The term “air core coil” describes an inductor that does not use a magnetic core made of a ferromagnetic material. The coils are wound on plastic, ceramic, or other nonmagnetic forms, as well as those that actually have air inside the windings.
Air Core Coil Characteristics:
lower inductance than ferromagnetic core coils
are often used at high frequencies because they are free from energy losses called
core losses that occur in ferromagnetic cores, which increase with frequency.
Air Core Side Effect:
Inductance of the coil may change due to mechanical vibrations because the coil is not rigidly supported by a coil form.