Terahertz Wave Absorbing Properties of Double-coils Randomly Distributed in Cellulose Nanofibers

For 6G application, we fabricated a broadband sub-terahertz (THz) and THz wave absorber made of micrometer-sized metallic double coils randomly dispersed in cellulose nanofiber (CNF) foam. Double coils can work as “3D metamaterial,” and exhibit resonance with electromagnetic waves in various orientations. Therefore, they can effectively absorb waves even when they are randomly distributed. Eco-friendly CNF was found to be a suitable material to uniformly disperse double coil particles in its foam. A shielding efficiency $\lt -20$ dB and absorbance $\gt98$% at 150–1000 GHz were observed by THz-time domain spectroscopy. Our absorber has a cost advantage because double coils can be mass-produced through machine processing and are usable in random distribution configuration without alignment.