Ultrathin and Simple 3-D Rasorber Based on Ferrites with Embedded Epsilon-Near-Zero Waveguides

An ultrathin and simple three-dimensional (3-D) frequency-selective rasorber with a passband located between two absorption bands is proposed. The absorption bands are obtained by employing commercial magnetic materials in the absorption channel and the passband is realized using epsilon-near-zero tunneling waveguides. The attractively ultrathin and simple feature is achieved by utilizing tunneling effect at the cutoff frequency of metallic waveguides with arbitrary length, permitting the overall thickness shrink into the same as that of the absorber. A prototype with a thickness of only 0.108 λc ( λc is the free-space wavelength at the transmission frequency) is fabricated and measured, exhibiting a transmission band with −3 dB fractional bandwidth (FBW) of 35.7% and a minimum insertion loss of 1 dB, and an FBW of 135.6% for reflection coefficient less than −10 dB. The lumped-components-free and lithography-free features greatly facilitate the fabrication, which is promising in practical low-cost applications.