Cellulose‐Nanofiber‐Based Layered Sub‐Terahertz Absorbing Sheets for B5G/6G Applications

For the sustainable development of beyond fifth‐generation (B5G) or sixth‐generation (6G) wireless communication technologies operating in the sub‐terahertz and terahertz range, it is highly desirable to utilize environmentally friendly materials in B5G/6G devices. Here, we report a sub‐terahertz absorbing sheet made of biodegradable cellulose‐nanofiber (CNF), which can be useful for achieving electromagnetic compatibility (EMC) in B5G/6G devices in a green manner. The absorber consists of one pure CNF layer sandwiched between two layers of carbon‐nanotube (CNT)‐dispersed CNF layers. The CNT concentration is engineered to be low (0.15 wt.%) in the layer on the wave‐incident side and high (6 wt.%) in the layer on the opposite side, emulating the resistive and reflective layers of a Salisbury screen absorber, respectively. The total thickness of our absorber is as thin as 120 µm. Terahertz time‐domain spectroscopy (THz‐TDS) reveals its good shielding effectiveness of 28.5 dB, low reflectance of 2.5%, and high absorptance of 97.4% at 300 GHz. Additionally, an absorptance higher than 80% is achieved over a broadband frequency range from 250 to 480 GHz. Good agreement between the measured results and calculated results based on the ABCD matrix method confirms that the cancellation of reflected waves is realized as designed.