Measurement of the dielectric properties of materials by using time domain reflectometry

The authors present some TDR (time-domain-reflectometry) applications for complex permittivity measurements for strong polar liquid in the frequency range of 1 to 35 GHz, liquid crystal from 100 kHz to 1 GHz, and ionic microemulsion at frequencies between 30 MHz and 20 GHz. In each case, the necessary TDR techniques for optimal condition are given. The new TDR system (HP54120A+HP54121A) used has excellent stability compared with the earlier TDR system (HP181). It was found that, for methanol, the TDR system implemented can obtain information about the complex permittivity in the frequency range up to 25 GHz with sufficient accuracy and can possibly go up to 35 GHz using a bilinear correction. In the case of the liquid crystal, it is shown that the method is powerful not only in the microwave range but also in the radio frequency range. From the measurement of the ionic microemulsion system, it is clear that the TDR technique is applicable to the measurement of the complex permittivity of a sample with high DC conductivity.<>