Planar wallpaper group metamaterial for novel terahertz applications
  We present novel metamaterial structures based upon various planar wallpaper groups, in both hexagonal and square unit cells. An investigation of metamaterials consisting of one, two, and three unique sub-lattices with resonant frequencies in the terahertz (THz) was performed. We describe the theory, and perform simulations and experiments to characterize these multiple element metamaterials. A method for using these new structures as a means for bio / chemical hazard detection, as well as electromagnetic signature control is proposed. 
Christopher M. Bingham, Hu Tao, Xianliang Liu, Richard D. Averitt, Xin   Zhang, and Willie J. Padilla