Enhanced Electromagnetic Interference Shielding via Magnetic Field–Induced Alignment and Asymmetric Structure Design in Polylactic Acid‐Based Conductive/Magnetic Multilayer Films

ABSTRACT The advancement of lightweight and miniaturized electronic devices has intensified the need for efficient electromagnetic interference (EMI) shielding materials. However, traditional polymer composites often show restricted EMI shielding effectiveness (SE) and poor mechanical strength due to the disorderly distribution of magnetic nanoparticles, inappropriate concentration levels, and flawed structural design. To address these challenges, a novel strategy was developed to directionally align Fe 3 O 4 ‐loaded basalt fibers (BF@Fe 3 O 4 ) within a polylactic acid (PLA) matrix via magnetic field guidance, thereby significantly enhancing the mechanical properties of BF@Fe 3 O 4 /PLA. Furthermore, an asymmetric multilayer architecture was engineered via the integration of a conductive carbon nanotube/PLA (CNT/PLA) layer with the magnetic BF@Fe 3 O 4 /PLA layer, synergistically enhancing the overall EMI SE. BF@Fe 3 O 4 /CNT/PLA ‐U (“U” signifies uniform magnetic field processing) demonstrates a total EMI SE of 52 dB and a minimal transmission coefficient in 18.0–26.5 GHz. Finite element simulations support the experimental results and confirm the effectiveness of the microstructure modulation. Additionally, the 0.3 mm thick BF@Fe 3 O 4 /PLA ‐U achieves superior mechanical performance, with tensile strength and elongation at break reaching 29.8 MPa and 5.9%, outperforming unmodified BF@Fe 3 O 4 /PLA. This work presents a synergistic approach combining electromagnetic structure engineering and magnetic alignment, offering a promising route toward next‐generation EMI shielding materials for high‐frequency applications.