• 한국전자파학회논문지
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• 제21권10호
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• pp.1103-1108
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• 2010

본 논문에서는 PIFA의 급전점과 단락점을 둘러싸는 급전 루프 내부에 커패시터 구조를 삽입하는 새로운 타입의 4중 대역(GSM900/DCS/PCS/W-CDMA) PIFA 설계를 제안한다. 커패시터의 삽입을 통해서 병렬 공진점인 2.01 GHz에서의 반사 계수 -2.73 dB를 -6.26 dB로 낮추는 효과를 얻을 수 있었다. 병렬 공진에서의 좋지 못한 방사 특성을 개선시킴으로써 고차 대역(DCS/PCS/W-CDMA)에서의 광대역 특성을 나타내었다.

• 한국소음진동공학회논문집
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• 제15권9호
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• pp.1003-1008
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• 2005

The acoustic absorption of a multiple layer perforated plate system is very good near the resonance frequency region, while it has been regarded as a demerit that its frequency bandwidth is considerably narrow. In order to overcome such a demerit, the parallel perforated plates with different porosities are proposed. The sound absorption of such system composed of a parallel perforated plate is calculated by an equivalent electroatoustic circuit approach and validated by comparing the calculated absorption coefficients with those measured by the two-microphone impedance tube method. The sound absorptive characteristics and performance of parallel perforated plate systems are discussed from a standpoint of frequency bandwidth related with sound absorption.

• 전기학회논문지P
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• 제57권4호
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• pp.370-376
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• 2008

Power capacitors is widely used for power factor correction and component of passive filter in the user power systems. Recently, application of non-linear load is gradually increased. Non-linear load produces harmonic components of current. There are series resonance and parallel resonance when capacitors are applied in the user electrical application. If this harmonic component matches resonance, voltage and current is magnified and has severely an influences on capacitor. This paper purposes a new method for the magnitude of voltage and current by the frequency scan analysis without equivalent circuit for the actual circuit at the resonance condition.

• 전기학회논문지
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• 제66권4호
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• pp.643-650
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• 2017

This pap4er analyzes resonance characteristics of a slave motor that is not controlled by load and parameter differences between Dual motors during parallel operation in middle-low speed. Dual SPMSMs(Surface mounted Permanent Magnet Synchronous Motor) connected in parallel to a single inverter controlled by the master and slave control in this paper. Based on the stability analysis of the SPMSM for a variation of torque angle, the 6th nonlinear state equation of the torque angle variation in the SIMM(Single Inverter Multi Motor) structure is derived according to a mathematical model for the dual motors. In general, an analysis of the 6th order nonlinear state equation is complex. Therefore, a resonance frequency generated from the slave motor is found from the characteristic equation of the 2nd order system obtained by linearization and model reduction near steady state operation point. Through simulations and experiments, it is confirmed that the stability analysis of the SPMSMs and state equation models are useful for the variation of the torque angle analyzed in this paper.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.180-180
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• 2012

A microplasma system source based on microwave parallel stripline resonator (MPSR) was developed for the generation of microplasmas in a wide range of pressure from some torr to 760 torr. This source was operated at its resonance frequency that much depends upon not only its discharge gap size but also operated pressure. This paper applied a simple circuit model to analyze the effects of discharge gap size and pressure to resonance frequency and impedance of MPSR in the cases with and without plasma exist inside the discharge gap. In the process of calculating, the conformal mapping method was used to estimate the capacitance of the MPSR. The calculating results by using circuit model agree well with the simulation results that using commercial CST microwave studio software.

• Current Optics and Photonics
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• 제5권1호
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• pp.66-71
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• 2021

The resonance characteristics of H-shaped metamaterials, whose widths were varied while keeping the height constant, were investigated in the terahertz (THz) frequency range. The H-shaped metamaterials were numerically analyzed in two modes in which the polarization of the incident THz electric field was either parallel or perpendicular to the width of the H-shaped structure. The resonant frequency of the metamaterial changed stably in each mode, even if only the width of the H shape was changed. The resonant frequency of the metamaterial operating in the two modes increases without significant difference regardless of the polarization of the incident electromagnetic wave as the width of the H-shaped metamaterial increases. The electric field distribution and the surface current density induced in the metamaterial in the two modes were numerically analyzed by varying the structure ratio of the metamaterial. The numerical analysis clearly revealed the cause of the change in the resonance characteristics as the width of the H-shaped metamaterial changed. The efficacy of the numerical analysis was verified experimentally using the THz-TDS (time-domain spectroscopy) system. The experimental results are consistent with the simulations, clearly demonstrating the meaningfulness of the numerical analysis of the metamaterial. The analyzed resonance properties of the H-shaped metamaterial in the THz frequency range can be applied for designing THz-tunable metamaterials and improving the sensitivity of THz sensors.

• 전력전자학회논문지
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• 제26권2호
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• pp.75-81
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• 2021

This study analyzes the resonance characteristics caused by the mutual interference between LCL filters and the grid impedance under the parallel operation of the grid-connected inverter using the LCL filter. These characteristics are verified through simulation and experiment. Two inverters are used to connect to the grid in parallel, and the system parameters, including the LCL filter, are set to the same conditions. In the case of inverters running in parallel at the point of common coupling, the presence of grid impedance causes mutual interference between the LCL filters of each inverter, and the deviation of the filter resonance frequency is analyzed to understand the parallel inverter. The correlation between the number of devices and the size of grid impedance is simulated by PSIM and verified by MATLAB. By connecting the real-time digital simulator Typhoon HILS to the DSP 28377 control board, the mutual interference characteristics are tested under the condition of two inverters running in parallel. The experimental and analysis results are the same, indicating the validity of the analysis.

• 한국소음진동공학회논문집
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• 제21권3호
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• pp.258-263
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• 2011

The direction of the cutting tool plays a critical role in elliptical vibration cutting(EVC) where the cutting tool cuts workpiece in a trochoidal motion. In this study, EVC cutting device was developed using two parallel piezoelectric materials and it was observed that the rotation direction of the tool reverses as the EVC device undergoes resonance at which either flexural(cutting direction) or longitudinal( thrust direction) mode shapes occurs. To analytically explain reversal of the rotation direction, kinematic motion analysis of the tool was modified to incorporate amplification of the vibration amplitude and phase introduced by resonance. It successfully demonstrated, through Matlab simulation, reversal of the rotation direction of the cutting tool as the excitation frequency increases beyond resonance frequencies at which either flexural or longitudinal vibration occurs.

• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.166-173
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• 2011

In this paper, we implemented and analyzed a wireless power transfer (WPT) system with a CSPR topology. CSPR refers to constant current source, series resonance circuit topology of a transmitting coil, parallel resonance circuit topology of a receiving coil, and pure resistive loading. The transmitting coil is coupled by a magnetic field to the receiving coil without wire. Although the electromotive force (emf) is small (about 4.5V), the voltage on load resistor is 148V, because a parallel resonance scheme was adopted for the receiving coil. The implemented WPT system is designed to be able to transfer up to 1 kW power and can operate a LED TV. Before the implementation, the EMF reduction mechanism based on the use of ferrite and a metal shield box was confirmed by an EM simulation and we found that the EMF can be suppressed dramatically by using this shield. The operating frequency of the implemented WPT system is 30.7kHz and the air gap between two coils is 150mm. The power transferred to the load resistor is 147W and the real power transfer efficiency is 66.4 %.

• Investigative Magnetic Resonance Imaging
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• 제24권3호
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.