Dielectric measurements of water in the radio and microwave frequencies by time domain reflectometry

Merabet, M.; Bose, T. K.

doi:10.1021/j100332a059

Cited by 21 publications

(9 citation statements)

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“…Once this data has been corrected, a decrease in real permittivity can be seen between 20 • C and 60 • C. This corrected negative gradient and corresponding ε 1 values now closely match the literature values calculated from the equations developed by Kaatze [15]. This also matches closely with the values seen in the literature [16], [17]. The errors for these measurements were also calculated and compared with the literature values, as shown in Table I.…”

Section: Methods and Resultssupporting

confidence: 82%

Temperature Correction Using Degenerate Modes for Cylindrical Cavity Perturbation Measurements

Barter

Partridge

Slocombe

et al. 2019

IEEE Trans. Microwave Theory Techn.

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Microwave cavity perturbation measurements are a useful way to analyze material properties. Temperature changes can be introduced during these measurements either intentionally or as a result of some other process. The microwave cavity itself also has a temperature-dependent response, which can affect the results. A common method to correct is to use another resonant mode separately to the measurement mode, which is not affected by the sample. Instead of using independent modes, this paper describes a method to use split degenerate TM m10 modes of cylindrical cavities. TM m10 consists of two modes with identical field patterns with a relative rotation between them and identical resonant frequencies. A strategically placed perturbation reduces the frequency of one of the TM m10 modes and affects the coupling of both modes by reconfiguring the fields. This can be used for temperature correction by placing a sample such that both modes are equally coupled. The lower frequency, the perturbed mode is used as a measurement mode. The higher mode is used as a reference for temperature correction as it is unaffected by the sample. This technique was verified by measuring the permittivity of pure water using an aluminum microwave cavity resonator at 3.96 GHz. The temperature was swept between 20 • C and 60 • C, and the results was verified against the literature.

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Section: Methods and Resultssupporting

confidence: 82%

Temperature Correction Using Degenerate Modes for Cylindrical Cavity Perturbation Measurements

Barter

Partridge

Slocombe

et al. 2019

IEEE Trans. Microwave Theory Techn.

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“…Therefore, the relaxation of macromolecules contributes to the impedance spectrum. Most important in the range between 2 GHz and 25 GHz is the relaxation of the water molecules [45]. Since the dispersion of the water dipoles is well defined, microwave spectroscopy is useful for assessment of the water content.…”

Section: Microwave Measurementmentioning

confidence: 99%

Bioimpedance: A Review for Food Processing

Pliquett

2010

Food Eng. Rev.

113

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Electrical measurement is a simple innocuous tool for material characterization. Unlike for instance milk or dairy products, the majority of naturally grown food is composed of cells. The cells of meat or vegetables are surrounded by an insulating membrane, while the cytosol and the extracellular fluids are electrolytes. Despite the high permittivity of water, electrolytes behave like ohmic resistors up to hundreds of MHz. In contrast, membranes form capacitive elements due to their high resistance. The typical time constant for charging cell membranes is of the order of a microsecond. Thus, cells influence the impedance in a frequency range up to several MHz. At higher frequencies, the cytosolic content, i.e., macromolecules, gives rise to characteristic relaxation processes. Using the impedance in the microwave range where water dipoles show a distinct dispersion, humidity of dried matter can be addressed. Moreover, with sensitive measurement setup and proper models, one can determine the dry content in mashes and slurries as well. Several quality standards correlate well with the permeability of the membranes or the total water content. Because of the comparatively simple measurement of the electrical impedance together with advanced mathematical modeling, it is often a good approach in quality assessment of agricultural products. The change in conductivity of a culture medium contains information about the metabolism of incubated cells. Using specific culture media and time-lapse conductivity monitoring allows a high sensitivity and selectivity in microbial detection. Because the electrical impedance is very sensitive to the permeability of cell membranes, it is a great choice for the assessment of changes due to high voltage application. Today, many attempts to use impedance measurement in food technology show fast success in research but fail in practice. The reason is often an overestimation especially of the selectivity while underestimating the uncertainties in a harsh environment of a food-processing plant. Established, however, is the use of robust process measurement systems and the limitation of impedance measurement to applications with highly significant outcome or as supplemental measurement in a multiparameter approach. This review introduces the basics of bioimpedance measurement, points to sources of uncertainty, and presents successful applications in food industry.

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“…The permittivity shows a slight decrease around 8 GHz in accordance with the expected relaxation of free water. 24 The noise artifacts occurring around 10 MHz have been removed by calibration with the saline reference.…”

Section: A Real Permittivitymentioning

confidence: 99%

Monitoring of cement hydration by broadband time-domain-reflectometry dielectric spectroscopy

Hager

Domszy

2004

Journal of Applied Physics

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The broadband complex permittivity is monitored continuously in hydrating cement paste over the frequency range of 10kHz–8GHz and from initial mixing to several weeks of cure. Measurements are made by time domain reflectometry (TDR) dielectric spectroscopy, using an adjustable capacitance sensor, which can be embedded in the material in situ. The results are fit to a relaxation model, which includes terms representing (1) a Cole-Davidson relaxation near 1MHz, which grows initially and then decreases with an advancing cure; (2) a Debye relaxation near 100MHz, which grows initially and then decreases with an advancing cure; (3) a free-water relaxation near 10GHz, which decreases with an advancing cure; and (4) an ion conductivity and electrode polarization, which decreases with an advancing cure. The model is fit continuously as function of cure time extracting parameters for the relaxation amplitudes, relaxation frequencies, and distribution parameters as a function of cure time. The results are contrasted with measurements in tricalcium silicate and tricalcium silicate with varying ion content, revealing differences that may indicate the nature of the processes involved. Alternative methods for extracting reaction-rate information directly from the TDR transient are presented, providing a robust monitoring procedure usable in the field. Such methods are demonstrated using a variation in temperature and comparison with measurements of reaction heat obtained by calorimetry.

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Dielectric measurements of water in the radio and microwave frequencies by time domain reflectometry

Cited by 21 publications

References 0 publications

Temperature Correction Using Degenerate Modes for Cylindrical Cavity Perturbation Measurements

Temperature Correction Using Degenerate Modes for Cylindrical Cavity Perturbation Measurements

Bioimpedance: A Review for Food Processing

Monitoring of cement hydration by broadband time-domain-reflectometry dielectric spectroscopy

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