Self-Referencing TDR Dielectric Spectroscopy Using Reflection-Decoupled Analysis With a Mismatched Section

Abstract

An innovative self-referencing time-domain reflectometry (TDR) dielectric spectroscopy method is introduced. The method extracts the first reflection from a mismatched section (MS) immediately before the sensing section (SS) to capture the source characteristics and effect of leading sections. A reflection-decoupled analysis (RDA) is derived to characterize the complex dielectric permittivity (CDP) in the ss. Conventional time-domain spectroscopy (TDS) offers a more cost-effective alternative to frequency-domain methods, but its accuracy may suffer from input function variation, system mismatches, and probe design restrictions. RDA with MS approach provides an efficient, robust, and flexible dielectric spectroscopy technique including its calibration, which inherits all advantages of conventional TDS while using more economic TDR device and more flexible probe design. It adopts a nonconductive and nondispersive MS to serve as a reflector for reliable reference source directly embedded in a single TDR signal. Spectral ratios between the reflection from MS and all other reflections from the SS are experimentally determined and matched to the RDA-derived values as a function of CDP. RDA is inherently independent of source function, instrument mismatch, and cable resistance. There are only four frequency-independent system parameters that can be easily calibrated once and for all using a measurement of well-known material. The method is presented in a general framework without major restrictive assumptions, which explicitly expresses all probe parameters, allowing greater flexibility in probe design (e.g., geometric impedance, probe length, and end condition). Robustness of RDA was verified by numerical and experimental investigations using eight materials of different dielectric characteristics.