High-Performance Flexible Microwave Absorption Films with Dynamic Adjustable Macrostructures and Alterable Electromagnetic Field Polarizations.

Abstract

Electromagnetic wave absorption materials that can be utilized for freewill adhering or peeling from the target substrate remain a challenge to be solved. Compared to powder-based slurry and coatings, microwave absorption films possess clear advantages for their good flexibility and machinability. However, the matching thickness and effective bandwidth of 2D microwave absorption films cannot satisfy the current application requirements. As a result, it is necessary to complete a rational structural design based on flat films. In view of the fact that common film-forming methods based on blocks or hard bases cannot be changed or replaced easily once the structural construction is done, here solvent evaporation molding combined with phase change material filling was proposed for the first time to accomplish continuous structural transformation for flexible films. Unlike the original reflection loss (RL) peaks of flat films at around 17.0 GHz, a new absorption peak near 12.25 GHz was generated thanks to the design of coherent structures, resulting in the peaks' boundary merging and effective bandwidth extension. Specifically, 4.56 GHz of absorption bandwidth (RL < -5 dB) at 1.0 mm and 4.27 GHz (RL < -10 dB) of absorption bandwidth at 2.3 mm could be obtained by arch testing under electrical field polarization. Importantly, correlations between EM field polarizations and coherent structures as well as the rules of the absorption peak generation and frequency shift related to the structural variation have all been figured out. The presented laws of EM pattern evolutions for structural films in this work lay the foundation for the applications of high-efficiency microwave absorption materials in complex surfaces and switchable scenes.