![]() However, simply controlling the position usually leads to instability, due to the small time delays in the inductance of the coil and in sensing the position. The feedback circuit controls the electromagnet to try to keep the suspended object at the correct position. The position of the suspended object can be detected optically or magnetically, other schemes may sometimes be used. To reduce average power requirements, often the electromagnetic suspension is used only to stabilise the levitation, and the static lift against gravity is provided by a secondary permanent magnet system, often pulled towards a relatively inexpensive soft ferromagnetic material such as iron or steel. Therefore, a combination of permanent magnets with electromagnets is an optimal arrangement for levitation purposes. This field is easily manipulated by passing a varying current in the wire. The strength of this field can be greatly increased by placing a ferromagnetic material in the center of the coil. When a wire is coiled, this generated magnetic field is concentrated through the center of the coil. The strength of the generated magnetic field is proportional to the current through the wire. When a current passes through a wire, a magnetic field around that wire is generated. The first commercial Maglev train for routine service was opened in Birmingham, England in 1984, using electromagnetic suspension, and a linear induction motor for propulsion.īackground Electromagnets In 1979 the Transrapid electromagnetically suspended train carried passengers for a few months as a demonstration on a 908 m track in Hamburg for the first International Transportation Exhibition (IVA 79). In 1934 Hermann Kemper applied Bachelet’s concept to the large scale, calling it “monorail vehicle with no wheels attached.” He obtained Reich Patent number 643316 for his invention and is also considered by many to be the inventor of maglev. His invention was first intended to be applied to smaller mail carrying systems but the potential application to larger train-like vehicles is certainly apparent. He was awarded a patent in March 1912 for his “levitating transmitting apparatus” (patent no. Įmile Bachelet applied Earnshaw's theorem and the Braunbeck extension and stabilized magnetic force by controlling current intensity and turning on and off power to the electromagnets at desired frequencies. ![]() Braunbeck’s extension (1939) states that a system of permanent magnets must also contain diamagnetic material or a superconductor in order to obtain stable, static magnetic levitation or suspension. Likewise, due to limitations on permittivity, stable suspension or levitation cannot be achieved in a static magnetic field with a system of permanent magnets or fixed current electromagnets. Samuel Earnshaw was the one to discover in 1839 that “a charged body placed in an electrostatic field cannot levitate at stable equilibrium under the influence of electric forces alone”. The application of magnetic levitation is most commonly known for its role in Maglev trains. It also avoids wear and has very low maintenance requirements. Magnetic levitation technology is important because it reduces energy consumption, largely reduces friction. Many systems use magnetic attraction pulling upwards against gravity for these kinds of systems as this gives some inherent lateral stability, but some use a combination of magnetic attraction and magnetic repulsion to push upwards. In EMS a feedback loop which continuously adjusts one or more electromagnets to correct the object's motion is used to cancel the instability. Although static fields cannot give stability, EMS works by continually altering the current sent to electromagnets to change the strength of the magnetic field and allows a stable levitation to occur. In these kinds of fields an unstable equilibrium condition exists. ![]() In most cases the levitation effect is mostly due to permanent magnets as they don't have any power dissipation, with electromagnets only used to stabilize the effect.Īccording to Earnshaw's Theorem a paramagnetically magnetised body cannot rest in stable equilibrium when placed in any combination of gravitational and magnetostatic fields. Magnetic levitation with a feedback loop.Įlectromagnetic suspension ( EMS) is the magnetic levitation of an object achieved by constantly altering the strength of a magnetic field produced by electromagnets using a feedback loop. Suspension of objects through a feedback loop of magnetic field strength changes Floating globe.
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