Electromagnetic (EM) wave absorption properties of cementitious building composites containing MnZn ferrite: Preferable effective bandwidth and thickness via iron and graphite addition

Abstract

Long-term EM radiation seriously affects human physical and mental health. MnZn ferrite can improve the microwave absorbing property of cementitious composites, while obvious shortcomings are narrow effective bandwidth and large thickness. In this work, the intensified effects of metallic iron and graphite powders addition on the magnetic properties, impedance matching, EM wave attenuation, and reflection loss (RL) of cementitious composites containing MnZn ferrite were investigated by VSM and VNA. The phase composition, microstructure, and hydration of the composites were analysed by XRD, XPS, SEM–EDS, and FTIR analyses to explore the relationship between the physicochemical properties and EM properties. The favorable EM wave absorption of composites lies in the magnetic loss and dielectric loss with the addition of iron and graphite powder. MnZn ferrite and iron powder addition can effectively improve the dissipation of electric energy and magnetic energy, and reduce the “superior” thickness range (STR) of the composites. 3% iron powder addition can decrease the STR from over 17.3 mm to 9.4–16.3 mm. Taking the thickness of 11.5 mm as an example, the minimum RL and the mean RL of the composite were reduced by 101.3% and 13.2%, respectively, while the effective bandwidth (RL < − 10 dB) was increased from 1.78 GHz to 2.61 GHz. 3% graphite addition decreased the minimum RL of the composite containing both MnZn ferrite and iron powder from −35.3 dB to −43.9 dB at a thickness of 11.5 mm. Meanwhile, the mechanical strength of cementitious composites is sufficient to satisfy the requirements in most building applications.