3D-printed Metasurfaces of Capped Helices Providing Broadband Negative Mode Index

Using structures of subwavelength metallic capped helices with both negative electric and magnetic couplings, we demonstrate a broadband negative mode index metasurface. Numerical and experimental results are presented for the structure with negative dispersion bandwidth of 44% compared to the resonant frequency of individual capped helices. Optimisation of such structures in terms of their size, element geometry and operational passband width is demonstrated