Ilmainduktorit

An air-core inductor, here represented by the Estonian term ilmainduktorit, is an inductor that lacks a magnetic core. It consists of a coil of conductor wound on a non-magnetic former, with air as the magnetic medium. The absence of a ferromagnetic core eliminates core losses and saturation effects, making these inductors favorable at high frequencies.

Inductance is determined mainly by the coil geometry: the number of turns, the cross-sectional area, and the coil length. For a long solenoid, L ≈ μ0 N^2 A / l, where μ0 is the vacuum permeability. Real designs include parasitic capacitance between turns, which gives a self-resonant frequency (SRF) above which the inductor behaves capacitively rather than inductively. Achieving larger inductance requires more turns or a larger diameter, which increases parasitics and physical size.

Applications include RF filters, tuning circuits, impedance matching networks, and laboratory test setups. They are preferred in high-frequency circuits where magnetic-core materials would introduce losses, nonlinearity, or saturation. Disadvantages include relatively large size for a given inductance, potentially lower Q at certain frequencies, and sensitivity to stray capacitances and mechanical tolerances.

Variants exist, including air-core solenoids, and air-core coils with various geometries. The performance of ilmainduktorit depends on wire gauge, turn spacing, and former quality. In summary, ilmainduktorit offer clean, high-frequency inductance with minimal core effects, at the expense of size and parasitic limitations.