Everything about Magnetostriction totally explained
Magnetostriction is a property of
ferromagnetic materials that causes them to change their shape when subjected to a
magnetic field. The effect was first identified in
1842 by
James Joule when observing a sample of
nickel.
(Compare with electrostriction)
This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
Explanation
Internally, ferromagnetic materials have a structure that's divided into
domains, each of which is a region of uniform magnetic polarization. When a magnetic field is applied, the boundaries between the domains shift and the domains rotate, both these effects causing a change in the material's dimensions.
The reciprocal effect, the change of the susceptibility of a material when subjected to a mechanical stress, is called the
Villari effect. Two other effects are related to magnetostriction: the
Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a
torque and the
Wiedemann effect is the twisting of these materials when a helical magnetic field is applied to them.
The
Villari Reversal is the change in sign of the magnetostriction of
iron from positive to negative when exposed to magnetic fields of approximately 40000 A/m (500
oersteds).
On magnetization a magnetic material under goes changes in volume which are small - of the order 10
-6.
Magnetostrictive materials
Magnetostrictive materials can convert magnetic energy into
kinetic energy, or the reverse, and are used to build
actuators and
sensors. The property can be quantified by the magnetostrictive coefficient,
L, which is the fractional change in length as the magnetization of the material increases from zero to the
saturation value. The effect is responsible for the familiar "
electric hum" which can be heard near
transformers and high power electrical devices (depending on country, either 50 or 60
hertz, plus
harmonics).
Cobalt exhibits the largest room temperature magnetostriction of a pure element at 60
microstrain. Among alloys, the highest known magnetostriction is exhibited by
Terfenol-D, (Ter for
terbium, Fe for
iron, NOL for
Naval Ordnance Laboratory, and D for
dysprosium). Terfenol-D,
x1-x, exhibits about 2000 microstrains in a field of 2 kOe (160 kA/m) at room temperature and is the most commonly used engineering magnetostrictive material
(External Link
).
Further Information
Get more info on 'Magnetostriction'.
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