Ionic Polarisation occurs when ions move in response to an electric field. The ions are electrically charged and recieve kinetic energy from the field, this kinetic energy is converted to heat when the ions collide with each other. At high frequencies the rate of collision is increased and is detectable as a temperature rise within the material. The rate of dissipation of energy increases as the frequency is raised, however as the frequency continues to increase a point is reached where the ability of the ions to follow the field oscillations is diminished due to ion inertia. See Fig 3 below.

Dipole Rotation is dependant on the existance of polar molecules. Normally, polar molecules are randomly oriented, however in the presence of an electric field the molecules align themselves with the field. As the field oscillates and the electric field polarity varies at a rate dictated by the frequency, the molecules attempt to follow the changing field, causing friction between the molecules thus heating up the material. This effect is frequency sensitive because the amount of energy dissipated is constant per cycle of applied alternating field, however in practice there are mechanical resonances within molecules which result in peaks of power absorption at specific frequencies.


Fig 3 - Frequency response of permittivity and loss
factor for a typical dielectic material showing
various phenomena.
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