Metal detectors use electromagnetic fields to detect the presence of metallic objects. They exist in a variety of walk-through, hand-held, and vehicle-mounted models and are used to search personnel for hidden metallic objects at entrances to airports, public schools, courthouses, and other guarded spaces; to hunt for landmines, archaeological artifacts, and miscellaneous valuables; and for the detection of hidden or unwanted metallic objects in industry and construction. Metal detectors detect metallic objects, but do not image them. An x-ray baggage scanner, for example, is not classed as a metal detector because it images metallic objects rather than merely detecting their presence.
Metal detectors use electromagnetism in two fundamentally different ways, active and passive. (1) Active detection methods illuminate some detection space
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