Dielectric permittivity simulations of layered composites with rough interfacial surfaces | IEEE Journals & Magazine | IEEE Xplore

Dielectric permittivity simulations of layered composites with rough interfacial surfaces


Abstract:

Finite difference quasi-electrostatic simulations are used to predict the interfacial dielectric permittivity of a rough-surfaced contact zone between two distinct materi...Show More

Abstract:

Finite difference quasi-electrostatic simulations are used to predict the interfacial dielectric permittivity of a rough-surfaced contact zone between two distinct materials in a layered composite. Fractional Brownian surfaces, which have fractal geometry, are used to represent the rough interfaces in a model space. The interfacial simulations are combined with a macroscopic analytic model for planar dielectric layers, which allows the calculation of composite permittivity for a layered composite with an arbitrary ratio of surface roughness-to-layer thickness and arbitrary volumetric filling fractions of the constituents. Examples are given for a ceramic-polymer system, and the effects of alternate ratios of constituent dielectric permittivities and changes in surface fractal character are also explored. Compared to the behavior of composites with perfectly flat interfaces, the rough-surfaced composite exhibits a significantly earlier increase in permittivity as a function of the volumetric filling fraction of the higher permittivity material. The behavior with extremely rough surfaces tends towards the predictions of the effective medium approximation
Page(s): 287 - 295
Date of Publication: 10 April 2007

ISSN Information:


I. Introduction

A critical issue in dielectric science is the prediction of the complex relative dielectric permittivity of a composite based on the volume fractions of the constituents and their individual complex permittivity values. For simple, idealized geometries, well-known analytic dielectric mixing laws can be used [1], [2]. However, for more complicated (and hence more realistic) microstructural geometries, computer simulations of the composite permittivity using quasi-electrostatic finite difference or finite element methods are required [3]–[7]. The ultimate goal is the complete modeling of composite materials for capacitors and sensors at the microstructure level, including both mesoscale features (individual particles, layers, or ensembles of particles in a matrix) and the truly microscopic features (interfacial effects, coatings, local dipolar interactions in surface layers, etc.). Such a capability would allow experimental synthesis to be focused on the most promising microstructural approaches, without the need to physically test each idea. Within a specific class of microstructures, the computational capability would provide explicit guidance to synthesis efforts, for example allowing the intelligent selection of particle shapes, loading fractions, surface coatings, and hierarchical assembly strategies. Finally, computational techniques provide a means of understanding experimental results on existing and new materials.

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