Single-layer and double-layer microwave absorbers based on Co67Ni33 microspheres and Ni0.6Zn0.4Fe2O4 nanocrystals

Co67Ni33 microspheres and Ni0.6Zn0.4Fe2O4 nanocrystals were synthesized by hydrothermal method. The complex permeability and complex permittivity of the as-prepared powders dispersing in wax (60 wt% powder) were measured using a vector network analyzer in 2-18 GHz frequency range. The calculated microwave absorption of single-layer and double-layer absorbers based on Co67Ni33 microspheres and Ni0.6Zn0.4Fe2O4 nanocrystals were analyzed in 2-18 GHz frequency range. The results show that the Ni0.6Zn0.4Fe2O4nanocrystals with the relatively low permittivity and Co67Ni33 microspheres with the relatively high dielectric loss and magnetic loss can be used as proper matching layer and excellent absorption layer, respectively. The double-layer absorber with a coating thickness of 2.1 mm exhibits a maximum reflection loss of −43.8 dB as well as a bandwidth (reflection loss less than −10 dB) of 5 GHz. Moreover, their absorption peak and the absorption intensity can be adjusted easily through changing the stacking order and each layer thickness.