Dielectric metrology with coaxial sensors

Abstract

Coaxial sensors are used in applications that require accurate and traceable measurements of complex permittivity. For example, coaxial sensors are often used for measurement of the complex permittivity of tissue equivalent materials (TEMs) used in specific absorption rate (SAR) measurements of exposure to RF fields. It is therefore important that well-founded metrological techniques for their use are developed and published. Although there are many published papers on coaxial sensors, few discuss the experimental techniques required to obtain the most accurate results. In this paper experimental approaches for obtaining the most accurate measurements are described. Common pitfalls with the technique are discussed. A Monte Carlo modelling (MCM) technique is used to provide estimates of uncertainty which are compared to those of measurements on reference liquids made with 3.5 mm, 7 mm and 15.1 mm diameter sensors. The MCM technique allows uncertainties to be estimated when measuring dielectrics for which there are no reference materials that have comparable properties, for example for TEMs at frequencies below 100 MHz.

Hydration and sodium-ion binding of trifluoroacetate in aqueous solution

“…[12]. the reflection measurements fitted κ values deviate slightly from directly measured data due to imperfections of the probes [19]. Accordingly, experimental conductivities were chosen as a starting approximation in the fitting procedure but were generally 1-2% greater than the fitted values used.…”

Temperature Dependence of the Dielectric Properties and Dynamics of Ionic Liquids

“…In practice, conductivities obtained by fitting differ slightly from the directly measured values due to fringing field effects that arise from the geometry of the VNA probe. [43,50] Accordingly, as in our previous work, [26,43,51] experimental k values were taken as the starting point for the conductivity correction but were adjusted slightly to give the best fit to the dielectric data. While these adjustments are small for the present RTILs (typically < 10 % in k), they are larger than those observed for typical aqueous electrolyte solutions.…”

Factors affecting the microwave coking of coals and the implications on microwave cavity design

“…During the measurement a swept frequency signal was transmitted from the VNA into the liquid via the coaxial line, and the reflection coefficient was recorded. The amplitude and the phase of  were fed into a computer program, which utilised a modal analysis [25,[35][36][37] to calculate the real (dielectric constant, ɛ') and imaginary parts (dielectric loss, ɛ'') of the complex permittivity. Figure 2 shows the differential weight loss with temperature for Coal A treated for 120 minutes at a range of powers from 0.75 kW to 3 kW.…”