Quantitative and Qualitative Characterization of Liquid Materials - Broadband Reflectometry for Enhanced Diagnostics and Monitoring Applications - page 51

Chapter 4
Quantitative and Qualitative Characterization
of Liquid Materials

'Science exists, moreover, only as a journey toward troth.
Stifle dissent and you end that journey.'
John Charles Polanyi

Abstract. In this chapter, broadband microwave reflectometry (BMR)-based meth-
ods for measuring simultaneously the levels and the dielectric characteristics of liq-
uid materials are presented.
First, an approach based solely on time domain reflectometry (TDR) measure-
ments and on the analysis of TDR waveforms is described.
Secondly, a further enhancement of this method is accomplished by resorting
to the combination of TDR with frequency domain reflectometry (FDR). Also this
method provides, in one shot, the level and the dielectric permittivity of the con-
sidered liquids (this time, the complete spectral signature is obtained in terms of
Cole-Cole parameters). This approach is considered the optimal solution especially
when dealing with dispersive media. In this second measurement method, the ac-
curacy is enhanced also through the adoption of a transmission line (TL) modeling
of the measurement cell and through the realization of a custom-made fixture that
allows performing short-open-load (SOL) calibration measurements.
Finally, BMR-based measurements of the dielectric characteristics are extended
to edible liquids: in particular, vegetable oils are considered.
Reported results show that all the proposed methods have strong potential for
possible practical implementation in the field of industrial monitoring.
It will be evident how, in all the considered approaches, the design of the probe
is crucial for enhancing the final measurement accuracy.

4.1 Introduction

In recent years, dielectric spectroscopy measurements performed through broad-
band microwave reflectometry (BMR) have become an effective tool for extracting
information on the qualitative and quantitative status of materials, thus opening in-
teresting perspectives for several monitoring applications.