Quality Factor

The quality factor defines the sharpness of resonance.

It is defined as:
where
Q = quality factor
ω0 = resonance frequency [rads-1]
ω1 = is the frequency below resonance for which the average power has dropped to half that at resonance [rads-1]
ω2 = is the frequency above resonance for which the average power has dropped to half that at resonance [rads-1]

It is an inherent characteristic of an oscillator that influences its stability. Generally speaking, the higher the Q, the more stable the oscillator, since a high Q means that an oscillator will stay close to its natural resonance frequency.

Examples
Oscillator TypeQuality Factor, Q
Tuning Fork103
Quartz Wristwatch104
Oven Controlled Crystal Oscillator106
Rubidium107
Caesium Beam108
Hydrogen Maser109
Caesium Fountain1010
Mercury Ion Optical Standard1014

In a reactive circuit, the quality factor is the ratio of the reactance in ohms divided by the resistance in ohms.

See also: Resonance.

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Subjects: Electronics Noise & Vibration Physics