Tuning the impedance matching of microsphere Co for strong broadband absorption

Abstract

Efficient absorption bandwidth and attenuation capability are two crucial indicators for evaluating the high-performance microwave absorbers. Proper impedance matching is the precondition for obtaining broadband absorption, while it still remains a challenge to fabricate the absorbers with better impedance matching and strong attenuation over a wide frequency range. Here, we successfully prepared Co powders by a simple ethylene glycol reduction process and researched the corresponding structures, morphologies and electromagnetic (EM) parameters. The normalized input impedance |Z| (|Zin/Z0|) values of Co at various reaction times were calculated to investigate the effect of morphology on the impedance matching. It was demonstrated that Co powders were composed of fcc-Co and hcp-Co. Compared with the compact structures, the loose ones can cause the EM wave multiple scattering and reflections and increase the EM energy dissipation, however, the balance between the attenuation and impedance matching is suboptimal. The compact microspheres Co exhibited the optimal microwave absorption performance when the reaction time was 8 h. The distribution area of |Z|~1.0 is relatively broad. When the thickness varies from 1.15 to 5.00 mm, the effective absorption bandwidth (EABW, RL ≤ −10 dB) covers the bands of 3.45–18 GHz. The EABW as large as 8.16 GHz and the minimum reflection loss of −64.67 dB have been reached at a sample thickness of only 1.83 mm. We believe that this research may serve as an effective guideline for the synthesis of other optimal broadband absorbers.