Qfaktorn

Qfaktorn, or the quality factor, is a dimensionless parameter that describes how effectively a resonant system stores energy relative to how much energy it loses per cycle. It provides a measure of the system’s selectivity or sharpness of resonance: a higher Q indicates a narrower, more selective resonance and lower damping, while a lower Q corresponds to broader resonance and greater losses. In steady-state operation at the resonant frequency, Q can be defined as Q = ω0 × (energy stored) / (power loss) and can also be expressed as Q = f0 / Δf, where Δf is the bandwidth over which the response falls to half its peak value.

In electrical engineering, Q is commonly discussed for resonant circuits. For a series RLC circuit with resonant angular frequency ω0 = 1/√(LC), the quality factor is Q = ω0L/R = 1/(ω0RC). For a parallel RLC circuit, Q = R/(ω0L) = ω0RC, depending on the chosen form of the circuit model. The energy storage is split between the inductor (E_L = 1/2 L I^2) and the capacitor (E_C = 1/2 C V^2), while losses occur in the resistance (P_loss = I^2R or V^2/R). The bandwidth of the resonance is roughly Δf ≈ f0/Q, linking Q directly to selectivity.

Qfaktorn is also used in mechanical, acoustical, and optical resonators. In optics, the Q of a resonant cavity relates to spectral linewidth (Δω ≈ ω0/Q). In all domains, measuring or designing for the appropriate Q involves balancing energy storage against dissipation, coupling, and external loading.