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15 May 2005

Volume 97, Issue 10, Articles (10xxxx)

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back to top Computational Magnetism

Application of magnetostriction measurements for the computation of deformation in electrical steel

Tom Hilgert, Lieven Vandevelde, and Jan Melkebeek

J. Appl. Phys. 97, 10E101 (2005); http://dx.doi.org/10.1063/1.1847951 (3 pages) | Cited 6 times

Online Publication Date: 6 May 2005

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In this paper, a method is presented to calculate the deformation of electrical steel due to magnetic forces and magnetostriction by using the finite element method. The magnetostrictive properties of the steel are determined experimentally in a small single-sheet tester with strain gauges fitted on the sheet. This method is applied to an inductor with a small airgap. The results from the computations are verified with measurements on the test object.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

The governing electrodynamic equations of electromagnetic acoustic transducers

R. Jafari-Shapoorabadi, A. Konrad, and A. N. Sinclair

J. Appl. Phys. 97, 10E102 (2005); http://dx.doi.org/10.1063/1.1851393 (3 pages) | Cited 2 times

Online Publication Date: 6 May 2005

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This paper presents the governing electrodynamic equations of electromagnetic acoustic transducers (EMATs) and extends them to the derivation of the magnetic- and acoustic-field equations in terms of the magnetic vector potential (MVP) and the acoustic wave particle displacement vector (PDV), respectively. It also provides formulations for calculating forces and current densities in the case of two-dimensional (2D) models of EMAT configurations in Cartesian coordinates. Existing methods solve the governing electrodynamic equations for field quantities to analyze EMATs. However, they ignore skin and proximity effects and rely on simple 2D configurations for EMAT coils. Taking into account skin and proximity effects in complex 2D EMAT coil configurations requires the application of the finite element method (FEM). The FEM can be applied to solve the equations stated in terms of the MVP and PDV in the modeling of EMATs. These formulations and expressions facilitate the development and presentation of the FEM for the modeling and analysis of EMATs.
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43.38.Dv
43.60.Qv
02.70.Dh Finite-element and Galerkin methods

Single sheet tester efficiency macromagnetic analysis

E. Antonelli, E. Cardelli, and A. Faba

J. Appl. Phys. 97, 10E103 (2005); http://dx.doi.org/10.1063/1.1851956 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2005

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We present here a macromagnetic numerical analysis of single sheet testers, as measuring systems for grain oriented laminated Si–Fe steels. The modeling is in time domain, and hysteresis, anisotropy and nonlinearity are suitably taken into account. The curves B(H), and the specific losses, as measured by the magnetic frame, are predicted, and compared with the local “true” values. The numerical analysis allows us to extrapolate some remarks about the efficiency and the accuracy of the measuring frame versus the applied magnetic field, the induced magnetic induction, and the rating frequency.
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07.55.-w Magnetic instruments and components
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Three-dimensional (3D) eddy current time-domain integral equation with Coulomb gauge condition

O-Mun Kwon, M. V. K. Chari, and Sheppard J. Salon

J. Appl. Phys. 97, 10E104 (2005); http://dx.doi.org/10.1063/1.1852293 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2005

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A method is proposed to find eddy currents in massive bodies with relative motion. An integral equation solution in the time domain is proposed in this paper. This method can also be applied to magnetic-resonance imaging magnets to study transient effects occurring due to the sudden application of current. These effects may include perturbations of the homogeneity of the main field or the far field.
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84.50.+d Electric motors
85.70.Ay Magnetic device characterization, design, and modeling
02.30.Rz Integral equations

Comparison between three-dimensional (3D) equivalent magnetic circuit network method and 3D finite element method for magnetic-field computation

Yon Do Chun, Jae-Eung Oh, Yasushi Fujishima, Shinji Wakao, Ju Lee, and Yun-Hyun Cho

J. Appl. Phys. 97, 10E105 (2005); http://dx.doi.org/10.1063/1.1853195 (3 pages) | Cited 2 times

Online Publication Date: 6 May 2005

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In this article, in order to investigate the merits of three-dimensional (3D) equivalent magnetic circuit network (EMCN) method, a 3D standard benchmark model proposed by the Institute of Electrical Engineers of Japan is analyzed. We also examine the accuracy of analysis results, the computer storage, and the computation time through the systematical comparison between 3D EMCN method and 3D finite element method based on hexahedral edge element. The incomplete Cholesky conjugate gradient method was selected for the solver. From the results, we can confirm the usefulness of 3D EMCN method.
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85.70.Ay Magnetic device characterization, design, and modeling
84.30.Bv Circuit theory
02.70.Dh Finite-element and Galerkin methods
02.60.-x Numerical approximation and analysis

Modeling of giant magnetoresistance isolator for high speed digital data transmission utilizing spin valves

S. Park, J. Kim, and S. Jo

J. Appl. Phys. 97, 10E106 (2005); http://dx.doi.org/10.1063/1.1853913 (3 pages)

Online Publication Date: 6 May 2005

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Giant magnetoresistance isolator was modeled for effective transmission of high speed digital data, and the output voltage characteristics depending on pulse width of input signal, inductor coil turn, and existence of external circuit of the planar inductor were investigated in time domain. The planar coil was modeled as a lumped element R, L, C circuit and the coil current was calculated using SPICE. The corresponding magnetic field was substituted to the measured magnetoresistance-H curve to obtain the resistance values of the spin valves, which were used to obtain the output voltage wave form of the isolator. Effective maximum transmission speed of 250 Mbit/s was estimated. Even though the coil current wave form was much deformed with damping, the transmitted output voltage wave form was very close to the rectangular wave form of the input signal due to hysteretic characteristics of the spin valves.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Ay Magnetic device characterization, design, and modeling
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A method for an accurate T1 relaxation-time measurement compensating B1 field inhomogeneity in magnetic-resonance imaging

Hiroaki Mihara, Masaki Sekino, Norio Iriguchi, and Shoogo Ueno

J. Appl. Phys. 97, 10E107 (2005); http://dx.doi.org/10.1063/1.1857393 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2005

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Two-point gradient echo methods are practical means for estimating T1 value in magnetic-resonance (MR) imaging. Meanwhile, the inhomogeneity of the transmitted B1 field and the imperfect slice profile severely distorts the estimated T1 value. We propose a method for an accurate T1 measurement compensating the inhomogeneity of the B1 field and the effects of the imperfect slice profile. Three MR images of a whole human brain were obtained by multisliced spoiled gradient echo sequences on a 1.5-T scanner with different repetition times and flip angles to calculate the quantitative T1 maps. The histograms of the T1 maps showed two distinguishable peaks of the white matter (672.9±15.5 ms) and the gray matter (921.1±24.7 ms) of the human brain. The results indicate that the T1 value was properly estimated compensating the B1 field inhomogeneity and the slice profile imperfection. The proposed method is applicable to images obtained on any scanners with different parameters, because the method needs neither the information of the flip angle calibrations nor the phantom data to compensate the B1 field inhomogeneity.
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87.61.Tg Clinical applications
87.10.-e General theory and mathematical aspects
87.50.C- Static and low-frequency electric and magnetic fields effects

Evaluation of the mechanical deformation in incompressible linear and nonlinear magnetic materials using various electromagnetic force density methods

Se-Hee Lee, Xiaowei He, Do-Kyung Kim, Shihab Elborai, Hong-Soon Choi, Il-Han Park, and Markus Zahn

J. Appl. Phys. 97, 10E108 (2005); http://dx.doi.org/10.1063/1.1859771 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2005

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Mechanical deformation in incompressible linear and nonlinear magnetic materials was evaluated using various conventional electromagnetic volume and surface force density methods. These conventional force density methods are the Maxwell stress tensor method, Korteweg-Helmholtz force density method (KH), magnetic charge method, magnetizing current method, and Kelvin force density method (KV). The total force values obtained using these different force density methods were found to be the same and equal to the total force using the principle of virtual work, but the distribution of force density values calculated using the given force density methods was found to be different from each other. Using the given five force density methods, the mechanical deformations were evaluated and compared to one another. The KH and KV in incompressible material were shown to give the same mechanical deformation by employing the finite element method (FEM), verifying the theoretical equivalence. To implement the KV, the derivative of magnetic field intensity with respect to the geometrical position was calculated using a linear shape function of FEM along with the nodal field values in each element. A magnetic systems was tested to compare the mechanical deformation in linear and nonlinear magnetic materials.
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75.40.Mg Numerical simulation studies
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Finite element method-based calculation of the theoretical limit of sensitivity for detecting weak magnetic fields in the human brain using magnetic-resonance imaging

Tomohisa Hatada, Masaki Sekino, and Shoogo Ueno

J. Appl. Phys. 97, 10E109 (2005); http://dx.doi.org/10.1063/1.1861553 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2005

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Detection of weak magnetic fields induced by neuronal electrical activities using magnetic-resonance imaging is a potentially effective method for functional imaging of the brain. In this study, we performed a numerical analysis of the theoretical limit of sensitivity for detecting weak magnetic fields induced in the human brain. The limit of sensitivity was estimated from the intensities of signal and noise in the magnetic-resonance images. The signal intensity was calculated with parameters which are commonly used in measurements of the human brain. The noise due to the head was calculated using the finite element method. The theoretical limit of sensitivity was approximately 10−8 T.
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87.61.-c Magnetic resonance imaging
87.10.-e General theory and mathematical aspects
87.18.Sn Neural networks and synaptic communication
87.19.L- Neuroscience
02.70.Dh Finite-element and Galerkin methods
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