air-core

[air-kawr, -kohr]
adjective Electricity.
  1. having a nonmagnetic core, as one of fiber or plastic, encircled by a coil (air-core coil), or containing one or more such coils: air-core transformer.

Origin of air-core

First recorded in 1890–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018