How Does a Metal Detector Work

VLF (very low frequency) ground canceling metal detectors work on the principle of conductivity. These metal detectors will locate any metal with a conductive surface within 45-60 cm (18" to two feet) of the ground surface. A signal is heard because an electromagnetic field is generated and caused to flow out into space away from the search coil. As the lines of the electromagnetic field penetrate the surface of the metal, tiny circulating electrical currents called eddy currents are caused to flow in the surface of the metal. These eddy currents then generate their own electromagnetic fields which radiate in all directions in space. Those currents which radiate directly upwards toward the receiver's search coil windings are picked up. A reduced voltage is then fed into the amplifying wires where it is conditioned to drive a loudspeaker, meter or headphones. The larger the surface, the greater the signal.

Metal detectors do not react to mass but to surface area. In other words, a flat coin will make a larger signal than a coin on its edge.

The metal detecting industry is filled with competitive "bells & whistles" offerings from all the manufacturers; read and understand the claims and detector features before making your next metal detector purchase. The best way to select a detector is to first find a knowledgeable resource for unbiased information such as Casanova's who carry all brand of metal detecting equipment.

1) Control Unit - This is where the electronics are housed that makes up the main metal detector circuits which includes a transceiver (a transmitter and receiver in one unit). The units may contain: outside control knobs and key pads, in some cases a microprocessor, an LCD display screen, meters, digital circuits, loud speaker, light indicators, batteries, and headphone jack..

2) Searchcoil Rods - Many designs incorporate a built-in arm rest. The built-in armrests are designed to counter balance the unit's searchcoil weight. It also provides a stable sideways swing motion to facilitate the search method used to detect for the presence of metal below the searchcoil.

3) Searchcoil - This is the transmitting and receiving antenna array imbedded into composite materials. Searchcoils are found at the end of the searchcoil stem which holds the searchcoil to the metal detector's control unit. Most metal detectors are designed to use several different size searchcoils. Searchcoils must be tuned in manufacturing for specific metal detector transceiver circuits. Therefore, searchcoils of different sizes can be interchanged only with specified metal detector models of the same manufacturer. searchcoils can not be interchanged between manufacturers.

Most searchcoils are basically round and a few specialized searchcoils are elliptical in shape to increase desired performance for certain uses and indented target materials. There are several different basic technologies used today for different performance levels and desired detection patterns and target materials. Searchcoils for the most part are waterproof and work in water. There are also searchcoils designed for water use as in SCUBA diving models.

4) Searchcoil Stem - The searchcoil stem provides the means to hold the searchcoil while conducting a search with the metal detector. Many models today are designed to function as hip-mount units with just a well balanced searchcoil and armrest to hold. This gives a lighter weight unit to swing while searching over ground and beaches. The lighter weight translates into comfort for longer periods of searching.

Most searchcoil stems are made from Aluminum with fully quick-adjustable shafts. There are a few manufacturers that offer a more higher performance design lower searchcoil rod that uses plastic or fiber to replace the metal near the searchcoil.  By removing the metal near the searchcoil, the sensitivity of the detection circuits can be increased; yielding more detected targets.

1. TR - Transmit Receive
2. VLF - Very Low Frequency
3. PI - Pulse Induction
4. BFO - Beat-Frequency Oscillation

Hybrid technologies have been and may be available utilizing some form of the above technologies. Real advancements as well as some unbelievable claims will be found on the market.

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