Dissipation factor

Dissipation factor

In physics, the dissipation factor (DF) is a measure of loss-rate of power of a mechanical mode, such as an oscillation, in a dissipative system.

For example, electric power is lost in all dielectric materials, usually in the form of heat. DF is expressed as the ratio of the resistive power loss to the capacitive power, and is equal to the tangent of the loss angle.

The dissipation factor in the case of capacitors is also referred to as the loss tangent and approximates to the power factor:

tan delta = frac { varepsilon_{Im} } { varepsilon_{Re} } = frac { sigma } { omega varepsilon }

where varepsilon is the permittivity (varepsilon = varepsilon_r varepsilon_0)

sigma is the conductivity

omega is the angular frequency (i.e. omega = 2 pi f)

varepsilon_{Re} and varepsilon_{Im} refer to the real and imaginary parts of the permittivity.

This is equivalent to expressing DF as the ratio of a capacitor's equivalent series resistance (R) to its capacitive reactance (X_{c}). DF is usually expressed as a percentage.

DF = frac {R} {X_{c}} times 100% = frac {R} { (frac {1} {omega C} ) } times 100% = omega RC times 100%

DF will vary depending on the dielectric material. In low dielectric constant (low-k), temperature compensating, ceramics DF of 0.1 to 0.2% is typical. In high dielectic constant ceramics, DF can be 1 to 2%. However, lower DF is usually an indication of quality capacitors when comparing similar dielectric material.

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