|Oct26-09, 01:34 AM||#1|
Using a magnetic core for an electromagnet
I would like to know what would happen if you used a permanent magnet for the core of an electromagnet, instead of the standard ferromagnetic core? Can you increase the magnetic field strength of the permanent magnet by putting current through the coil? Also, could you effectively cancel the permanent magnet's field by reversing the current's direction?
|Oct26-09, 10:59 AM||#2|
Your question is related to Magnetic Hysteresis term in electrical engineering. Hysteresis is associated with the inherent memory of ferromagnetic materials that allows for the creation of permanent magnets. After a magnetic field is applied to a ferromagnet, some of the magnetization is retained, even after the applied field is turned off. So even though you brought the applied field back to its original starting point, the material has not returned to its original state. At the microscopic level, there is a force that tends to oppose the realignment of the microscopic magnets. The dependence of the material’s state on its past history is known as hysteresis.
In addition to memory effects, hysteresis also causes energy loss. When you apply a magnetic field that realigns the microscopic magnets, a frictional effect occurs, and energy is lost to heat. Therefore magnetic hysteresis effects can be useful or non-useful in practice regarding the role of magnetic material which used in construction of electromagnetic systems.
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|Oct26-09, 11:43 AM||#3|
[QUOTE=MaJiK9021;2410872 Also, could you effectively cancel the permanent magnet's field by reversing the current's direction? [/QUOTE]
If you put a permanent magnet in a coil with say H = 400,000 amp-turns per meter, the permanent magnet will be reversed. It is more difficult to cancel the field but it can be done. You will need to put the permanent magnet in a flux integrating coil (attached to an op-amp) and cycle the H amp-turns until the flux integrator output is zero.
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