Magnetostriction is a property of ferromagnetic materials that causes them to change their shape when subjected to a
magnetic fieldMagnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges...
. The effect was first identified in 1842 by James Joule when observing a sample of
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
.
(Compare with electrostrictionElectrostriction is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. - Explanation :...
)
This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
Internally, ferromagnetic materials have a structure that is divided into
domains, each of which is a region of uniform magnetic polarization.
Magnetostriction is a property of ferromagnetic materials that causes them to change their shape when subjected to a
magnetic fieldMagnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges...
. The effect was first identified in 1842 by James Joule when observing a sample of
nickelNickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
.
(Compare with electrostrictionElectrostriction is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. - Explanation :...
)
This effect can cause losses due to frictional heating in susceptible ferromagnetic cores.
Explanation
Internally, ferromagnetic materials have a structure that is 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 cause 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 thus related to magnetostriction: the Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a
torqueTorque, also called moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
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
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
from positive to negative when exposed to magnetic fields of approximately 40000 A/m (500
oerstedOersted is the unit of magnetizing field in the CGS system of units.-History:...
s).
On magnetization a magnetic material undergoes changes in volume which are small - of the order 10
-6.
Magnetostrictive materials
Magnetostrictive materials can convert magnetic energy into
kinetic energyThe kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its...
, or the reverse, and are used to build
actuatorAn actuator is a mechanical device for moving or controlling a mechanism or system. An actuator typically is a mechanical device that takes energy, usually created by air, electricity, or liquid, and converts that into some kind of motion....
s and
sensorA sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass...
s. 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
saturationSeen in some magnetic materials, saturation is the state reached when an increase in applied external magnetizing field H cannot increase the magnetization of the material further, so the total magnetic field B levels off...
value. The effect is responsible for the familiar "
electric humElectric hum, mains hum, or power line hum is an audible oscillation of alternating current at the frequency of the mains electricity, which is usually 50 Hz or 60 Hz, depending on the local electric utility configuration...
" which can be heard near
transformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
s and high power electrical devices (depending on country, either 100 (=2*50) or 120 (=2*60)
hertzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
, 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-DTerfenol-D is an alloy of the formula Tb Dy Fe, developed in the 1950's at the Naval Ordnance Laboratory in America. It is named after terbium, iron , Naval Ordnance Laboratory , and the D comes from dysprosium....
, (Ter for
terbiumTerbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
, Fe for
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
, NOL for
Naval Ordnance LaboratoryThe Naval Ordnance Laboratory , now disestablished, formerly located in White Oak, Maryland was the site of considerable work that had practical impact upon world technology. The White Oak site of NOL has now been taken over by the Food and Drug Administration.-History:The U.S...
, and D for
dysprosiumDysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
). Terfenol-D,
x1-x, exhibits about 2,000 microstrains in a field of 2 kOe (160 kA/m) at room temperature and is the most commonly used engineering magnetostrictive material
See also
- Electrostriction
Electrostriction is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field. - Explanation :...
- Piezoelectricity
Piezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is closely related to a change of polarization density within the material's volume...
- Piezomagnetism
Piezomagnetism is a phenomenon observed in some antiferromagnetic crystals. It is characterised by a linear coupling between the system's magnetic polarisation and mechanical strain...
- SoundBug
Soundbug is a small device that can turn any resonant flat surface into a distributed mode loudspeaker , allowing one to listen to media devices without using traditional speakers. Devices such as mp3 players, cd players, and computers can be used, by plugging the Soundbug into any headphone jack...
- FeONIC
FeONIC is a commercial company specialising in the design and development of Magnetostrictive Audio products as a spin off from Hull University.- Technology :...
Developer of Audio products using Magnetostriction
External links