Rational design of mesoporous MnO2 microwave absorber with tunable microwave frequency response

To design a single-component absorber with optimizing reflections loss and tunable absorption frequency, the unique lightweight MnO2 microspheres are successfully synthesized by a template-free method. The as-synthesized MnO2 microspheres are of mesoporous in diverse specific surface area. By controlling the pH value of the reacting solution, the specific surface area of MnO2 microspheres is adjustable. The maximum specific surface area of MnO2 microspheres with mesoporous nature being 90.52 m(2)/g for specimens is obtained from solution of pH = 5. The complex permittivity and permeability of manganese dioxide are tailored to obtain proper impedance matching. Thus, the resultant MnO2 microspheres exhibit remarkable microwave characteristic in a wax matrix. The minimum reflection loss reaches - 31.79 dB at 14.60 GHz, with the effective absorbing bandwidth below -10 dB being 5.78 GHz with a 2 mm thickness. The effective absorption broadband also changes from 10.27 to 13.75 GHz to 12.56-18.00 GHz as the increasing pH value. Such an outstanding microwave absorption performance ascribes to the unique mesoporous structure with designable specific surface area, giving rise to the multiple scattering and reflecting, interfacial polarization, and dielectric relaxation from the abundant interfaces and curved surfaces and impedance matching.