Complex Permittivity and Permeability of SiO_2 and Fe_3O_4 Powders in Microwave Frequency Range between 0.2 and 13.5 GHz

摘要

The real and imaginary parts of relative complex permittivity (ε' and ε") and relative complex permeability (μ' and μ") were measured for powder and bulk SiO_2 and Fe_3O_4 in the frequency range of 200 MHz-13.5 GHz. The ε' and ε" values of SiO_2 powder samples are in good agreement with the previous data. The e' values of powder SiO_2 and Fe_3O_4 samples with the relative density below 1 are smaller than the values estimated using the linear relation between ε' and the relative density, and larger than those estimated using the Lichtenecker's logarithm mixed law. The μ" values of powder Fe_3O_4 samples show the peaks in the frequency range of 706 MHz to 3.21 GHz. The frequency at the peak of the μ" vs. frequency curve decreases with an increase in the particle size of Fe_3O_4 sample. All the powder samples with an identical relative density have almost the same μ" values around 2 to 3 GHz irrespective of the particle size. Above ca. 3 GHz, the μ" values of all samples become smaller as the measurement frequencies become higher. These results suggest that 2.45 GHz, the frequency of the most commercially prevailing microwave generators, may be the most suitable one for microwave heating of iron ores.