Editing Metal detector (section)

==Uses==

Large portable metal detectors are used by [[archaeologist]]s and [[treasure hunters]] to locate metallic items, such as [[jewelry]], [[coins]], [[button|clothes button]]s and other accessories, [[bullets]], and other various [[artifact (archaeology)|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 [[Battle of the Little Bighorn|Little Big Horn]]. However archaeologists oppose the use of metal detectors by "artifact seekers" or "site looters" whose activities disrupt archaeological sites.<ref>{{cite journal|jstor=25616646|title=Metal Detector Use in Archaeology: An Introduction|first1=Melissa|last1=Connor|first2=Douglas D.|last2=Scott|date=1 January 1998|journal=Historical Archaeology|volume=32|issue=4|pages=76–85|doi=10.1007/BF03374273|s2cid=163861923}}</ref> 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.<ref name="NYT011617">{{cite news|author1=Tyler J. Kelley|title=Archaeologists and Metal Detectorists Find Common Ground|work=The New York Times |url=https://www.nytimes.com/2017/01/16/science/archaeology-metal-detectorists-pequot.html|access-date=21 January 2017|issue=The New York Times|date=16 January 2017|quote=The difference between archaeology and looting, explained Brian Jones, Connecticut’s state archaeologist, is the recording of context.}}</ref>

====England and Wales====
In [[England and Wales]], metal detecting is legal provided that the landowner has granted permission and that the area is not a [[Scheduled Ancient Monument]], a [[site of special scientific interest]] (SSSI), or covered by elements of the [[Countryside Stewardship Scheme]].

The [[Treasure Act 1996]] governs whether or not items that have been discovered are defined as treasure.<ref>{{cite web|url=https://www.legislation.gov.uk/ukpga/1996/24/crossheading/meaning-of-treasure|title=Treasure Act 1996 – Meaning of "treasure"|publisher=HMSO|access-date=18 February 2018}}</ref> 
Finders of items that the Act defines as treasure must report their finds to the local coroner.<ref>{{cite web|url=https://www.legislation.gov.uk/ukpga/1996/24/crossheading/coroners-jurisdiction|title=Treasure Act 1996 – Coroners jurisdiction|publisher=HMSO|access-date=18 February 2018}}</ref>
If they discover items which are not defined as treasure but that are of cultural or historical interest, finders can voluntarily report them to the [[Portable Antiquities Scheme]]<ref>{{cite web|url= https://www.gov.uk/treasure|title=Report Treasure|publisher=HM Government|access-date=18 February 2018}}</ref> and the UK Detector Finds Database.

====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.<ref>{{Cite web|url=https://www.louvre.fr/oeuvre-notices/plat-aux-poissons-du-tresor-de-graincourt |archive-url=https://web.archive.org/web/20130617020446/https://www.louvre.fr/oeuvre-notices/plat-aux-poissons-du-tresor-de-graincourt |title=Plat aux poissons du Trésor de Graincourt |language=fr |archive-date=17 June 2013 |website=www.louvre.fr}}</ref> 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."{{citation needed|date=April 2022}}

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,<ref>{{cite journal|title=Le Prospecteur|issue=5|issn= 1169-3835}}</ref> and then, to be visible on the internet, scanned with permission of the author of the magazine on a French metal detection website.<ref>{{cite web|url=https://www.prospection-de-loisir.fr/trouver-or-detecteur-de-metaux/|title=Detecteur-de-metaux.com – Or natif et trésor – Conseils et guide d'achat|date=30 December 2021 }}</ref>

====Northern Ireland====
In [[Northern Ireland]], it is an offence to be in possession of a metal detector on a scheduled or a State Care site without a licence from the [[Department for Communities]]. It is also illegal to remove an archaeological object found with a detector from such a site without written consent.<ref>{{Cite web|url=https://www.communities-ni.gov.uk/articles/guide-metal-detecting-archaeology-and-law|title=A Guide to Metal Detecting, Archaeology and the Law &#124; Department for Communities|date=November 12, 2019|website=Communities}}</ref><ref>{{Cite web|url=https://www.communities-ni.gov.uk/articles/advice-finders-treasure-northern-ireland|title=Advice for finders of treasure in Northern Ireland &#124; Department for Communities|date=November 8, 2019|website=Communities}}</ref><ref>{{Cite web|url=https://www.nidirect.gov.uk/articles/archaeology-and-treasure|title=Archaeology and treasure &#124; nidirect|date=November 12, 2015|website=www.nidirect.gov.uk}}</ref>

====Republic of Ireland====
In the [[Republic of Ireland]], 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]], and it is illegal to promote the sale or use of detection devices for the purposes of searching for archaeological objects.<ref>{{Cite web|url=https://www.museum.ie/en-IE/Collections-Research/The-Law-on-Metal-Detecting-in-Ireland|title=The Law on Metal Detecting in Ireland|website=National Museum of Ireland}}</ref>

====Scotland====
Under the Scots law principle of ''[[bona vacantia]]'', the Crown has claim over any object of any material value where the original owner cannot be traced.<ref>{{Cite web|url=http://www.treasuretrovescotland.co.uk|title=Treasure Trove Scotland}}</ref> 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.<ref name="NYT011617"/>

===As a hobby===
[[File:Metaldetectorbeach-odaiba-japan-2016-6-19.webm|thumb|A man metal detecting on a beach in [[Japan]], 2016]]
{{Redirect|Detectorist|the comedy series|Detectorists{{!}}''Detectorists''}}
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[[File:Stringer156 nugget.jpg|thumb|This {{convert|156|ozt|kg|adj=on}} [[gold nugget]], known as the [[Mojave Nugget]], was found in 1977 by an individual prospector in the Southern California Desert using a metal detector.]]

There are various types of hobby activities involving metal detectors:
* Coin shooting is specifically targeting coins.<ref>{{Cite web|url=http://www.metaldetectingworld.com/coin_shooting.shtml|title=Coin Shooting Tips|website=www.metaldetectingworld.com}}</ref> Some coin shooters conduct historical research to locate sites with potential to give up historical and collectible coins.
* [[Prospecting]] is looking for valuable metals like [[gold]], [[silver]], and [[copper]] in their natural forms, such as nuggets or flakes.<ref>{{cite web|url=http://www.goldgold.com/the-fundamentals-of-electronic-prospecting.html | author=Dave McCracken |title=The Fundamentals of Electronic Prospecting :: goldgold.com| date=23 November 2011 }}</ref>
* Metal detectors are also used to search for discarded or lost,<ref>{{cite web|url=https://www.detecting.us/2012/09/30/gold-ring-recovery-from-farm-field/ | author=Scott Clark |title=Finding Jewelry with Metal Detector| date=30 September 2012 }}</ref> 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]] gold, sold for £3,285,000, the gold Celtic [[Newark Torc]], the [[Ringlemere Cup]], [[West Bagborough Hoard]], [[Milton Keynes Hoard]], Roman [[Crosby Garrett Helmet]], [[Stirling Hoard]], [[Collette Hoard]] and thousands of smaller finds.
* [[Beach combing]] 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 [[coastal erosion|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.<ref>{{cite web|url=https://www.detecting.us/metal-detecting-jargon-for-coinshooters|title=Metal Detecting Jargon Glossary|website=detecting.us}}</ref>{{importance inline|date=April 2022}}

====Politics and conflicts in the metal detecting hobby in the United States====
{{Globalize|section|USA|2name=the United States|date=June 2013}}

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]] in 1987 and [[Petersburg National Battlefield]] serve as evidence against allowing unsupervised metal detecting in historic locations.<ref>{{cite web|url=http://usnews.nbcnews.com/_news/2012/03/23/10827391-civil-war-relic-thief-engaged-in-heartbreaking-destruction?lite|title=Civil War relic thief engaged in 'heartbreaking' destruction|publisher=NBC News}}</ref>

===Security screening===
[[File:Flughafenkontrolle.jpg|thumb|Metal detectors at [[Berlin Schönefeld Airport]]]]

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.<ref>[https://books.google.com/books?id=L5c1AQAAIAAJ&pg=1408 "The Radio Watchman at the Gate"], April 1926, Dr. K. Schuett, ''Radio News'', April 1926, pp. 1408, 1493.</ref>

A series of [[aircraft hijacking]]s led the United States in 1972 to adopt metal detector technology to screen airline passengers, initially using [[magnetometers]] that were originally designed for logging operations to detect [[Tree spiking|spikes in trees]].<ref>{{Cite web|url=https://savvytraveler.publicradio.org/show/features/2000/20000915/security.shtml|title=The History of Airport Security|website=savvytraveler.publicradio.org}}</ref> The Finnish company [[Outokumpu]] adapted mining metal detectors in the 1970s, still housed in a large cylindrical pipe, to make a commercial walk-through security detector.<ref>Jarvi, A, Leinonen, E, Thompson, M, and Valkonen K, ''Designing Modern Walk-through Metal Detectors, Access Security Screening: Challenges and Solutions'', ASTM STP 1127 TP Tsacoumis Ed, American Society for Testing of Materials, Philadelphia 1992, pp. 21–25
</ref> The development of these systems continued in a spin-off company and systems branded as [[Rapiscan Systems|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 ===
<ref>{{cite web|url=https://extremedetector.com |title= Industrial metal detectors |access-date=22 October 2023}}</ref> 

Contamination of food by metal shards from broken processing machinery during the manufacturing process is a major safety issue in the food industry. Most food processing equipment is made of [[stainless steel]], and other components made of plastic or elastomers can be manufactured with embedded metallic particles, allowing them to be detected as well. 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<ref>{{cite web |title=History of Goring Kerr |url=https://goring-kerr.com/about-us |url-status=live |archive-url=https://web.archive.org/web/20161023140957/http://industrial-machinery-news.com/history-of-goring-kerr/ |archive-date=23 October 2016 |access-date=27 February 2024 |website=Goring Kerr|date=27 May 2012 }}</ref>
pioneered the use and development of the first industrial metal detector. [[Mars Incorporated]] was one of the first customers of Goring Kerr using their Metlokate metal detector to inspect [[Mars bar]]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]]) transmitting coil and two receiving coils one on either side of the [[transmitter]]. The design and physical configuration of the receiving coils are instrumental in the ability to detect very small metal contaminates of 1&nbsp;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,<ref>{{cite web|url=http://www.foodprocessing.com/articles/2007/169/|title=Detecting Foreign Matter|first=Mike|last=Pehanich|work=foodprocessing.com|date=16 July 2007}}</ref> even when inspecting conductive products.<ref>{{Cite web|url=https://www.fortresstechnology.com/company/|title=Company &#124; Fortress Technology|date=10 November 2016 }}</ref>

When a metal contaminant is introduced into the product an unequal disturbance is created. That creates a very small electronic signal. After suitable amplification a mechanical device mounted to the [[conveyor]] 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===
{{Unreferenced section|date=August 2023}}
In civil engineering, special metal detectors ([[cover meter]]s) are used to locate [[Rebar|reinforcement bars]] inside walls.

The most common type of metal detector is a hand-held metal detector or [[Electromagnetic coil|coil]]-based detectors using oval-shaped disks with built-in [[copper]] 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 [[Analogue electronics|analog]] or digital indicator.

The metal detectors were first invented and manufactured commercially in the [[United States]] 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.

=== Military ===
{{Unreferenced section|date=August 2023}}
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]] invented the triode in 1907 metal detectors used [[vacuum tube]]s to operate and became more sensitive but still quite cumbersome. One of the early common uses of the first metal detectors, for example, was the detection of landmines and [[Unexploded ordnance|unexploded bombs]] in a number of European countries following the First and [[World War II|Second World Wars.]]

==== Uses and benefits ====
Metal detectors have several [[Demining|military uses]], including:

*Exposing mines planted during the war or after the end of the war
*Detecting dangerous explosives and [[Cluster munition|cluster bombs]] 
*Searching  people for [[weapon]]s and [[explosive]]s using hand-held metal detectors

==== War mine detection ====
[[Demining]], 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]]s and [[blast wave]]s.

Humanitarian demining aims to clear all landmines to a certain depth and make the land secure for human use. Landmine detection techniques have been studied in various forms. Detection of mines can be done by a specially designed metal detector tuned to detect mines and [[bomb]]s. Electromagnetic technologies have been used in conjunction with ground-penetrating radar. 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.<ref>{{Cite web|url=https://goldgold.com/history-of-treasure-gold-detectors.html|title=A chronological account of the development of treasure and gold locators from 1830 to 1930.|date=23 November 2011 }}</ref> 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]] 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 two sharp points connected to a battery and a bell. Contact with metal completed the circuit and rang the bell.<ref>''Morning Herald (London)'', 1862 Nov 13, p. 5</ref> In 1867, Mr. Sylvan de Wilde had a similar detector and an extractor also wired to a bell.<ref>[https://babel.hathitrust.org/cgi/pt?id=hvd.32044103082012&view=1up&seq=463 "An ingenious bullet detector "], ''The Lancet'', 1867 July, p. 457</ref>
In 1870, [[Gustave Trouvé]], a French electrical engineer also had a similar device however his buzzer made a different sound for lead and iron.<ref>[https://babel.hathitrust.org/cgi/pt?id=nnc1.cu05649617&view=1up&seq=55 "A new method of probing wounds"], ''American artisan'', 1870 Jan 19, p. 45</ref>
The electric bullet locators were in use until the advent of X-rays.

=== Technology development ===

====Gerhard Fischer====

[[Gerhard Fischer (inventor)|Gerhard Fischer]] developed a portable metal detector in 1925. His model was first marketed commercially in 1931; he was responsible for the first large-scale hand-held metal detector development.

Gerhard Fisher studied [[electronics]] at the [[TU Dresden|University of Dresden]] before emigrating to the United States. When working as a research engineer in [[Los Angeles]], he came up with the concept of a portable metal detector while working with [[Aircraft Radio Corporation|aircraft radio]] detection finders. Fisher shared the concept with [[Albert Einstein]], who foresaw the widespread use of hand-held metal detectors.

Fisher, the founder of Fisher Research Laboratory, was contracted by the [[Federal Telegraph Company|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; 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. 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.<ref>{{Cite web|title=The History of the Metal Detector {{!}} MetalDetector.com|url=https://www.metaldetector.com/learn/metal-detector-history/history-of-the-metal-detector|access-date=10 May 2021|website=www.metaldetector.com}}</ref>

====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 engineering|electrical engineer]] 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 [[industry (manufacturing)|industrial]] purposes. De-mining (the detection of [[Land mine|landmines]]), the detection of [[weapon]]s such as [[Knife|knives]] and [[gun]]s (particularly in [[airport security]]), [[Geophysics|geophysical]] prospecting, [[archaeology]], and [[treasure hunting]] 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. The building industry uses them to find wires buried in walls or floors.

=== Discriminators and circuits ===
The development of [[transistor]]s, discriminators, modern search coil designs, and [[Wireless|wireless technology]] significantly impacted the design of metal detectors as we know them today: lightweight, compact, easy-to-use, and deep-seeking systems. The invention of a tunable induction device was the most significant technological advancement in detectors. Two [[Electromagnetically induced acoustic noise|electro-magnetically]] tuned coils were used in this method. One coil serves as an [[Rf transmitter module|RF transmitter]], while the other serves as a receiver; in some situations, these coils may be tuned to [[Frequency|frequencies]] ranging from 3 to 100&nbsp;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]] and [[copper]], while shorter waves (higher frequency) select for low conductivity targets like [[iron]]. Unfortunately, ground [[mineralization (geology)|mineralization]] interference affects high frequency as well. This selectivity or discrimination allowed the development of detectors that can selectively detect desirable metals.

Even with discriminators, avoiding undesirable metals was difficult because some of them have similar phase responses (for example, [[Tin foil|tinfoil]] and [[gold]]), 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.