Design and Experimental Validation of a Broadband Microwave Absorber Using Agricultural Waste-Derived Carbon Composites

Background: Broadband microwave absorbers are essential components in electromagnetic compatibility shielding and radar cross-section reduction applications. Agricultural waste-derived carbon composites offer a sustainable and potentially low-cost alternative to synthetic absorber materials with untapped potential in Nigeria. Aim: This study designed and experimentally validated a broadband microwave absorber using carbon composites derived from Nigerian palm kernel shell agricultural waste. Methods: Palm kernel shell-derived activated carbon was prepared by chemical activation and incorporated into a polydimethylsiloxane matrix at loading fractions of 10 to 40 weight percent. Dielectric properties were measured from 2 to 18 GHz using a vector network analyser and coaxial transmission line fixture. Absorber structures were designed using genetic algorithm optimisation and validated by free-space measurement. Results: A two-layer graded-index absorber achieved greater than 10 dB reflection loss bandwidth from 4.2 to 17.8 GHz. The 40 wt% carbon composite layer exhibited complex permittivity of 8.4 to j3.2 at 10 GHz. Overall absorber thickness was 4.8 mm with a mass per area of 6.2 kg/m2. Conclusion: Palm kernel shell-derived carbon composites provide effective, wide-band microwave absorption. The low-cost sustainable fabrication pathway makes this approach highly relevant for Nigerian electronics and defence applications. Keywords: microwave absorber, agricultural waste carbon, electromagnetic shielding, broadband, palm kernel shell.