Flexible thin microwave absorbing patch: flake carbonyl iron and chopped carbon fibers oriented in resin matrix

Microwave absorbing patches are used in a wide range of applications including mobile devices, digital devices and electronic products. Here, we used flake carbonyl iron (FCI) and chopped carbon fibers (CF) as double absorbers to fabricate thin microwave absorbing patches by tape-casting method. FCI and CF were oriented in polyurethane-modified epoxy resin (PMER) matrix, resulting in strong anisotropy of the microstructure. The effects of CF content (from 0 to 0.3 wt%) on thermal stability, electromagnetic properties and microwave absorbing properties were investigated. The prepared patches exhibit good flexibility, and the addition of CF is beneficial to enhance the thermal stability of composites. A suitable amount of CF can reduce the thickness of absorber and broaden the absorption bandwidth. The oriented FCI/CF/PMER composite containing 60 wt% FCI and 0.3 wt% CF shows a wide absorbing bandwidth of 11 GHz (RL < - 5 dB) with a thickness as thin as 0.7 mm. Excellent microwave absorbing properties with a thin thickness are ascribed to the synergistic effect of dual absorbents, multiple interface polarization, balanced impedance match and structural anisotropy in the composites. These provide an effective idea to tune the peak frequency of RL and absorbing bandwidth.