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The first metal detector was invented by Alexander Graham Bell in the year 1881, just after the invention of telephone in 1876. Later, Fischer came out with a portable one in the year 1931. Today, metal detectors are used in many fields starting from treasure hunt to security purposes. These are electronic devices and are used to locate signs of metal. It is used to search on the ground, people or goods. The materials can be on the ground may be a piece of iron, aluminum, etc or it can even indicate buried metal could be anything from discarded pieces of aluminum to buried resources. These detectors can penetrate various non-metallic substances like soil, wood, sand, etc. Metal detectors have electronic boxes with a battery case on one end and a handle for the operative's arm on the other. It has a coil made of insulated wire wound around a telescoping shaft that is inside a plastic disk. The device is held parallel to the ground due to the angle at which the disk comes out of the shaft. The electronic box is held in the hand, the power is put on and the coil end is slowly swept over the ground. If the trace of metal is there on or buried in the ground, an electronic beep is heard when the device sweeps the ground. The discovery of Electromagnetism was by Hans Christian Oersted in the year 1820. It is the science of combined effect of electric and magnetic field. As stated in wikipedia, Electromagnetism is the science of the electromagnetic field. That is, a field, surrounding all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. This principle of electromagnetism is on which the Metal detectors work. Since the metals are good conductor of electricity and magnetism, the electromagnetism affects on them. Magnetic field is generated in this device through the transmitter (high-powered coil), getting power from the battery attached. When this electromagnetic field penetrates the ground the metals tend to get charged with magnetism. When this happens the coil detects the electromagnetic behaviour and sends a signal to the electronic box. The speaker attached to the electronic box beeps and the operator hears it and comes to know of the presence of metal. The latest detectors comprises of microprocessors in the electronic box that can give you the type of metal present. It can measure the time between charging of metal and the receiving the beep that concludes the type of metal and this length of time is known as phase shift. There are adjustments in the device when searching for a particular kind of metal. There are 3 types of metal detectors following 3 different technologies: 1. Beat Frequency Oscillator: Such detectors have a coil acting as an inductor inside an oscillator. With frequency change there is a change in inductance. There is a second oscillator that generates a close frequency. The beeps heard between them indicate the presence of metal. 2. Induction Balance Detector: This type has 2 coils that overlie each other. One sends waves and the other receives. The two are kept adjusted so that when there is absence of metal they do not indicate or beep. 3. Pulse Induction Detector: This type produces pulses by putting off an indicator. A coil sends the pulse and the detector searches for echos. If you have a metal detector, I wish you luck in finding all kinds of treasures. You never know what "rare find" you'll come up with, and it's fun to look. Copyright (c) 2006
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