Rational design of yolk-shell C@C microspheres for the effective enhancement in microwave absorption

Carbon materials, as a typical dielectric loss medium, are always the most attractive candidates for microwave absorption due to their characteristic advantages; however, much less attention has been paid to upgrading their performance by rational design on the microstructure. According to the transmission behavior and loss mechanism of electromagnetic waves, uniform yolk-shell C@C microspheres are innovatively fabricated through a coating-coating-etching route as a novel microwave absorber. The unique microstructure endows yolk-shell C@C microspheres with improved BET surface and pore volume as compared to solid carbon microspheres. The microwave absorption properties are evaluated in the frequency range of 2-18 GHz, and as expected, yolk-shell C@C microspheres exhibit excellent reflection loss characteristics, where strong reflection loss (-39.4 dB at 16.2 GHz) and ultra-wide response bandwidth (4.5-18.0 GHz over -20 dB) can be achieved. Such good performance is indeed superior to most carbon absorbers ever reported. Electromagnetic parameters reveal that the yolk-shell structure is favorable for the matching of characteristic impedance, and more importantly, desirable dielectric loss ability can be achieved at matched characteristic impedance. It is believed that the multiple reflections between cores and shells are responsible for the improved dielectric loss. (C) 2015 Elsevier Ltd. All rights reserved.