Illustration: Top left: Schurig et al.
]; bottom left: Smolyaninov et al.
]; top and bottom right: Valentine et al.
(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 8.5 GHz. (Bottom left) A proposed design for an optical version of the cloak, incorporating metal wires in a dielectric host and designed to operate at 632.8 nm 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.