H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
H01F21/00—Variable inductances or transformers of the signal type
H01F21/02—Variable inductances or transformers of the signal type continuously variable, e.g. variometers
H01F21/08—Variable inductances or transformers of the signal type continuously variable, e.g. variometers by varying the permeability of the core, e.g. by varying magnetic bias