Rigid composite materials for anechoic chamber application

[Display omitted] •Dielectric properties of epoxy foams loaded with carbon particles have been studied.•These composites show low dielectric losses (tanδmax=0.15 at 8GHz for 7%wt. load).•Comparison between polyester and epoxy resin loaded composites has been done.•Electrical measurements show a percolation threshold at 1.2wt.% carbon load.•A chemical reaction is presumed between the carbon black and the hardener. An electromagnetic absorbing material is developed to replace the polyurethane foam currently used in anechoic chambers. In order to solve issues related to the polyurethane foam (flexibleness, imprecise cut and inhomogeneous load dispersion), we propose the synthesis of new absorbent composites made of epoxy foam loaded with carbon particles. Our elaboration method leads to homogenous and rigid materials which allow a precise cut into pyramids and other complex shapes. Two kinds of carbon are used in association with epoxy foam. The dielectric characterization of these composites highlights low dielectric losses, contrary to expectation. In order to see if a chemical reaction between epoxy components and carbon black occurs, epoxy and polyester resins loaded with carbon are compared. Conductivity measurements on loaded epoxy resins revealed a percolating network, but this one doesn’t show any effect on dielectric properties; the occurrence of chemical reactions between carbon and epoxy matrix is proposed.