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Barkhausen effect 1
Barkhausen effect
Magnetization (J) or flux density (B) curve as a function of magnetic field intensity
(H) in ferromagnetic material. The inset shows Barkhausen jumps.
Domain wall motion with a Barkhausen jump
The Barkhausen effect is a name given to
the noise in the magnetic output of a
ferromagnet when the magnetizing force
applied to it is changed. Discovered by
German physicist Heinrich Barkhausen in
1919, it is caused by rapid changes of size of
magnetic domains (similarly magnetically
oriented atoms in ferromagnetic materials).
Barkhausen's work in acoustics and
magnetism led to the discovery, which
provided evidence that magnetization affects
whole domains of a ferromagnetic material,
rather than individual atoms alone. TheBarkhausen effect is a series of sudden
changes in the size and orientation of
ferromagnetic domains, or microscopic
clusters of aligned atomic magnets (spins),
that occurs during a continuous process of
magnetization or demagnetization. The
Barkhausen effect offered direct evidence
for the existence of ferromagnetic domains,
which previously had been postulated
theoretically. Heinrich Barkhausendiscovered that a slow, smooth increase of a
magnetic field applied to a piece of
ferromagnetic material, such as iron, causes
it to become magnetized, not continuously
but in minute steps.
Barkhausen noise
A coil of wire wound on the ferromagnetic
material can demonstrate the sudden,
discontinuous jumps in magnetization. The
sudden transitions in the magnetization of
the material produce current pulses in the
coil. These can be amplified to produce a series of clicks in a loudspeaker. This sounds as crackle, complete with
skewed pulses which sounds like candy being unwrapped, Rice Krispies, or a pine log fire. Hence the name
Barkhausen noise. Similar effects can be observed by applying only mechanical stresses (e.g. bending) to the
material placed in the detecting coil.
These magnetization jumps are interpreted as discrete changes in the size or rotation of ferromagnetic domains.
Some microscopic clusters of atomic spins aligned with the external magnetizing field increase in size by a suddenreversal of neighbouring spins; and, especially as the magnetizing field becomes relatively strong, other whole
http://en.wikipedia.org/w/index.php?title=Spin_%28physics%29http://en.wikipedia.org/w/index.php?title=Rice_Krispieshttp://en.wikipedia.org/w/index.php?title=Loudspeakerhttp://en.wikipedia.org/w/index.php?title=Coilhttp://en.wikipedia.org/w/index.php?title=Demagnetizationhttp://en.wikipedia.org/w/index.php?title=Magnetizationhttp://en.wikipedia.org/w/index.php?title=Spin_%28physics%29http://en.wikipedia.org/w/index.php?title=Atomhttp://en.wikipedia.org/w/index.php?title=Magnetismhttp://en.wikipedia.org/w/index.php?title=Acousticshttp://en.wikipedia.org/w/index.php?title=Magnetic_domainhttp://en.wikipedia.org/w/index.php?title=Heinrich_Barkhausenhttp://en.wikipedia.org/w/index.php?title=Ferromagnethttp://en.wikipedia.org/w/index.php?title=File%3ABarkhausensprung.gifhttp://en.wikipedia.org/w/index.php?title=File%3ABarkhausen_jumps.svg -
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Barkhausen effect 2
domains suddenly turn into the direction of the external field. Simultaneously, due to exchange interactions the spins
tend to align themselves with their neighbours. The tension between the various pulls creates avalanching, where a
group of neighbouring domains will flip in quick succession to align with the external field. So the material
magnetizes neither gradually nor all at once, but in fits and starts.
Practical use
A set-up for non-destructive testing of ferromagnetic materials: green -
magnetising yoke, red - inductive sensor, greysample under test.
The amount of Barkhausen noise for a given
material is linked with the amount of
impurities, crystal dislocations, etc. and can
be a good indication of mechanical
properties of such a material. Therefore, the
Barkhausen noise can be used as a method
of non-destructive evaluation of the
degradation of mechanical properties in
magnetic materials subjected to cyclic
mechanical stresses (e.g. in pipeline
transport) or high-energy particles (e.g.
nuclear reactor) or materials such as
high-strength steels which may be subjected to damage from grinding. Schematic diagram of a simple
non-destructive set-up for such a purpose is shown on the right.
Barkhausen noise can also indicate physical damage in a thin film structure due to various nanofabrication processes
such as reactive ion etching or using an ion milling machine.[1]
References
External links
Barkhausen Effect (http://www.youtube.com/watch?v=iWdbRX5Nyg4) Video demonstrating the effect
Barkhausen Noise grinding burn and heat treat defect monitoring (http://www.stresstechgroup.com/content/
en/1034/1113/Barkhausen Noise Analysis.html)
http://www.stresstechgroup.com/content/en/1034/1113/Barkhausen%20Noise%20Analysis.htmlhttp://www.stresstechgroup.com/content/en/1034/1113/Barkhausen%20Noise%20Analysis.htmlhttp://www.youtube.com/watch?v=iWdbRX5Nyg4http://en.wikipedia.org/w/index.php?title=Ion_milling_machinehttp://en.wikipedia.org/w/index.php?title=Reactive_ion_etchinghttp://en.wikipedia.org/w/index.php?title=Nanofabricationhttp://en.wikipedia.org/w/index.php?title=Thin_filmhttp://en.wikipedia.org/w/index.php?title=Nuclear_reactorhttp://en.wikipedia.org/w/index.php?title=High-energy_particlehttp://en.wikipedia.org/w/index.php?title=Pipeline_transporthttp://en.wikipedia.org/w/index.php?title=Pipeline_transporthttp://en.wikipedia.org/w/index.php?title=Non-destructive_evaluationhttp://en.wikipedia.org/w/index.php?title=Mechanical_propertieshttp://en.wikipedia.org/w/index.php?title=Mechanical_propertieshttp://en.wikipedia.org/w/index.php?title=Dislocationhttp://en.wikipedia.org/w/index.php?title=File%3ABarkhausen_sensor.svghttp://en.wikipedia.org/w/index.php?title=Sensorhttp://en.wikipedia.org/w/index.php?title=Yoke -
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Article Sources and Contributors 3
Article Sources and ContributorsBarkhausen effect Source: http://en.wikipedia.org/w/index.php?oldid=561929401 Contributors: Andreasmperu, BWDuncan, Hydrargyrum, K Eliza Coyne, Karol Langner, LightYear, Meisam,
Mild Bill Hiccup, Mmarre, Oli Filth, Pearle, Pegua, Physicistjedi, Pieter Kuiper, Pinestone, Pixelface, Rayc, RockMagnetist, Rossiya, Slawojarek, Slimey.limey, Stannered, The wub, Tone,
Topbanana, Zureks, 19 anonymous edits
Image Sources, Licenses and ContributorsImage:Barkhausen jumps.svg Source: http://en.wikipedia.org/w/index.php?title=File:Barkhausen_jumps.svg License: Creative Commons Attribution-ShareAlike 3.0 Unported Contributors:
User:Stannered
Image:Barkhausensprung.gif Source: http://en.wikipedia.org/w/index.php?title=File:Barkhausensprung.gifLicense: Public Domain Contributors: Denkwrdig, Denniss, Kersti Nebelsiek, Kri,
Mattes, Pieter Kuiper
Image:Barkhausen sensor.svg Source: http://en.wikipedia.org/w/index.php?title=File:Barkhausen_sensor.svg License: Creative Commons Attribution-ShareAlike 3.0 Unported Contributors:
User:Stannered
License
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