor and in particular the so-called bandgap surface. It is summarized that a soft surface normally will have better performance than a bandgap surface when the purpose is to stop waves propagating along a surface for dual or circular polarization. We will also explain how the hard surface can be used to make cylindrical objects invisible, and that this was experimentally proven to have decent bandwidth in a journal article in 1996, ten years before the promised theoretical metamaterial cloak published last year. The invisibility is correctly and conveniently characterized in terms of an equivalent blockage width that characterizes the forward scattered field. There will be presented recent results in which the performance of hard surface cloaks and metamaterials cloaks are compared, showing the superiority of the hard surface cloak.