an insulated conductor wound into a spiral and having considerable inductance, relatively low capacitance, and low effective resistance. An inductance coil consists of an insulated single-strand, less frequently multistrand, wire wound on a cylindrical, toroidal, or rectangular frame made from a dielectric; frameless inductance coils are also used. The, winding may be single-layer (row winding with a pitch) or multilayer (row, random, or universal winding). To increase inductance, cores are made of ferromagnetics, such as electrical steel, Permalloy, iron carbonyl, or ferrites. Cores are also used to produce small changes in the inductance of resonant circuits.

The inductance of an inductance coil is proportional to the linear dimensions of the coil, to the square of the number of turns in the winding, and to the magnetic permeability of the core; it ranges from a few tenths of a microhenry to dozens of henrys. Among the main parameters of an inductance coil are loss resistance, quality factor, temperature coefficient of inductance, and self-capacitance. Inductance coils are widely used as components of filters and of oscillatory circuits, in transformers, as chokes, in relays, and in magnetic amplifiers and electromagnets.

Special inductance coil designs include the windings of electrical machines, frame antennas and ferrite antennas, and flat print-ed-circuit coils used in micromodules.