• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1224-1230
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• 2007

Recently, wireless LAN are often applied in home or office because of its various of convenience. Frequency rage of wireless LAN specified by IEEE 802.11a is at 5.2 GHz and IEEE 802.11b is 2.4 GHz. But in offices with wireless LAN devices, reflection of waves against walls, ceilings, floors and desks made of metal creates multipath problems that reduce communication speed and lose data. These problems can be solved by using EM wave absorber. In this paper, we designed and fabricated EM wave absorbers using MnZn-ferrite, sendust, carbon and CPE(Chlorinated Polyethylene). The EM wave absorber with the ratio of MnZn-Ferrite : sendust : CPE=64 : 16 : 20 wt.% has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz and the EM wave absorber with the ratio of MnZn-ferrite : carbon : CPE=40 : 15 : 45 wt.% has thickness of 3.8 mm and absorption ability more than 23 dB at 5.2 GHz.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.11-11
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• 2002

Huge applications of soft magnetic films can be expected as integrated passives in the infest IT devices, including CMOS compatible RF integrated inductors and transformers, transmission line devices, electromagnetic noise countermeasure, sensors, etc. A new 1MHz-9GHz permeameter has been completed and clarified the possibility of modern magnetic films for applications in integrated passives. The films evaluated include CoNbZr, CoZro, CoAlPdO, electroplated NiZn(Co) ferrite, etc. (omitted)

• Journal of Magnetics
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• v.22 no.2
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• pp.344-351
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• 2017

Wireless magnet pumps are used in medical applications and are particularly useful as artificial heart ventricular assist devices (VADs). To investigate wireless operation of magnetic pumps, we fabricated three types of magnetic impellers using bonded magnets by blending magnetic powders of SmFeN, NdFeB, and Sr-ferrite. We investigated the magnetic properties of the fabricated magnetic impellers, which are driven by the application of magnetic coupling with an external driving magnet or external coil system, without a driving motor, shaft, or mechanical bearings. The use of wireless magnetic pumps is therefore not complicated by critical issues of size, heat, and vibration, which are very important issues for blood pumps. The magnetic properties of the impellers, such as their rotational speed, driving torque and hydrodynamic performance, determine their wireless driving ranges. We conducted performance evaluations of the impeller's magnetic wireless manipulation, heat, and vibration. In addition, we carried out an animal test to confirm the suitability of the wireless magnetic pumps for use as biventricular assist devices (BiVADs).

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.06a
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• pp.183-184
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• 2009

In this paper the internal or external of the ships mounted electronic devices due to the propagation of electromagnetic interference and to prevent malfunction EMC filter was designed and fabricated. It was designed and fabricated with Ni-Zn ferrite beads of high permeability to make large inductance as the inductor and Feed-through capacitors, which did not have any resonance point, to restraint resonance effectively, and the characteristics was evaluated. The results from the 0 kHz$\sim$1.5 GHz bandwidth of $25{\sim}70$ dB were able to obtain excellent attenuation characteristics. And, when the Electric Fast Transient (EFT) of 4 kV in the level 4 of IEC 61000-4-4 was induced, it was soon attenuated more than 1/6 to 600 V. Therefore, it was confirmed that the developed EMC filter can be used for suppressing ships mounted electromagnetic interference between electronic devices.

• Journal of the Korean Magnetics Society
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• v.25 no.1
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• pp.22-26
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• 2015

In this paper, a magneto-inductive wave generated in a chain of LC resonators fabricated with Ni-Zn ferrite cores and chip capacitors is presented. RF signal propagates to neighbor resonator one by one as a consequence of the magnetical coupling between two resonators in the device. The magnetical coupling is due to the mutual inductances along the chain of resonators. So, the signal amplitude (${\approx}$ coupling intensity) is dependent of the mutual inductance which can be adjusted by applied magnetic field. In order to demonstrate the device, some experiments have been carried out systemically. The transmission characteristics of a magneto-inductive wave could be controlled by applied external magnetic field. The device composed of 5 resonators; the center frequencies were estimated to be 32 MHz and 38 MHz with the external magnetic flux density of 75 Oe and 222 Oe, respectively. We expect that the reported results could open a promising way to a high variety of applications in one- and two-dimensional functional devices, such as transducers, delay lines, power dividers and couplers.

• Advances in nano research
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• v.1 no.4
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• pp.183-192
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• 2013

One-dimensional multiferroic nanostructured composites have drawn increasing interest as they show tremendous potential for multifunctional devices and applications. Herein, we report the synthesis, structural and dielectric characterization of barium titanate ($BaTiO_3$)-bismuth ferrite ($BiFeO_3$) composite fibers that were obtained using a novel sol-gel based electrospinning technique. The microstructure of the fibers was investigated using scanning electron microscopy and transmission electron microscopy. The fibers had an average diameter of 120 nm and were composed of nanoparticles. X-ray diffraction (XRD) study of the composite fibers demonstrated that the fibers are composed of perovskite cubic $BaTiO_3$-$BiFeO_3$ crystallites. The magnetic hysteresis loops of the resultant fibers demonstrated that the fibers were ferromagnetic with magnetic coercivity of 1500 Oe and saturation magnetization of 1.55 emu/g at room temperature (300 K). Additionally, the dielectric response of the composite fibers was characterized as a function of frequency. Their dielectric permittivity was found to be 140 and their dielectric loss was low in the frequency range from 1000 Hz to $10^7$ Hz.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.7
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• pp.8-12
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• 1989

In this paper, dielectric waveguide gratings, which can be applied to the nonreciprocal devices such as isolators, are proposed. Those grating structures can be considered as cascade connections of step discontinuities between uniform dielectric waveguides and another uniform dielectric waveguides with a ferrite layer. Therefore, the nonreciprocal scattering characteristics of such gratings can be obtained form the scattering characteristics of step discontinuities and uniform dielectric wave guides. For the periodic grating structures, band-reject characteristics can be located inside or outside the frequency range of interest. Numerical analyses are performed at 35GHz and experimental results at X-band are also presented.

• Transactions on Electrical and Electronic Materials
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• v.16 no.1
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• pp.37-41
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• 2015

The most common structure of the current transformer (CT) consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. Therefore, the primary circuit of CT consists of a single turn of the conductor, with a secondary circuit of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry the current through the magnetic core. However, when the large current flows into a wire, it is difficult to measure its magnitude of current because the core is saturated and the core shows magnetic nonlinear characteristics. Therefore, we proposed a newly designed CT which has an air gap in the core to decrease the generated magnetic flux. Adding the air gap in the magnetic path increases the total magnetic reluctance against the same magnetic motive force (MMF). Using a ferrite core instead of steel also causes the generation of low magnetic flux. These features can protect the magnetic saturation of the CT core compared with the steel core. This technique can help the design of the CT to obtain a special shape and size.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2552-2564
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• 2020

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neigh-bouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.

• Journal of Power Electronics
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• v.17 no.2
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• pp.411-421
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• 2017

An approach based on a 2D lumped model is presented to quantify the voltage transfer gain (VTG) in power converter low power planes. The advantage of the modeling approach is the ease with which typical noise reduction devices such as decoupling capacitors or ferrite beads can be integrated into the model. This feature is enforced by a new modular approach based on effective matrix partitioning, which is presented in the paper. This partitioning is used to decouple power plane equations from external device impedance, which avoids the need for rewriting of a whole set of equation at every change. The model is quickly solved in the frequency domain, which is well suited for an automated layout optimization algorithm. Using frequency domain modeling also allows the integration of frequency-dependent devices such inductors and capacitors, which are required for realistic computation results. In order to check the precision of the modeling approach, VTGs for several layout configurations are computed and compared with experimental measurements based on scattering parameters.