Chapter 4: Dielectric Materials

Dielectric Materials

Dielectrics as the Choice of Materials

• Dielectrics are used in various forms:
  • Liquid: Transformer oils used in oil-immersed transformers.
  • Solid: Papers insulating winding coils, porcelain insulators, polymeric insulators, and glass insulators.

εr(f) for a Material Having All Three Polarization Types

• The graph of $"\varepsilon_r(f)"$ typically does not have values on the vertical axis because it represents a general behavior applicable to all dielectrics.
• Specific values of $"\varepsilon_r'"$ are particular to each dielectric material.
• For each type of polarization (orientation, ionic, electronic), $"\varepsilon_r'"$ remains constant as frequency (f) changes.
• $"\varepsilon_r'"$ decreases abruptly each time one of the three polarization mechanisms stops functioning.

Dielectric Constants of Materials at Different Frequencies

• At frequencies below 10^8 Hz (e.g., 60 Hz and 1 MHz), all three polarization mechanisms (orientation, ionic, and electronic) are present.
• The dielectric constant changes very little between 60 Hz and 1 MHz for most materials.

Table of Dielectric Constants

The following table lists dielectric constants for various materials at 60 Hz and 1 MHz:

Material Definitions

• Ceramic Material:
  • Obtained by shaping clay or similar plastic substances and firing at high temperatures.
• Titanate Ceramic Material:
  • A special class of ceramic materials with extremely high dielectric constants.
  • Example: Barium titanate (BaTiO3).
  • Applications include capacitors for storing a large quantity of charge.
• Mica:
  • A mineral of the silicate group, constituting over 90% of the Earth’s crust.
  • Monoclinic structure.
  • Complex chemical formula: $(K,Na,Ca)(Al,Mg,Fe,Li)<em>{2-3}(OH)</em>2(Si,Al)<em>{4-5}O</em>{10}$.
  • Resistant to high temperatures (up to 900°C), used to replace glass in ovens in metallurgy.
• Steatite:
  • A variety of talc, the softest mineral in the world (hardness 1 on Mohs scale).
  • Mohs Hardness Scale was developed by Friedrich Mohs in 1812.
  • The face of the statue