Plug-and-Play Multilayer Impedance Engineering in Dry-Processed CNTs/PI/PTFE Films for Broadband Microwave Absorption

Broadband microwave absorbing (MA) materials that are lightweight and thin are highly desirable for advanced electromagnetic protection applications. Multilayer absorber architectures offer an effective route to broaden absorption bandwidth via stepwise impedance matching, yet film fabrication processes for incorporating powder absorbers often suffer from limited scalability and thickness controllability. Herein, we report a solvent-free dry-process strategy to fabricate MA films. Polyimide (PI) is employed as the dielectric matrix, carbon nanotubes (CNTs) as the lossy phase, and polytetrafluoroethylene (PTFE) as the binder, which forms a continuous 3D microfibrillar network under mechanical shear. This dry-processed approach affords uniform filler dispersion, precise thickness control, and high mechanical integrity without solvent-induced phase separation. Benefiting from the well-defined thickness and modularity of the dry-processed films, multilayer absorbers are fabricated via alternating stacking of the films with low-density dielectric foam layers. The resulting structure delivers an effective absorption bandwidth of 12.45 GHz at a total thickness of about 6 mm, spanning the X-Ku frequency range. This work demonstrates that dry-processed film fabrication coupled with multilayer impedance engineering offers a scalable preparation pathway toward broadband, lightweight, and customizable microwave absorbers.