Reluktans

Reluktans, or reluctance, is a property of magnetic circuits that quantifies opposition to the establishment of magnetic flux. In analogy with electrical resistance, the magnetomotive force drives flux through a magnetic path, and the flux is related by Φ = F / R_m, where F is the magnetomotive force (in ampere-turns) and R_m is the reluctance of the path.

Reluctance is defined as R_m = l / (μ A), where l is the length of the magnetic path, A is the cross-sectional area, and μ is the permeability of the material (μ = μ0 μ_r; μ0 ≈ 4π×10^-7 H/m). The unit of reluctance is ampere-turns per weber (A·turn/Wb). For a composite path, reluctances in series add: R_total = Σ l_i / (μ_i A_i). If flux splits between parallel paths, their reluctances combine in reciprocal fashion.

Materials with high permeability (high μ_r) have low reluctance, allowing flux to be concentrated in a circuit. Soft magnetic materials such as iron and ferrites are common core materials precisely because they reduce reluctance. Air gaps or nonmagnetic regions increase reluctance and can be used to control flux in a magnetic circuit.

Reluktans is a useful modeling concept in the design of transformers, inductors, magnetic sensors, and relays, enabling simple linear analysis of flux with magnetomotive force. In practice, nonlinearity of μ with flux, saturation, hysteresis, and eddy currents limit the accuracy of the simple model, especially at high flux densities.