Ultrathin Microwave Absorbing Structures at the K‐Band From PDA‐Implanted CNTs, Doped Conjugated Carbon Using Peganum Harmala Seeds and Turpentine Derivatives

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Abstract
In this study, a sustainable biomass‐derived structure from Harmal seed peganum (HSP) is used as a substrate to facilitate the growth of carbon nanotubes (CNTs) by Ni as a catalyst. The unique toutia‐like morphology of the implanted biomass‐derived structure is coated with polydopamine (PDA) via an in situ polymerization process. Persian turpentine (PT) is chosen as a novel, green, sustainable, practical, and polarizable medium, and is selected as a capable microwave absorbing medium. The influence of interfacial interaction on the microwave absorbing performance is carefully dissected with the addition of polyvinyl alcohol (PVA). With an ultrathin thickness of 200 µm, the CNT‐implanted sample coated with PDA and enhanced with PT (HSP/Ni‐CNT/PDA/PT) achieved a maximum RL of −79.88 dB at 18.22 GHz and an efficient bandwidth of 7.17 GHz. Interestingly the architected sample totally shields ≥95% of k‐band frequencies. The promoted impedance matching and other effective mechanisms in HSP/Ni‐CNT/PDA/PVA/PT and HSP/Ni‐CNT/PDA/polyethylene (PE) nanocomposites lead to the highest maximum RL of −92.87 dB at 25.39 GHz with 0.90 mm in thickness and the broadest efficient bandwidth as wide as 8.50 GHz with a thickness of 1.20 mm, respectively.

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