Capacitance and dielectric breakdown of metal loaded dielectrics

Abstract

The authors review and extend analytic, numerical and experimental work on the capacitance, C(f), and dielectric breakdown field, Eb(f), of a simple insulator containing volume fraction, f, of randomly located metal inclusions. In the case of spherical inclusions, they find Eb(f)=Eb(0)/(1+kc(ln V/ mod ln f mod )alpha ). V is the sample volume divided by the average volume of an inclusion, kc is a constant and 1/2< alpha <1 for large ln V/ mod ln f mod . In the dilute inclusion limit, the statistics of the dielectric breakdown field are shown to be of a modified Gumbel form. The scaling theory of capacitance in composites with percolation microstructures is outlined, and the authors discuss extensions to include hard core repulsion between inclusions. They have fabricated many samples of paraffin wax (a simple insulator) containing various concentrations of stainless-steel spheres (size range 10-65 mu m). The capacitance and dielectric breakdown field of these samples is presented and the results are compared with theory.

Heterogeneous solid propellants: from microstructure to macroscale properties

“…(2)), the results are displayed in terms of the mean nearest-neighbor distance d. Figure 5 shows the present simulation results together with some experimental data from Duxbury et al [14] obtained on steel balls embedded in wax. In present case, the RVE size is chosen to L = 1 mm with D = 100 μm particles in order to comply with experiments [14]. Present computations are in very good accordance with the experiments but also with the simple law of Eq.…”

Length scales of interactions in magnetic, dielectric, and mechanical nanocomposites

“…However, the energy product of a pennanent magnet does not exceed Ms2/4, so that this coercivity increase is not an option. The second example is metallic inclusions in dielectrics, which enhance the permittivity but tend to reduce the breakdown field and the electrostatic-energy density in a capacitor made from the composite material [17,21,35,36,37). Elastic moduli are important for construction materials, but very often the main considerations are mechanical toughness and fraction behavior [38).…”

“…Fluctuations often determine the main figures of merit of materials. For example, mechanical fracture tends to start at cracks [14], the dielectric storage capacity is limited by the maximum local electric field [35] (as contrasted to the average field), and the coercivity of permanent magnets is determined by the local rather than average anisotropy [9,22]. In fact, the dielectric contrast caused by the embedding of a single high-e particle in a low-e matrix is known to shift field strength and energy density from the particles into the matrix and to substantially reduce the breakdown field.…”

“…In fact, the dielectric contrast caused by the embedding of a single high-e particle in a low-e matrix is known to shift field strength and energy density from the particles into the matrix and to substantially reduce the breakdown field. The effect depends on geometrical factors such as surface curvature of the particle surface [35].…”

“…In fact, metallic [35,36] particles have an infinite permittivity und are ideally suited for E-enhancement. The dielectric constant can be enhanced by embedding highly permittive particles in a matrix or using structures such as metallic grains separated by non-metallic grain boundaries [37].…”