Mechanically Responsive Microwave Absorption and Shielding in Hierarchical Heterogeneous Architectures for Electromagnetic Interference Protection

ABSTRACT With the rapid advancement of next‐generation flexible electronics, stretchable electromagnetic interference (EMI) protection materials that enable tailorable and simultaneous shielding and absorption properties are urgently needed in complex and dynamic electromagnetic environments. However, integrating tunable functionalities within a single flexible composite system remains a challenge due to inherently conflicting principles of shielding and absorption. Herein, a mechanically responsive hierarchical Fe 3 O 4 @polypyrrole@cellulose nanofibers/Ecoflex/liquid metal (FPCEL) composite was constructed by judiciously incorporating polypyrrole‐ and Fe 3 O 4 ‐functionalized cellulose nanofibers (FPCNFs) and liquid metal (LM) into a stretchable silicone elastomer. Benefiting from hierarchical asymmetric architecture, with distinctive LM‐enriched bottom layers and FPCNFs top layers, the composite enabled strain‐dependent electromagnetic response and promoted multi‐step electromagnetic energy dissipation via absorption‐reflection‐reabsorption mechanism. The balance between shielding and absorption properties can be achieved by adjusting LM contents or applying external stress. With increased LM loadings, shielding effectiveness (SE) increased while absorption was suppressed, indicating a shift from absorption‐dominated to reflection‐dominated energy dissipation mechanism. Remarkably, the FPCEL‐30 composite exhibited pronounced strain‐driven transition from reflection‐dominated shielding (SE = 27.76 dB) to absorption‐enhanced behavior (RL min = −15.03 dB) under strains from 0% to 250%. This work provides a convenient strategy for designing flexible EMI materials with tunable response, suitable for stress‐adaptive EMI protection systems.