Broadband complex permittivity measurements by time-domain spectroscopy

The complex permittivity measurements of some materials, taken by using the time-domain reflectometry (TDR) method, are presented. As an example of the wide frequency measurement capability, both at the radio and microwave frequencies, the complex permittivity measurement of a liquid crystal is presented in the frequency range between 100 kHz and 1 GHz. The measurement of an ionic water-in-oil microemulsion system is given to describe the case of a conductive sample. From the measurement of this system, it is clear that the TDR technique can be used to measure the complex permittivity of a sample with high DC conductivity. Even if the sample has a small dielectric absorption hidden behind the high DC conductivity, the method should be able to distinguish between the two. Complex permittivity measurements of strongly polar liquids are presented to show the highest frequency attainable by the TDR system. The result indicates that the complex permittivity can be measured up to 25 GHz with sufficient accuracy if the cutoff frequency of the TDR system is higher than 25 GHz. This high-frequency limit is due to the limitation of the system given by the performance of the sampling system.< >