X-Band circuit-analog absorbers using unidirectional carbon fiber

This letter explores single-ply pre-impregnated (pre-preg) unidirectional carbon-fiber-reinforced polymer (CFRP) laminas for use in X-band (8.2-12.4 GHz) absorbers. Specifically, the unidirectional CFRP sheets were used as lossy frequency selective surfaces in single- and two-layer circuit-analog absorbers (CAAs). The aim of this letter was to assess the feasibility of using only the fiber orientation and areal weight of the material as a tuning aid. A free-space materials characterization system was used to characterize the anisotropic complex permittivity and anisotropic surface impedance of two different areal weight unidirectional CFRP samples. The absorbers were prototyped in a mechanically reconfigurable fixture with the aid of a vacuum-bagging system. The reconfigurable approach allowed reflectivity measurement performance to be measured without the need to fabricate cured sandwich constructions. Reflectivity measurements were compared to transmission-line models as well as full-wave models developed using commercial simulation software. Regions of validity for the transmission line models were identified. The results show that single-ply pre-preg unidirectional CFRP laminas have the potential to be used in single- and two-layer CAA configurations for use in X-band absorbers.