Microwave dielectric sensing of moisture in MSWIbottom ash – Comparison of frequency vs. time domain reflectometry / Fukthaltsmätning i bottenaska med dielektriska metoder – en jämförelse mellan mätningar i tids- och frekvensdomän
This paper presents the detection of moisture content in municipal solid waste incineration bottom ash (MSWI BA) with two different measurement techniques. The study used a frequency domain coaxial probe and a short TDR probe to evaluate and compare the performance of the both probes for lossy materials. Instead of using complex data conversion algorithms, between the two domains, the study directly compared the results measured in time and frequency domain as a function of water content. The samples of BA were prepared at four different volumetric water contents (0.10, 0.20, 0.30, and 0.40 m3 m–3) and the measurements were made without varying the bulk densities. The results were analysed with principle component analysis (PCA) to highlight the variable groupings and differences among the techniques. The results showed that frequency domain method was better for moisture estimation in lossy materials such as BA. The TDR under predicted the water content under similar experimental conditions and its performance reduced with the increasing salinities and water contents. Thus, it was concluded that FDR measurements between 300 MHz and 1.5 GHz were suitable for moisture content detection in lossy materials.