A coil in a circuit is an inductor. The guide wires are wound one by one, the wires are insulated from each other, and the insulating tubes may be hollow, or may include a core or a magnetic powder core, referred to as an inductor. Inductors can be divided into fixed inductors and variable inductors. Fixed inductor coils are referred to as inductors or coils. Expressed by L, the unit is Henry (H), milli-henry (mH), micro-Henry (uH), 1H = 10^3mH = 10^6uH.