![B020311e - PFC Generett and SGT Rutledge probe in yard of house](https://upload.wikimedia.org/wikipedia/commons/e/e2/B020311e_-_PFC_Generett_and_SGT_Rutledge_probe_in_yard_of_house.png)
A metal detector is an
instrument that detects the nearby presence of
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
. Metal detectors are useful for finding metal objects on the surface, underground, and under water. The unit itself, consist of a control box, and an adjustable shaft, which holds a pickup coil, which can vary in shape and size. If the pickup coil comes near a piece of metal, the control box will register its presence by a changing tone, a flashing light, and or by a needle moving on an indicator. Usually the device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary "walk through" metal detectors used at access points in
prison
A prison, also known as a jail, gaol (dated, standard English, Australian, and historically in Canada), penitentiary (American English and Canadian English), detention center (or detention centre outside the US), correction center, correc ...
s,
courthouse
A courthouse or court house is a building that is home to a local court of law and often the regional county government as well, although this is not the case in some larger cities. The term is common in North America. In most other English-spe ...
s,
airport
An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports usually consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surface ...
s and
psychiatric hospital
Psychiatric hospitals, also known as mental health hospitals, behavioral health hospitals, are hospitals or wards specializing in the treatment of severe mental disorders, such as schizophrenia, bipolar disorder, eating disorders, dissociative ...
s to detect concealed
metal weapons on a person's body.
The simplest form of a metal detector consists of an
oscillator
Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
producing an
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
that passes through a coil producing an alternating
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
. If a piece of electrically conductive metal is close to the coil,
eddy currents
Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magn ...
will be induced (
inductive sensor
An inductive sensor is a device that uses the principle of electromagnetic induction to detect or measure objects. An inductor develops a magnetic field when a current flows through it; alternatively, a current will flow through a circuit contain ...
) in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a
magnetometer
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...
), the change in the magnetic field due to the metallic object can be detected.
The first industrial metal detectors were developed in the
1960s
File:1960s montage.png, Clockwise from top left: U.S. soldiers during the Vietnam War; the Beatles led the British Invasion of the U.S. music market; a half-a-million people participate in the 1969 Woodstock Festival; Neil Armstrong and Buzz ...
and were used extensively for mineral prospecting and other industrial applications. Uses include detecting
land mine
A land mine is an explosive device concealed under or on the ground and designed to destroy or disable enemy targets, ranging from combatants to vehicles and tanks, as they pass over or near it. Such a device is typically detonated automati ...
s, the detection of weapons such as knives and guns (especially in
airport security
Airport security includes the techniques and methods used in an attempt to protect passengers, staff, aircraft, and airport property from malicious harm, crime, terrorism, and other threats.
Aviation security is a combination of measures and hum ...
),
geophysical
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' som ...
prospecting
Prospecting is the first stage of the geological analysis (followed by exploration) of a territory. It is the search for minerals, fossils, precious metals, or mineral specimens. It is also known as fossicking.
Traditionally prospecting reli ...
,
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
and
treasure hunting
Treasure hunter is the physical search for treasure. For example, treasure hunters try to find sunken shipwrecks and retrieve artifacts with market value. This industry is generally fueled by the market for antiquities. The practice of treasure ...
. Metal detectors are also used to detect foreign bodies in food, and in the
construction industry
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and come ...
to detect
steel reinforcing bars in concrete and pipes and wires buried in walls and floors.
History and development
![Metal detector from World War 1](https://upload.wikimedia.org/wikipedia/commons/9/90/Metal_detector_from_World_War_1.jpg)
In 1841 Professor
Heinrich Wilhelm Dove
Heinrich Wilhelm Dove (6 October 1803 – 4 April 1879) was a Prussian physicist and meteorologist.
Early years
Dove was born in Liegnitz in the Kingdom of Prussia. Dove studied history, philosophy, and the natural sciences at the University of B ...
published an invention he called the "differential inductor". It was a 4 coil induction balance, with 2 glass tubes each having 2 well insulated copper wire solenoids wound around them. Charged Leyden jars (high voltage capacitors) were discharged through the 2 primary coils, this current surge induced a voltage in the secondary coils. When the secondary coils were wired in opposition the induced voltages cancelled as confirmed by the Professor holding the ends of the secondary coils. When a piece of metal was placed inside one glass tube the Professor received a shock.
This then was the first magnetic induction metal detector, and the first pulse induction metal detector.
In late 1878 and early 1879 Professor (of music)
David Edward Hughes
David Edward Hughes (16 May 1830 – 22 January 1900), was a British-American inventor, practical experimenter, and professor of music known for his work on the printing telegraph and the microphone. He is generally considered to have bee ...
published his experiments with the 4 coil induction balance. He used his own recent invention the microphone and a ticking clock to generate regular pulses and a telephone receiver as detector. To measure the strength of the signals he invented a coaxial 3 coil induction balance which he called the "electric sonometer". Hughes did much to popularize the induction balance, quickly leading to practical devices that could identify counterfeit coins. In 1880 Mr. J. Munro, C.E. suggested the use of the 4 coil induction balance for metal prospecting. Hughes's coaxial 3 coil induction balance would also see use in metal detecting.
In July 1881
Alexander Graham Bell
Alexander Graham Bell (, born Alexander Bell; March 3, 1847 – August 2, 1922) was a Scottish-born inventor, scientist and engineer who is credited with patenting the first practical telephone. He also co-founded the American Telephone and Te ...
initially used a 4 coil induction balance to attempt to locate a bullet lodged in the chest of American President
James Garfield. After much experimenting the best bullet detection range he achieved was only 2 inches. He then used his own earlier discovery, the partially overlapping 2 coil induction balance, and the detection range increased to 5 inches. But the attempt was still unsuccessful because the metal coil spring bed Garfield was lying on confused the detector. Bell's 2 coil induction balance would go on to evolve into the popular double D coil.
On Dec 16 1881 Captain Charles Ambrose McEvoy applied for British Patent No. 5518, Apparatus for Searching for Submerged Torpedoes, &c., which was granted Jun 16 1882. His US269439 patent application of Jul 12 1882 was granted Dec 19 1882. It was a 4 coil induction balance for detecting submerged metallic torpedoes and iron ships and the like. Given the development time involved this may have been the earliest known device specifically constructed as a metal detector using magnetic induction.
In 1892 George M. Hopkins described an orthogonal 2 coil induction balance for metal detecting.
In 1915 Professor
Camille Gutton developed a 4 coil induction balance to detect unexploded shells in farmland of former battlefields in France. Unusually both coil pairs were used for detection. The 1919 photo at the right is a later version of Gutton's detector.
Modern developments
The modern development of the metal detector began in the 1920s.
Gerhard Fischer had developed a system of radio direction-finding, which was to be used for accurate navigation. The system worked extremely well, but Fischer noticed there were anomalies in areas where the terrain contained ore-bearing rocks. He reasoned that if a radio beam could be distorted by metal, then it should be possible to design a machine which would detect metal using a search coil resonating at a radio frequency. In 1925 he applied for, and was granted, the first patent for an electronic metal detector. Although Gerhard Fischer was the first person granted a patent for an electronic metal detector, the first to apply was Shirl Herr, a businessman from Crawfordsville, Indiana. His application for a hand-held Hidden-Metal Detector was filed in February 1924, but not patented until July 1928. Herr assisted Italian leader
Benito Mussolini
Benito Amilcare Andrea Mussolini (; 29 July 188328 April 1945) was an Italian politician and journalist who founded and led the National Fascist Party. He was Prime Minister of Italy from the March on Rome in 1922 until his deposition in 194 ...
in recovering items remaining from the
Emperor Caligula's galleys at the bottom of
Lake Nemi
Lake Nemi ( it, Lago di Nemi, la, Nemorensis Lacus, also called Diana's Mirror, la, Speculum Dianae) is a small circular volcanic lake in the Lazio region of Italy south of Rome, taking its name from Nemi, the largest town in the area, that ...
, Italy in August 1929. Herr's invention was used by Admiral Richard Byrd's Second Antarctic Expedition in 1933, when it was used to locate objects left behind by earlier explorers. It was effective up to a depth of eight feet.
However, it was one
Lieutenant
A lieutenant ( , ; abbreviated Lt., Lt, LT, Lieut and similar) is a commissioned officer rank in the armed forces of many nations.
The meaning of lieutenant differs in different militaries (see comparative military ranks), but it is often sub ...
Józef Stanisław Kosacki, a Polish officer attached to a unit stationed in
St Andrews
St Andrews ( la, S. Andrea(s); sco, Saunt Aundraes; gd, Cill Rìmhinn) is a town on the east coast of Fife in Scotland, southeast of Dundee and northeast of Edinburgh. St Andrews had a recorded population of 16,800 , making it Fife's fou ...
,
Fife
Fife (, ; gd, Fìobha, ; sco, Fife) is a council area, historic county, registration county and lieutenancy area of Scotland. It is situated between the Firth of Tay and the Firth of Forth, with inland boundaries with Perth and Kinross (i ...
, Scotland, during the early years of
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, who refined the design into a practical
Polish mine detector
The Mine detector (Polish) Mark I () was a metal detector for landmines developed during World War II. Initial work on the design had started in Poland but after the invasion of Poland by the Germans in 1939, and then the Fall of France in mid- ...
.
These units were still quite heavy, as they ran on vacuum tubes, and needed separate battery packs.
The design invented by Kosacki was used extensively during the
Second Battle of El Alamein
The Second Battle of El Alamein (23 October – 11 November 1942) was a battle of the Second World War that took place near the Egyptian Railway station, railway halt of El Alamein. The First Battle of El Alamein and the Battle of Alam el Halfa ...
when 500 units were shipped to
Field Marshal Montgomery
Field Marshal Bernard Law Montgomery, 1st Viscount Montgomery of Alamein, (; 17 November 1887 – 24 March 1976), nicknamed "Monty", was a senior British Army officer who served in the First World War, the Irish War of Independence and ...
to clear the minefields of the retreating Germans, and later used during the
Allied invasion of Sicily
The Allied invasion of Sicily, also known as Operation Husky, was a major campaign of World War II in which the Allied forces invaded the island of Sicily in July 1943 and took it from the Axis powers ( Fascist Italy and Nazi Germany). It bega ...
, the
Allied invasion of Italy
The Allied invasion of Italy was the Allied amphibious landing on mainland Italy that took place from 3 September 1943, during the Italian campaign (World War II), Italian campaign of World War II. The operation was undertaken by General (Unit ...
and the
Invasion of Normandy
Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 (D-Day) with the Norm ...
.
As the creation and refinement of the device was a wartime military research operation, the knowledge that Kosacki created the first practical metal detector was kept secret for over 50 years.
Beat Frequency Induction
Many manufacturers of these new devices brought their own ideas to the market. White's Electronics of Oregon began in the 1950s by building a machine called the Oremaster Geiger Counter. Another leader in detector technology was
Charles Garrett, who pioneered the BFO (
Beat Frequency
In acoustics, a beat is an interference pattern between two sounds of slightly different frequencies, ''perceived'' as a periodic variation in volume whose rate is the difference of the two frequencies.
With tuning instruments that can produce ...
Oscillator) machine. With the invention and development of the transistor in the 1950s and 1960s, metal detector manufacturers and designers made smaller, lighter machines with improved circuitry, running on small battery packs. Companies sprang up all over the United States and Britain to supply the growing demand. Beat Frequency Induction requires movement of the detector coil; akin to how swinging a conductor near a magnet induces an electric current; except the pulse is electric EMF and not magnetic
EMF.
Refinements
Modern top models are fully computerized, using integrated circuit technology to allow the user to set sensitivity, discrimination, track speed, threshold volume, notch filters, etc., and hold these parameters in memory for future use. Compared to just a decade ago, detectors are lighter, deeper-seeking, use less battery power, and discriminate better.
State of the art metal detectors have further incorporated extensive wireless technologies for the earphones, connect to
Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...
networks and
Bluetooth
Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is limi ...
devices. Some also utilize built in
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
locator technology to keep track of searching location and the location of items found. Some connect to
smartphone
A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...
applications to further extend functionality.
Discriminators
The biggest technical change in detectors was the development of a tunable induction system. This system involved two coils that are electro-magnetically tuned. One coil act as an
RF transmitter the other as a receiver; in some cases these can be tuned to between 3 and 100 kHz. When metal is in their vicinity, a signal is detected owing to eddy currents induced in the metal. What allowed detectors to discriminate between metals was the fact that every metal has a different
phase response
In signal processing, phase response is the relationship between the phase of a sinusoidal input and the output signal passing through any device that accepts input and produces an output signal, such as an amplifier or a filter.
Amplifiers, filt ...
when exposed to alternating current; longer waves (low frequency) penetrate ground deeper, and select for high conductivity targets like silver, and copper; than shorter waves (higher frequency) which, while less ground penetrating, select for low conductivity targets like iron. Unfortunately, high frequency is also sensitive to ground
mineralisation interference. This selectivity or discrimination allowed detectors to be developed that could selectively detect desirable metals, while ignoring undesirable ones.
Even with discriminators, it was still a challenge to avoid undesirable metals, because some of them have similar phase responses (e.g. tinfoil and gold), particularly in alloy form. Thus, improperly tuning out certain metals increased the risk of passing over a valuable find. Another disadvantage of discriminators was that they reduced the sensitivity of the machines.
New coil designs
Coil designers also tried out innovative designs. The original induction balance coil system consisted of two identical coils placed on top of one another. Compass Electronics produced a new design: two coils in a D shape, mounted back-to-back to form a circle. This system was widely used in the 1970s, and both concentric and double D type (or widescan as they became known) had their fans. Another development was the invention of detectors which could cancel out the effect of
mineralization in the ground. This gave greater depth, but was a non-discriminate mode. It worked best at lower frequencies than those used before, and frequencies of 3 to 20 kHz were found to produce the best results. Many detectors in the 1970s had a switch which enabled the user to switch between the discriminate mode and the non-discriminate mode. Later developments switched electronically between both modes. The development of the induction balance detector would ultimately result in the motion detector, which constantly checked and balanced the background mineralization.
Pulse induction
At the same time, developers were looking at using a different technique in metal detection called pulse induction. Unlike the beat frequency oscillator or the induction balance machines which both used a uniform alternating current at a low frequency, the pulse induction (PI) machine simply magnetized the ground with a relatively powerful, momentary current through a search coil. In the absence of metal, the field decayed at a uniform rate, and the time it took to fall to zero volts could be accurately measured. However, if metal was present when the machine fired, a small eddy current would be induced in the metal, and the time for sensed current decay would be increased. These time differences were minute, but the improvement in electronics made it possible to measure them accurately and identify the presence of metal at a reasonable distance. These new machines had one major advantage: they were mostly impervious to the effects of
mineralization, and rings and other jewelry could now be located even under highly
mineralized black sand
Black sand is sand that is black in color. One type of black sand is a heavy, glossy, partly magnetic mixture of usually fine sands containing minerals such as magnetite, found as part of a placer deposit. Another type of black sand, found on ...
. The addition of computer control and digital signal processing have further improved pulse induction sensors.
One particular advantage of using a pulse induction detector includes the ability to ignore the minerals contained within heavily
mineralized soil; in some cases the heavy mineral content may even help the PI detector function better. Where a VLF detector is affected negatively by soil
mineralization, a PI unit is not.
Uses
Large portable metal detectors are used by
archaeologist
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
s and
treasure hunters
Treasure hunter is the physical search for treasure. For example, treasure hunters try to find sunken shipwrecks and retrieve artifacts with market value. This industry is generally fueled by the market for antiquities. The practice of treasur ...
to locate metallic items, such as
jewelry
Jewellery ( UK) or jewelry (U.S.) consists of decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be attached to the body or the clothes. From a western ...
,
coins
A coin is a small, flat (usually depending on the country or value), round piece of metal or plastic used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in large quantities at a mint in order to ...
,
clothes buttons and other accessories,
bullets
A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. Bullets are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax. Bullets are made in various shapes and con ...
, and other various
artifacts buried beneath the surface.
Archaeology
Metal detectors are widely used in archaeology with the first recorded use by military historian Don Rickey in 1958 who used one to detect the firing lines at
Little Big Horn. However archaeologists oppose the use of metal detectors by "artifact seekers" or "site looters" whose activities disrupt archaeological sites. The problem with use of metal detectors in archaeological sites or hobbyist who find objects of archeological interest is that the context that the object was found in is lost and no detailed survey of its surroundings is made. Outside of known sites the significance of objects may not be apparent to a metal detector hobbyist.
England and Wales
In
England and Wales
England and Wales () is one of the three legal jurisdictions of the United Kingdom. It covers the constituent countries England and Wales and was formed by the Laws in Wales Acts 1535 and 1542. The substantive law of the jurisdiction is Eng ...
metal detecting is legal provided that the landowner has granted permission and that the area is not a
Scheduled Ancient Monument
In the United Kingdom, a scheduled monument is a nationally important archaeological site or historic building, given protection against unauthorised change.
The various pieces of legislation that legally protect heritage assets from damage and d ...
, a
site of special scientific interest
A Site of Special Scientific Interest (SSSI) in Great Britain or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland is a conservation designation denoting a protected area in the United Kingdom and Isle of ...
(SSSI), or covered by elements of the
Countryside Stewardship Scheme The Countryside Stewardship Scheme was originally an agri-environment scheme run by the United Kingdom Government set up in 1991. In its original form it expired in 2014. It was relaunched for the Rural Development Programme England (RDPE) 2014-2020 ...
.
The
Treasure Act 1996
The Treasure Act 1996 is a UK Act of Parliament, defining which objects are classified as treasure, legally obliging the finder to report their find.
Provisions
The Act is designed to deal with finds of treasure in England, Wales and Northern Ire ...
governs whether or not items that have been discovered are defined as treasure.
Finders of items that the Act defines as treasure must report their finds to the local coroner.
If they discover items that are not defined as treasure but that are of cultural or historical interest, finders can voluntarily report them to the
Portable Antiquities Scheme
The Portable Antiquities Scheme (PAS) is a voluntary programme run by the United Kingdom government to record the increasing numbers of small finds of archaeological interest found by members of the public. The scheme begun in 1997 and now covers m ...
and the
UK Detector Finds Database
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
.
France
The sale of metal detectors is allowed in France. The first use of metal detectors in France which led to archaeological discoveries occurred in 1958: people living in the city of Graincourt-lès-Havrincourt who were seeking copper from World War I bombshell with military mine detector found a Roman silver treasure. The French law on metal detecting is ambiguous because it refers only to the objective pursued by the user of a metal detector. The first law to regulate the use of metal detectors was Law No. 89–900 of 18 December 1989. This last is resumed without any change in Article L. 542–1 of the code of the heritage, which states that "no person may use the equipment for the detection of metal objects, for the purpose of research monuments and items of interest prehistory, history, art and archeology without having previously obtained an administrative authorization issued based on the applicant's qualification and the nature and method of research."
Outside the research of archaeological objects, using a metal detector does not require specific authorization, except that of the owner of the land. Asked about Law No. 89–900 of 18 December 1989 by a member of parliament, Jack Lang, Minister of Culture at the time, replied by letter the following: "The new law does not prohibit the use of metal detectors but only regulates the use. If the purpose of such use is the search for archaeological remains, prior authorization is required from my services. Apart from this case, the law ask to be reported to the appropriate authorities an accidental discovery of archaeological remains." The entire letter of Jack Lang was published in 1990 in a French metal detection magazine, and then, to be visible on the internet, scanned with permission of the author of the magazine on a French metal detection website.
Northern Ireland
In
Northern Ireland
Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
, it is an offence to be in possession of a metal detector a scheduled or a State Care site without a licence from the
Department for Communities
The Department for Communities (DfC, Irish: ''An Roinn Pobal'', Ulster Scots: ''Depairtment fur Commonities'') is a devolved Northern Ireland government department in the Northern Ireland Executive. The minister with overall responsibility f ...
. It is also illegal to remove an archaeological object found with a detector from such a site without written consent.
Republic of Ireland
In the
Republic of Ireland
Ireland ( ga, Éire ), also known as the Republic of Ireland (), is a country in north-western Europe consisting of 26 of the 32 counties of the island of Ireland. The capital and largest city is Dublin, on the eastern side of the island. A ...
, laws against metal detecting are very strict: it is illegal to use a detection device to search for archaeological objects anywhere within the State or its territorial seas; without the prior written consent of the
Minister for Culture, Heritage and the Gaeltacht
The Minister for Tourism, Culture, Arts, Gaeltacht, Sport and Media ( ga, An tAire Turasóireachta, Cultúir, Ealaíon, Gaeltachta, Spóirt agus Meán) is a senior minister in the Government of Ireland and leads the Department of Tourism, Cultu ...
, and it is illegal to promote the sale or use of detection devices for the purposes of searching for archaeological objects.
Scotland
Under the Scots law principle of ''
bona vacantia
Unowned property includes tangible, physical things that are capable of being reduced to being property owned by a person but are not owned by anyone. ' (Latin for "ownerless goods") is a legal concept associated with the unowned property, which e ...
'', the Crown has claim over any object of any material value where the original owner cannot be traced. There is also no 300 year limit to Scottish finds. Any artifact found, whether by metal detector survey or from an archaeological excavation, must be reported to the Crown through the Treasure Trove Advisory Panel at the National Museums of Scotland. The panel then determines what will happen to the artifacts. Reporting is not voluntary, and failure to report the discovery of historic artifacts is a criminal offence in Scotland.
United States
The sale of metal detectors is allowed in the United States. People can use metal detectors in public places (parks, beaches, etc.) and on private property with the permission of the owner of the site. In the United States, cooperation between archeologists hunting for the location of colonial-era Native American villages and hobbyists has been productive.
As a hobby
There are various types of hobby activities involving metal detectors:
* Coin shooting is specifically targeting coins. Some coin shooters conduct historical research to locate sites with potential to give up historical and collectible coins.
*
Prospecting
Prospecting is the first stage of the geological analysis (followed by exploration) of a territory. It is the search for minerals, fossils, precious metals, or mineral specimens. It is also known as fossicking.
Traditionally prospecting reli ...
is looking for valuable metals like
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
,
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
, and
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
in their natural forms, such as nuggets or flakes.
* Metal detectors are also used to search for discarded or lost, valuable man-made objects such as jewelry, mobile phones, cameras and other devices. Some metal detectors are waterproof, to allow the user to search for submerged objects in areas of shallow water.
* General metal detecting is very similar to coin shooting except the user is after any type of historical artifact. Detectorists may be dedicated to preserving historical artifacts, and often have considerable expertise. Coins, bullets, buttons, axe heads, and buckles are just a few of the items that are commonly found by relic hunters; in general the potential is far greater in Europe and Asia than in many other parts of the world. More valuable finds in Britain alone include the
Staffordshire Hoard of
Anglo-Saxon
The Anglo-Saxons were a Cultural identity, cultural group who inhabited England in the Early Middle Ages. They traced their origins to settlers who came to Britain from mainland Europe in the 5th century. However, the ethnogenesis of the Anglo- ...
gold, sold for £3,285,000, the gold Celtic
Newark Torc
The Newark Torc is a complete Iron Age gold alloy torc found by a metal detectorist on the outskirts of Newark-on-Trent, Nottinghamshire, England, in February 2005.
The torc is made from electrum, an alloy of gold, silver and copper, weighs ...
, the
Ringlemere Cup
The Ringlemere Gold Cup is a Bronze Age vessel found in the Ringlemere barrow near Sandwich in the English county of Kent in 2001.
Description
The body of the cup was created by hammering a single piece of gold, with the handle cut from a flat s ...
,
West Bagborough Hoard
The West Bagborough Hoard is a hoard of 670 Roman coins and 72 pieces of hacksilver found in October 2001 by metal detectorist James Hawkesworth near West Bagborough in Somerset, England.
Discovery, excavation and valuation
The hoard was disco ...
,
Milton Keynes Hoard
The Milton Keynes Hoard is a hoard of Bronze Age gold found in September 2000 in a field at Monkston Park in Milton Keynes, England. The hoard consisted of two torcs, three bracelets, and a fragment of bronze rod contained in a pottery vesse ...
, Roman
Crosby Garrett Helmet
The Crosby Garrett Helmet is a copper alloy Roman cavalry helmet dating from the late 2nd or early 3rd century AD. It was found by an unnamed metal detectorist near Crosby Garrett in Cumbria, England, in May 2010. Later investigations found tha ...
,
Stirling Hoard,
Collette Hoard
The Collette Hoard was found in fields near Berwick-upon-Tweed, Northumberland, England by metal detectorist John Minns in April 2005. The hoard is named after Collette, the eight-year-old daughter of Minns, rather than the location it was foun ...
and thousands of smaller finds.
*
Beach combing
Beachcombing is an activity that consists of an individual "combing" (or searching) the beach and the intertidal zone, looking for things of value, interest or utility. A beachcomber is a person who participates in the activity of beachcombing. ...
is hunting for lost coins or jewelry on a beach. Beach hunting can be as simple or as complicated as one wishes to make it. Many dedicated beach hunters also familiarize themselves with tide movements and
beach erosion.
* Metal detecting clubs exist for hobbyists to learn from others, show off finds from their hunts and to learn more about the hobby.
Hobbyists often use their own metal detecting lingo when discussing the hobby with others.
Politics and conflicts in the metal detecting hobby in the United States
The metal detecting community and professional archaeologists have different ideas related to the recovery and preservation of historic finds and locations. Archaeologists claim that detector hobbyists take an artifact-centric approach, removing these from their context resulting in a permanent loss of historical information. Archaeological looting of places like
Slack Farm
Slack Farm ( 15 UN 28) is an archaeological site of the Caborn-Welborn variant of the Mississippian culture. Slack Farm is located near Uniontown, Kentucky close to the confluence of the Ohio River and the Wabash Rivers. The site included a Native ...
in 1987 and
Petersburg National Battlefield
Petersburg National Battlefield is a National Park Service unit preserving sites related to the American Civil War Siege of Petersburg (1864–65). The Battlefield is centered on the city of Petersburg, Virginia, and also includes outlying compon ...
serve as evidence against allowing unsupervised metal detecting in historic locations.
Security screening
![Flughafenkontrolle](https://upload.wikimedia.org/wikipedia/commons/e/e7/Flughafenkontrolle.jpg)
In 1926, two Leipzig, Germany scientists installed a walk-though enclosure at a factory, to ensure that employees were not exiting with prohibited metallic items.
A series of
aircraft hijacking
Aircraft hijacking (also known as airplane hijacking, skyjacking, plane hijacking, plane jacking, air robbery, air piracy, or aircraft piracy, with the last term used within the special aircraft jurisdiction of the United States) is the unlawfu ...
s led the United States in 1972 to adopt metal detector technology to screen airline passengers, initially using
magnetometers
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
that were originally designed for logging operations to detect
spikes in trees. The Finnish company
Outokumpu
Outokumpu Oyj is a group of international companies headquartered in Helsinki, Finland, employing 10,600 employees in more than 30 countries. Outokumpu is the largest producer of stainless steel in Europe and the second largest producer in the A ...
adapted mining metal detectors in the 1970s, still housed in a large cylindrical pipe, to make a commercial walk-through security detector. The development of these systems continued in a spin-off company and systems branded as
Metor Metal Detectors evolved in the form of the rectangular gantry now standard in airports. In common with the developments in other uses of metal detectors both alternating current and pulse systems are used, and the design of the coils and the electronics has moved forward to improve the discrimination of these systems. In 1995 systems such as the Metor 200 appeared with the ability to indicate the approximate height of the metal object above the ground, enabling security personnel to more rapidly locate the source of the signal. Smaller hand held metal detectors are also used to locate a metal object on a person more precisely.
Industrial metal detectors
Industrial metal detectors are used in the pharmaceutical, food, beverage, textile, garment, plastics, chemicals, lumber, mining, and packaging industries.
Contamination of food by metal shards from broken processing machinery during the manufacturing process is a major safety issue in the food industry. Metal detectors for this purpose are widely used and integrated into the production line.
Current practice at garment or apparel industry plants is to apply metal detecting after the garments are completely sewn and before garments are packed to check whether there is any metal contamination (needle, broken needle, etc.) in the garments. This needs to be done for safety reasons.
The industrial metal detector was developed by Bruce Kerr and David Hiscock in 1947. The founding company Goring Kerr
pioneered the use and development of the first industrial metal detector.
Mars Incorporated
Mars, Incorporated is an American multinational manufacturer of confectionery, pet food, and other food products and a provider of animal care services, with US$40 billion in annual sales in 2021.
Mars was ranked as the fourth-largest privat ...
was one of the first customers of Goring Kerr using their Metlokate metal detector to inspect
Mars bar
Mars, commonly known as Mars bar, is the name of two varieties of chocolate bar produced by Mars, Incorporated. It was first manufactured in 1932 in Slough, England by Forrest Mars, Sr. The bar consists of caramel and nougat coated with mi ...
s.
The basic principle of operation for the common industrial metal detector is based on a 3 coil design. This design utilizes an AM (
amplitude modulated
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to t ...
) transmitting coil and two receiving coils one on either side of the
transmitter
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which i ...
. The design and physical configuration of the receiving coils are instrumental in the ability to detect very small metal contaminates of 1 mm or smaller. Today modern metal detectors continue to utilize this configuration for the detection of tramp metal.
The coil configuration is such that it creates an opening whereby the product (food, plastics, pharmaceuticals, etc.) passes through the coils. This opening or aperture allows the product to enter and exit through the three coil system producing an equal but mirrored signal on the two receiving coils. The resulting signals are summed together effectively nullifying each other. Fortress Technology innovated a new feature, that allows the coil structure of their BSH Model to ignore the effects of vibration, even when inspecting conductive products.
When a metal contaminant is introduced into the product an unequal disturbance is created. This then creates a very small electronic signal. After suitable amplification a mechanical device mounted to the
conveyor
A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transport of heavy or bulky materials. Conveyor systems allow ...
system is signaled to remove the contaminated product from the production line. This process is completely automated and allows manufacturing to operate uninterrupted.
Civil engineering
In civil engineering, special metal detectors (
cover meter
A cover meter is an instrument to locate rebars and measure the exact concrete cover. Rebar detectors are less sophisticated devices that can only locate metallic objects below the surface. Due to the cost-effective design, the pulse-induction m ...
s) are used to locate
reinforcement bars inside walls.
American metal finders are a term that refer to the devices and equipment or instruments made by American companies or
manufacturers
Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to a range ...
, that can be used to find or detect
metal objects nearby or buried underground such as
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
or
golden
Golden means made of, or relating to gold.
Golden may also refer to:
Places United Kingdom
*Golden, in the parish of Probus, Cornwall
* Golden Cap, Dorset
*Golden Square, Soho, London
*Golden Valley, a valley on the River Frome in Gloucestershi ...
coins or small
jewelry
Jewellery ( UK) or jewelry (U.S.) consists of decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be attached to the body or the clothes. From a western ...
and so on.
Metal finders' more accurate term is: Metal Detectors, as the metal detector's main function is to detect the presence of metal objects including buried metal targets such as gold treasures,
bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
statues,
archaeological artifacts
An artifact, or artefact (see American and British English spelling differences), is a general term for an item made or given shape by humans, such as a tool or a work of art, especially an object of archaeological interest. In archaeology, the ...
made of different
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
types.
The most common type of metal detector is a hand-held metal detector or
coil-based detectors using oval-shaped disks with built-in
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
coils. The search coil works as sensing probe and must be moved over the ground to detect potential metal targets buried underground. When the search coil detects metal objects, the device gives an audible signal via speaker or earphone. In most units, the feedback is an
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analog ...
or digital indicator as a unique number called Target ID based on target metal type.
These metal detectors first invented and manufactured commercially in
United States of America
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
by Fisher Labs in the 1930s; other companies like Garrett established and developed the metal detectors in terms of technology and features in the following decades to reach the current form of metal detector that is in common use by hobbyists, treasure
hunters
Hunting is the human practice of seeking, pursuing, capturing, or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest food (i.e. meat) and useful animal products (fur/ hide, bone/tusks, horn/antler, et ...
or gold prospectors.
Skilled prospectors have put their confidence in American metal detectors due to the high quality of their industry and low cost of production, they are known all over the world.
Military
The first metal detector proved inductance changes to be a practical metal detection technique, and it served as the prototype for all subsequent metal detectors.
Initially these machines were huge and complex. After
Lee de Forest
Lee de Forest (August 26, 1873 – June 30, 1961) was an American inventor and a fundamentally important early pioneer in electronics. He invented the first electronic device for controlling current flow; the three-element "Audion" triode va ...
invented the triode in 1907 metal detectors used
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
s to operate and became more sensitive but still quite cumbersome.
Nonetheless, it proved to be useful, and it grew in popularity among users and prospectors for specific applications.
One of the early common uses of the first metal detectors, for example, was the detection of landmines and
unexploded bombs in a number of European countries following the First and
Second World Wars.
Uses and benefits
Metal detectors can be used if for several
military uses, which can be summarized as follows:
*Exposing the mines planted in the fields during the war or after the end of the war
*Detect dangerous explosives and
cluster bombs
A cluster munition is a form of air-dropped or ground-launched explosive weapon that releases or ejects smaller submunitions. Commonly, this is a cluster bomb that ejects explosive bomblets that are designed to kill personnel and destroy vehicl ...
dangerous to people's lives
*Hand-held metal detectors can be used to search people for
weapon
A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
s and
explosive
An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
s
War mine detection
Demining
Demining or mine clearance is the process of removing land mines from an area. In military operations, the object is to rapidly clear a path through a minefield, and this is often done with devices such as mine plows and blast waves. By contra ...
, also known as mine removal, is the method of clearing a field of landmines.
The aim of military operations is to clear a path through a minefield as quickly as possible, which is mostly accomplished using equipment like
mine plow
A mine plow (plough in British English) is a device designed to clear a lane through a minefield, allowing other vehicles to follow. A mine plow is typically mounted to a tank or military engineering vehicle. Buried land mines are plowed up and ...
s and
blast wave
In fluid dynamics, a blast wave is the increased pressure and flow resulting from the deposition of a large amount of energy in a small, very localised volume. The flow field can be approximated as a lead shock wave, followed by a self-similar sub ...
s.
Humanitarian demining, on the other hand, aims to clear all landmines to a certain depth and make the land secure for human use.
The process of finding or detection of mines done by a special designed metal detector exclusively developed to detect mines and
bomb
A bomb is an explosive weapon that uses the Exothermic process, exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-t ...
s.
Landmine detection techniques have been studied in a wide range of ways.
Electromagnetic technologies are most popular, and one of them (ground penetrating radar) has been used in conjunction with metal detectors.
Mine casings produce a cavity that can be detected using acoustic methods or sensors to detect vapor leakage from landmines. Rats and mongooses, for example, can walk safely over a minefield and detect explosives, and animals can even be used to screen air samples over possible minefields. Bees, plants, and bacteria may all be useful. Nuclear quadrupole resonance and neutron probes can also be used to detect explosives in landmines.
Specially trained dogs are often used to focus the search and confirm that an area has been cleared, mines are often cleared using mechanical equipment such as flails and excavators.
First idea
The first metal detector was likely the simple electric conduction metal detector ca. 1830. Electric conduction was also used to locate metal ore bodies by measuring the conductivity between metal rods driven into the ground.
In 1862 Italian General
Giuseppe Garibaldi
Giuseppe Maria Garibaldi ( , ;In his native Ligurian language, he is known as ''Gioxeppe Gaibado''. In his particular Niçard dialect of Ligurian, he was known as ''Jousé'' or ''Josep''. 4 July 1807 – 2 June 1882) was an Italian general, patr ...
was wounded in the foot. It was difficult to distinguish between bullet, bone, and cartilage. So Professor Favre of Marseilles quickly built a simple probe that was inserted into the track of the bullet. It had 2 sharp points connected to a battery and a bell. Contact with metal completed the circuit and rang the bell.
In 1867 Mr. Sylvan de Wilde had a similar detector and an extractor also wired to a bell.
In 1870
Gustave Trouvé
Gustave Pierre Trouvé (2 January 1839 – 27 July 1902) was a French electrical engineer and inventor in the 19th century.
Trouvé was born on 2 January 1839 in La Haye-Descartes (Indre-et-Loire, France) and died on 27 July 1902 in Paris. A pol ...
, a French electrical engineer also had a similar device but his buzzer made a different sound for lead and iron.
These electric bullet locators were in use until the advent of X-rays.
Technology development
Gerhard Fischer
Gerhard Fischer developed a portable metal detector in 1925. Fischer's model was first marketed commercially in 1931, and he was responsible for the first large-scale hand-held metal detector development.
Gerhard Fisher studied
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
at the
University of Dresden before immigrating to the United States. When working as a Research Engineer in
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...
,
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, he came up with the concept of a portable metal detector while working with
aircraft radio detection finders. Fisher shared the concept with
Albert Einstein
Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
, who foresaw the widespread use of hand-held metal detectors.
Gerhard Fisher, the founder of Fisher Research Laboratory, was contracted by the
Federal Telegraph Company and Western Air Express to establish airborne direction finding equipment in the late 1920s. He received some of the first patents in the area of radio-based airborne direction finding. He came across some unusual errors in the course of his work, and once he figured out what was wrong, he had the foresight to apply the solution to a totally unrelated area, metal and mineral detection."
Fisher received the patent for the first portable electronic metal detector in 1925, and in 1931, he marketed his first Fisher device to the general public, and he established a famous Fisher Labs company that started to manufacture and develop hand-held metal detectors and sell it commercially.
Charles Garrett
Despite the fact that Fisher was the first to receive a patent for an electronic metal detector, he was only one of many who improved and mastered the device. Charles Garrett, the founder of Garrett Metal Detectors, was another key figure in the creation of today's metal detectors.
Garrett, an
electrical engineer
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
by profession, began metal detecting as a pastime in the early 1960s. He tried a number of machines on the market but couldn't find one that could do what he needed. As a result, he started developing his own metal detector. He was able to develop a system that removed oscillator drift, as well as many special search coils that he patented, both of which effectively revolutionized metal detector design at the time.
To present day
In the 1960s, the first industrial metal detectors were produced, and they were widely used for mineral prospecting and other
industrial
Industrial may refer to:
Industry
* Industrial archaeology, the study of the history of the industry
* Industrial engineering, engineering dealing with the optimization of complex industrial processes or systems
* Industrial city, a city dominate ...
purposes. De-mining (the detection of
landmines
A land mine is an explosive device concealed under or on the ground and designed to destroy or disable enemy targets, ranging from combatants to vehicles and tanks, as they pass over or near it. Such a device is typically detonated automati ...
), the detection of
weapon
A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
s such as
knives
A knife ( : knives; from Old Norse 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced ...
and
gun
A gun is a ranged weapon designed to use a shooting tube (gun barrel) to launch projectiles. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, p ...
s (particularly in
airport security
Airport security includes the techniques and methods used in an attempt to protect passengers, staff, aircraft, and airport property from malicious harm, crime, terrorism, and other threats.
Aviation security is a combination of measures and hum ...
),
geophysical
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' som ...
prospecting,
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
, and
treasure hunting
Treasure hunter is the physical search for treasure. For example, treasure hunters try to find sunken shipwrecks and retrieve artifacts with market value. This industry is generally fueled by the market for antiquities. The practice of treasure ...
are just some of the applications.
Metal detectors are also used to detect foreign bodies in food, as well as steel reinforcement bars in concrete and pipes, as well as wires buried in walls or floors in the building industry.
Discriminators and circuits
Transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s,
discriminators, modern search coil designs, and
wireless technology
Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...
, all of which were developed in 1947 by
John Bardeen
John Bardeen (; May 23, 1908 – January 30, 1991) was an American physicist and engineer. He is the only person to be awarded the Nobel Prize in Physics twice: first in 1956 with William Shockley and Walter Brattain for the invention of the tran ...
,
Walter Brattain
Walter Houser Brattain (; February 10, 1902 – October 13, 1987) was an American physicist at Bell Labs who, along with fellow scientists John Bardeen and William Shockley, invented the point-contact transistor in December 1947. They shared the ...
, and
William Shockley
William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointly ...
, have had a significant impact on the advancement of metal detectors as we know them today. Both of these factors, as well as others, have contributed to the metal detector's current status as a lightweight, compact, easy-to-use, deep-seeking system.
The invention of a tunable induction device was the most significant technological advancement in detectors. Two
electro-magnetically tuned coils were used in this method. One coil serves as an
RF transmitter, while the other serves as a receiver; in some situations, these coils may be tuned to
frequencies
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
ranging from 3 to 100 kHz.
Due to eddy currents induced in the metal, a signal is detected when metal is present. The fact that every metal has a different phase response when exposed to alternating current allowed detectors to differentiate between metals. Longer waves (low frequency) penetrate the ground deeper and select for high conductivity targets like
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
and
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, while shorter waves (higher frequency) select for low conductivity targets like
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
. Unfortunately, ground
mineralization interference affects high frequency as well. This selectivity or discrimination allowed the development of detectors that could only detect desirable metals.
Unfortunately, ground mineralization interference affects high frequency as well. This selectivity, or discrimination, allowed the development of detectors that could detect desirable metals while ignoring undesirable metals.
Even with discriminators, avoiding undesirable metals was difficult because some of them have similar phase responses (for example,
tinfoil
Tin foil, also spelled tinfoil, is a thin foil made of tin. Tin foil was superseded after World War II by cheaper and more durable aluminium foil, which is still referred to as "tin foil" in many regions (an example of a misnomer).
History
Fo ...
and
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
), particularly in alloy form. As a result, tuning out those metals incorrectly increased the chance of missing a valuable discovery. Discriminators also had the downside of lowering the sensitivity of the devices.
Manufacturers and companies
Since the beginning of the invention of the metal detector and its commercial sale, many manufacturers of metal detectors were established during the twentieth century in the
United States of America
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
.
These companies provided dozens of new products and various multi-purpose metal detectors suitable for all prospectors categories from beginners to professionals, and these companies contributed to the development of device technology and its features. By providing improvements and additions to the general design of metal detectors.
Fisher Labs
History
Dr. Gerhard Fisher, the engineer and inventor who was the first to obtain a patent for the electronic metal detector, founded Fisher Research Labs in 1931. Fisher Research Labs began in Fisher's garage and has grown from there. Fisher Labs, the world's oldest metal detector company, uses
cutting-edge technologies to create reliable devices.
Dr. Fisher was a Research Engineer in
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...
in the late 1920s when he received the first patent for
aircraft radio direction finders. He was a German refugee who studied
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
at the University of Dresden.
Dr. Albert Einstein was impressed with his groundbreaking work in aviation. Dr. Einstein expected the widespread use of radio direction finders in the air, on land, and at sea after seeing a demonstration of Fisher's equipment.
Fisher Research Labs was built in Fisher's garage in
Palo Alto
Palo Alto (; Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a coastal redwood tree known as El Palo Alto.
The city was estab ...
, California, in 1931. He and four coworkers created the "Metallascope", a tough, user-friendly metal detector. It was an ungainly unit, with two wide, flat
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
en boxes containing basic copper coils, five
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
s, and a few assorted parts, by today's standards of lightweight handheld detectors. The Metallascope quickly captured the nation's and, within a brief period, the world's imagination.
To meet the increasing demand for the Metallascope, also known as the M-Scope, Fisher Labs relocated to a small building at 745 Emerson St. in Palo Alto in 1936. Dr. Fisher received a patent for his invention not long ago. For all forms of electronic metal detection, the M-Scope became the agreed standard.
It was used by
geologist
A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s to find ore, fortune seekers to find
treasure
Treasure (from la, thesaurus from Greek language ''thēsauros'', "treasure store") is a concentration of wealth — often originating from ancient history — that is considered lost and/or forgotten until rediscovered. Some jurisdictions leg ...
, service companies to identify underground tubing, timber mills to detect metal inclusions in sawn logs, and law enforcement to discover lost and concealed weapons.
Fisher relocated to a larger apartment in Palo Alto in 1939, shortly before World War II, at 1961 University Ave. Fisher Research Labs was called upon to devote its scientific expertise to the war effort during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
and the
Korean Conflict
The Korean conflict is an ongoing conflict based on the division of Korea between North Korea (Democratic People's Republic of Korea) and South Korea (Republic of Korea), both of which claim to be the sole legitimate government of all of Korea ...
, but the M-Scope industry was never ignored.
Fisher Labs relocated to a new manufacturing plant in
Belmont, California, in 1961. Dr. Fisher's reputation and career had left an indelible imprint on the world of
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
by the time he retired in 1967. Fisher Research Labs expanded and relocated to
Los Banos, Calif., in 1974, where it remained until 2006, when it was purchased by First Texas Holdings Corporation. First Texas relocated the firm to El Paso, Texas.
Technologies developed
Fisher was the pioneer in metal detection technology and it is the first to introduce new innovations and technologies in metal detection, treasure detection and security products. The company invented or enhanced existed technologies in
electromagnetic
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
engineering for devices.
Search Systems
Search systems in Fisher's metal detectors include multiple search technologies that rely on electromagnetic technology including
VLF
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave a ...
, Pulse Induction and other derived technologies for detection of metal using a special features for metal discrimination through signal based Target ID or acoustic output based on metal type.
Some devices incorporate a mechanism to select predefined settings known as search modes or detection modes that offer a different system for multiple purposes and conditions based on ground terrain, soil type and other factors.
Search coils developed
F75 & F70
* 5" DD Round White Coil - Item 5COIL-F75
* 6-1/2" White Elliptical Concentric Closed Coil - Item 6COIL-E
* 10" Concentric Elliptical Coil - Item 10COIL-F70
* 10" DD White Elliptical Closed Coil - Item 10COILDD-F75
* 11"DD Elliptical Open Coil - Item 11COIL-F75
* 15" DD Round Open Coil - Item 15COIL-F75
F5
* 5" DD Round White Coil - Item 5COIL-F5F
* 8" Concentric Open Coil - Item 8COIL-7TEK
* 10" Concentric Elliptical Coil - Item 10COIL-F5F
* 10" DD White Elliptical Closed Coil - Item 10COILDD-FRL
* 11"DD Elliptical Open Coil - Item 11COIL-F5F
F4 & F2
* 4” Round Black Concentric Coil-Item 4COILF
* 8” Concentric Coil-Item 8COIL-7BLKF
* 10” Concentric Coil-Item 10COILF
* 11" Elliptical Open Coil - Item 11COIL-F2F
* 11” DD Bi-Axial Black Coil-Item 11COIL-F4F
F19
* 5” DD Round White Coil-Item 5COIL-GBUG
* 10" DD White Elliptical Closed Coil - Item 10COILDD-FRL
* 11"DD Elliptical Open Coil - Item 11COIL-F5F
Gold Bug / Pro / DP
* 5” DD Round White Coil-Item 5COIL-GBUG
* 10” Solid DD White Elliptical Coil-Item 10COILDD-GB
* 11” DD Bi-Axial Black Coil-Item 11COIL-GB
Gold Bug 2
* 6-1/2” White Concentric Elliptical Coil-Item 6 COILE-7-GB2
* 10” White Concentric Elliptical Coil-Item 10 COIL-GB2
* 14” White Concentric Elliptical Coil-Item 14 COIL-7-GB
F44
* 4" Round Search Coil - Item 4COIL-FS
* 7" Round Coil - Item 7COIL-RE-F
* 9" Concentric Teardrop Coil - Item 9COIL-EE
* 11" Concentric Teardrop Coil - Item 11COIL-EE
* 11" DD Elliptical Coil - Item 11COIL-FRL
* 4" Coil Cover - Item 4COVER
* 7" Round Coil Cover - Item 7COVER-RE
* 9" Teardrop Coil Cover - 9COVER-EE
* 11" Coil Cover - Item COVER-11DD
Bounty Hunter
History and Establishing
Metal detectors from the
Bounty Hunter
A bounty hunter is a private agent working for bail bonds who captures fugitives or criminals for a commission or bounty. The occupation, officially known as bail enforcement agent, or fugitive recovery agent, has traditionally operated outsid ...
business are plain, fast, and inexpensive devices for the hobby of searching for gold and lost metal items such as rings, coins, and so on.
The Bounty Hunter corporation is headquartered in
El Paso
El Paso (; "the pass") is a city in and the seat of El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the U.S. Census Bureau was 678,815, making it the 23rd-largest city in the U.S., the s ...
, Texas, and its parent company, First Texas, comprises several metal detector manufacturers, such as Fisher Labs and Teknetics, as well as firms that specialize in other areas, such as night vision systems.
Technologies They Developed
The company produces a wide range of metal detector models with various features, including metal detectors for kids, coin shooting detectors for amateurs, and even gold prospectors metal detectors.
All of the company's metal detectors use electromagnetic equipment, such as very low technology
VLF
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave a ...
with a search coil system, and they have a search area and a very shallow depth of less than 2 meters underground.
Throughout its existence, the company has manufactured approximately 55 products, including various devices and related accessories in various models, as well as search coils for various purposes.
Search Systems
Multiple search technologies based on electromagnetic technology are available in Bounty Hunter's metal detectors, including VLF, Pulse Induction, and other derived technologies for metal detection using special features.
Some systems provide a mechanism for selecting predefined settings called search modes or detection modes, which have a different method for different purposes and conditions depending on ground terrain, soil type, and other variables.
See also
*
List of metal detecting finds
*
DEMIRA
DEMIRA, or DEMIRA Deutsche Minenräumer e.V. (''German mine clearers''), is an international, humanitarian, non-governmental organization (NGO) registered in Germany. DEMIRA was founded in 1996 in order to provide humanitarian mine clearance, EOD ...
*
Detectorists
''Detectorists'' is a British comedy television series first broadcast on BBC Four in October 2014. It is written and directed by Mackenzie Crook, who also stars alongside Toby Jones.
The series is set in the fictional small town of Danebury i ...
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Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
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* Grosvenor, Edwin S. and Wesson, Morgan. ''Alexander Graham Bell: The Life and Times of the Man Who Invented the Telephone''. New York: Harry N. Abrahms, Inc., 1997. .
* Colin King (Editor), Jane's Mines and Mine Clearance,
* Graves M, Smith A, and Batchelor B 1998: Approaches to foreign body detection in foods, Trends in Food Science & Technology 9 21-27
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