What is a Metal Detector?

The metal detector is a device used to detect as the name indicates-metal or the occurrence/presence of metal around. They are particularly used to find metals hidden within objects or objects such as treasure, coins, etc. that may be found underground. Metal detectors are usually units that are handheld and have a sensor probe that is swept over the ground or area in which the user suspects have metals they are looking for.

When the sensor comes within the metal area, there is a change in tone in the headphones, or in some models, the needle moves on the indicator. The way the device works is that it gives more of the indication of distance, i.e., it changes tone going higher and higher. The needle goes higher as the metal detector gets closer to the metal in question.

One other type of metal detectors you may be familiar with is the “walk-through” which is stationary and used in security searching and screening at important access points like, airports, prisons, and courthouses to find and detect weapons that have been concealed on a person’s body without actually giving them a full body search.

There are different types of metal detectors, which we will look into in separate posts, but, in general, they include: Industrial, Pulse induction, beat-frequency oscillation, and very low frequency metal detectors.

The most basic form of metal detectors has an oscillator that produces an alternate current that goes through a coil, which produces an alternating magnetic field. Assuming a piece of metal that can conduct electricity is around the coil, eddy currents will automatically be created or induced (inductive sensor) in said metal. This, in turn, creates its magnetic field.

Now, assuming another coil is then used to measure said magnetic field (that is a magnetometer), the resulting change around and within the magnetic field could then be detected and measured. It looks like a lot, but we will be looking at this further down. Industrial detectors were first invented in 1960 and were mostly used for mineral mining and other industrial uses.

Metal detectors can be used for locating land mines, weapons like knives and guns (mainly in airport security), geophysical mining, archaeology, and treasure hunting. Detectors are sometimes used to locate objects that don’t belong in foods and also in the construction industry to locate metal strengthening bars in concrete and pipes and wires embedded in walls and floors.

How metal detectors work

All metal detectors function in diverse ways, here’s the way regarding the ones that are alike. Metal detectors have a coil of wire known as the transmitter coil (tied around the circular head at the bottom of the handle). There is a magnetic field formed around it when an electric current drift around the coil.

While you move the metal detector all around a metal object, the atoms in the metals are affected by the moving magnetic field. This alters the manner of movement of electrons- these are little particles that rotate around atoms.

If there is a moving magnetic field inside the metal, this always says to us that that we should make sure there is an electric current moving there also. This also means the detector induces an electrical current in the metal. But there is also another intriguing thing we learn from this: a little magnetism is formed when electricity moves over a little metal. Another magnetic field is formed around the metal because of the magnetic field that comes from the metal
detector. The detector only detects the second magnetic field around the metal.

There is a circuit in the metal detectors that contains a loudspeaker and has another coil of wire in its head- called the receiver coil. When you move the detector over a metal, the magnetic field formed due to the metal pieces
through the coil. Electricity flows through metal if you pass it through a magnetic field, that’s how a generator works.

The metal detector then starts to beep or indicate with its pointer; this means you have found something. And as you move the metal detector closer to the source of the metal, the stronger the magnetic field becomes around it. This forms in the transmitter coil and is then transferred to the receiver coil.

The more you move towards the metal, the louder the tone.

What are metal detectors used for?

Archaeology

Metal detectors are commonly used in archaeology with the very first documented use by military historian Don Rickey in 1958, who was using one to detect the firing lines in Little Big Horn. That being said, archaeologists object to the use of metal detectors by “artifact searchers” or “site looters” whose actions destroy historical sites.

The major issue with the use of metal detectors in historical sites or hobbyists who discover objects of archaeological benefit is that the context in which the object was found is lost, and no comprehensive investigation of its surroundings is carried out. A metal detector hobbyist may not be aware of the importance of artifacts outside of known sites.

Industrial detectors for metals

Throughout the pharmaceutical, food, beverage, clothing, fabric, plastics, chemicals, timber, mining, and packaging industries, industrial metal detectors are used. Food contamination by metal shards from broken processing machines during the production system is a major safety risk for the food industry. Metal detectors are commonly used and incorporated into the production line for this purpose.

The current practice in clothing or textile industry is to apply metal detection after the clothing is fully sewn and before clothing is packed, to test if there’s any metal contamination (needle, broken needle, etc.) in clothing.

Security Screening

Walk-through security cases created to search for people without actually touching them used to detect metals such as guns, knives, and other contrabands at certain places like airports and hotels.

Hobby

There are various types of leisure activities, including metal detectors: Beachcombing is searching for loose coins or diamonds on the sand. Beach hunting can be as easy or as difficult as one chooses to do. Most devoted beach seekers are already concerned with tidal movements and shore erosion.

Metal detector clubs all over the United States, the United Kingdom, and Canada give hobbyists the ability to learn from others, show off their hunting finds, and learn more about the hobby.

Metal detectors are often used to search for abandoned or missing items,[useful man-made items such as coins, gold, silver, as well as other devices. Many metal detectors are also waterproof to allow the consumer to check for underwater items in shallow water environments.

Coin shooting is targeted directly at money. Many coin shooters carry out historical work to find locations with the ability to offer up historical and collectible coins.

Prospecting is searching for precious metals like gold, silver, and copper in their natural sources, such as nuggets or flakes.