Tailoring the input impedance of FeCo/C composites with efficient broadband absorption.

Proper impedance matching and strong attenuation capabilities are crucial factors for an excellent microwave absorbent. Significant attention and effort have been focused on the attenuation capabilities, whereas little attention has been paid to impedance matching, which is particularly important to design broadband absorbing materials. In this study, coin-like porous FeCo/C composites were successfully prepared by a simple carbon thermal reduction method. The Zin/Zo values of the FeCo/C composites were calculated to investigate the effects of the Fe/Co molar ratio and structure on the impedance matching. The results show that the coin-like porous samples were equipped with optimal impedance matching (Zin/Zo ≈ 1) and broad frequency bandwidth. The coin-like porous structure can induce multiple scattering and extend the travel path of the waves, which is in favour of electromagnetic loss. In this way, the effective frequency bandwidth (RL < -10 dB) as large as 6 GHz (from 11.36 to 17.36 GHz) has been achieved at a thickness of 2 mm when the Fe/Co molar ratio is 4 : 6. In addition, the average frequency broadband reached 5.57 GHz in the thickness range of 2-2.6 mm. We believe that this study may provide a new strategy for tuning the impedance matching for optimal broadband absorbers.