The History and Use of Metal Detectors

In 1881, Alexander Graham Bell invented the first metal detector. As President James Garfield lay dying of an assassins bullet, Bell hurriedly invented a crude metal detector in an unsuccessful attempt to locate the fatal slug. Bells metal detector was an electromagnetic device he called the induction balance. Gerhard Fischar In 1925, Gerhard Fischar invented a portable metal detector. Fischars model was first sold commercially in 1931 and Fischar was behind the first large-scale production of metal detectors. According to the experts at AS Company: In the late 1920s, Dr. Gerhard Fisher, the founder of Fisher Research Laboratory, was commissioned as a research engineer with the Federal Telegraph Co. and Western Air Express to develop airborne direction finding equipment. He was awarded some of the first patents issued in the field of airborne direction finding by means of radio. In the course of his work, he encountered some strange errors and once he solved these problems, he had the foresight to apply the solution to a completely unrelated field, that of metal and mineral detection. Other Uses Simply put, a metal detector  is an  electronic instrument  which detects the presence of  metal  nearby. Metal detectors can help people find metal inclusions hidden within objects, or metal objects buried underground. Metal detectors often consist of a handheld unit with a sensor probe which the user can sweep over the ground or other objects. If the sensor comes near a piece of metal, the user will hear a tone, or see a needle move on an indicator. Usually, the device gives some indication of distance; the closer the metal is, the higher the tone or the higher the needle goes. Another common type is the stationary walk through metal detector which is used for  security screening  at access points in prisons, courthouses, and airports to detect concealed metal weapons on a persons body. The simplest form of a metal detector consists of an  oscillator  producing an alternating current that passes through a coil producing an alternating  magnetic field. If a piece of electrically conductive metal is close to the coil,  eddy currents  will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a  magnetometer), the change in the magnetic field due to the metallic object can be detected. The first industrial metal detectors were developed in the 1960s and were used extensively for mineral prospecting and other industrial applications. Uses include  de-mining  (the detection of  land mines), the detection of weapons such as knives and guns (especially in  airport security),  geophysical prospecting,  archaeology,  and  treasure hunting. Metal detectors are also used to detect foreign bodies in food as well as in the  construction industry  to detect  steel reinforcing bars  in concrete and pipes plus wires buried in walls or floors.