Fig. 3: Characterization of the full-polarization trapezoid conformal-skin cloak under normal incidence.

a Photograph of the fabricated sample with the magnified picture and phase profile along the centered x axis shown in the inset. Here, the phase profile is given only for half-cloak on xz plane since it is symmetric about the x axis for the left-half counterpart. The trapezoid bump is with a tilt angle of ψ = 22.5^o and a cross section of L × H = 387 mm × 50.5 mm. There are totally 24 meta-atoms on each slope, 26 meta-atoms on the top side along the x direction, while 40 meta-atoms along the y direction (P = 220 mm) of the cloak. b Measured NF E_x distributions of the bare bump under \(\left| {\sigma _x} \right\rangle\) (b). c–f Measured NF E-field distributions (copolarized component) of cloaked bump under \(\left| {\sigma _x} \right\rangle\) (c), \(\left| {\sigma _y} \right\rangle\) (d), \(\left| {\sigma _ - } \right\rangle\) (e), and \(\left| {\sigma _ + } \right\rangle\) (f) at 15.5 GHz. g Comparison of copolarized FF scattering patterns on linear scale of 0–1 between FDTD simulations and experiments at 15 GHz on the xz plane for both cloaked bump under \(\left| {\sigma _x} \right\rangle\), \(\left| {\sigma _y} \right\rangle\), \(\left| {\sigma _{\pi /4}} \right\rangle\), \(\left| {\sigma _ - } \right\rangle\), and \(\left| {\sigma _ + } \right\rangle\), respectively, and bare metallic bump of the same size under \(\left| {\sigma _x} \right\rangle\). Here, all NF and FF results are normalized to their respective maximum with identical units and scales. The cloak sample is designed using a computer-aided design (CAD) process and prepared based on a four-step dual-sided fabrication process by combining 3D-printing and flexible printed circuit board (PCB) technique, see Sample preparing and fabrication in Methods. The commonly available 0.1-mm-thick F4B board with ε_r = 2.65 and tanδ = 0.001 is utilized as the flexible thin substrate and backed ground. By taking the stability and rigidity into consideration, the 2.5-mm-thick polymer ABS-M30 with ε_r = 2.7 and tanδ = 0.005 is chosen as the 3D-printing material to preserve the perfect shape of the supporting platform, and thus hold the well-designed phase profiles