US Patent 7295107 Ferromagnetic detection pillar

A ferromagnetic detection pillar having one or more applied magnetic field sources and one or more magnetic field sensors, with the magnets and sensors arranged and adapted to detect a ferromagnetic threat object on one side of the pillar. A detection device, such as a motion detector or infrared detector, is also provided, to detect the presence of an object on a selected side of the pillar. A single free-standing pillar can be used, or two or more free-standing pillars can be arranged to constitute a variable aperture detection portal. Single sensors or multiple-sensor configurations can be used.