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63-408: The locomotives have three sending and receiving magnets and there are two trackside magnets near the signals . Integra-Signum requires the train driver to confirm distant signals that show stop and distant or home signals that show caution. If no confirmation is received or a home signal that shows stop is passed without authority, the train is stopped automatically. This is achieved by interrupting

126-521: A coercivity of 400 oersteds (32 kA/m), double that of the best magnet steels of the time. Alnico alloys can be magnetised to produce strong magnetic fields and have a high coercivity (resistance to demagnetization), thus making strong permanent magnets. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500  gauss (0.15  tesla ), or about 3000 times

189-471: A pacemaker has been embedded in a patient's chest (usually for the purpose of monitoring and regulating the heart for steady electrically induced beats ), care should be taken to keep it away from magnetic fields. It is for this reason that a patient with the device installed cannot be tested with the use of a magnetic resonance imaging device. Children sometimes swallow small magnets from toys, and this can be hazardous if two or more magnets are swallowed, as

252-401: A torque tending to orient the magnetic moment parallel to the field. The amount of this torque is proportional both to the magnetic moment and the external field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space, the magnet is subject to no net force, although it

315-415: A combination of aluminium , nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as

378-776: A common ground state in the manner of a Bose–Einstein condensate . The United States Department of Energy has identified a need to find substitutes for rare-earth metals in permanent-magnet technology, and has begun funding such research. The Advanced Research Projects Agency-Energy (ARPA-E) has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects. Iron nitrides are promising materials for rare-earth free magnets. The current cheapest permanent magnets, allowing for field strengths, are flexible and ceramic magnets, but these are also among

441-416: A different issue, however; correlations between electromagnetic radiation and cancer rates have been postulated due to demographic correlations (see Electromagnetic radiation and health ). If a ferromagnetic foreign body is present in human tissue, an external magnetic field interacting with it can pose a serious safety risk. A different type of indirect magnetic health risk exists involving pacemakers. If

504-427: A high- coercivity ferromagnetic compound (usually ferric oxide ) mixed with a resinous polymer binder. This is extruded as a sheet and passed over a line of powerful cylindrical permanent magnets. These magnets are arranged in a stack with alternating magnetic poles facing up (N, S, N, S...) on a rotating shaft. This impresses the plastic sheet with the magnetic poles in an alternating line format. No electromagnetism

567-571: A magnet can be magnetized with different directions and strengths (for example, because of domains, see below). A good bar magnet may have a magnetic moment of magnitude 0.1 A·m and a volume of 1 cm , or 1×10  m , and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter. Such a large value explains why iron magnets are so effective at producing magnetic fields. Two different models exist for magnets: magnetic poles and atomic currents. Although for many purposes it

630-533: A melting temperature of 1200 - 1450 °C. As of 2018, Alnico magnets cost about 44  USD /kg (US$ 20/lb) or US$ 4.30/BH max . Alnico magnets are traditionally classified using numbers assigned by the Magnetic Materials Producers Association (MMPA), for example, alnico 3 or alnico 5. These classifications indicate chemical composition and magnetic properties. (The classification numbers themselves do not directly relate to

693-492: A metal. Trade names for alloys in this family include: Alni, Alcomax, Hycomax, Columax , and Ticonal . Injection-molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties. Flexible magnets are composed of

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756-402: A net contribution; shaving off the outer layer of a magnet will not destroy its magnetic field, but will leave a new surface of uncancelled currents from the circular currents throughout the material. The right-hand rule tells which direction positively-charged current flows. However, current due to negatively-charged electricity is far more prevalent in practice. The north pole of a magnet

819-410: A north and south pole. However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets. In this approach, the divergence of the magnetization ∇· M inside a magnet is treated as a distribution of magnetic monopoles . This is a mathematical convenience and does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution

882-399: A partially occupied f electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare-earth magnets are samarium–cobalt and neodymium–iron–boron (NIB) magnets. In

945-551: A permanent magnet has a large influence on its magnetic properties. When a magnet is magnetized , a demagnetizing field will be created inside it. As the name suggests, the demagnetizing field will work to demagnetize the magnet, decreasing its magnetic properties. The strength of the demagnetizing field H d {\displaystyle H_{d}} is proportional to the magnet's magnetization M {\displaystyle M} and shape, according to Here, N d {\displaystyle N_{d}}

1008-446: A simple magnetic dipole; for example, quadrupole and sextupole magnets are used to focus particle beams . Alnico Alnico is a family of iron alloys which, in addition to iron are composed primarily of aluminium (Al), nickel (Ni), and cobalt (Co), hence the acronym al-ni-co . They also include copper , and sometimes titanium . Alnico alloys are ferromagnetic , and are used to make permanent magnets . Before

1071-445: A soft magnetic material. After the heat treatment alnico becomes a composite material, named " precipitation material"—it consists of iron- and cobalt-rich precipitates in a rich-NiAl matrix. Alnico's anisotropy is oriented along the desired magnetic axis by applying an external magnetic field to it during the precipitate particle nucleation, which occurs when cooling from 900 °C (1,650 °F) to 800 °C (1,470 °F), near

1134-400: A strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a magnet

1197-430: A strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization. The field strength at the poles of any permanent magnet depends very much on the shape and is usually well below the remanence strength of the material. Alnico alloys have some of the highest Curie temperatures of any magnetic material, around 800 °C (1,470 °F), although the maximal working temperature

1260-566: Is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic ). These include the elements iron , nickel and cobalt and their alloys, some alloys of rare-earth metals , and some naturally occurring minerals such as lodestone . Although ferromagnetic (and ferrimagnetic) materials are

1323-423: Is anisotropic, meaning that the magnetic direction of the grains is randomly oriented when initially made. Anisotropic alnico magnets are oriented by heating above a critical temperature and cooling in the presence of a magnetic field. Both isotropic and anisotropic alnico require proper heat treatment to develop optimal magnetic properties. Without it, alnico's coercivity is about 10 Oe, comparable to technical iron,

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1386-416: Is called the demagnetizing factor, and has a different value depending on the magnet's shape. For example, if the magnet is a sphere , then N d = 1 3 {\displaystyle N_{d}={\frac {1}{3}}} . The value of the demagnetizing factor also depends on the direction of the magnetization in relation to the magnet's shape. Since a sphere is symmetrical from all angles,

1449-443: Is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct north or south particles on opposing sides. If a bar magnet is broken into two pieces, in an attempt to separate the north and south poles, the result will be two bar magnets, each of which has both

1512-579: Is defined as the pole that, when the magnet is freely suspended, points towards the Earth's North Magnetic Pole in the Arctic (the magnetic and geographic poles do not coincide, see magnetic declination ). Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth's magnetic field. As a practical matter, to tell which pole of a magnet

1575-405: Is highest for alnico magnets at over 540 °C (1,000 °F), around 300 °C (570 °F) for ferrite and SmCo, about 140 °C (280 °F) for NIB and lower for flexible ceramics, but the exact numbers depend on the grade of material. An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid . When electric current flows through

1638-513: Is known, then the pole model gives the magnetic field H . Outside the magnet, the field B is proportional to H , while inside the magnetization must be added to H . An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism. Another model is the Ampère model, where all magnetization is due to the effect of microscopic, or atomic, circular bound currents , also called Ampèrian currents, throughout

1701-462: Is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization . An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel , which greatly enhances

1764-464: Is north and which is south, it is not necessary to use the Earth's magnetic field at all. For example, one method would be to compare it to an electromagnet , whose poles can be identified by the right-hand rule . The magnetic field lines of a magnet are considered by convention to emerge from the magnet's north pole and reenter at the south pole. The term magnet is typically reserved for objects that produce their own persistent magnetic field even in

1827-530: Is produced by conventional methods using resin bonded sand molds, which can be intricate and detailed, thereby allowing for complex shapes to be produced. The produced alnico magnet typically has a rough surface. This process has higher initial tooling costs for mold creation. Sintered alnico magnets are formed using powdered metal manufacturing methods. While sintering can also produce a range of shapes, it may not be as suitable for extremely intricate or detailed designs compared to casting. Most alnico produced

1890-476: Is specified by two properties: In SI units, the strength of the magnetic B field is given in teslas . A magnet's magnetic moment (also called magnetic dipole moment and usually denoted μ ) is a vector that characterizes the magnet's overall magnetic properties. For a bar magnet, the direction of the magnetic moment points from the magnet's south pole to its north pole, and the magnitude relates to how strong and how far apart these poles are. In SI units,

1953-400: Is subject to a torque. A wire in the shape of a circle with area A and carrying current I has a magnetic moment of magnitude equal to IA . The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M , with units A / m . It is a vector field , rather than just a vector (like the magnetic moment), because different areas in

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2016-476: Is typically limited to around 538 °C (1,000 °F). They are the only magnets that have useful magnetism even when heated red-hot . This property, as well as its brittleness and high melting point, results from the strong tendency toward order due to intermetallic bonding between aluminum and other constituents. They are also one of the most stable magnets if handled properly. Alnico magnets are electrically conductive, unlike ceramic magnets. Alnico 3 has

2079-410: Is used to generate the magnets. The pole-to-pole distance is on the order of 5 mm, but varies with manufacturer. These magnets are lower in magnetic strength but can be very flexible, depending on the binder used. For magnetic compounds (e.g. Nd 2 Fe 14 B ) that are vulnerable to a grain boundary corrosion problem it gives additional protection. Rare earth ( lanthanoid ) elements have

2142-903: The Curie point . There are local anisotropies of different orientations without an external field due to spontaneous magnetization. The precipitate structure is a "barrier" against magnetization changes, as it prefers few magnetization states requiring much energy to get the material into any intermediate state. Also, a weak magnetic field shifts the magnetization of the matrix phase only and is reversible. Alnico magnets are widely used in industrial and consumer applications where strong permanent magnets are needed. Examples are electric motors , electric guitar pickups , microphones , sensors , loudspeakers , magnetron tubes, and cow magnets . In many applications they are being superseded by rare-earth magnets , whose stronger fields (B r ) and larger energy products (B·H max ) allow smaller-size magnets to be used for

2205-515: The horseshoe magnet was invented by Daniel Bernoulli in 1743. A horseshoe magnet avoids demagnetization by returning the magnetic field lines to the opposite pole. In 1820, Hans Christian Ørsted discovered that a compass needle is deflected by a nearby electric current. In the same year André-Marie Ampère showed that iron can be magnetized by inserting it in an electrically fed solenoid. This led William Sturgeon to develop an iron-cored electromagnet in 1824. Joseph Henry further developed

2268-429: The 1990s, it was discovered that certain molecules containing paramagnetic metal ions are capable of storing a magnetic moment at very low temperatures. These are very different from conventional magnets that store information at a magnetic domain level and theoretically could provide a far denser storage medium than conventional magnets. In this direction, research on monolayers of SMMs is currently under way. Very briefly,

2331-595: The Earth's magnetic field would leave the iron permanently magnetized. This led to the development of the navigational compass , as described in Dream Pool Essays in 1088. By the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. A straight iron magnet tends to demagnetize itself by its own magnetic field. To overcome this,

2394-464: The Swiss network do not need the class B system SIGNUM and ZUB. Magnet A magnet is a material or object that produces a magnetic field . This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials , such as iron , steel , nickel , cobalt , etc. and attracts or repels other magnets. A permanent magnet

2457-689: The absence of an applied magnetic field. Only certain classes of materials can do this. Most materials, however, produce a magnetic field in response to an applied magnetic field – a phenomenon known as magnetism. There are several types of magnetism, and all materials exhibit at least one of them. The overall magnetic behavior of a material can vary widely, depending on the structure of the material, particularly on its electron configuration . Several forms of magnetic behavior have been observed in different materials, including: There are various other types of magnetism, such as spin glass , superparamagnetism , superdiamagnetism , and metamagnetism . The shape of

2520-660: The availability of magnetic materials to include various man-made products, all based, however, on naturally magnetic elements. Ceramic, or ferrite , magnets are made of a sintered composite of powdered iron oxide and barium / strontium carbonate ceramic . Given the low cost of the materials and manufacturing methods, inexpensive magnets (or non-magnetized ferromagnetic cores, for use in electronic components such as portable AM radio antennas ) of various shapes can be easily mass-produced. The resulting magnets are non-corroding but brittle and must be treated like other ceramics. Alnico magnets are made by casting or sintering

2583-401: The braking distance away from the signal, which is especially a problem with fast trains. To address this issue, Zugbeeinflussung ZUB has been introduced. Despite that Integra-Signum aims to prevent accidents, there was also an accident caused by it. In 1959, an Integra-Signum magnet mounted on a SBB-CFF-FFS RBe 540 EMU tore out a wooden sleeper on a level crossing near Gland , which led to

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2646-461: The demagnetizing factor only has one value. But a magnet that is shaped like a long cylinder will yield two different demagnetizing factors, depending on if it's magnetized parallel to or perpendicular to its length. Because human tissues have a very low level of susceptibility to static magnetic fields, there is little mainstream scientific evidence showing a health effect associated with exposure to static fields. Dynamic magnetic fields may be

2709-466: The derailment of the entire train at 125 km/h. Since 2008, Euro-Signum has been used for new and upgraded signal installations. Euro-Signum uses Eurobalises instead of magnets - these transmit Integra-Signum data in the additional Packet 44 (the typical ETCS telegram is left empty). This migration required installation of a "Eurobalise Transmission Module" on rolling stock that uses the Swiss network. Euro-Signum should not be confused with ETCS, which

2772-502: The development of rare-earth magnets in the 1970s, they were the strongest permanent magnet type. Other trade names for alloys in this family are: Alni, Alcomax, Hycomax, Columax , and Ticonal . The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the rest is Fe. The development of alnico began in 1931, when T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had

2835-416: The electromagnet into a commercial product in 1830–1831, giving people access to strong magnetic fields for the first time. In 1831 he built an ore separator with an electromagnet capable of lifting 750 pounds (340 kg). The magnetic flux density (also called magnetic B field or just magnetic field, usually denoted by B ) is a vector field . The magnetic B field vector at a given point in space

2898-455: The first magnetic compasses . The earliest known surviving descriptions of magnets and their properties are from Anatolia, India, and China around 2,500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia in the 1st century AD. In 11th century China, it was discovered that quenching red hot iron in

2961-403: The following ways: Magnetized ferromagnetic materials can be demagnetized (or degaussed) in the following ways: Many materials have unpaired electron spins, and the majority of these materials are paramagnetic . When the spins interact with each other in such a way that the spins align spontaneously, the materials are called ferromagnetic (what is often loosely termed as magnetic). Because of

3024-527: The magnet's properties; for instance, a higher number does not necessarily indicate a stronger magnet.) These classification numbers, while still in use, have been deprecated in favor of a new system by the MMPA, which designates Alnico magnets based on maximum energy product in megagauss-oersteds and intrinsic coercive force as kilo oersted, as well as an IEC classification system. Alnico magnets are produced by casting or sintering processes. Cast alnico

3087-400: The magnetic field emitted by the second magnet outside the track: Stop (home signals): positive - negative, concurrent Caution (distant signals): negative - positive, concurrent Caution (home signal): positive - positive, not concurrent Because Integra-Signum can only stop a train when it's "too late", i.e. after the red signal, it is not sufficient if there is an obstacle less than

3150-613: The magnetic field produced by the coil. Ancient people learned about magnetism from lodestones (or magnetite ) which are naturally magnetized pieces of iron ore. The word magnet was adopted in Middle English from Latin magnetum "lodestone", ultimately from Greek μαγνῆτις [λίθος] ( magnētis [lithos] ) meaning "[stone] from Magnesia", a place in Anatolia where lodestones were found (today Manisa in modern-day Turkey ). Lodestones, suspended so they could turn, were

3213-403: The magnetic moment is specified in terms of A·m (amperes times meters squared). A magnet both produces its own magnetic field and responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an external magnetic field, produced by a different source, it is subject to

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3276-437: The magnets can pinch or puncture internal tissues. Magnetic imaging devices (e.g. MRIs ) generate enormous magnetic fields, and therefore rooms intended to hold them exclude ferrous metals. Bringing objects made of ferrous metals (such as oxygen canisters) into such a room creates a severe safety risk, as those objects may be powerfully thrown about by the intense magnetic fields. Ferromagnetic materials can be magnetized in

3339-416: The material. For a uniformly magnetized cylindrical bar magnet, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of electric current flowing around the surface, with local flow direction normal to the cylinder axis. Microscopic currents in atoms inside the material are generally canceled by currents in neighboring atoms, so only the surface makes

3402-533: The only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism . Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron , which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in

3465-400: The power supply to the motors and applying the emergency brake. The locomotive's sending magnet is a strong permanent magnet, which induces a current in the receiving magnet in the middle of the track, if the signal's short-circuit contact is closed. The receiving magnet on the locomotive consists of two magnet field detectors, which detect the signal's state according to polarity and timing of

3528-639: The strength of Earth's magnetic field . Some alnico brands are isotropic and can be efficiently magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic , each having a preferred direction of magnetization , or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico's remanence ( B r ) may exceed 12,000  G (1.2  T ), its coercivity ( H c ) can be up to 1000 oersteds (80 kA/m), its maximum energy product (( BH ) max ) can be up to 5.5 MG·Oe (44 T·A/m). Therefore, alnico can produce

3591-502: The strongest. These cost more per kilogram than most other magnetic materials but, owing to their intense field, are smaller and cheaper in many applications. Temperature sensitivity varies, but when a magnet is heated to a temperature known as the Curie point , it loses all of its magnetism, even after cooling below that temperature. The magnets can often be remagnetized, however. Additionally, some magnets are brittle and can fracture at high temperatures. The maximum usable temperature

3654-429: The two main attributes of an SMM are: Most SMMs contain manganese but can also be found with vanadium, iron, nickel and cobalt clusters. More recently, it has been found that some chain systems can also display a magnetization that persists for long times at higher temperatures. These systems have been called single-chain magnets. Some nano-structured materials exhibit energy waves , called magnons , that coalesce into

3717-459: The way their regular crystalline atomic structure causes their spins to interact, some metals are ferromagnetic when found in their natural states, as ores . These include iron ore ( magnetite or lodestone ), cobalt and nickel , as well as the rare earth metals gadolinium and dysprosium (when at a very low temperature). Such naturally occurring ferromagnets were used in the first experiments with magnetism. Technology has since expanded

3780-473: The weakest types. The ferrite magnets are mainly low-cost magnets since they are made from cheap raw materials: iron oxide and Ba- or Sr-carbonate. However, a new low cost magnet, Mn–Al alloy, has been developed and is now dominating the low-cost magnets field. It has a higher saturation magnetization than the ferrite magnets. It also has more favorable temperature coefficients, although it can be thermally unstable. Neodymium–iron–boron (NIB) magnets are among

3843-421: The wire, a magnetic field is generated. It is concentrated near (and especially inside) the coil, and its field lines are very similar to those of a magnet. The orientation of this effective magnet is determined by the right hand rule . The magnetic moment and the magnetic field of the electromagnet are proportional to the number of loops of wire, to the cross-section of each loop, and to the current passing through

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3906-540: The wire. If the coil of wire is wrapped around a material with no special magnetic properties (e.g., cardboard), it will tend to generate a very weak field. However, if it is wrapped around a soft ferromagnetic material, such as an iron nail, then the net field produced can result in a several hundred- to thousandfold increase of field strength. Uses for electromagnets include particle accelerators , electric motors , junkyard cranes, and magnetic resonance imaging machines. Some applications involve configurations more than

3969-552: Was installed on the Swiss network later. By 2017 Switzerland had almost completed installing ETCS Level 1 throughout the railway network, however most trains continue to use Integra-Signum and ZUB (in the form of Euro-Signum and Euro-ZUB). Integra-Signum will also remain in service for a few years more on a small number of special lines; one of these is the Uetliberg railway line , which will first be converted from DC to AC electrification. From beginning 2018, new vehicles running on

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