Size modulated electromagnetic properties and highly efficient microwave absorption of magnetic iron oxide ceramic opened hollow microspheres
Abstract Hollow structured nanomaterials are considered as one of the most promising candidates of thin broadband absorbers due to the potential multiple scattering and resonance of electromagnetic waves. Here, magnetic iron oxide ceramics opened hollow microspheres with tunable size were fabricated based on hydrothermal route and carbothermal reduction method. The electromagnetic parameters are obviously dependent on microsphere size due to size dependent relaxation time of polarization and magnetization. The opened hollow microspheres with diameter of 500 nm achieve the 10 dB absorption bandwidth of 6.1 GHz covering 7.5 13.6 GHz at only 2 mm thickness, which is the widest bandwidth in all reported nanostructures of magnetic iron oxide composites. Moreover, the broadband absorption covering the X band at such thin thickness is competitive in all absorbing materials. Such excellent microwave absorption benefits from the outstanding impedance matching caused by the multiple scattering of electromagnetic waves in large size open hollow microspheres. This work provides a physical insight for obtaining high performance microwave absorber.