Hierarchical hybrid materials combining wideband electromagnetic absorption and mechanical performance

by Pierre Bollen

Institution: Université Catholique de Louvain
Department: Pôle en ingénierie électrique
Year: 2015
Keywords: Nanocomposite; Carbon Nanotube; Foam Filled Honeycomb; Electromagnetic absorption; Multifunctionnal
Record ID: 1076323
Full text PDF: http://hdl.handle.net/2078.1/157883


Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over reflection in certain instances, is attained by simultaneously minimizing the reflection and transmission. This requires, in the gigahertz range, to combine a low dielectric constant, ideally equal to 1, with an electrical conductivity around 1 S/m which are antagonist properties in the world of materials. For some transport application, the need of EM shielding goes along with mechanical shielding while bearing in mind to be as lightweight as possible. In this thesis, a multimaterial and multiscale approach is proposed towards a multifunctional sandwich with optimized mechanical and EM absorption performances. The strategy starts at the nanoscale, using a carbon nanotube reinforced polymer. The conductivity of a polymer can be increased to the range of 1 S/m with a low amount of fillers (typically 1-2wt%). At the microscale, foaming the nanocomposite polymer reduces the permittivity. When such foam is filling a metallic honeycomb lattice, the absorption of the resulting hybrid material is improved compared to the composite foam alone. The combination of metallic honeycomb and polymeric foam also give excellent crushing performance. The last advantage of the metallic honeycomb is the increase of the thermal conductivity. Finally at the mesoscale, the hybrid is used as the core of a sandwich panel, obtained by the addition of two EM transparent face-sheets to offer high bending stiffness versus density performance. The results show that a careful design of face-sheets improves the absorption performances of the hybrid. An experimental level of absorption around 95% is achieved over the 10-40 GHz frequency band with a 9mm thick sandwich panel. (FSA - Sciences de l)  – UCL, 2015