US Patent 11378711 Systems, methods, and apparatus for detecting ferromagnetic foreign objects in a predetermined space

An apparatus for detecting a presence of an object includes an inductive sensing coil that is configurable to generate a first magnetic field. The inductive sensing coil is configured to have an electrical characteristic that is detectable when generating the first magnetic field. The electrical characteristic is configured to vary as a function of a second time-varying magnetic field simultaneously applied to the object. The apparatus comprises a controller configured to detect a change in the electrical characteristic and determine a presence of the object based on the detected change in the electrical characteristic. The electrical characteristic comprises one or more of an equivalent resistance, an equivalent inductance, an equivalent impedance, and an impulse response of the inductive sensing coil. The object comprises one or more of a ferromagnetic object, a metallic film and a metallic foil.