Opencoil

Opencoil is a term used in electrical engineering to describe a coil configuration in which the magnetic circuit is intentionally open or incomplete. In practice this means coils that are air-core or have a deliberate gap or non-ferromagnetic surrounding, so the flux is not confined to a continuous ferromagnetic path. This contrasts with closed-core inductors or transformers that use a continuous magnetic circuit to concentrate flux.

Construction and design: An opencoil consists of a conductor wound into turns on a non-conductive former. The core, if present, is either non-magnetic or broken by gaps, and the coil may operate without a magnetic core (air-core). The inductance is lower than comparable closed-core coils and is strongly influenced by the coil geometry, number of turns, and the surrounding medium. Parasitic capacitance and resistance set performance limits at higher frequencies.

Operation and characteristics: Because magnetic flux is not confined, fringing fields extend into the surroundings. The coil’s behavior is well described by standard inductor equations with corrections for air or non-magnetic cores; Q factors can be high at certain frequencies but are generally sensitive to environment and orientation.

Applications: Opencoils appear in RF inductors, passive components in resonant circuits, test and measurement setups, and educational demonstrations of inductance without a magnetic core. They are also used in certain proximity sensing and coil antenna designs where a broader field is acceptable.

See also: Inductor, air-core inductor, ferrite core, transformer, magnetic circuit.