Bi-phase metallic cobalt with efficient broadband absorption in X and Ku bands

Abstract

Broadband and lightweight microwave absorbers have gained considerable research interest in overcoming electromagnetic interference pollution. Here, mixture of two phase (fcc and hcp) metallic cobalt powders with broadband absorption was synthesized through solvothermal method using ethylene glycol as the reducing agent. The effect of NaOH content on the structure and morphology of the prepared Co powders is investigated by X-ray diffraction and field-emission scanning electron microscopy. Ring samples of 7.00/3.04 mm of out/inner diameter were prepared with paraffin for microwave absorption testing by vector network analyzer. It was observed that the increase of NaOH content caused a relative higher generation of hcp-Co phase and formation of irregular microspheres. The reflection loss (RL) peak and effective absorbing bandwidth (EABW, RL ≤ − 10 dB) shifted towards lower frequency when the sample thickness increased from 1.00 to 3.00 mm with EABW covering almost all the C, X and Ku bands (4–18 GHz). The bi-phase Co prepared in a low base solution exhibited enhanced microwave absorption properties. The width of largest EABW has reached 6.33 GHz covering partial Ku band and almost all the X band with optimal RL of − 56.95 dB at a sample thickness of only 1.85 mm, which is superior to EABW of Co crystals reported earlier. We proposed that such a wide EABW is due to the fact of Z values closed to 1.0 (0.8 ≤ |Z| ≤ 1.2) at almost the whole frequency range. This indicates that the prepared bi-phase Co powders are excellent microwave absorbers with large bandwidth, have good prospects.