ce520 lec #5 magnetostrictive

8/17/2019 CE520 Lec #5 Magnetostrictive

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CE 520: Introduction to Smart Structures Technologies

Magnetostrictive Materials

Hoon Sohn

Department of Civil and Environmental Engineering

Korea Advanced Institute of Science and Technology

Daejeon, Korea(Lecture #5)


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2Civil and Environmental Engineering Department CE520: Smart Structures Technologies

Working Principle of Magnetostrictive Material

The material may be thought of as an ellipse where the magnetizationruns along the longest axis. Applying a field to the ellipse has theresult of rotating the magnetization in the direction of the field andsubsequently observing a change in shape.


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Magnetostrictive Materials

Magnetostrictive materials are broadly defined asmaterials that undergo a change in shape due to changein the magnetization state of the material.

Nearly all ferromagnetic materials exhibit a change inshape resulting from magnetization change.

– In most common materials, nickel, iron, and cobalt, the change inlength is on the order of 10 parts per million (ppm). But, the changein volume is very small.

– This type of magnetostriction has been termed Joulemagnetostriction after James P. Joule’s discovery in the 1850’s.


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Discovery of Giant Magnetostrictive Materials

The engineering era of magnetostrictive materials began

with the discovery of giant (1000’s of ppm)magnetostriction in rare earth alloys during the 1960’s byA.E. Clark and others. – In the 1960s the rare-earth elements terbium (Tb) and dysprosium

(Dy) were found to have between 100 and 10,000 times themagnetostrictive strains found in nickel alloys. However becausethis property only occurs at cryogenic (low) temperatures,applications operating at ambient temperature and above were notpossible.

What researchers were looking for was a material whichwould – operate at high temperatures, have a large magnetostrictive strain

but would only require a low magnetic field.


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Terfenol-D Magnetostrictive Material

The culmination of research into an engineering magnetostrictive

alloy was Terfenol-D, a specially formulated allow of Terbium,Dysprosium, and Iron that exhibits large magnetostriction atroom temperature and relatively small applied fields.

The resulting alloy Tb.27Dy.73Fe1.95 (commercially known asTerfenol-D) is at present the most widely used magnetostrictive

material. Tb and Dy generate the magnetostriction, and Fe stabilizes

magnetic ordering at ambient temperature (high Curietemperature).

Terfenol is capable of strains as high as 1500ppm and, since the

1980's, has been a commercially available material forapplication in many fields.

Change in shape is completely elastic - no fatigue.

Response of material is in microseconds, which allows for broadrange of frequencies / applications.


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Joule, Villari, Wiedemann and Matteuii Effects

Joule Effect: The change in dimension due to a change in

magnetization (similar to converse piezoelectric effect).

Villari Effect: Stress produced a change in magnetization (similarto direct piezoelectric effect).

Wiedemann Effect: Twisting in the rod due to a helical magneticfield.

Metteuii (or inverse Wiedemann) Effect: Twisting deformation

produced a helical magnetic field.


7/167Civil and Environmental Engineering Department CE520: Smart Structures Technologies

Classical Magnetostrictive Materials

Low MagnetostrictionStructural (strong)Low Curie temp

High MagnetostrictionBrittle

High Curie Temp

Ni: 50 ppm ( L/L) Terfenol-D:1800 ppm ( L/L)

Fe-Ga: 200 – 400 ppm



Comparison of Terfenol-D and PZT

Properties Terfenol-D PZT Ni-alloy

Saturation Strain (ppm)Coupling CoefficientDensity( g/cm3)Frequency Range

15000.759.25DC to KHz

1000.657.6KHz to MHz

400.28.7DC to KHz

1 m rod

1 m rod

1 m rod



TERFENOL-D Applications

High Frequency

Applications

15,000-30,000HZ

Low Frequency

Applications

10-200HZ

Mid Frequency

Applications

250-10,000HZ



Terfenol-D Transducer Design



Hysteresis and Constitutive Nonlinearity



The Effect of Compressive Preload

Magnetostriction and magnetization of Terfenol-D at room temperaturefor compressive preload from 4 to 39 MPa



Robust Control Design considering SaturationNonlinearity and Hysteresis



Wiedemann Effect

• Wiedemann effect is creation of a torsional deformation when longitudinal

and circumferential magnetic forces are applied to a ferromagnetic rod.

• In the presence of the longitudinal magnetic field, introduction of an

alternating current through the rod generates the magnetic force in the

circumferential direction.

• The resultant magnetic fields makes the rod twist. That means torsional

stresses can be generated by this effect.



Inverse Wiedmann (Metteuii) Effect

• Inverse Wiedemann effect is the reciprocal effect of Wiedemann

effect.

• When a magnetostrictive rod is subjected to a torque in the presenceof the longitudinal magnetic field, the rod creates a magnetic field in

the direction of helix.

• The change of the magnetic field in the direction of helix produces

current through the longitudinal direction.



Whispering Windows

• Low mechanical Q of T-D givesfull bandwidth for audiofrequencies

• Turns windows into soundproducing devices

• Allows audio message to beadded to a retail visual display

• Combining audio with the visualdisplay increases messageeffectiveness

ce520 lec #5 magnetostrictive

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