• 조명전기설비학회논문지
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• 제28권4호
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• pp.29-35
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• 2014

The purpose of high frequency transformer in the inverter is to reduce the voltage and current stresses of switch components when it operates at the large conversion ratio. But the loss of transformer is the major contributor in the efficiency of inverter. This paper presents the method of core design to minimize the loss of transformer. The total loss of transformer is minimized by adjusting the effective cross-sectional areas of core. The component ratio of losses are compared by using the finite-element analysis.

• 한국전기전자재료학회논문지
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• 제17권3호
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• pp.340-347
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• 2004

Ultra-small size, high-performance, solenoid-type RF chip inductors utilizing low-loss A1$_2$O$_3$ core materials were investigated. The dimensions of the RF chip inductors fabricated were 1.0mm${\times}$0.5mm${\times}$0.5mm and copper coils were used. The materials (96％ A1$_2$O$_3$) and shape (I-type) of the core, the diameters (40${\mu}{\textrm}{m}$) and position (middle) of the coil, and the lengths (0.35mm) of solenoid were determined by a high-frequency structure simulator (HFSS) to maximize the performance of the inductors. The high-frequency characteristics of the inductance (L) and quality-factor (Q) of the developed inductors were measured using a RF impedance/material analyzer (E4991A with E16197A test fixture). The developed inductors exhibit an inductance of 11 to 11.3nH and a qualify factor of 22.3 to 65.7 over the frequency ranges of 250 MHz to 1.7 GHz, and show results comparable to those measured for the inductors prepared by Coilcraft$^{TM}$. The simulated data described the high-frequency data of the L and Q of the fabricated inductors well.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.587-590
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• 2003

The first attention in designing a transformer for low temperature rise should be to reduce losses. Leakage inductance and temperature rise are two of the more impotent problems facing the magnetic core technology of today's high frequency transformers. Excessive leakage inductance increases the stress on the switching transistors and limits the duty-cycle, and excessive temperature rise can lead the design limitation of high frequency transformer with high current. The flat transformer technology provides a very good solution to the problems of leakage inductance and thermal management for high frequency power. The critical magnetic components and windings are optimized and packaged within a completely assembled module. The turns ratio in a flat transformer is determined as the product of the number of elements or modules times the number of primary turns. The leakage inductance increase proportionately to the number of elements, but since it is reduced as the square of the turns, the net reduction can be very significant. The flat transformer modules use cores which have no gap. This eliminates fringing fluxes and stray flux outside of the core. The secondary windings are formed of flat metal and are bonded to the inside surface of the core. The secondary winding thus surrounds the primary winding, so nearly all of the flux is captured.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권11호
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• pp.555-561
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• 2001

In this paper, the low power (1.5 W) solenoid-type magnetic thin-film transformers utilizing a $Ni_{81}Fe_{19)$ core material were designed and fabricated for 5 MHz-drive DC-DC converter application. The $20\mum$ thick copper films were used as the coils. The transformers fabricated in this work have the sizes of $3.08 mm\times25.5 mm\; and\; 6.15 mm\times12.75 mm.$ The optimum design of solenoid-type magnetic thin film transformers was performed utilizing the conventional equations, a Maxwell computer simulator (Ansoft HFSS V7.0 for PC), and parameters obtained from the magnetic properties of NiFe magnetic core materials. frequency characteristics of inductance, dc resistance (R), coupling factor (k) and gain of developed transformers were measured using HP4194A impedance and gain-phase analyzer. The fabricated transformers with the size of $6.15 mm\time12.75 mm$ exhibit the inductance of $0.83 \muH$, the dc resistance of $2.3\Omega$$\Omega$, the k of 0.91 and the gain of -1 dB at 5 MHz, which show the comparable results to those reported in the recent literatures. The measured high-frequency characteristics for the fabricated transformers agreed well with those obtained by theoretical calculations .

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.812-813
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• 2011

This paper presents the characteristic of newly developed electrical steel and motor performance analysis for HEV/EV. This material is developed and optimized for high frequency operation to reduce the core losses in traction motors to increase fuel efficiency. Four types of electrical steel are introduced, which are optimized for high flux density (PNHF), high frequency low core loss (PNF), high punchability (PNS) and high strength (PNT) to meet different specifications from different types of traction motors. To identify the motor performance with this material, finite element analysis was used to calculate core loss as well as Ld and Lq for efficiency map. Also structure analysis was performed to calculate stress on bridge rotor.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.288-294
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• 2015

Recently, the module-integrated converter has shown an interest in the photovoltaic generation system. In this system, the high frequency transformer should be compact and efficient. The proposed method is based on the correlation characteristic between the copper and core loss to minimize the loss of transformer. By sizing an effective cross-sectional area and window area of core, the amount of loss is minimized. This paper presents the design and analysis of high frequency transformer by using the 3D finite element model coupled with DC-DC converter circuit for more accurate analysis by considering the nonlinear voltage and current waveforms in converter circuit. The current waveform in each winding is realized by using the ideal DC voltage source and switching component. And, the thermal analysis is performed to satisfy the electrical and thermal design criteria.

• 대한한의학방제학회지
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• 제30권3호
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• pp.145-154
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• 2022

Objective : This study aims to study core herbs and formulas in Internal medicine on Spleen system, to enhance efficiency in teaching Internal medicine on Spleen system, Herbalogy, Formula science, and to increase integration of the courses. Methods : Frequency notion, which was generally used in previous studies, was used in this study along with network analysis. Results : Frequently used herbs, herbs with high centrality, frequently combined herbs and core formula were found in this study. The herb with the highest frequency and centrality was 'Citri Unshius Pericarpium', and 'Atractylodis Rhizoma Alba - Citri Unshius Pericarpium' was the most frequent herb combination. The results of network analysis showed a total of 5 herbal communities of combination. Conclusion : Core herbs were found based on the frequency notion, which is a traditional analysis method. Also, core herbs, herbal combinations, formulas that can that may be overlooked when using frequency notions were found by using network analysis. The results may lead to enhancing efficiency in the education of Internal medicine on Spleen system, Herbalogy, Formula science courses and the integration of courses.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.703-709
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• 2001

In this paper, we analyzed the laminated composite sandwich plate structure of truss core with changing values of the designing parameters. As a result, in designing parameters of that, the more height and thickness of the laminated composite plate's core, the more increase of natural frequency. In this type of structure, in the case of applying core of the laminated composite plate and antisymmetric stacking, natural frequency has high value and we calculated the optimum angle-ply making natural frequency maximum. Natural frequency of CFRP is higher than that of GFRP. Both are materials of the laminated composite plate. The mode shapes are various along with the angle-ply of the laminated composite plate.

• 한국자기학회지
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• 제7권6호
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• pp.327-333
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• 1997

페라이트, 비정질 코아등의 고주파 연자성재료의 고주파 자기특성 데이터를 디지타이징 방법으로 얻고, 철손 및 B-H 곡선, 투자율을 자동적으로 측정할 수 있는 고주파 자기특성측정장치를 제작하였다. 본 시스템은 교류 인가를 위한 신호발생기와 전력증폭기, 인가자장을 게측하기 위한 전류측정용 저항, H 및 B 신호를 디지타이징 (digitizing)하기 위한 대역폭 500 MHz, 샘플링속도 1 Gs/s의 디지털 오실로스코프, 시스템 제어에 사용되는 GPIB 케이블 및 퍼스널 컴퓨터로 구성되었다. 자계 H 계측을 위한 전류센서로서 저항기(resistor)와 Rogowski 코일을 비교 검토한 결과 고주파 변류기 (current transformer : 이하 CT)가 주파수 특성과 노이즈 억제효과에서 보다 우수하였다. 측정시스템에 동작자속밀도 설정, 비대칭 B-H 곡선의 보정, 구형파등의 다양한 파형지원등의 기능을 부가하였다.

• Journal of the Optical Society of Korea
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• 제18권5호
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• pp.453-458
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• 2014

A novel high birefringent polymer terahertz (THz) fiber with a suspended elliptical core is proposed in this paper. The introduction of an elliptical core can enhance asymmetry to realize high mode birefringence, and a large porous outer cladding effectively isolates the core-guided mode from interacting with the surrounding environment. A full-vector finite element method(FEM) is used to analyze the characteristics of the THz fiber. Simulation results show that the suspended elliptical fiber exhibits high mode birefringence on a level of $10^{-2}$ over a wide frequency range, and an extremely large mode birefringence(${\approx}0.06226$) is obtained when ellipticity is 0.2. Moreover, a suspended hollow elliptical core fiber is also discussed for the purpose of lower loss, however high mode birefringence and low relative absorption loss can not coexist in such a kind of fiber.