Abstract
We study how surface distortions of liquid samples due to a meniscus and a tilt of a semi-open coaxial test cell affect errors in a broadband permittivity determination. The study is based on the scattering parameters, obtained using the electromagnetic simulations of samples with flat and distorted surfaces in a broad frequency range up to 18 GHz. The parameters are processed with the classic Nicolson–Ross–Weir (NRW) method and our new meniscus removal technique. We analyze the errors for several samples of different properties, such as distilled water and propan-2-ol. The results show that the meniscus removal technique is more robust and provides smaller errors in the permittivity determination compared to the classic NRW method. The effect of the cell tilt, to our best knowledge, has not been considered in the literature yet.
Highlights
The accurate value of liquid complex permittivity ε r = ε r − jε r is desired in many fields of science and technology [1] such as medicine, biology, chemistry, agriculture, radio communication, remote sensing [2,3,4], etc
We employ the scattering parameters obtained with electromagnetic (EM) simulations of the liquid samples that do not suffer from the residual errors of vector network analyzers (VNAs) calibration
Permittivity characteristics determined with the NRW and the meniscus removal (MR) methods for IPA, IPA50% and distilled water are shown in Figure 6a–c, respectively
Summary
The T/R methods allow broadband permittivity characterization by measuring liquid samples in test cells with vector network analyzers (VNAs). To get rid of the meniscus effect, the authors of [22,23,24] applied a cell closed with two plugs that fix the volume and shape of the liquid sample Such a solution causes more problems with modeling the measurement and constrains its application to a predefined volume of liquid. We study the errors caused by the meniscus in the permittivity and sample column height determination To this end, we employ the scattering parameters obtained with electromagnetic (EM) simulations of the liquid samples that do not suffer from the residual errors of VNA calibration. To check the impact of the liquid surface distortions on the errors, we investigate two different algorithms: our meniscus removal (MR) method and the classic Nicolson–Ross–Weir (NRW) technique [26,27]
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