A simple inductive contactless switch

摘要

When a small coil wound around a fine core of low coercivity square‐loop Fe‐6 wt. % Ni alloy wire is excited with a 100‐kHz ac current it develops a peak voltage much greater than that obtained from a coreless coil. This effect can be used to sense motion of the core in and out of the coil or alternatively to sense motion of an external biasing magnet. Either way one has a position sensor which is extremely simple and which could be useful in a variety of applications, such as high‐reliability keypad switches, proximity switches, and switches for use in hazardous or corrosive atmospheres.