Abstract
We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar—a cost effective and eco-friendly material—are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz–8 GHz. A proper permittivity mixing formula allows obtaining other combinations, to enlarge the case studies. From complex permittivity, finally, we calculated the shielding efficiency, showing that tailoring the content of biochar allows obtaining a desired value of electromagnetic shielding, potentially useful for different applications. This approach represents a quick preliminary evaluation tool to design composites with desired shielding properties starting from physical parameters.
Highlights
We evaluated the shielding efficiency (SE) of the measured materials and composites, and of other combinations obtained by suitable mixing rules, allowing us to simulate the electromagnetic behavior of composites as a function of biochar loading
According to previously reported data, biochar used as filler shows graphitic crystallites in-plane size of up to 2.3 nm with an inter-layer spacing of up to 0.344 nm very close to the one of the graphite (0.355 nm) [40]
This increased conductivity, together with interfacial polarization [42], is the main mechanism contributing to EM shielding in biochar composites at these frequencies [43]
Summary
There is an increasing interest in shielding electronic devices and communication instruments against electromagnetic (EM) radiation, in order to improve their efficiency and lifetime. This requirement is sometime extended to entire buildings. There are particular places that should be well protected against EM interference, e.g., those dedicated to the health sector for applications, such as imaging or tomography, working with microwave- and millimeter-wave devices. In this cases, usually, shielding materials are applied as a coating on wall surfaces. The use of shielding elements directly mixed with currently used building materials has been considered only recently, and could represent a sustainable route, especially if the additional materials are eco-friendly and cost-effective [1,2]
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