Some consideration on the magnetoacoustic effect Nicolae Cretu Mihail Pop Physics Department Transilvania University Brasov-ROMANIA [email protected]@unitbv.ro;

Some consideration on Some consideration on the magnetoacoustic the magnetoacoustic

effecteffectNicolae CretuNicolae Cretu

Mihail PopMihail PopPhysics DepartmentPhysics Department

Transilvania University Brasov-ROMANIATransilvania University [email protected]@unitbv.ro; [email protected]; [email protected]

MFM image of magnetic MFM image of magnetic domains for Nidomains for Ni

H

The MAE and BN profiles (Y.H.Xu et al/J.Magn.Mag. The MAE and BN profiles (Y.H.Xu et al/J.Magn.Mag. Mat. 219(2000)166-172)Mat. 219(2000)166-172)

The profiles of MAE and BN The profiles of MAE and BN are in general quite are in general quite different since its different since its important contribution of important contribution of MAE is 90MAE is 90oo domain wall domain wall motion and of BN is 180motion and of BN is 180o o

domain wall motiondomain wall motion For NDE is important to For NDE is important to

explore the region with explore the region with H>Hmax, because in the H>Hmax, because in the presence of deffects we presence of deffects we need strong magnetic need strong magnetic forces which can produce forces which can produce the abrupt irreversible the abrupt irreversible magnetic domain wall magnetic domain wall motion.motion.

Ideea of our workIdeea of our work Is possible to obtain information about the internal deffects if we are Is possible to obtain information about the internal deffects if we are

able to produce the motion of the walls of the magnetic domains able to produce the motion of the walls of the magnetic domains pinning around the deffects.pinning around the deffects.

The necessary energy to produce wall mouvement of such domains The necessary energy to produce wall mouvement of such domains can be obtained from the stationary wave generated in the sample.can be obtained from the stationary wave generated in the sample.

The time-varying magnetic field has the same frequency as the The time-varying magnetic field has the same frequency as the eigenfrequencies of the sample. In this case the oscillations of eigenfrequencies of the sample. In this case the oscillations of magnetic field are correlated with the standing elastic wave from magnetic field are correlated with the standing elastic wave from the sample, and the domain wall motion become a forced oscillation. the sample, and the domain wall motion become a forced oscillation.

The exploration of the line shape, will give information about the The exploration of the line shape, will give information about the magnetoelastic interactions of the magnetic walls magnetoelastic interactions of the magnetic walls

The paper contain investigations on MAE in the standing wave state The paper contain investigations on MAE in the standing wave state of ferromagnetic carbon steel rods. The influence of the artificial of ferromagnetic carbon steel rods. The influence of the artificial defects on the shape of the velocity line is investigated.defects on the shape of the velocity line is investigated.

Experimental setupExperimental setup The magnetoelastic signal The magnetoelastic signal

was detected by a noncontact was detected by a noncontact method using a Bruel&Kjaer method using a Bruel&Kjaer Laser Velocity Transducer Laser Velocity Transducer Type 3544 (with excellent Type 3544 (with excellent results in velocity results in velocity measurements) attached to a measurements) attached to a linear preamplifier RFT Type linear preamplifier RFT Type 20027 connected to a USB 20027 connected to a USB acquisition board NI DAQ acquisition board NI DAQ Pad6015. The spectral Pad6015. The spectral decomposition of the signals, decomposition of the signals, the filtering and other data the filtering and other data processing were obtained processing were obtained using the Signal Analysis using the Signal Analysis Module in Lab View and TEST Module in Lab View and TEST POINT.POINT.

. . The shape of the amplitude of the velocity of MAE effect The shape of the amplitude of the velocity of MAE effect obtained by axial magnetostriction measurements for the first obtained by axial magnetostriction measurements for the first

fours eigenfrequenciesfours eigenfrequencies

The Lorentzian shape formulaThe Lorentzian shape formula

2 222 0

0 2 2 20

2

20 2

20

( ) ( )

2( )

2

A A

A

Linewidth obtained by fitting with the LorentzianLinewidth obtained by fitting with the Lorentzian

The change of the area of resonance plot of MAE for The change of the area of resonance plot of MAE for

the first four natural frequenciesthe first four natural frequencies

The influence of deffects (artificial created deffects)The influence of deffects (artificial created deffects)

CONCLUSIONSCONCLUSIONS

The sources of MAE are the domain The sources of MAE are the domain wall motion, the domain wall wall motion, the domain wall nucleation and annihilationnucleation and annihilation

The strength of MAE is proportional to The strength of MAE is proportional to the magnetostriction[]the magnetostriction[]

The main parameters which can give The main parameters which can give information for NDE are :frequency information for NDE are :frequency change; peak hight exploration; line change; peak hight exploration; line width change in the presence of width change in the presence of defects defects

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