Editing Mu-metal (section)

==History==
[[File:Mu-metal_cable.svg|thumb|Mu-metal submarine cable construction]]
Mu-metal was developed by British scientists Willoughby S. Smith and Henry J. Garnett<ref name="Patent279549">{{Cite patent|number=GB279549A|title=New and improved magnetic alloys and their application in the manufacture of telegraphic and telephonic cables|gdate=1927-10-27|url=https://patents.google.com/patent/GB279549A/en}}</ref><ref name="Patent1582353" >[https://patents.google.com/patent/US1582353 US Patent 1582353] Willoughby Statham Smith, Henry Joseph Garnett, ''Magnetic Alloy'', filed January 10, 1924, granted April 27, 1926</ref><ref name="Patent1552769" >[https://patents.google.com/patent/US1552769 US Patent 1552769] Willoughby Statham Smith, Henry Joseph Garnett, ''Magnetic Alloy'', filed January 10, 1924, granted September 8, 1925</ref> and patented in 1923 for [[inductance|inductive]] loading of [[submarine telegraph cable]]s by The Telegraph Construction and Maintenance Co. Ltd. (now Telcon Metals Ltd.), a British firm that built the Atlantic undersea telegraph cables.<ref>{{cite web| last = Green| first = Allen| title = 150 Years Of Industry & Enterprise At Enderby's Wharf| work = History of the Atlantic Cable and Undersea Communications| publisher = FTL Design| date = 2004| url = http://atlantic-cable.com/Article/EnderbyAG/index.htm| access-date = 2008-12-14}}</ref> The conductive seawater surrounding an undersea cable added a significant [[capacitance]] to the cable, causing distortion of the signal, which limited the [[Bandwidth (signal processing)|bandwidth]] and slowed signaling speed to 10–12 words per minute. The bandwidth could be increased by adding [[inductance]] to compensate. This was first done by wrapping the conductors with a helical wrapping of metal tape or wire of high magnetic permeability, which confined the magnetic field. 

Telcon invented mu-metal to compete with [[permalloy]], the first high-permeability alloy used for cable compensation, whose patent rights were held by competitor [[Western Electric]]. Mu-metal was developed by adding copper to permalloy to improve [[ductility]]. {{Convert|80|km|mi}} of fine mu-metal wire were needed for each 1.6&nbsp;km of cable, creating a great demand for the alloy. The first year of production Telcon was making 30 tons per week. In the 1930s this use for mu-metal declined, but by World War II many other uses were found in the [[electronics industry]] (particularly shielding for [[transformer]]s and [[cathode-ray tube]]s), as well as the [[fuze]]s inside [[naval mine|magnetic mines]]. Telcon Metals Ltd. abandoned the trademark "MUMETAL" in 1985.<ref>{{Cite web|url=http://tsdr.uspto.gov/#caseNumber=73431306&caseType=SERIAL_NO&searchType=statusSearch|title=Trademark Status & Document Retrieval|website=tsdr.uspto.gov|language=en|access-date=2017-07-28}}</ref> The last listed owner of the mark "MUMETAL" is Magnetic Shield Corporation, Illinois.<ref>{{Cite web|url=http://tsdr.uspto.gov/#caseNumber=73410422&caseType=SERIAL_NO&searchType=statusSearch|title=Trademark Status & Document Retrieval|website=tsdr.uspto.gov|language=en|access-date=2017-07-28}}</ref>