AC Electrical Characterization Research Articles

AC Electrical Characterization of Epoxy/Whiskers Composites Coated with Titanium Nitride

This article deals with the AC electrical characterization of epoxy reinforced with neat silicon carbide (SiC) whiskers and SiC whiskers coated with titanium nitride. The AC electrical characterization was studied as a function of frequency in the range from 100 kHz to 1.2 MHz, temperature in the range from 20°C to 110°C. It was found that AC electrical conductivity increases with reinforcements, temperature, and frequency. Some AC electrical characterization of SiC whiskers composites as dielectric constants, activation energy, and relaxation time were determined. The observed enhancement in AC conductivity is attributed to increase in the number of conduction paths created by the whiskers contacts in the epoxy matrix gives higher electrical conductivity. It was found that the coated whiskers enhanced AC conductivity better than the uncoated. The universal power-law model of AC conductivity is observed for composites. The calculated Power exponent (about unity) is physically acceptable within this applied model.

Impedance spectroscopy and optical characterization of polymethyl methacrylate/indium tin oxide nanocomposites with three-dimensional Voronoi microstructures

This study describes the optical and ac electrical characterization of polymethyl methacrylate (PMMA)/indium tin oxide (ITO) nanocomposites containing a Voronoi-type segregated network microstructure. Optical transmission microscopy, scanning electron microscopy (SEM), and impedance spectroscopy were used to investigate the microstructure and electrical properties of the composites. The complex refractive index values of the composites were measured by using a modified version of the internal reflection intensity analysis (IRIA) method. SEM images of the composites reveal that the microstructure consists of polyhedral-shaped PMMA particles, where the ITO nanoparticles become concentrated along the edges of the PMMA to form a percolated network. Electrical measurements as a function of filler content indicate that the percolation threshold is <0.50 vol % ITO. The in-plane and through-plane refractive indices obtained by the modified IRIA method suggest that the microstructure is isotropic. The estimated extinction coefficients increase with higher ITO content, which is expected for a percolating system. A microstructural model, which takes into account the accumulation of the ITO nanoparticles at the edges of the polyhedron-shaped PMMA particles, is proposed that can predict the percolation threshold in composites that have Voronoi-type segregated network microstructures.

DC and AC Electrical Characterization of Stacks of HTS Tapes

Today the Bi-2223 tape represents a suitable candidate for the use in various HTS devices. The LHC current leads use Bi-2223 tapes soldered together in short lengths, forming stacks of rugged HTS conductors. Critical current and AC loss measurements were performed on BSCCO stacks, in the temperature range of 65 K and 77 K and in magnetic fields of up to 0.5 T. The experimental results reported in this paper give a broad description of the stacks behavior in the range of current and field values of practical interest, and provide design parameters for the optimization of current leads operating both in DC and pulsed conditions.

AC and DC electrical imaging of biosamples at the nanoscale by Atomic Force Microscopy

We present a new tool and measurement protocol based on Atomic Force Microscopy for the AC and DC electrical characterization of biological samples at the nanoscale. The new developments allow performing a variety of electrical measurements (DC conductivity, A C small signal impedance) both in spectroscopic mode (i.e. in a single point) as well as in imaging mode (i.e. by providing a map of the electrical properties with nanometric spatial resolution) with minimum sample damage. Successful test measurements have been carried out on Purple Membrane.

The AC electrical characterization of the solid-state reaction derived CaSnO3

The potential of CaSnO3 (calcium metastannate) for its application as a capacitor component possessing small temperature coefficient of capacitance (TCC) in electrical systems, is examined via the ac small-signal measurements. The ac electrical data were acquired on these samples sintered at various combinations of temperature-time frames (1200°C ≤ T ≤ 1350°C; 24 h ≤ t ≤ 60 h) in the frequency range from 5 Hz to 13 MHz. The measurements were carried out over the temperature range 25–300°C. The electrical response was found to exhibit relaxation processes in more than one complex plane formalism in a simultaneous fashion. The resistance of the sintered samples was dominated by the grain boundaries. The capacitance showed almost linear behavior in this measurement temperature range. The resulting electrical behavior has been discussed with the evolved microstructure in the sintered bodies.

AC Electrical Characterization of Heterogeneous Catalysts

At operating temperatures, heterogeneous catalysts behave like lossy dielectrics. The technique of impedance spectroscopy has been used in conjunction with other AC methods to differentiate between different loss processes. At low frequencies and high temperatures, thermally activated hopping of relatively free charges is dominant, whilst at higher frequencies and lower temperatures relaxation losses from dipoles at the surface and in the bulk of the material prevail. The principal use of impedance spectroscopy is in the determination of geometry-independent parameters. These help to elucidate the roles of the insulating and conducting components in a catalyst and define the frequency and temperature ranges over which various processes predominate. In general, the dielectric-frequency relationships are in agreement with the models for the "universal" dielectric behaviour of solids. The electrical parameters are highly sensitive to inherent changes in catalysts and hence these AC methods offer potential in-situ techniques for studying factors such as chemisorption, deactivation, activity, selectivity, phase changes, and solid-state reactions.