Optimal design of 3D macro-structures for multi-layer foams achieving ultra-broadband microwave absorption properties and high retention after immersion in brine

A novel flexible microwave absorbing material (C-MCM-FAS) with a cone-shaped sandwich structure is proposed, which is constructed by carbonyl iron-carbon nanotubes/PDMS foams and SiC-morchella biochar/PDMS film. To enhance broadband absorption properties, a three-level scale design has been creatively introduced into C-MCM-FAS, encompassing millimeter, micron and nano scales. The rational structural parameters of C-MCM-FAS are determined by CST simulation, leading to the preparation of C-MCM-FAS with an impressive minimum reflection loss (RLmin) of-43.26 dB and an effective absorption band (EB) covering the entire C2, X, and Ku bands at 11.79 GHz. Encouragingly, the measured results are basically consistent with the simulation results (an RLmin of-35.78 dB and an EB of 14.68 GHz), which verifies the accuracy of the theoretical simulation and the feasibility of the method. It holds great significance that the investigation of the adsorption retention rate of C-MCM-FAS after immersing it in 3.5 wt% NaCl solution for 21 days. The measured RLmin reaches-48.41 dB with a retention rate of 111.9 %, and the EB reaches 8.56 GHz with a retention rate of 72.6 %. This work presents a groundbreaking concept for designing structural absorbers, expecting the C-MCM-FAS to become a strong contender for application in special environments like microwave detection in the nautical field.

Automated summary

A novel flexible microwave absorbing material with a cone-shaped sandwich structure has been proposed, which shows impressive broadband absorption properties. The experimental and simulation results are in good agreement, confirming the accuracy and feasibility of the method. The investigation also demonstrates the material's adsorption retention rate in saline solution.