By covering a corrugated surface with a layer of carefully designed metasurface of skin-like thickness, the wavefront of the reflected waves can be properly modified so as to imitate plane waves reflected from a flat surface 34, 35, 36, 37, creating the illusion 8, 17 of a plane mirror 5. With the use of metasurfaces, the thickness and complexity of invisibility cloaks have been significantly reduced 34, 35, 36, 37, 38. Recently, metasurfaces, which are ultrathin metamaterials composed of tailored planar microstructures, have demonstrated extraordinary abilities to control the phase, amplitude, and polarization of electromagnetic waves 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38. However, invisibility cloaks designed by transformation optics 1, 2 are normally bulky devices with complex spatial distributions of material parameters. The intriguing concept of invisibility cloaks has aroused great enthusiasm 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 in the past decade. Our work paves a path for novel optical and electromagnetic devices based on the integration of metasurfaces and metamaterials. The principle also reveals exciting possibilities for realizing skin-thick ultrathin cloaking shells in transmission geometry, which can eliminate the need for spatially varying extreme parameters. The cloaking effect is verified by both full-wave simulations and microwave experimental results. For experimental demonstration, we constructed a rhombic double-layer cloaking shell composed of a highly transparent metasurface and a double-zero medium consisting of dielectric photonic crystals with Dirac cone dispersions. The principle is general and applicable to arbitrary shapes.
In this work, by integrating the wavefront tailoring functionality of transparent metasurfaces and the wave tunneling functionality of zero-index materials, we have realized a unique type of hybrid invisibility cloak that functions in transmission geometry. However, the previous scheme is based on reflection-type metasurfaces and is thus limited to reflection geometry. Recently, metasurface-based invisibility cloaks have been proposed and realized with significantly reduced thickness and complexity of the cloaking shell. The invisibility cloak, a long-standing fantastic dream for humans, has become more tangible with the development of metamaterials.
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