Electromagnetic Wave Absorption Properties Of Gypsum Board And Mineral Wool Board With Carbon Black

In this paper, gypsum boards and mineral wool boards with carbon black(C B) as absorbing agent for building decoration, which have excellent microwave absorbing properties, were designed and prepared, aiming at controlling the increasingly severe electromagnetic pollution. Structure and performance of the raw materials and prepared materials were characterized by Scanning Electron Microscope(SEM), Transmission Electron Microscope(TEM), X-Ray Diffraction(XRD), and Vector Network Analyzer(VNA) etc, and the mechanism of the influence of micro-structure on the absorbing performance were discussed.It can be founded through the measurement of the electromagnetic parameters that gypsum and mineral wool don’t have the ability to loss the electromagnetic wave(EMW). CB is a kind of resistance loss absorbing agent with large electronic constant and electronic loss tangent value, nanoscale particle size and high structural are benefit to the EMW attenuation. Expanded perlites can be used to improve the absorbing property as the lower permittivity and better transmission characteristic.The wave absorbing properties of gypsum boards can be improved by mixing with a certain proportion of expanded perlites, and the optimum volume content is 40%. When the samples with 20 mm thickness, 40 vol% expanded perlites which particle size is 1mm, in the frequency ranges of 2-18 GHz, if the mass fraction of CB is 2%, the minimum reflectivity value is-20 d B; if the mass fraction of CB is 3%, the bandwidth of the reflectivity below-10 d B can be reaches 11.5GHz. The impedance matching between absorber and free space is improved by expanded pertiles, through adjusting the electromagnetic parameters of the composite. As well as, the ability of EMW attenuation can be enhanced by scattering and multiple reflections of the expanded perlites.The special three-dimensional networkstructures of mineral wool materials can provide transmission pathes for the incident waves and improve the impedance matching, meanwhile the loss of electromagnetic wave can be increased by the scattering and multiple reflections of the insolated conductive particles and the mineral wool fibers with CB particles on surface. So, the mineral wool boards with C B as absorbing agent have excellent wave absorbing properties. For the single layer mineral wool board, when the C B content is 2% and the thickness is 20 mm, the bandwidth of reflectivity less than-10 d B is 10.4 GHz, and the lowest reflectivity value reaches-20.8 d B, in the frequency ranges of 2-18 GHz. Furthermore, the EMW absorbing performance of the double layer samples with 20 mm thickness, 1% CB in the matching layer and 5% CB in the absorbing layer is under-10 d B in the whole 2-18 GHz.It can be founded, through the comparison of the wave absorbing properties and the electromagnetic loss mechanism, that micro-structure of mineral wool board is more conducive to the absorbing of electromagnetic wave.