Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio.

A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with the miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10 s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system’s impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 min. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1 s. Overall, the new microfluidic device can be used for the dielectric characterization of biological cells in physiological buffers for various cell screening applications.

Применение метода диэлектрической спектроскопии для исследования свойств сыворотки крови мышей со злокачественным асцитом

The article presents the results of a study by the method of dielectric spectroscopy of high-frequency relaxation processes in the blood serum of intact mice and mice vaccinated with an oncological disease - Ehrlich's ascites carcinoma. Using the formalism of the electrical module, the relaxation parameters were calculated for the serum samples of the two studied systems.

Dielectric spectroscopy of aluminum oxide (γ-Al2O3)

Aluminum oxide (Al2O3) are continuously demonstrating the functional characteristics in devices. The physiochemical properties of hydrothermally as-grown Aluminum oxide (Al2O3) have been investigated in this research article. The as-prepared material was confirmed as γ- phase formation of Al2O3. The average crystallite size was found ∼ 78 nm, whereas the particles were found in nano scale too. Moreover, the absence of impurity in EDS analysis, and the presence of the bending vibrations of Al-O-Al and Al-O band in FTIR characterization further confirmed the absence of impurity in the material. Evaluated dielectric properties such as a relatively high dielectric constant, and low dielectric loss indicated the good optical quality of γ- Al2O3. Impedance and modulus spectroscopic studies showed the non-Debye type relaxation in γ- Al2O3 with an average relaxation time of 5.8 μs. Overall, the dielectric spectroscopy analysis of γ- Al2O3 indicates the promising applications of γ- Al2O3 in devices as dielectrics.

A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system’s impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 minutes. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1s. Overall the new microfluidic device can be used for dielectric characterization of biological cells in physiological buffers for various cell screening applications.

Keratinocyte cellular damage induced by pesticide doses below the cytotoxic level evidenced by electrical impedance and broadband dielectric spectroscopy

Cellular response of a normal human keratinocyte cell line exposed to non-cytotoxic doses of a deltamethrin-based pesticide was investigated by means of two different electrical impedance data spectroscopy approaches: Nyquist plot and broadband dielectric spectroscopy. The measurements have shown that the membrane capacity increases with pesticide concentration and this facilitates the electric current through cell membranes. Furthermore, the impedance of the extracellular matrix also increases with pesticide concentration, thus reducing the electric current outside the cell. Dielectric permittivity changes in the cellular samples at frequency larger than 100 Hz. Fluorescence measurements emphasized an increase of neutral membrane lipids as consequence of the pesticide exposure. Comparison of fluorescence response of pesticide exposed cells with the control ones showed a time increase of the emission intensity, suggesting the existence of a membrane lipid response aimed at repairing of the cell damage due to pesticide exposure. Therefore, both the spectroscopic techniques have demonstrated to be potential means to investigate the response to cell stress and damage. This opens up new possibilities in the early diagnosis of cellular modifications related to pesticides exposure of cells.

A 4 × 4 Array of Complementary Split-Ring Resonators for Label-Free Dielectric Spectroscopy

In this study, complementary split-ring resonator (CSRR) metamaterial structures are proposed for label-free dielectric spectroscopy of liquids in microplates. This novel combination of an array of sensors and microplates is readily scalable and thus offers a great potential for non-invasive, rapid, and label-free dielectric spectroscopy of liquids in large microplate arrays. The proposed array of sensors on a printed circuit board consists of a microstrip line coupled to four CSRRs in cascade with resonant frequencies ranging from 7 to 10 GHz, spaced around 1 GHz. The microwells were manufactured and bonded to the CSRR using polydimethylsiloxane, whose resonant frequency is dependent on a complex relative permittivity of the liquid loaded in the microwell. The individual microstrip lines with CSRRs were interconnected to the measurement equipment using two electronically controllable microwave switches, which enables microwave measurements of the 4 × 4 CSRR array using only a two-port measurement system. The 4 × 4 microwell sensor arrays were calibrated and evaluated using water-ethanol mixtures with different ethanol concentrations. The proposed measurement setup offers comparable results to ones obtained using a dielectric probe, confirming the potential of the planar sensor array for large-scale microplate experiments.