A Combined TD–FD Method for Enhanced Reflectometry Measurements in Liquid Quality Monitoring

Measurement and control of the dielectric parameters of liquids play a major role in industrial quality-control applications. Although several techniques are currently available to this aim, none of them is simultaneously accurate, cost-effective, and reasonably quick. On the other hand, reflectometry has become a very attractive method for monitoring applications, mostly thanks to its accuracy and flexibility. In this paper, a combined method based on time-domain reflectometry (TDR) and frequency-domain (FD) analysis is presented: the aim is to substantially improve the measurement accuracy of the dielectric parameters of liquids. Starting with typical TDR measurements, the associated FD evaluation of the dielectric parameters is considerably enhanced through the combined effect of the following: 1) specific data-processing techniques; 2) the implementation of a calibration procedure; and 3) the final modeling and minimization routine. Furthermore, to definitively assess the proposed combined procedure, results are compared with measurements directly performed in the FD through a vector network analyzer (VNA). The ultimate goal of the work is to pave the way for the adoption of inexpensive and portable TDR devices in practical industrial monitoring applications.