The Nanocrystalline FeSiBCuNb Finemet Absorption Properties at Microwaves

The reflection and absorption properties of powdered nanocrystalline FeSiBCuNb (“Finemet”) alloy at microwaves have been presented. To visualize the shielding ability of this material, the complex permittivity and permeability of pulverized Finemet in the frequency range from 0.2 to 10 GHz have been studied. To measure the permittivity and permeability of powdered Finemet, the modification of the Nicolson, Ross, and Weir method was presented. The modification of this method was mainly based on the unwrapping technique of the measured S-parameter phases. The investigation of permittivity and permeability was realized for pure powders. Four groups of powders with different particle sizes below 200 μm have been investigated. To assess the shielding effectiveness of the nanocrystalline Finemet, two attempts were analyzed. The investigation of the reflection loss of material layer with metal sheet attached to the backside as a reflector was investigated. On the other hand, the reflection and absorption factors of 3-mm-thick layer in free space were additionally analyzed. The obtained results show that the pulverized nanocrystalline Finemet alloy with particle size below 25 μm possesses good absorption properties and, for such particles, the absorption factor is significantly higher than the reflection factor.