On the choice of the dielectric characterization method for foam composite absorber material

Abstract

This paper presents the characterization by three different techniques of a new lossy material made of carbon fibers loaded epoxy foam that can be used as an absorber in anechoic-chambers. The composite was characterized using free space, waveguide and coaxial probe techniques. Dielectric characteristics obtained from the three techniques are different and this is explained by the required dimensions of measured samples, not always representative of the porous form of the composites loaded with long fibers. Our study points out that the free space technique is the most appropriate to measure such composite samples with porosities and load having millimeter dimensions. Dielectric probe and waveguide are not suitable due to a small volume of measure which is not representative of the entire composite. The achieved prototype confirmed this result with a measured reflection coefficient very close to the simulation achieved with the dielectric characteristics obtained by the free space technique.