• Progress in Superconductivity and Cryogenics
• /
• v.16 no.1
• /
• pp.27-31
• /
• 2014

2G HTS tapes are widely used for various electric machines. In addition, stacked or parallel connected HTS tapes are essentially used to raise transport current level for large capacity electric machines. Therefore, critical current characteristic of stacked tapes need to be studied. Recently developed 2G HTS tapes are fabricated with various defects doping so that tapes possess pinning center to improve the critical current characteristic. During this process, the critical current is determined minimum value in not perpendicular magnetic field but a specific magnetic field angle according to the reported research. However, the effects of magnetic field angle to critical current of multi-stacked 2G HTS tapes have not been examined. In this paper, field coil which is a race-track coil wound by using an HTS tape with iron-core was fabricated to apply angle adjustable magnetic field to the 2G HTS tape samples. We measured critical current of single and multi-stacked two tapes that have different characteristic depending on various magnetic field angle and magnitude in liquid nitrogen environment. Furthermore, results of single and multi-stacked tapes were compared and analyzed.

• Proceedings of the KIEE Conference
• /
• 2003.07b
• /
• pp.961-963
• /
• 2003

Magnetization losses of HTS depend strongly on the orientation of external magnetic field because of anisotropy characteristics. For parallel and perpendicular magnetic field, analytical models to calculate the loss are well known but there is no analytical model for magetic fields which are applied to surface of HTS with arbitrary angle. In this paper, magnetization losses are measured for various incidence angles($15^{\circ}$, $35^{\circ}$, $45^{\circ}$, $60^{\circ}$) and compared with parallel and perpendicular loss. As a result, magnetization losses in HTS are strongly affected by perpenducular magnetic field component of external magnetic field.

• Investigative Magnetic Resonance Imaging
• /
• v.22 no.4
• /
• pp.218-228
• /
• 2018

Purpose: The objective of this study is to determine the effect of physical changes on MR temperature imaging at 7.0T and to examine proton-resonance-frequency related changes of MR phase images and T1 related changes of MR magnitude images, which are obtained for MR thermometry at various magnetic field strengths. Materials and Methods: An MR-compatible capacitive-coupled radio-frequency hyperthermia system was implemented for heating a phantom and swine muscle tissue, which can be used for both 7.0T and 3.0T MRI. To determine the effect of flip angle correction on T1-based MR thermometry, proton resonance frequency, apparent T1, actual flip angle, and T1 images were obtained. For this purpose, three types of imaging sequences are used, namely, T1-weighted fast field echo with variable flip angle method, dual repetition time method, and variable flip angle method with radio-frequency field nonuniformity correction. Results: Signal-to-noise ratio of the proton resonance frequency shift-based temperature images obtained at 7.0T was five-fold higher than that at 3.0T. The T1 value increases with increasing temperature at both 3.0T and 7.0T. However, temperature measurement using apparent T1-based MR thermometry results in bias and error because B1 varies with temperature. After correcting for the effect of B1 changes, our experimental results confirmed that the calculated T1 increases with increasing temperature both at 3.0T and 7.0T. Conclusion: This study suggests that the temperature-induced flip angle variations need to be considered for accurate temperature measurements in T1-based MR thermometry.

• Progress in Superconductivity and Cryogenics
• /
• v.7 no.3
• /
• pp.34-38
• /
• 2005

Multi-stacked HTS tapes are needed to conduct large current in the power application. In this paper, magnetization losses of the multi-stacked YBCO coated conductor and the BSCCO tape have been measured and compared. Magnetization losses of single tape, 2-stacked, 3-stacked and 4-stacked HTS tapes have been presented in this paper. Multi-stacked tapes have been fabricated using face-to-face type stacking method. Measurements of magnetization loss were performed under various angle of external magnetic field to consider the anisotropic characteristics of HTS tapes. Test results show that loss density per unit volume decreased for both YBCO coated conductors and BSCCO tapes when the stacking number of tapes is increased. The magnetization losses of YBCO CC are larger than those of BSCCO tapes when the external magnetic field is increased.

• Journal of Magnetics
• /
• v.15 no.1
• /
• pp.17-20
• /
• 2010

The relationship between ferromagnet anisotropic magnetization and the antiferromagnet atomic spin configuration was investigated for various angles of the uniaxial deposition magnetic field of the FeMn layer in the Corning glass/Ta(5nm)/NiFe(7nm)/FeMn(25nm)/Ta(5nm) multilayer that was prepared by the ion beam sputter deposition. The exchange bias field ($H_{ex}$) obtained from the measurement of the easy-axis MR loop decreased to 40 Oe at the deposition field angle of $45^{\circ}$, and to 0 Oe at the angle of $90^{\circ}$. When the difference between the uniaxial axis between the ferromagnet NiFe and the antiferromagnet FeMn was $90^{\circ}$, the strong antiferromagnetic dipole moment of FeMn caused the weak ferromagnetic dipole moment of NiFe to rotate in the interface.

• Journal of Magnetics
• /
• v.17 no.4
• /
• pp.308-315
• /
• 2012

Experimental investigations of the magnetization, magnetostriction and magnetoelectric (ME) effects were performed on sandwich - type Metglas/PZT/Metglas laminate composites. The results have been analyzed by taking into account the demagnetization contribution. The study has pointed out that the magnetic flux concentration is strongly improved in piezomagnetic laminates with a narrower width leading to a significant enhancement of the ME effects. The piezomagnetic laminates with the optimal area dimension were integrated to form a 2-D geomagnetic device, which simultaneously can precisely detect the strength as well as inclination of the earth's magnetic field. In this case, a magnetic field resolution of better than $10^{-4}$ Oe and an angle precision of ${\pm}0.1^{\circ}$ were determined. This simple and low-cost geomagnetic-field device is promising for various applications.

• Steel and Composite Structures
• /
• v.25 no.2
• /
• pp.141-155
• /
• 2017

This paper presents an investigation into the magneto-thermo-mechanical vibration and damping of a viscoelastic functionally graded-carbon nanotubes (FG-CNTs)-reinforced curved microbeam based on Timoshenko beam and strain gradient theories. The structure is surrounded by a viscoelastic medium which is simulated with spring, damper and shear elements. The effective temperature-dependent material properties of the CNTs-reinforced composite beam are obtained using the extended rule of mixture. The structure is assumed to be subjected to a longitudinal magnetic field. The governing equations of motion are derived using Hamilton's principle and solved by employing differential quadrature method (DQM). The effect of various parameter like volume percent and distribution type of CNTs, temperature change, magnetic field, boundary conditions, material length scale parameter, central angle, viscoelastic medium and structural damping on the vibration and damping behaviors of the nanocomposite curved microbeam is examined. The results show that with increasing volume percent of CNTs and considering magnetic field, material length scale parameter and viscoelastic medium, the frequency of the system increases and critically damped situation occurs at higher values of damper constant. In addition, the structure with FGX distribution type of CNTs has the highest stiffness. It is also observed that increasing temperature, structural damping and central angle of curved microbeam decreases the frequency of the system.

• Journal of the Korean Magnetics Society
• /
• v.25 no.3
• /
• pp.74-78
• /
• 2015

We measured the low field microwave absorption (LFMA) and ferromagnetic resonance (FMR) signals at various magnetic field angle in exchange biased CoFe/MnIr thin film. The LFMA signals were dominantly related to the magnetization rotation process. In order to analyze the LFMA signal, we calculated transverse magnetization ($M_{\tau}$) and permeability (${\mu}_{\tau}$) for CoFe/MnIr thin film by using S-W model, which magnetic parameters of exchange bias ($H_{ex}$ = 58.5 Oe) and uniaxial anisotropy field ($H_k$ = 30Oe) was obtained from FMR signals. The LFMA signal at hard axis showed similar behavior compared with that of $M_{\tau}$. As the magnetic field angle approach to the perpendicular to hard axis, the LFMA signals were depending on both of $M_{\tau}$ and ${\mu}_{\tau}$.

• Journal of Magnetics
• /
• v.5 no.3
• /
• pp.85-89
• /
• 2000

The hysteretic characteristics of giant magnetoimpedance (GMI) profiles have been measured in Co-based amorphous ribbon with various anisotropy angles $\theta_k$, and they have been analyzed by using the Stoner-Wohl-farth model. Two-peaks behavior with a dip near zero field is revealed in the measured GMI profile at 10 MHz irrespective of $\theta_k$. The negligible hysteresis of the field fur the dip is close to the calculation assuming the magnetization jump from a metastable to stable state. However, the hysteretic asymmetry far the angle range of $20^\circ\leq\theta_k < 60^\circ$ is well described by the divergence in the calculation without the magnetization jump. The asymmetry for $\theta_k\geq60^\circ$ may be due to the divergence, but the shapes of measured profiles are quite different from the calculations with single peak near zero field, indicating that Stoner-Wohlfarth model can be well used to describe GMI characteristics for the anisotropy angle range of $20^\circ\leq\theta_k < 60^\circ$at the frequency of 10 MHz in Co-based amorphous ribbons.

• Investigative Magnetic Resonance Imaging
• /
• v.15 no.1
• /
• pp.11-21
• /
• 2011

Purpose : Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. Materials and Methods : Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional ($90^{\circ}$ view) and $45^{\circ}$ oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. Results : There was least field inhomogeneity along the $45^{\circ}$ line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with $45^{\circ}$ oblique-view was coincided regardless of susceptibility. And with $45^{\circ}$ oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the $45^{\circ}$ oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. Conclusion : We suggested the method for accurate localization of electrode using $45^{\circ}$ oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.