Alexander Graham Bell invented the metal detector in July 1881 in an attempt to save the life of James A. Garfield. Garfield had been shot about three weeks earlier, and his team of doctors had been unsuccessful in locating the bullet. Because of this, Bell quickly constructed a metal detector. However, when he tried to find the bullet, he was unsuccessful. This was because the White House had mattresses with metal springs, a new invention. Bell’s metal detector would have probably worked had he moved Garfield off the bed. Unfortunately, after doctors enlarged the wound while searching unsuccessfully for the bullet, Garfield died in September. After the autopsy, it was determined that Garfield probably would have lived if the doctors had not tried to find the bullet at all.

The metal detector uses a coil of wire that is part of an oscillating circuit. The frequency of oscillation depends on the inductance of the coil, which is changed when metal is brought nearby. This frequency is mixed with another fixed frequency. The mixed signal is then sent to a speaker which produces audible beats.

The metal detector is used in many applications today. Uses for the metal detector range from airport security, to detecting buried metal.

*Pictures from Encarta Encyclopedia