• Journal of Korea Foundry Society
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• v.26 no.5
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• pp.205-210
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• 2006

The structural control of Al-Si alloy, which was not studied among various electromagnetic processing of materials, was considered applying the alternating current and direct current magnetic flux density. The main aim of the present study is to investigate the effects of electromagnetic vibration on the macro and microstructure of Al-Si alloy in order to develop a new process of structural control in Al-Si alloy. When the electromagnetic vibration is conducted for changing the shape of primary aluminum, at low frequency(>60Hz), the shape of dendrite is changed speroidal shape. When the electromagnetic vibration is conducted for changing the shape of eutectic silicon, the fact that a morphological change of the eutectic silicon from coarse platelet flakes to fine fiber shape is observed and the improvement of the mechanical properties is achieved with EMV (Electro Magnetic Vibration) process at high frequency(>500Hz).

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.464-470
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• 2010

The integrity of the industrial equipment in use under high temperature and high pressure must be assessed by regularly measuring the degraded mechanical properties during service time. In order to nondestructively monitor the degraded mechanical properties of industrial equipment, a measuring method of the reversible permeability(RP) using surface type probe is presented. The method for measuring the RP is based on that RP is the differential value of hysteresis loop. The RP is exactly the foundation hatmonics induced in a detecting coil measured by lock-in amplifier tuned to a frequency of the alternating perturbing magnetic field. The peak of RP is measured around the coercive force. Steel material used in this work was 12Cr ferritic heat resisting steel. The eleven kinds of samples aged during different times under same temperature ($700^{\circ}C$) were prepared. Peak interval of reversible permeability(PIRP), Vickers hardness, and tensile strength measured for the aged samples decreased abruptly for short aging time (below 500 h), but the change became small at a long aging time. Vickers hardness and tensile strength linearly decreased as RIRP decreased, so the degraded mechanical properties of 12Cr ferritic heat resisting steel could be nondestructively evaluated by measuring RIRP.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1293_1294
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• 2009

The sintering and high frequency electro-magnetic properties of Ba-hexagonal ferrite were investigated. All samples of the Ba-hexagonal ferrite were prepared by the conventional mixed oxide method and sintered at $1150^{\circ}C$~$1400^{\circ}C$. From the X-ray diffraction patterns of sintered Ba-hexagonal ferrite, the $Ba_3Co_2Fe_{24}O_{41}$ phase was represented as main phase in the almost sintering conditions. The bulk densities with sintering temperature and decreased at $1400^{\circ}C$. The permittivity ($\varepsilon$') and loss tangent of permittivity ($\varepsilon$"/$\varepsilon$') of $Ba_3Co_2Fe_{24}O_{41}$ ceramics increased and decreased with sintering temperature, respectively. The permeability of $Ba_3Co_2Fe_{24}O_{41}$ ceramics decreased with sinteirng temperature. The loss tangent of permeability was not changed compared each other with sintering temperature. The bulk density of $Ba_3Co_2Fe_{24}O_{41}$ ceramics sintered at $1300^{\circ}C$ was 4.79 g/$cm^3$. The permittivity, loss tangent of permittivity and permeability, loss tangent of permeability were 19.896, 0.1718 and 14.218, 0.2046 at 210 MHz, respectively.

• Polymer(Korea)
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• v.32 no.1
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• pp.90-93
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• 2008

We developed a variety of polymeric jelly phantoms that can be used in hyperthermia using an electromagnetic wave as an auxiliary cancer therapy. Particularly, using an appropriate material composed of polyethylene, deionized water, and sodium chloride, jelly phantoms for brain was prepared. Also, their electrical properties were characterized by measuring the dielectric constant and conductivity. As the results, overall electrical values of the phantoms decreased with increasing the amount of the components of the materials, excepted for sodium chloride. Additionally, storage characteristics of the phantoms showed a sustainable stability up to 6 months. Based on the experimental results, it can be proposed that jelly phantoms containing a ferro-magnetic particle could be a potential material for cancer therapy following the further study on the temperature elevation effect and the evaluation of electromagnetic properties of the materials.

• Journal of Sensor Science and Technology
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• v.9 no.1
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• pp.22-27
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• 2000

Amorphous FeCoSiB films with high saturation magnetostriction and excellent soft magnetic properties have been studied to evaluate their strain sensitivity. Films were subjected to a strain by bending of their substrates, which caused a change in the magnetic anisotropy of films via magnetoelastic coupling. Films were exhibited a figure of merit $F=({\Delta}{\mu}/{\mu})/{\varepsilon}$ (change in film permeability $\mu$ per unit strain $\varepsilon$) of $1.2{\times}10^5$, which is comparable with that of amorphous ribbons. To make a study of application of magnetostrictive films as strain sensor elements, we have prepared a micro-patterned film by means of the photolithography and ion milling processes. Impedance change in the patterned films, when strain was applied, was measured over the frequency range from 1 MHz to 1 GHz. Reflecting a large value of figure of merit F, a variation of 46% impedance of films was shown at 100 MHz frequency when a strain of $300{\times}10^{-6}$ was applied.

• Journal of the Korean Magnetics Society
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• v.12 no.6
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• pp.218-223
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• 2002

We investigated the magnetic properties of High Flux-type $Ni_{x}Fe_{100-x}$(x=40∼50, wt.％) permalloy powders and dust cores. The powder was prepared by conventional gas atomization in mass production scale. At the composition of $Ni_{x}Fe_{55}$, saturation magnetization was maximum. In case of lower Ni content than X=45, the $M_{s}$, decreased largely with the decrease in Ni content, which is due to the invar effect. The permeability of compressed powder cores increased with the decrease in Ni content, which was considered to be due to the decrease in the magnetostriction. In addition, the dust core with Ni=45％ showed the lowest core loss because of the increase in electrical resistivity leading to the low eddy current loss. From the better frequency dependence of permeability, larger Q value and superior DC bias characteristics of Ni=45％ than those of Ni=50％ core, it was confirmed that the 45％Ni-55％Fe powder alloy was better material for the dust core than commercial High Flux core materials.

• Journal of Magnetics
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• v.5 no.4
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• pp.120-123
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• 2000

Co-Ni-Fe-N thin films were fabricated by a $N_2$ reactive rf magnetron sputtering method. The nitrogen partial pressure ($P_{N2}$) was varied in the range 0~10% . As$P_{N2}$ increases in this range, the saturation magnetization $B_s$ linearly decreases from 19.8 kG to 14 kG and the electrical resistivity ($\rho$) increases from 27 to 155 $\mu\Omegacm$. The coercivity $H_c$ exhibits the minimum value at 4% $P_{N2}$. The magnetic anisotropy fields ($H_k$) are in the range of 20$\sim$50 Oe. High frequency characteristics of $(Co_{22.2}Ni_{27.6}Fe_{50.2})_{100-x}N_x$ films are excellent in the range of 3$\sim$5% of $P_{N2}$. In particular, the effective permeability of the film fabricated at 4% $P_{N2}$ is 800, which is maintained up to 600 MHz. This film also shows Bs of 17.5 kG, $H_c$/ of 1.4 Oe, resistivity of 98$\mu\Omegacm$ and $H_k$ of about 25 Oe. Also, the corrosion resistance of $(Co_{22.2}Ni_{27.6}Fe_{50.2})_{100-x}N_x$ films was imp roved with increasing N concentration.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.492-499
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• 2000

Co-Ni-Fe-N thin films were fabricated by a N$\sub$2/ reactive rf magnetron sputtering method. The nitrogen partial pressure (P$\sub$N2/) was varied in the range of 0∼10%. As P$\sub$N2/ increases in this range, the saturation magnetization (B$\sub$s/) linearly decreases from 19.8 kG to 14 kG and the electrical resistivity ($\rho$) increased from 27 to 155 ${\mu}$$\Omega$cm. The coercivity (H$\sub$c/) exhibits the minimum value at 4% of P$\sub$N2/. The magnetic anisotropy (H$\sub$k/) are in the range of 20∼50 Oe. High frequency characteristics of (Co$\sub$22.2/Ni$\sub$27.6/Fe$\sub$50.2/)$\sub$100-x/N$\sub$x/ films are excellent in the range of 3∼5% of P$\sub$N2/. Especially the effective permeability of the film fabricated at 4% of P$\sub$N2/ is 800, which is maintained up to 600 MHz. This film also shows Bs of 17.5 kG, H$\sub$c/ of 1.4 Oe, resistivity of 98 $\Omega$cm and H$\sub$k/ of about 25 Oe. Also, the corrosion resistance of (Co$\sub$22.2/Ni$\sub$27.6/Fe$\sub$50.2/)$\sub$100-x/N$\sub$x/ were improved with the increase in N concentration.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.611-614
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• 2018

Laminate composites composed of $0.95Pb(Zr_{0.52}Ti_{0.48})O_3-0.05Pb(Mn_{1/3}Sb_{2/3})O_3$ piezoelectric ceramic and Fe-Si-B based magnetostrictive amorphous alloy are fabricated, and the effect of control of the areal dimensions and the thickness of the piezoelectric layer on the magnetoelectric(ME) properties of the laminate composites is studied. As the aspect ratio of the piezoelectric layer and the magnetostrictive layer increases, the maximum value of the ME voltage coefficient(${\alpha}_{ME}$) increases and the intensity of the DC magnetic field at which the maximum ${\alpha}_{ME}$ value appears decreases. Moreover, as the thickness of the piezoelectric layer decreases, ${\alpha}_{ME}$ tends to increase. The ME composites exhibit ${\alpha}_{ME}$ values higher than $1Vcm^{-1}Oe^{-1}$ even at the non-resonance frequency of 1 kHz. This study shows that, apart from the inherent characteristics of the piezoelectric composition, small thicknesses and high aspect ratios of the piezoelectric layer are important dimensional determinants for achieving high ME performance of the piezoelectric-magnetostrictive laminate composite.