Current-controlled variable self-inductor for filter circuit - consists of two-half permeable core whose flux level is controlled by external field

摘要

The device is intended for filter circuits and uses an electrical method of inductance variation rather than a manual one. The inductor coil (1) is wound on a cylindrical part (4) which is an integral part of a plate (5a) made from a magnetically permeable material. Two similar plates (5a,5b) have rims (6a,6b,7a,7b) which align so that they form two halves of a magnetic circuit. The magnetic circuit so formed is positioned between and in contact with, the pole-pieces (12a, 13a, 12b, 13b) of a two-yoke electromagnet. Coils (30a,30b) are wound on each half of the electromagnet core. When the electromagnet is energised by a direct current, a flux-loop is established in the inner magnetic circuit. Current from the input signal to the inductor sets up flux which lies in the same path as that established by the electromagnet. The permeability, and hence the self inductance of the inductor, is variable according to the electromagnet current. The devices is also described in a cylindrical form where standard ferrite inductor cores and pots are used.