A parallel-plate capacitor used to determine the complex permittivity of supercooled aqueous solutions in the 1 MHz range

Abstract

To evaluate temperature-dependent stretching experiments of biological cells down to sub-zero temperatures in a high-frequency electric field, knowledge of the electrical parameters of the suspension is necessary. A measuring system was developed to determine the relative permittivity ε r (f , T ) and the ionic conductivity γ (f , T ) of supercooled aqueous solutions and suspensions in the frequency range 0.1-2 MHz. A parallel-plate capacitor was used in connection with an impedance analyser and a cryostat. The errors caused by the cables needed between analyser and cooled capacitor were minimized. Field homogenization within the measuring space is realized by correcting the reference potential at the guard ring. The starting capacitance at each temperature was reproduced by testing the 0 • C value after re-assembling the capacitor. Damaging of the capacitor by ice formation is prevented. For testing, a comparison was made with literature data and first measurements of supercooled aqueous solutions.

Dielectric Properties for Nanocomposites Comparing Commercial and Synthetic Ni- and Fe3O4-Loaded Polystyrene

“…The dielectric properties of the prepared nanocomposites were analyzed by measuring the capacitance of the nanocomposites as a function of frequency to assess the real (ε′) and imaginary (ε″) components of the complex permittivity. , In Figure , the frequency dependence of the real permittivity (ε′) is plotted for the nanocomposites and fits in Figure to the Looyenga model. The imaginary permittivity is shown in the Supporting Information (Figure S12), and the loss tangent is plotted in Figure .…”

Measuring the dielectric properties of materials. Ninety-year development from low-frequency techniques to broadband spectroscopy and high-frequency imaging

“…Simple equations for the evaluation of the complex permittivity or complex conductivity of material filling a parallel-plate capacitor exist only for plane electrodes of equal size and an electric field configuration perpendicular to the electrodes. As with normal parallel-plate capacitors fringing fields at the plate edges prevent such favourable conditions, three-terminal guard-ring cells [99,120,[130][131][132][133][134][135][136][137][138][139] are frequently employed in alternating measurements and transient methods as well. Such guard-ring assembly, of which one plate is subdivided in a central disc and a concentric ring, is sketched in figure 5.…”

Broadband dielectric spectrometry of liquids and biosystems

“…The extension of the measuring range to frequencies as small as 10 −6 Hz has revived the use of specimen cells which basically consist of circular cylindrical plate capacitors [85][86][87][88][89]. Such cells are employed in investigations up to 10 7 Hz.…”

“…Since the inhomogeneity of the field distribution around the edges of the capacitor depends on the permittivity of the sample between the plates [88], use of simple capacitor cells and evaluation of the measured capacitances in terms of the Kirchhoff formula may be questioned. For this reason three-terminal cells with guarded electrodes are frequently applied [85,86,88]. The, as thin as possible, gaps between the measuring electrodes and the guard rings are usually filled with an insulating and chemically inert Teflon film.…”

“…This relation indicates that, in contradiction to the requirements for the achievement of small effects from fringing fields, the electrode spacing d should be as large as possible, in order to enhance the sample term in equation ( 30) relative to the electrode polarization term. Larger electrode separations d at tolerable field inhomogeneities are enabled by three-terminal guarded electrode cells [85,86,88,91]. Additionally, the first terms in equation ( 30) can be reduced relative to the third term by using electrode material with the lowest possible resistance and the largest possible capacitance [92].…”