LuftkernInduktoren

LuftkernInduktoren, or air-core inductors, are passive components that store energy in a magnetic field without using a ferromagnetic core. They consist of a winding of conductor, typically copper, wound around a non-magnetic form such as plastic or ceramic, with air as the magnetic medium between the windings.

Construction and variants: The most common forms are solenoidal coils and toroidal windings. In air-core designs there is no magnetic material inserted into the magnetic path, which eliminates core losses and hysteresis. Winding geometry, wire gauge, and the number of turns determine the inductance and its distribution of parasitics. These inductors are widely used in RF and high-frequency circuits where core saturation and nonlinearity would be problematic.

Electrical characteristics: The inductance L approximately follows L = N^2 μ0 A_eff / l_eff, where N is the number of turns, μ0 is the permeability of free space, and A_eff and l_eff depend on the winding geometry. Air-core inductors are linear with current up to very high flux levels, since there is no ferromagnetic material to saturate. They typically exhibit high quality factors (Q) at RF due to the absence of core losses, but their performance is limited by parasitic capacitance and resistance. The self-resonant frequency, arising from the winding’s parasitic capacitance, sets the upper usable limit.

Applications and considerations: LuftkernInduktoren are favored in RF tuning, filter networks, impedance matching, and high-frequency resonant circuits where stability and linearity are important. They offer broad bandwidth and temperature stability relative to ferrite or iron-core inductors but require more physical space to achieve the same inductance. They are sensitive to external magnetic fields and mechanical tolerances, and their inductance grows slowly with added turns, making high inductance bulky.

In summary, air-core inductors provide linear, high-frequency performance without core losses, at the expense of inductance density and size for a given value.