科研之友
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摘要
The efficient manipulation of the electromagnetic wavefrontusingmetasurfaces (MSs) has attracted a continuous amount of attentionin recent years. MSs with arbitrarily controllable amplitude and phaseare highly desirable in many emerging fields. However, in previousresearch, the resonance effect has mainly been used to accomplishthe task. This article presents a nonresonant metamaterial elementwith stronger capacitive coupling. The broadband sandwich-structuredmeta-atom achieves an enhanced refractive index ranging from 2.44to 8.90. By using the enhanced refractive index elements, the proposedtransmissive MS has an ultrathin thickness (0.23 free-space wavelength).It consists of a specially designed gradient index MS placed on topof the transmitting antenna. The MS is designed to convert the sphericalsurface wave into a plane wave with high efficiency. One core layer(CL) gradient index MS and two impedance matching layers (IMLs) havebeen designed to transform the magnitude and phase of the radiationbeam from the transmitting antenna. An efficient transmissive MS hasbeen designed and experimentally evaluated with a maximum measuredefficiency of over 85%. The proposed control strategy increases thedesign flexibility of the MS and shows great potential for broadbandapplications in the realization of efficient functional devices.
