  Symmetry-protected resonances can be made to couple with free space by
introducing a small degree of geometric asymmetry, leading to
controllably-sharp spectral response. Here, we experimentally demonstrate a
broken-symmetry metasurface for the technologically important low millimeter
wave spectrum. The proposed metasurface is fabricated on an ultrathin polyimide
substrate, resulting in a low loss and flexible structure. Measurements inside
an anechoic chamber experimentally verify the theoretically predicted sharp
spectral features corresponding to quality factors of several hundreds. The
demonstrated sharp response is also observed with the complementary structure
which responds to the orthogonal linear polarization (Babinet's principle). The
designed metasurfaces can be exploited in diverse applications favoured by a
controllably-sharp spectral response, e.g., filtering, sensing, switching,
nonlinear applications, in either reflection or transmission mode operation.
More generally, the demonstrated fabrication process provides a generic
platform for low-cost, large-scale engineering of metasurfaces with minimal
substrate-induced effects.
