Microwave electromagnetic properties of polyimide/carbonyl iron composites

The electromagnetic characteristics of polyimide/carbonyl iron absorbers synthesized by compression molding using the polyimide precursors (poly (amic acid) solution (PAA)) and different shape of carbonyl iron (CI) were studied at 8.2 - 12.4 GHz. Curing process of polyimide was monitored by Fourier transform infrared spectroscopy (FT-IR). The influences of CI filler loading and morphology on the microstructure, electromagnetic properties and flexural strength were characterized. The distribution of filler is uniform throughout the polyimide matrix. The X-ray diffraction (XRD) results show the polyimide matrix can protect the CI particles from oxidation. Both the complex permittivity and complex permeability increase with increasing the CI volume fraction. The minimum reflection loss containing spherical CI is -11 dB at 12.4 GHz and flaky CI is 9.7 at 10.3GHz for the composites with 60 wt.% CI. The flexural strengths of the composites are up to 73 MPa and 68 MPa for flaky CI and spherical CI composites, respectively.