Efficient Anomalous Refraction of THz Beams With a Multilayer Metal–Polymer Huygens' Metasurface

We describe design principles, fabrication techniques, and experimental testing for a Huygens' metasurface, which deflects a normally incident radiation beam at
$f\approx 0.172$
THz toward an angle of 52
$^\circ$
in transmission. The metasurface is comprised of a cascade of five spatially-modulated aluminum impedance sheets photolithographically patterned on 100-
$\mu$
m-thick polypropylene substrates, stacked together via ultrathin adhesive layers. The physical geometries realizing the five-layer Huygens' meta-atoms are designed using a semianalytical model while the expected deflection, associated with negligible reflection and low diffractive losses, is verified by full-wave simulations and measurements. For the implemented deflector, with a working aperture diameter of 75 mm, the experimentally measured refraction efficiency reached 58%, with 20% and 22% losses attributed to spurious diffraction and absorption, respectively. Despite the suboptimal performance, our results establish the proposed methods of synthesis and fabrication as promising for realizing quasi-optical THz components with unique characteristics, unattainable in this challenging regime with alternative approaches.