From Omnexus

What is Dielectric Constant?

• Use of materials in the production of capacitors used in radios and other electrical equipment. Commonly used by circuit designers to compare different printed-circuit-board (PCB) materials.
• Development of materials for energy storage applications.

How to Calculate Dielectric Constant?

• C = capacitance using the material as the dielectric capacitor
• C0 = capacitance using vacuum as the dielectric
• ε0 = Permittivity of free space (8.85 x 10-12 F/m i.e. Farad per metre)
• A = Area of the plate/sample cross section area
• T = Thickness of the sample
• The test can be conducted at different frequencies, often between the 10Hz and 2MHz range
• The sample must be flat and larger than the 50mm (2 in) circular electrodes used for the measurement.

Polar Plastics Vs Non-polar Plastics

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  In polar polymers (PMMA, PVC, Nylon, PC etc.), dipoles are created due to imbalance in the distribution of electrons. These dipoles tend to align in the presence of electric field. Hence, this creates dipole polarization of the material making these materials only moderately good as insulators.
  
  
• While non-polar polymers (PTFE, PP, PE, PS) have symmetrical molecules and are truly covalent. There are no polar dipoles present in them and hence in presence of electric field does not align the dipoles. However, slight electron polarization occurs due to the movement of electrons in the direction of electric field, which is effectively instantaneous. These polymers have high resistivities and low dielectric constant.

Factors Influencing Dielectric Constant

• Frequency - Dielectric constant decreases abruptly as frequency increases
• Moisture &Temperature
• Voltage
• Structure & morphology (see polar plastics vs non-polar plastics)
• Presence of other materials in the plastic
• Weathering and Deterioration

Dielectric Constant Values of Several Plastics