• Journal of electromagnetic engineering and science
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• v.16 no.4
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• pp.206-209
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• 2016

This letter proposes a reconfigurable directional coupler that uses a variable impedance mismatch reflector to achieve high isolation characteristics in the antenna front end. The reconfigurable coupler consists of a directional coupler and a single-pole four-throw (SP4T) switch with different load impedances as a variable load mismatch reflector. Selection of the load impedance by the reflector allows cancellation of the reflected signal due to antenna load mismatch and the leakage from the input to isolation port of the directional coupler, resulting in high isolation characteristics. The performance of the proposed architecture in separating the received (Rx) signal from the transmitted (Tx) signal in the antenna front end was verified by implementing and testing the reconfigurable coupler at 917 MHz for UHF radio-frequency identification (RFID) applications. The proposed reconfigurable directional coupler showed an improvement in the isolation characteristics of more than 20 dB at the operation frequency band.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.69-77
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• 1996

We analyzed wideband propagation characteristics of a microstrip transmission line based on FR-4 composite substrate using the wideband complex dielectric constant model and the phenomenological loss equivalence method. The loss calculated by constant relative permittivity and loss tangent is greatly overestimatd compared to that calculated by the frequency-dependent complex relative permittivity. This wideband analysis can be helpful to characterize high-speed and high-density transmission lines associated with the wideband dielectric characteristics and shows that the FR-4 composite substrate has high potential of high frequency circuit applications in terms o fthe propagation loss.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.3
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• pp.25-37
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• 1995

The phenomenological loss equivalence method incorporated into the wideband lossy transmission line model is applied to the characterization of high desity digital transmission lines. The pulse propagation characteristics are analyzed using the calculated frequency characteristics and the discrete Fourier transformation. This approach has been verified by comparing the calculated frequency characteristics with the FEM and the esperimental results. This method is very suitable for computer-aided analysis of high density/high speed interconnection circuits because of the simple calculation as well as the calculation accuracy. We have found that pulse ftransmission speed and dispersion of hgih density digital transmission lines can be optimized by managing the conductor and dielectric losses in addition to the impedance matching.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.704-706
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• 1993

This paper, introduces a Current-fed type High-Frequency Inverter with self turning devices. By replacing Thyrisors used for power source of heat treatment with high speed switching element, MOSFET in current type Inverter, the proposed Inverter makes high speed performance with several 100kHz. This paper also depicts some operating principles of the proposed circuits and general operating characteristics. Steady state solution on state variables in analysis of the proposed circuit is described generally by using normalized parameter and its characteristics depending on separate ratio(n) is also shown.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.233-243
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• 1998

The demand of high speed machining is increasing due to the high speed cutting and grinding provides high efficiency of process, short process time, improved metal removal capacity and better surface finish. Active magnetic bearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting or grinding. This paper describes a design process of an active magnetic bearing system for a high speed grinding spindle with power 5.5kW and maximum speed 60,000rpm. Magnetic actuators are designed by the magnetic circuit theory considering static load condition, and examined with FEM analysis. Dynamic characteristics are also considered, such as bandwidth, stiffness, natural frequency and static deflection. System characteristics are simulated with a rigid rotor model.

• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.27-28
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• 2017

In this paper, design method for a high frequency transformer with high insulation is presented. The insulation performance of the high frequency transformer is determined by the distance between primary and secondary windings, and the characteristics of dielectric material. For the voltage strength safty, a high frequency transformer model is designed. By using computer simulation, the transformer model is evaluated.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.38-42
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• 1999

We prepared hish T$_c$ Josephson junctions that have different I$_c\;'s$ and R$_n\;'s$ and studied their microwave properties. We measured the current-voltage characteristics of the junctions under the irradiation of 22 GHz electromagnetic wave at various temperatures. from the Shapiro steps, we calculated the maximum detectable frequency and the microwave received power of the junctions. Increasing critical current values increase both maximum detectable frequency and sensitivity. However, increasing temperature increase sensitivity but decrease maximum detectable frequency.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.239-240
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• 2006

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.1056-1061
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• 1998

In this paper, a novel zero current switching (ZCS) high frequency inverter for induction heating is proposed. The ZCS characteristics are investigated from both the numerical analysis and the experiment.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.1036-1041
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• 1998

A novel ZCS high frequency inverter in complex resonance applied for reduction of PM is developed. This inverter is suppressed the switching stress by using complex resonance. The stable operation is realized by ZCS using overlapping commutation phenomenon. The ZCS characteristics are investigated based on numerical analysis and experimental results.