Design and Full Characterization of a 3-D-Printed Hyperbolic Pyramidal Wideband Microwave Absorber

Abstract

A fully 3-D-printed wideband metamaterial absorber, characterized by an absorptivity above 0.95 in the X and Ku-bands and with a fractional bandwidth of 0.71, is presented in this letter. A 250 mm × 250 mm sample, with a total thickness of 6.3 mm (0.26λ0), is fabricated exploiting the fused deposition modeling technique with commercial filaments. To achieve a wideband absorption, a hyperbolic metamaterial with a pyramidal shape is designed by vertically stacking multiple resonant cavities. Lossy filaments are used to increase the dissipative losses and cavities with tailored dimensions are designed to absorb equidistant frequencies to obtain a unitary and flat absorption. The measurements are performed for different azimuth and incident angles, for both vertical and horizontal polarizations in anechoic and nonanechoic chambers. For normal incidence, thanks to the symmetry of the structure, quasi-unitary absorption is obtained over a wide frequency range from 8.2 to 17.2 GHz for azimuthal rotations of 90°. For oblique incidence, the absorption behavior in vertical polarization is better than the one in horizontal polarization. Two cases at azimuth angles of 0° and 30°, corresponding to the best and the worst performances of the presented absorber, are demonstrated in this letter.