Enhancing communication technology requires better protection of electronic devices from electromagnetic (EM) pollution. Electromagnetic interference (EMI) shielding materials are therefore essential to improve device efficiency and reduce EM wave pollution. In this study, a novel polyester-based composite reinforced with Cissusquadrangularis fiber, biomass-derived silver nanoparticles (AgNPs), and carbon quantum dots (CQDs) was developed and comprehensively characterized for EMI shielding applications. Among the fabricated composites, PCF2 (polyester with 40 vol.% fiber, 1.5 vol.% AgNPs, and 1.5 vol.% CQDs) exhibited superior fatigue resistance, lap shear strength, and EMI shielding performance. PCF2 showed fatigue strengths of 24,711, 21,711, and 18,741 cycles at 25%, 50%, and 75% of UTS, respectively, demonstrating excellent cyclic loading resistance and achieving a maximum lap shear strength of 23.16 MPa. It also achieved a total shielding effectiveness of 68.25 dB at 18 GHz, dominated by absorption (34.65 dB) and reflection (19 dB at 12 GHz), confirming its strong EM attenuation capability. Meanwhile, PCF3 (with 2.5 vol.% AgNPs and 1.5 vol.% CQDs) displayed the highest magnetic permeability values, with a real permeability of 5.5 at 20 Hz and an imaginary permeability of 1.47, indicating excellent energy storage and dissipation characteristics. The increased filler content enhanced magnetic polarization, making PCF3 suitable for magnetic applications. Overall, the results highlight the potential of natural fibers and biomass-derived nanoparticles in developing sustainable, high-performance polymer composites for lightweight EMI shielding in biomedical, aerospace, and defense applications.
