Flexible composites of Ni-Fe fiber/NBR for effective electromagnetic wave absorption

Highly efficient microwave absorbents and multilayer composite structures are crucial methods for enhancing electromagnetic wave (EMW) absorbent performance and broadening the bandwidth of materials. Herein, Ni-Fe/NBR microwave-absorbing composite sheets were prepared for the first time by uniformly dispersing Ni-Fe alloy fiber absorbers into a nitrile butadiene rubber (NBR) matrix using a mechanical mixing method. By varying the content and length of Ni-Fe fibers, thickness of Ni-Fe/NBR and blowing agent content (AC), a series of composites with low reflectivity and different frequency bands were obtained in the 2–18 GHz frequency. As a result, the single-layer NBR sheet with a Ni-Fe fiber content of 15% and fiber length of 3 mm can reach a minimum reflection loss (RL_min) of − 11.92 dB at a thickness of 2.7 mm. Secondly, it is noteworthy that double-layer stacked single-layer NBR absorbers can broaden the absorption bandwidth and improve the absorption effect. Furthermore, varying the positions of the upper and lower layers of sheet materials can yield disparate outcomes. The double-layer Ni-Fe/NBR absorber can achieve an RL_min of − 38.05 dB. Its effective absorption bandwidth (EAB) is 5.06 GHz in the C band and 3.44 GHz in the Ku band. This work provides new ideas for the design of efficient wave-absorbing flexible composites with structural functionalization.