MATCHING MATRIX AND FILLER DIELECTRIC CONSTANTS TO INCREASE DIELECTRIC BREAKDOWN STRENGTH

摘要

We investigate lightweight polymer matrix composite [PMC] capacitive devices capable of replacing bulky high energy pulsed power capacitors on mobile platforms. The glass fiber/polymer structural dielectric used in these capacitors often suffers from limited energy density due to premature dielectric breakdown, possibly precipitated by the mismatch in dielectric constant [ε'] at the glass/polymer interface. This mismatch effectively serves as an electrical stress raiser and may act as the critical flaw in dielectric breakdown. In this work we attempt to address this problem by modifying the dielectric properties of the matrix so as to more closely match the dielectric constant of the glass filler. Since it has been shown that, unlike larger reinforcements, nanometer scale reinforcements do not precipitate dielectric breakdown, we fill the matrix with high dielectric constant nanofiller in order to match the dielectric constant of the matrix with that of the micron-sized reinforcements. By reducing the mismatch in dielectric constant at the matrix-filler interface, we mitigate the buildup of field concentrations responsible for the premature breakdown events. The following study presents the improved characteristics in dielectric breakdown strength observed for PMCs composed of bisphenol E cyanate ester [BECy] monomer resin modified with nanometer sized barium titanate [BaTiO_3] particles, designed to produce a low viscosity slurry with a matching dielectric constant value to E-glass microsphere filler, ε' = 5.8. Glass spheres are used instead of fibers to facilitate sample preparation.