Magazine article Security Management

The Steely Eye of the Metal Detector

Magazine article Security Management

The Steely Eye of the Metal Detector

Article excerpt

METAL DETECTION originated in ancient China more than two thousand years ago. Since that time, metal detectors have progressed from a simple magnet with the ability to attract only ferrous metals to today's sophisticated electronic marvels capable of detecting any conductive metal. Modern walk-through security metal detectors can be set to detect the smallest of weapons while ignoring coins in a patron's pocket.

The principle limitations of today's metal detectors are due to operators' deficiencies and not electronic failures. A properly trained operator, using the latest in metal detection technology, can control and maintain an environment free of weapons and contraband.

Metal detectors are used in a variety of venues for security purposes, including emergency rooms, gold mining operations, sporting events, government buildings, art exhibitions, and the lumber industry where environmental groups drive large metal spikes into trees marked for harvest.

Other uses include archaeological displays, political conventions, protection of VIP and government officials, homeless shelters, inner city housing, and public transportation. Prisons were among the first institutions to recognize the efficacy of using metal detectors as a first line of security defense. In response to the escalating threat of violence, virtually all U.S. courts use detectors to screen those attending high profile trials.

Metal detection has given corporate America a weapon to deal with the prospective employee offender. One example of metal detection's effectiveness took place at a large jewelry distributor after the company discovered that it had suffered inventory losses of more than a quarter of a million dollars during a one-year period. After determining that these losses were due to employee theft, the company installed a metal detector, through which all exiting employees were required to pass. Losses from employee theft ceased and $50,000 in lost inventory reappeared on company shelves. Installation of a metal detector proved to be an inexpensive answer to a troublesome and costly corporate dilemma.

How detectors work. Simply stated, metal detection occurs as a result of transmitted and received radio waves. When a radio signal is produced or transmitted by a metal detector, an electromagnetic field is generated that flows out from its search coil into the surrounding medium, whether it be air, cloth, skin, paper, leather, wood, concrete, or any other type of material.

Metal detectors have the ability not only to transmit but to receive signals that result from the detection of metals. When electromagnetic field lines strike the surface of metal, the electromagnetic field is disturbed and deformed and a small current, which is called an eddy current, is generated around the metal object. As the eddy currents flow around the metal surface, they create a radio signal that is sent back to the metal detector antenna. When these small signals are received, they are relayed to the electronics center of the detector where they are analyzed, interpreted, and amplified. An audio or visual response is then produced.

Operation techniques. Modern walk-through and hand-held metal detectors should have the capability of responding to metal regardless of where it is concealed on the body. A razor blade secreted in long hair or a knife hidden in a boot must not be overlooked any more than the midnight special handgun strapped to the inside of a person's thigh.

Security officers must devote sufficient time to familiarize themselves with their metal detection equipment. By adjusting the sensitivity of a walk-through metal detector, one can quickly learn the capabilities and limitations of the unit at its different intensity settings. Using this method, it is a simple matter to determine what the detector will locate or ignore when set at various sensitivity levels.

In some situations the security manager may desire to overlook small bits of metal while concentrating on larger offensive weapons. …

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