부산대학교 도서관

Composite materials and determination of their properties is a much-discussed topic not only in the field of the high voltage insulation systems. In this field, one of the most important parameters which may be determined is relative permittivity, also known as the dielectric constant. In some of the times, few mathematical formulas, e.g. linear, Birchak’s, Landau-Lifshitz-Looyeng’s or Lichtenecker-Rother’s, were valid. The basic problem of usage of these formulas occurred with the application of filler with nano-dimensions, where the dielectric properties are affected by interaction zone between the surface of the filler and the matrix. The main aim of this paper is to use these formulas for calculations at elevated temperatures and compare them with the results from prepared samples of nanocomposite material. The main contribution of this paper is placed in the knowledge of the temperature dependence of the magnesium oxide filler which was measured separately as a compressed pellet and may be used for precise calculation. The values of relative permittivity were measured from 30 to $120^{\circ}\mathrm{C}$. The different amount of filler was used for this investigation. Individual sample set contains 5 samples 10x10x0.1 cm for better statistical evaluation. The average values of the relative permittivity of each set were used for comparison with theoretical calculations and suggestion of modified formula.