Tunable Microwave Absorption Frequency by Aspect Ratio of Hollow Polydopamine@α-MnO₂ Microspindles Studied by Electron Holography

Abstract

A tunable response frequency is highly desirable for practical applications of microwave absorption materials but remains a great challenge. Here, hollow lightweight polydopamine@α-MnO2 microspindles were facilely synthesized with the tunable absorption frequency governed by the aspect ratio. The size of the hard template is a key factor to achieve the unique shape; the polymer layer with uniform thickness plays an important role in obtaining spindles with homogeneous size. With the aspect ratio increasing, the maximum reflection loss, as well as the absorption bandwidth (<-10 dB), increases and then decreases; meanwhile, the microwave absorption band shifts to the low frequency. The optimized aspect ratio of the cavity about the hollow polydopamine@α-MnO2 microspindles is ∼2.8. With 3 mm thickness at 9.7 GHz, the strongest reflection reaches -21.8 dB, and the width of the absorbing band (<-10 dB) is as wide as 3.3 GHz. Via electron holography, it is confirmed that strong charge accumulates around the interface between the polydopamine and α-MnO2 layers, which mainly contributes to the dielectric polarization absorption. This study proposes a reliable strategy to tune the absorption frequency via different aspect ratio polymer@α-MnO2 microspindles.

Simultaneous Synthesis of WO3−x Quantum Dots and Bundle‐Like Nanowires Using a One‐Pot Template‐Free Solvothermal Strategy and Their Versatile Applications

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Preparation and investigation of structural, magnetic, and microwave absorption properties of aluminum‐doped strontium ferrite/MWCNT/polyaniline nanocomposite at KU‐band frequency

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<strong>Preparation and characterization of MWCNT/Zn_0.25Co_0.75Fe₂O₄ nanocomposite and investigation of its microwave absorption properties at x-band by silicone rubber polymeric matrix</strong>

“…According to the transmission line theory, permeability and permittivity are the most important factors in the microwave absorbing properties that have been provided by magnetic nanoparticles, dielectric silicone rubber, and dielectric MWCNTs. Moreover, because of homogenous coating of nanoparticles base on the functionalized MWCNTs through the sonochemical and solvothermal complementary methods, interfacial polarization and Maxwell-Wagner effect was reinforced that enhanced charges accumulation and microwave absorption of sample [9,13]. Magnetic loss of the spinel ferrites because of eddy current loss effect and conductive loss of the MWCNTs according to the free electron theory caused the desirable microwave absorption in this nanocomposite [9,11].…”