kvalitetsfaktoren

Kvalitetsfaktoren, commonly called the quality factor and abbreviated Q, is a dimensionless parameter that characterizes how underdamped a resonant system is and how selective its frequency response is. It represents the ratio of energy stored in the system to the energy dissipated per cycle. A high Q means low losses and a narrow resonance; a low Q means broader resonance and higher damping.

In electrical circuits, Q is defined at the resonant angular frequency ω0. For a series RLC circuit, Q = ω0 L / R = 1/(ω0 R C). For a parallel RLC circuit, Q = R / ω0 L = R √(C/L). More generally, Q = f0/Δf = ω0/Δω, where Δω (or Δf) is the bandwidth between the half-power points around the resonance.

Physically, Q connects energy storage to energy dissipation: it is proportional to the number of oscillations over which the energy remains before decaying significantly. In mechanical systems, Q is related to damping (approximately Q ≈ 1/(2ζ) for light damping). High-Q systems have sharp, selective responses; low-Q systems are broadband.

Kvalitetsfaktoren is used across domains: electronic filters and oscillators, RF resonators and antennas, optical and microwave cavities, mechanical resonators, and acoustic instruments. It can be measured from the frequency response, from the decay time of free oscillations, or from quality indicators of materials and components. Actual Q values depend on temperature, drive level, and aging of components.

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