Application of Unidirectional Carbon-Fiber-Reinforced-Polymer Laminas in Circuit-Analog Absorbers

This paper explores the characteristics of unidirectional carbon-fiber-reinforced-polymer (CFRP) laminas and their use in electromagnetic absorber design. Unidirectional CFRP composites have been used for decades in structural applications. The electromagnetic properties of unidirectional CFRP composites have been well documented in the open literature. Since many structural applications may also have specific electromagnetic compatibility requirements, it is logical to exploit the useful electromagnetic properties of unidirectional CFRP. Specifically, this paper investigates circuit-analog absorbers (CAAs) made from a unidirectional CFRP lamina, foam spacer, and a ground plane. The unique properties of the unidirectional CFRP sheet provide the necessary resistive and reactive properties for the development of a CAA. To investigate such a CAA, the electromagnetic properties of several off-the-shelf unidirectional CFRP laminas were measured from 4 to 18 GHz using a free-space measurement system. A surface-impedance representation of the unidirectional CFRP lamina was used to build rigorous transmission-line models that provide insights about the properties of the absorbing structure. Transmission line as well as full-wave models were compared to measured absorption performance of fabricated prototypes. Maximum absorption configurations were found to be highly dependent on incident polarization relative to fiber orientation.