The Anatomy of a Metal Detector

HOW METAL DETECTORS WORK

Most hobby metal detectors use VLF Induction Balance technology. Here's how they work:

• The search coil (also called search head or loop) contains two electrical induction coils which are like antennas. One coil transmits a rapidly alternating magnetic field, illuminating the region surrounding the search coil. If metal is present, its electrical conductivity distorts the magnetic field. If iron metal is present, its magnetism also distorts the magnetic field, but in a different way, allowing the metal detector to distinguish between ferrous and nonferrous metals.
• The other coil is a receiving antenna which detects changes in the magnetic field caused by the presence of metal. Electronic circuits amplify this weak signal, analyze it to determine the changes which occur as the search coil sweeps over the target, and then convey the information to the user in the form of a visual display or audio tones. Most modern metal detectors perform many of these tasks in software running on an internal microcomputer.
• The iron minerals which are present in most soils also distort the magnetic field, obscuring the weak signals of small or deep objects. This can cause the object to go undetected, or to be misidentified when it is detected. Much of the technology that goes into modern metal detectors is devoted to the task of eliminating the unwanted signals from iron minerals in the soil, while not losing the signals from metal objects.

TERMINOLOGY

• Cache Hunting - Pronounced "cash". A cache is a buried or hidden valuable stored inside a case, strong box or bag.
• Coin Shooting - Finding buried coins is the most popular metal detecting application. The most valuable are very old; take care in unearthing them to avoid damage.
• Discrimination - When the detector emits different tones for different types of metals, and when the detector "eliminates" certain metals, we refer to this as the detector "discriminating" among different types of metals. Discrimination is a fixed-start-point elimination system.
• Elimination - Reference to a metal being "eliminated" means that the detector will not emit a tone, nor light up an LCD indicator, when a specified object passes through the coil's detection field.
• Ferrous - Metals which are made of, or contain, iron.
• Ground Balance - Ground Balancing is the ability of the detector to ignore, or "see through," the earth's naturally occurring minerals, and only sound a tone when a metal object is detected.
• Iron - A common, low-grade metal that is often an undesirable target in certain metal detecting applications (old cans, pipes, bolts, and nails). Sometimes, the desired target is made of iron (property markers or relics like cannon balls, old armaments, and parts of old structures and vehicles).
• Notch - Notching is the elimination of an item, or range of items, within the metallic spectrum. We "notch-out" an object selectively. Objects to the left and right on the metallic spectrum are retained. Notching creates a variable rejection window.
• Pinpointing - Pinpointing is the process of finding the exact location of a buried object. Long-buried metals can appear exactly like the surrounding earth, and can therefore be very hard to isolate.
• Pull-Tabs - Discarded pull-tabs from beverage containers are the most bothersome trash items for treasure hunters. They come in many different shapes and sizes. We have incorporated special features into the detector to let you automatically eliminate the most common types, using the AutoNotch Mode. Since there are many different types, some must be "Notched-Out" manually.
• Relic - A relic is an object of interest by reason of its age or its association with the past. Many relics are made of iron, but can also be made of bronze or precious metals.
• Waterproof - The search coil can be submerged in water. The control housing and cable-to-housing connection must, however, stay dry.