Metal Detectors
Metal Detectors Information
A metal detector is a portable electronic device which penetrates the ground magnetically in order to find traces of metal. This metal could either be discarded pieces of aluminum or valuable coins, jewelry and other buried treasures. Part of the appeal of metal detecting is this unknown factor, keeping amateurs and professionals on a constant scan for new sources of metal and more promising locations. These devices can usually penetrate sand, soil, wood and other non-metallic substances, making most areas fair game for treasure hunters. Some metal detectors can discriminate between various metals, allowing users to decide if a particular discovery would be worth digging up. A significant percentage of hits are indeed pieces of metallic trash or discarded building materials. Part of the appeal of this hobby, however, is discovering a lost class ring or a piece connected with local history. Some professional treasure hunters use very discriminating detectors set only for valuable metals, but hobbyists tend to explore even the less lucrative hits. Metal detectors are electronic devices that are used to find traces of metal usually from the ground, a person, or cargo. This metal could be anything from discarded pieces of aluminum to buried treasures. These devices can penetrate sand, soil, wood and other non-metallic substances. Most metal detectors, hand held, and the walk-through ones at the airport utilize a field-disturbance detector. That is a fancy name for a simple concept. When a conductor passes through a magnetic field, a portion of that magnetic field is disturbed, distorted and reduced. That reduction in the magnetic field is related to a small amount of current that is induced or created in the conductor. You can do the same thing by jumping rope with a piece of wire instead of the rope. As the wire cuts through the earth's magnetic field, a small amount of electricity is generated at the end of the wires. Electromagnetic induction is the creation of an electric field by a fluctuating magnetic field. The electric field may be produced, according to Faraday's law of induction in two ways: by the motion of a conductor cutting across the lines of magnetic flux of a magnetic field or by a change in the magnetic flux passing through a coil immersed in a non constant magnetic field. |
How Does Metal Detectors Work?
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| Mention the words metal detector and you'll get completely different reactions from different people. For instance, some people think of combing a beach in search of coins or buried treasure. Other people think of airport security, or the handheld scanners at a concert or sporting event. A basic metal detector consists of an electronic box and battery case on one end, with a brace or handle for the operator's arm. An insulated wire wraps around a telescoping shaft and into a round plastic disk called the coil. This disk comes off the shaft at an angle which allows it to be held parallel to the ground. The operator straps on or grips the electronic box and turns on the power. The idea is to slowly sweep the coil end over the ground until an electronic signal is heard. This lets the user know that some metallic element is buried directly beneath the area swept by the coil. |
Metal detectors work on the principal of electromagnetics and their effects on conductive metals. There are actually two separate elements in the coil of a typical unit. One is a high-powered coil of metal which uses the battery power to generate a penetrating magnetic field. This coil is called the transmitter. As the elecromagnetic field enters the ground, anything metallic will become charged with magnetism, similar to a paper clip become magnetized after contact with a standard bar magnet. Michael FARADAY observed (1831) that when a magnet is moved through a closed coil of wire, a current is induced in the wire. The direction of the current flow is such as to create a magnetic field opposite in direction to that of the change in the field produced by the magnet. Faraday then replaced the magnet with an electromagnet. Two coils were wound close together, the first being connected to a battery and the second to a galvanometer, which measures small currents. Metal detectors must also be adjusted to eliminate false positives generated by natural deposits of metal in the soil or sand itself. Most units allow users to change the sensitivity of the coil in order to cancel out the background clutter. Some other uses of metal detecting technology include security inspections at airports, government buildings and other public places. Construction crews and woodworkers also use hand-held metal detectors to find dangerous nails or other metallic debris in reclaimed building materials and trees. |
