Permittivity Determination of Fresh Cement-Based Materials by an Open-Ended Waveguide Probe Using Amplitude-Only Measurements

Abstract

Abstract-An open-ended waveguide probe has been adapted for complex permittivity determination and hence mechanical property inspection of cement-based materials. The probe uses amplitude-only reflection measurements at different frequencies for this goal, which is suitable for industrial based applications when cost and ease of use are important considerations. We have derived expressions by taking into account of the wave-material interaction. The reference plane for measurements is set inside the waveguide to measure solely the reflected signal of the dominant mode. It is shown that the measurement results are in good agreement with the theory.

Microwave Method for Thickness-Independent Permittivity Extraction of Low-Loss Dielectric Materials From Transmission Measurements

“…In addition, we note that, for medium-loss samples, while the accuracy of L determination using maximum values of |S 21 | is superior to other combinations, that of ε r becomes poorer. We expect that this happens as a consequence of the approximations given in (9) and (10) [27].…”

“…However, the analysis and the presented method in that paper still work if maximum |S 21 | value is utilized in the extraction process). After, using (14)- (19), we determined the initial guess of ε r and L using the above extreme values of |S 21 Figs. 2 and 3 demonstrate measured real and imaginary parts of ε r of the sample using above extracted L values by the proposed method (PM).…”

“…However, measured transmission S-parameter (S 21 ) has several superior advantages over measured reflection S-parameter (S 11 ) as: a) it provides longitudinal averaging of variations in sample properties, which is particularly important for relatively high-loss heterogeneous materials such as moist coal and cement-based materials [21]; b) it undergoes less deterioration from surface roughness at high frequencies [14]; and c) it offers a wide dynamic range for measurements [34].…”

“…where S m 21 and S 0 21 are, respectively, the measured transmission Sparameters when sample is present and when there is only air (empty line) between calibration planes; l 1 , l 2 , and L are, respectively, the distances between the sample and terminals of the sample holder and the length of the sample; |S 21 | and θ 21 are the magnitude and phase of normalized S 21 ; and γ and γ 0 are, respectively, propagation constants of the sample-and air-filled sections, which are given as…”

“…Assuming e jωt time convention, between calibration planes in Fig. 1, the normalized S 21 can be expressed as [24,38] …”