• Journal of Biosystems Engineering
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• v.33 no.1
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• pp.58-62
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• 2008

The need for position information in agriculture is gradually increasing for precise control farm vehicle and effective manage farm land. Though geomagnetic sensor has a lot of merits in estimating heading angle of vehicle because of low costs and sensing ability of magnetic north, it is easy that sensor outputs are distorted in electro magnetic field environment. This study was conducted to develop geomagnetic compass which could be available in measuring relative position from reference point correcting output distorted by external electro magnetic field in a small scale field. Magnetic inducing sensor (PNI's Vector2X) which wound enamel coated copper coil on ferrite core in order to measure and correct earth magnetic field. Magnetic azimuth was corrected using the algorithm which estimated amount of magnetic distortion from the difference between each outputs of magnetic sensors that located on the cross shaped base. Developed auto-tuning magnetic sensor was showed less then 5% as bearing accuracy in the strong magnetic field.

• Journal of Power Electronics
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• v.16 no.2
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• pp.786-797
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• 2016

This paper describes the design and development of a novel semiconductor-based solid-state switch for damped oscillating voltage test system. The proposed switch is configured as two identical series-connected switch stacks, each of which comprising 10 series-connected IGBT function units. Each unit consists of one IGBT, a gate driver, and an auxiliary voltage sharing circuit. A single switch stack can block 20 kV-rated high voltage, and two stacks in series are proven applicable to 30 kV-rated high voltage. The turn-on speed of the switch is approximately 250 ns. A flyback topology-based power supply system with a front-end power factor correction is built for the drive circuit by loosely inductively coupling each unit with a ferrite core to the primary side of a power generator to obtain the advantages of galvanic isolation and compact size. After the simulation, measurement, and estimation of the parasitic effect on the gate driver, a prototype is assembled and tested under different operating regimes. Experimental results are presented to demonstrate the performance of the developed prototype.

• Polymer(Korea)
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• v.30 no.2
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• pp.124-128
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• 2006

Heavy weight of the camouflage materials was always the main problem. To solve it, the low infrared emissivity fibers with the radar absorbing property (LIFR) were prepared. The low infrared emissivity fibers (LIF) were firstly melt-spun by co-extrusion of polypropylene (PP) and PP/various fillers master-batches using general conjugate spinning. The infrared emissivity of LW with AA and ZnO was decreased respectively compared with that of pure polypropylene fibers. The infrared emissivity of LIF with 15 wt% Al and 2 wt% ZnO in the sheath-part can reach 0.58. To improve LIF radar absorbing property, LIFR was prepared by filling the 50 wt% ferrite and bronze in the core-part of LIF. The radar absorbing efficacy of LIFR was good and the infrared emissivity was low. For the characterization, fiber electron intensity instrument and differential scanning calorimetry (DSC) were used for the analysis of mechanical properties, thermal and crystallization behavior of the spun-fibers. Scanning electron microscopy (SEM) was carried out to observe the particle distribution of the bicomponent fibers.

• Journal of Powder Materials
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• v.17 no.3
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• pp.230-234
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• 2010

Homogenous silica-coated $CoFe_2O_4$ samples with controlled silica thickness were synthesized by the reverse microemulsion method. First, 7 nm size cobalt ferrite nanoparticles were prepared by thermal decomposition methods. Hydrophobic cobalt ferrites were coated with controlled $SiO_2$ using polyoxyethylene(5)nonylphenylether (Igepal) as a surfactant, $NH_4OH$ and tetraethyl orthosilicate (TEOS). The well controlled thickness of the silica shell was found to depend on the reaction time and the amount of surfactant used during production. Thick shell was prepared by increasing reaction time and small amount of surfactant.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.1
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• pp.24-28
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• 2009

In this study, we investigated whether the anhysteretic demagnetization process would be applicable to remove a complicated magnetization of a steel tube as a part of the experimental earlier study for a deperming of naval vessel. The magnetic tube used in this study was a 10cm-long and 1cm-diameter steel tube, and magnetized with a E-shape ferrite core to form a nonuniform magnetization in it. In the anhysteretic demagnetization process, a dc magnetic field applied along the longitudinal direction of the tube decreased from ${\pm}$3kA/m to zero-field with the step of ${\pm}$300A/m. At the same time, an ac bias magnetic field with the frequency of 60Hz and the field intensity of 300A/m was excited along the circumstantial direction of the tube. It was found that the anhysteretic process was useful to demagnetize a small-object like a steel tube from the experimental results showing the residual magnetization reduced over 90%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.96-100
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• 2003

평면형 자심재료용으로 응용하기 위한 Mn-Zn 페라이트에서 저손실 조성의 전자기적 특성과 분위기 조건에 따른 특성변화를 관찰하였다. $Fe_{2}O_{3}$ : MnO : ZnO 의 물비가 53 : 36 : 11 일 때, 가장 우수한 특성을 나타내었으며, $SiO_{2}$와 CaO는 입계 저항층 형성을 통한 손실은 감소시키고, 이로 인해 성능지수는 증가하여 100kHz ~ 200kHz 범위에서 최대값을 나타내어 전자기적 효율이 극대화되었다. 산소분압의 제어는 승온과정부터 산소분압을 제어시켜주어야만 Zn-loss 현상의 증가와 $Fe^{2+}$이온 농도의 감소 및 $Fe^{2+}-Fe^{3+}$ 이온간의 호핑(hoping)현상 등에 의한 손실을 최소화 할 수 있으며, 높은 투자율을 얻을 수 있었다. 그리고 소결 또는 냉각 중 평형 산소분압이 유지되지 못하면 다량의 결함이 출현하게 되고, 특히 $600^{\circ}C$이하에서 스피넬 상의 분해-산화반응이 일어나면서 미세구조 상에 결함으로 남게 되어 전자기적 특성이 저하되었다.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.6
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• pp.409-416
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• 2005

For broadband high-data-rate power line communication with the allocated frequency bandwidth from 2 to 30 MHz on medium voltage (MV) distribution power lines, a signal coupling unit is developed. The coupling unit is composed of a coupling capacitor for coupling communication signal, a drain coil, and an impedance matching part. The coupling capacitor made of ceramic capacitor is designed for transmission property of better than 1 dB in the frequency range. The drain coil is used for preventing low frequency high voltage from junction of medium voltage power line in case that a coupling capacitor is not working properly any more. Also, using ferrite core, a novel broadband impedance matching transformer is developed. A complete coupling unit with a coupling capacitor, a drain coil, and a matching transformer is housed by polymer for good isolation and distinguishing from high voltage electric facilities. Each is fabricated and its frequency behavior is tested. Finally, complete signal couplers are equipped in a MV PLC test bed and their performance are measured. The measurement shows that the coupling capacitor works excellently.

• Journal of Power Electronics
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• v.16 no.1
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• pp.111-120
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• 2016

Generally, a single phase H-bridge converter feeding a single primary track is employed in conventional inductive power transfer systems. However, these systems may not be suitable for some high power applications due to the constraints of the semiconductor switches and the cost. To resolve this problem, a novel dual coupled primary tracks IPT system consisting of two high frequency resonant inverters feeding the tracks is presented in this paper. The primary tracks are wound around an E-shape ferrite core in parallel which enhances the magnetic flux around the tracks. The mutual inductance of the coupled tracks is utilized to achieve adjustable power sharing between the inverters by configuring the additional resonant capacitors. The total transfer power can be continuously regulated by altering the pulse width of the inverters' output voltage with the phase shift control approach. In addition, the system's efficiency and the control strategy are provided to analyze the characteristic of the proposed IPT system. An experimental setup with total power of 1.4kW is employed to verify the proposed system under power ratios of 1:1 and 1:2 with a transfer efficiency up to 88.7%. The results verify the performance of the proposed system.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.4
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• pp.274-281
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• 2010

This paper proposes a DFPS (Dual Frequency Power Source) impedance matching device for uniformity improvement of a semiconductor plasma etching system. The DFPS consists of two parts for safe plasma processing on large-area substrates. The first part is an ICP (Inductively Coupled Plasma) for high integration by using ferrite core. The second part is a CCP (Capacitive Coupled Plasma) to control uniformity of whole cells. Proposed DFPS can achieve high productivity improvement required for semiconductor equipment industry. The proposed plasma system is analyzed, simulated and experimentally verified with a matching equipment at 27.12MHz and 400kHz.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.3
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• pp.181-187
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• 2020

In this study, we propose a spherical flux concentration structure for omnidirectional wireless power transfer. Omnidirectional wireless power transfer technology is a method that can transmit power to a transmitter located in an arbitrary position in a two-dimensional or three-dimensional space. However, to improve the power transfer distance in a wireless power transfer system, the diameter of the coil or the number of windings must increase, thereby increasing the size of the transmitter. The proposed transmitter structure adds a ferrite core inside the transmitter coil so that the magnetic flux generated by the transmitter is directed toward the position of the receiver. As a result, the flux linkage and the mutual inductance increase. By implementing the omnidirectional wireless power transfer system using the proposed structure, the power transfer distance can be improved by 65% compared with the conventional system without increasing the size of the transmitter. Simulation shows that the proposed spherical flux concentration structure increases the mutual inductance of the omnidirectional wireless power transmission system.