Electromagnetic Parameters of Dielectric and Magnetic Mixtures Evaluated by Time-Domain Reflectometry

The frequency-domain analysis of time-domain reflectometry (TDR) data can be used to evaluate the electromagnetic (EM) parameters of a sample under test. The goal of this letter was to use TDR to determine EM parameters, assumed to be frequency independent, for various magnetite/glass-beads mixtures. The EM parameters are, in turn, used to determine the velocity and attenuation of propagating waves. The latter quantity is also obtained through the TDR voltage method. Velocities decrease, and attenuations increase with increasing magnetite content. The measurements of the present work are compared with the velocities and attenuations reported in the literature (measured via the network analyzer (NA) and LCR meter techniques). The velocities calculated using the various methods are in good agreement. In contrast, the attenuations determined by fitting the TDR data only agree with the NA measurements at high frequencies (450 MHz), while those obtained by the TDR voltage method match the low-frequency attenuations determined through the LCR meter. The reasons for these behaviors are discussed, and the need for precise handling of the TDR data is emphasized. The TDR fit procedure is recommended to obtain reliable EM parameters of materials.