Metal Detectors
Metal detectors are used primarily for the detection of weapons such as knives and guns, archaeology or treasure hunting, the detection of foreign bodies in food, and to detect steel reinforcing bars in concrete and pipes and wires buried in walls and floors.
In its simplest form, a metal detector consists of an oscillator producing an alternating current that passes through a coil producing a magnetic field. If a piece of electronically conductive metal is close to the coil eddy currents will be induced in the metal, and this produces an alternating magnetic field of its own. If another coil is used to measure the magnetic field the change in the magnetic field due to the metallic object can be detected.
One leader in metal detector technology was Charles Garrett, who pioneered the BFO (Beat Frequency Oscillator) machine. With the invention and development of the transistor in the 50's and 60's, metal detector manufacturers and designers made smaller lighter machines with improved circuitry, running on small battery packs. The metal detector was reduced to a size that even a child could use. Since then metal detectors evolved in the form of the rectangular gantry now standard in airports and government facilities.
