Illustration: Top left: Schurig et al. [11]; bottom left: Smolyaninov et al. [21]; top and bottom right: Valentine et al. [19]

Figure 4: (Top left) The first implementation of a cloak: resonant elements, shown inset, are incorporated in a metamaterial and tuned to give a magnetic response graded from the inner to outer radius. Dimensions are shown in mm. The cloak is designed to operate at $8.5GHz$. (Bottom left) A proposed design for an optical version of the cloak, incorporating metal wires in a dielectric host and designed to operate at $632.8nm$ in a cloak approximately 4 microns in diameter. The latter design has been simulated but not yet built. (Top right) A schematic of a “carpet cloak” designed to operate at near visible frequencies for light confined in a 2D waveguide. The cloaked area is approximately $4×0.4$ microns and the cloaking structure comprises holes of varying density drilled into a silicon wafer. (Bottom right) A scanning electron microscope image of a fabricated carpet cloak.