Time domain dielectric spectroscopy. advantages and disadvantages

摘要

The recent appearance of Time Domain Dielectric Spectroscopy (usually called TDS) precision measuring systems Cole et al (1), Hager (2), Nozaki and Bose (3), Feldman et al (4) may help resolve the problems of accuracy and sensitivity associatedwith this method when investigating different substances. However, even in the case of two channel bridge measuring systems it is necessary to make special calibration measurements and considerable calculations in order to overcome many of thedisadvantages inherent in TDS, such as shortcomings in the construction of coaxial lines, samplers, step generators, etc. These distortions and instabilities appear in the form of an altered shape of the incident pulse that cannot be compensated foreither by the ordinary difference method Cole et al (5), Bone (6), Feldman et al (7) or by apparatus correction of the pulse shape. In particular, these distortions have been crucial in the case of the system with parallel time nonuniform samplingErmolina et al (8). Corrections of the incident pulse shape by apparatus adjustments in the case of nonuniform sampling of the signals do not lead to noticeable improvement because of such procedure limitations as time borders of the "time window." As arule, distortions increase outside time interval bounds. In addition, TDS systems inherently have various general hardware problems due to instability in the time axis including jitter, time drift and variation of the sweep speed in the oscilloscope.These problems are all associated with the high frequency limitations of the measuring system. On the other hand, the slow drifts of the base line and effects of truncation at a long finite time limit are primarily connected with low-frequency limitations [1-3,8].