Flat Coils

Air core coils can be made in a flat configuration with thickness of about two diameters of the conducting atrand plus insulation. They can be wound of wire (WPI's: wound planar inductors) or made on printed circuit boards (PPI's: printed planar inductors). The area of these flat coils for a given inductance is equal to the projected area of the comparable helix plus the area of one turn of that helix. Advantages over conventional belical coils include greatly reduced bulk, increased mechanical aid electrical stability because of flat supporting mounting, high coefficients of coupling, the possibility of making them by etched circuit methods. Distributed capacitances are bigher and Q's slightly lower than for comparable helixes.