Composition-Dependent Microwave Shielding Performance of Kaolinite/Chopped-Strand Composites for Wide Frequency Range

The increasing demand for high-frequency electronic and communication systems has intensified the need for lightweight and efficient electromagnetic interference (EMI) shielding materials. In this study, the conventional oxide mixing method was used to form kaolinite-chopped strand composites. Natural kaolinite powder was calcined at 450 °C for 4 h to remove volatile and organic components before composite fabrication. Kaolinite/chopped-strand epoxy composites were fabricated and evaluated for their microwave shielding effectiveness in the 0–4.4 GHz frequency range. Composites with different kaolinite-to-chopped-strand weight ratios were prepared using a controlled mixing and molding process to obtain thin specimens with a uniform thickness of 1.4 mm. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used primarily to characterize the kaolinite powder. Because composite-level mapping was not performed, the uniformity of filler dispersion is interpreted cautiously. Microwave shielding effectiveness was measured using a two-port vector network analyzer (VNA). The composite containing 80 wt.% kaolinite and 20 wt.% chopped strands showed the highest shielding performance, with a maximum total shielding effectiveness of 21.57 dB at 0.58 GHz. The observed shielding behavior is consistent with absorption-dominated attenuation supported by S-parameter-derived reflection, transmission, and absorption trends. This can arise from polarization losses and interfacial charge accumulation in heterogeneous dielectric composites. The results indicate that kaolinite/chopped-strand epoxy composites are low cost and sustainable materials for broadband microwave shielding applications.