Wave-shape-keeping media.

By using the coordinate transformation theory, we propose a media that is used to control the propagation of electromagnetic (EM) waves with the front shape and size being kept and thus to guide the wave energy along one certain direction, whatever the wave shape may be. We obtain the general formula of designing such media and present the typical example in the cylindrical EM wave case. Such media have many potential applications such as super waveguides, high direction antennas, wave-shape adapters, and other types of EM devices. The approaches presented in this paper are also applicable to acoustic waves.