Degaussing is the process of decreasing or eliminating an unwanted magnetic field. It is named after Carl Friedrich Gauss, an early researcher in the field of magnetism. Due to magnetic hysteresis it is generally not possible to reduce a magnetic field completely to zero, so degaussing typically induces a very small "known" field referred to as bias. For other uses, see Brand New (disambiguation). ... Degausser is a song from Brand News 2006 album The Devil and God Are Raging Inside Me. ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ... Johann Carl Friedrich Gauss or Gauß ( ; Latin: ) (30 April 1777 – 23 February 1855) was a German mathematician and scientist who contributed significantly to many fields, including number theory, analysis, differential geometry, geodesy, electrostatics, astronomy, and optics. ... For other senses of this word, see magnetism (disambiguation). ... Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ...

The term was first used by (then) Cmdr. Charles F. Goodeve, RCNVR, during World War II while trying to counter the German magnetic mines that were playing havoc with the British fleet. The mines detected the increase in magnetic field when the steel in a ship concentrated the Earth's magnetic field over it. Goodeve developed a number of systems to induce a small "N-pole up" field into the ship to offset this effect, meaning that the net field was the same as background. Since the Germans used gauss as the measure of strength of the magnetic field in their mines' triggers (this was not yet a standard measure), Goodeve referred to the various processes to counter the mines as degaussing. The term became a common word. Charles Frederick Goodeve (21 February 1904 – 7 April 1980) was a Canadian chemist and pioneer in operations research. ... The Royal Navy Canadian Volunteer Reserve (RNCVR) was a naval reserve that was established on 14 May 1914. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... A naval mine is a stationary self-contained explosive device placed in water, to destroy ships and/or submarines. ... The gauss, abbreviated as G, is the cgs unit of magnetic flux density (B), named after the German mathematician and physicist Carl Friedrich Gauss. ...

The original method of degaussing was to install electromagnetic coils into the ships, known simply as coiling. In addition to being able to continually bias the ship, coiling also allowed the bias field to be reversed in the southern hemisphere, where the mines were set to detect "S-pole down" fields. British ships, notably cruisers and battleships, were well protected by about 1943. USS Port Royal (CG-73), a Ticonderoga-class guided missile cruiser (really an uprated guided missile destroyer), launched in 1992. ... For other uses, see Battleship (disambiguation). ... Year 1943 (MCMXLIII) was a common year starting on Friday (the link will display full 1943 calendar) of the Gregorian calendar. ...

Installing such special equipment was, however, far too expensive and difficult to service all ships that would need it, so the navy developed an alternative called wiping (devised by Goodeve), which simply dragged a large electrical cable along the side of the ship with about 2000 amps flowing through it. This induced the proper field into the ship in the form of a slight bias. It was originally thought that the pounding of the sea and the ship's engines would slowly randomize this field, but in testing this was found not to be a real problem. A more serious problem was later realized: as a ship travels through the Earth's magnetic field it will slowly pick up that field, counteracting the effects of the degaussing. From then on captains were instructed to change direction as often as possible to avoid this problem. Nevertheless the bias did wear off eventually, and ships had to be degaussed on a schedule. Smaller ships continued to use wiping through the war.

Controlpanel of the MES-device ("Magnetischer Eigenschutz" German: magnetic self protection) in a German submarine

After the war the capabilities of the magnetic fuses were greatly improved, by detecting not the field itself, but changes in it. This meant a degaussed ship with a magnetic "hot spot" would still set off the mine. Additionally, the precise orientation of the field was also measured, something a simple bias field could not remove, at least for all points on the ship. A series of ever-increasingly complex coils were introduced to offset these effects, with modern systems including no fewer than three separate sets of coils to reduce the field in all axes. Image File history File links Size of this preview: 662 × 599 pixelsFull resolution (1685 × 1525 pixel, file size: 576 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 662 × 599 pixelsFull resolution (1685 × 1525 pixel, file size: 576 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ...

Degaussing monitors

Today the most common use of degaussing is in CRT-based TV sets and computer monitors. For example, many monitors use a metal plate near the front of the tube to focus the electron beams from the back. This plate, the shadow mask, can pick up strong external fields and from that point produce discoloration on the display. Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... The shadow mask is one of two major technologies used to manufacture cathode ray tube (CRT) televisions and computer displays that produce color images (the other is aperture grille). ...

To minimize this, CRTs have a copper coil wrapped around the front of the display, known as the degaussing coil. Tubes without an internal coil can be degaussed using an external hand held version. Internal degaussing coils in CRTs are generally much weaker than external degaussing coils, since a better degaussing coil takes up more space. A degauss causes a magnetic field inside the tube to oscillate rapidly, with decreasing amplitude. This leaves the shadow mask with a small and somewhat randomized field, removing the discoloration. Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ... It has been suggested that pulse amplitude be merged into this article or section. ... The shadow mask is one of two major technologies used to manufacture cathode ray tube (CRT) televisions and computer displays that produce color images (the other is aperture grille). ...

A degaussing in progress

The high current surge which takes place during this automatic degauss is the cause of the audible 'thunk' which can be heard (and felt) when televisions and CRT computer monitors are switched on. Visually, this causes the image to shake dramatically for a second or so. Many televisions and monitors automatically degauss their picture tube when switched on, before an image has been displayed. A degauss in progress on my Dell UltraScan P991. ... A degauss in progress on my Dell UltraScan P991. ... Look up second in Wiktionary, the free dictionary. ...

In most commercial equipment the current surge to the degauss coil is regulated by a simple PTC thermistor device which initially has a low resistance but quickly changes to a high resistance due to the heating effect of the current flow. Such devices are designed for a one-off transition from cold to hot at power up, so 'experimenting' with the degauss effect by repeatedly switching the device on and off is not recommended as it may cause this component to fail. The effect will also be weaker, since the PTC hasn't had time to cool off. Positive Temperature Coefficient (PTC) referers to materials that when temperature is raised, the electrical resistance increases sharply. ... NTC thermistor, bead type, insulated wires Thermistor symbol A thermistor is a type of resistor used to measure temperature changes, relying on the change in its resistance with changing temperature. ...

Degaussing magnetic data storage media

Data is stored in magnetic media, such as hard drives, floppy disks and magnetic tape, by making very small areas called magnetic domains change their magnetic alignment to be in the direction of an applied magnetic field. This phenomenon occurs in much the same way a compass needle points in the direction of the earth's magnetic field. Degaussing, commonly called erasure, leaves the domains in random patterns with no preference to orientation, thereby rendering previous data unrecoverable. There are some domains whose magnetic alignment is not randomized after degaussing. The information these domains represent is commonly called magnetic remanence since it is due to remanent magnetization. Proper degaussing will ensure there is insufficient magnetic remanence to reconstruct the data.^[1] Typical hard drives of the mid-1990s. ... A floppy disk is a data storage device that is composed of a disk of thin, flexible (floppy) magnetic storage medium encased in a square or rectangular plastic shell. ... Compact audio cassette Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Remanence is the magnetization left behind in a medium after an external magnetic field is removed. ... A family of hysteresis loops for grain-oriented electrical steel (BR denotes remanence and HC is the coercivity. ...

Erasure via degaussing may be accomplished in two ways: in AC erasure, the media is degaussed by applying an alternating field that is reduced in amplitude over time from an initial high value (i.e., AC powered); in DC erasure, the media is saturated by applying a unidirectional field (i.e., DC powered or by employing a permanent magnet). A degausser is a device that can generate a magnetic field for degaussing magnetic storage media.^[2] City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Magnetic lines of force of a bar magnet shown by iron filings on paper A magnet is an object that has a magnetic field. ...

Alternative methods

Monitors without a degauss function can be degaussed by placing a degauss-enabled monitor face-to-face with the target monitor. Activating the degauss function on the enabled monitor can help degauss the other. Naresh^{[citation needed]}.

Degaussing can also help reduce the distortion due to static electricity that often results from long term usage of the monitor, especially in older monitors. ^{[citation needed]}

See also

• Data remanence
• Data recovery

It has been suggested that File wipe be merged into this article or section. ... Data recovery is the process of salvaging data from damaged, failed, corrupted or inaccessible primary storage media when it cannot be accessed normally. ...

Notes and references

External links

• Guide to degaussing TVs
• A Guide to Understanding Data Remanence in Automated Information Systems