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Cross-wavelength invisibility integrated with various invisibility tactics

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Science Advances  23 Sep 2020:
Vol. 6, no. 39, eabb3755
DOI: 10.1126/sciadv.abb3755
  • Fig. 1 Biological inspiration, schematic view, and practical sample of an optically transparent microwave invisibility cloak.

    (A) Photo of the hyperiid amphipod crustacean Cystisoma, which lives in a midwater oceanic environment. Photo credit: David Liittschwager, reproduced from (1), used with permission. (B) Schematic of the optically transparent microwave invisibility cloak. This cloak can conceal objects with preserved phases and microwave amplitudes (green beams with incident angle α and reflected angle ϕ). At the same time, the cloak can ensure that internal observers see external aircraft clearly (blue beams) and can decrease the optical scattering (yellow beams). (C) Example of the optically transparent microwave invisibility cloak. The metallic badge with the words “Jilin University” represents an object concealed inside. The enlarged section presents a schematic view of the metasurfaces composed of nano-Ag/Ni networks. Photo credit: Fu-Yan Dong, Jilin University.

  • Fig. 2 Boolean metamaterial design procedure for an optically transparent microwave cloak.

    (A and B) Schematic of the metasurface unit cell for the microwave regime and the phase shifts under different incident angles: (A) for TE-polarized incidence and (B) for TM-polarized incidence. The dotted line indicates the theoretically ideal phase compensation value at α=10°. (C) Cross-scale dispersion engineering with silver nanostructures. The silver ( ωp = 1.39 × 1016 s−1 and ωc = 3.22 × 1013 s−1) structure has a geometry of tm = 8 μm and pm = 200 μm, and wm/pm varies from 0.001 to 0.2. σmicrow and σopt represent the conductivities at 7 GHz and 580 nm, respectively. The underlying substrate is not considered here. (D) Boolean multiplication (denoted by ∧) performed to merge the structures with single-band engineered dispersion into an integrated metastructure with cross-scale engineered dispersion. M(xm, ym, zm), V(xv, yv, zv), and BM(xbm, ybm, zbm) are the coordinates for the microwave regime, the visible regime, and the final structure, respectively.

  • Fig. 3 Phase and amplitude response of ring resonators after the Boolean procedure.

    (A) Amplitude attenuation of a reflected wave for various sheet resistances. The amplitude is averaged under TE polarization incidence (θ = 20 ° and 40°), and the dotted curves are fits from simulations. The inset shows the average magnitude of ring resonators for the practical structure after the Boolean procedure with θ = 0°, 10°, 20°, 30°, and 40° for TE and TM illumination at 7 GHz. (B and C) Phase responses for TE and TM polarization. The models of the rings after the Boolean procedure are included in fig. S1.

  • Fig. 4 Optical characterization of the cloak.

    (A) SEM photo of ring 1 with the smallest radius (0.5 mm); scale bar, 100 μm. (B) SEM photo of the quasi-PEC layer; scale bar, 100 μm. The insets show a close-up view of the metal wires and their reliable electrical connections; scale bar, 10 μm. (C) Optical transparency of the outer-layer metasurface (black solid line), quasi-PEC film (orange dashed-dotted line), and bilayer structure (yellow dashed line). The bilayer transparency equals that of the ring resonators multiplied by that of the quasi-PEC film. (D) Experimental proof of how an internal observer sees through the cloak compared to (E) the case of direct observation without the cloak. Photo credit: Fu-Yan Dong and Dong-Dong Han, Jilin University.

  • Fig. 5 Experimental results in the microwave regime for the TE case (left column) and TM case (right column).

    Amplitude distribution of the reflected waves: (A and F) cloak, (B and G) ground, (C and H) transparent bump made from a transparent quasi-PEC layer, and (D and I) PEC bump made from aluminum. (E and J) Total scattering reduction with α = 6° (solid line), 10° (dashed line), 16° (dotted line), and 20° (dash-dotted line). The distributions are plotted for the incident angle α from 2° to 20° and reflected angle ϕ from −90° to 90° at 7 GHz. a.u., arbitrary units.

Supplementary Materials

  • Supplementary Materials

    Cross-wavelength invisibility integrated with various invisibility tactics

    Su Xu, Fu-Yan Dong, Wen-Rui Guo, Dong-Dong Han, Chao Qian, Fei Gao, Wen-Ming Su, Hongsheng Chen, Hong-Bo Sun

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    • Sections S1 to S9
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