Ultrathin metamaterials provide new possibilities for the realization of cloaking devices because of their ability to control electromagnetic waves. However, applications of metamaterials in cloaking devices have been limited primarily to reflection-type carpet cloaks. Hence, a transmissive free-space cloak was developed using a multilayer frame structure, wherein highly transparent metamaterials were used to guide incident waves into propagating around an object. The cloaking effect was quantitatively verified using near-field and far-field distributions. Metamaterials allow for the cloaking shells of transmissive cloaks to be developed without spatially varying extreme parameters. Moreover, a transmissive invisible cloak with metamaterial-based mirrors was designed. The design principle of this cloak with a frame structure consists of four metamaterial-based mirrors and two metal mirrors. After covered with the designed metamaterials-based mirrors cloak, the outgoing electromagnetic wave is restored greatly as if the wave passes directly through the obstacle without distortion. This cloak used the metamaterials mirrors to adjust the reflected angle, so that the outgoing electromagnetic wave does not change direction, thereby achieving the cloaking effect.
The application of metasurface in invisibility technology is mainly based on its phase control function, which provides a new choice for the design of ultra-thin carpet cloaking devices with arbitrary shape. At present, most of the carpet cloaking devices mainly focus on metal structure metasurfaces. The Ohmic loss of metallic materials seriously affects the efficiency of cloaking devices. To reduce Ohmic loss and improve reflection efficiency, a dielectric resonance cylindrical harmonic oscillator is proposed to construct the metasurface layer. Based on the analysis of the principle of carpet reflection cloaking, a dielectric metasurface layer is optimized to cover a triangular scatterer, making it invisible. The near field and far field scattering characteristics of dielectric metasurface carpet cloaking device are numerically simulated to confirm its cloaking effect.
Metasurfaces can control the phase, amplitude and polarization of electromagnetic waves, providing a new method for the design of cloaking devices. At present, most of the metasurface carpet cloaking devices are based on metal structure with larger ohmic loss, which severely limits the efficiency of the devices. Here, we propose to use all dielectric unit structure to construct metasurface layer. By using local phase compensation principle, all dielectric metasurface carpet cloaking can be designed in terahertz region. Based on the numerically simulation of near field and far field characteristics, the cloaking effect can be confirmed. The incident wavefront is reflected by the cloaking device and the plane wave characteristics can be recovered well. The cloaking effect can be effective in a broadband range from 0.3 to 0.58 THz. Moreover, the proposed all dielectric metasurface cloaking technology can be extended to the visible light and microwave range.
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