Unique frequency reversible conversion and bandwidth regulation of electromagnetic wave absorption performance for core-shell structured Fe3O4 and manganese oxide composites

Abstract

The utilization of electromagnetic wave (EMW) absorbing materials is prevalent in various industries, including communication, aerospace, electronics, and military sectors. In this study, a core-shell composite Fe₃O₄@MnOOH (FMO) was synthesized, where Fe₃O₄ serves as the core and MnOOH acts as the shell. The EMW absorbing material exhibits unique characteristics of frequency bandwidth reversible conversion between high and low frequency. Through heat treatment, a chemical transformation occurs in the shell of FMO enabling the regulation of frequency bandwidth movement towards lower or higher frequencies, within a range from 3.5 GHz to 18 GHz. Upon subjecting FMO to heat treatment at temperatures of 400 °C, 550 °C, and 1000 °C respectively, MnOOH undergoes conversion into MnO₂, Mn₂O₃, and Mn₃O₄, achieving FMO400, FMO550 and FMO1000 composites correspondingly. Consequently, the frequency bandwidth shifts from 5.1 to 9.2 GHz for FMO to higher frequencies for FMO400 (8.4−13.6 GHz), FMO550 (12.3−18.0 GHz), and lower frequencies for FMO1000 (3.5−9.3 GHz). Additionally, reversible conversion is achieved through inter-conversion between FMO and FMO400 by converting MnOOH to MnO₂ via heat treatment while allowing reversible conversion enables regulation back to MnOOH through hydrothermal reduction of MnO₂. This reversible conversion enables regulation of the frequency bandwidth from 8.4 to 13.6 GHz for FMO400 to 5.2−9.6 GHz for FMO. Furthermore, due to the synergistic effect and excellent impedance matching of the core-shell structure, FMO exhibits a minimum reflection loss of −65.2 dB and an effective absorption bandwidth of 4.4 GHz. These properties demonstrate superior EMW absorption performance within the frequency range of 2–18 GHz. Due to the unique reversible conversion and bandwidth regulation characteristics of high and low frequency, it has great potential in 5G communication, aerospace, and military equipment applications.