• Journal of electromagnetic engineering and science
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• v.17 no.2
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• pp.108-110
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• 2017

The global positioning system (GPS) is a useful system in civilian and military applications. However, because of the weak signal, GPS receivers are vulnerable to interference caused by unwanted signals or intentional jammers. To alleviate this issue, a controlled reception pattern antenna (CRPA) array can be employed to adaptively place radiation pattern nulls toward the direction of the signal interference. The performance of the CRPA array improves as the number of antenna elements increases. Therefore, antenna miniaturization is highly desirable for CRPA applications. We designed a compact CRPA array based on seven electrically miniaturized microstrip patch antennas (MPAs) on a 5-inch ground platform. We used a non-Foster matching circuit to match efficiently miniaturized MPAs on an FR-4 substrate. Experimental results show that the non-Foster matching circuit significantly improves such elements of antenna performance as return loss and antenna gain. In addition, we confirmed that the mutual coupling of the proposed CRPA array is less than -45 dB.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.152-161
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• 2008

This paper deals with a new wave shaping technique for cost effective harmonic mitigation in ac-dc converter feeding Vector Controlled Induction Motor Drives(VCIMD's) for improving power quality at the point of common coupling(PCC). The proposed harmonic mitigator consists of a polygon connected autotransformer based twelve-pulse ac-dc converter and a small rating passive shunt filter tuned for $11^{th}$ harmonic frequency. This ac-dc converter eliminates the most dominant $5^{th},\;7^{th},\;and\;11^{th}$ harmonics and imposes the reduction of other higher order harmonics from the ac main current, thereby improving the power quality at ac mains. The design of autotransformer is carried out for the proposed ac-dc converter to make it suitable for retrofit applications, where presently a 6-pulse ac-dc converter is used. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter in a wide operating range of the drive. Experimental results obtained on the developed laboratory prototype of the proposed harmonic mitigator are used to validate the model and design of the ac-dc converter.

• Analytical Science and Technology
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• v.23 no.6
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• pp.537-543
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• 2010

Dopamine (DA) is an important neurotransmitter molecule of catecholamines. Its deficiency could lead to brain disorder such as Parkinson's disease and schizophrenia. Therefore, it is necessary to establish a suitable analytical technique with sensitivity and simplicity. A competitive enzyme-linked immunosorbent assay for DA has been optimized and characterized. Assay sensitivity is controlled by two factors in competitive immunoassay. One is a nature and concentration of competitor, and the other is those of binder, antibody. Thus, optimization was performed: BSA-DA conjugate and antibody-avidin conjugate were prepared by dual heterobifunctional coupling method using SATA and SMCC. Assay condition was optimized with $6.66\;{\mu}gmL^{-1}$ of BSA-DA and $4.17{\times}10^{-10}\;M$ of antibody-avidin conjugate. A dose-response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to $2.3{\times}10^{-2}\;{\mu}g\;mL^{-1}$ and four orders of magnitude ($1.0{\times}10^{-7}\;M$ to $1.0{\times}10^{-3}\;M$), respectively. Calibration curve was constructed on dynamic range and least-squares regression of this data gave the following relationship: absorbance = -0.1098 log[DA]+0.0353 ($R^2$ = 0.9956).

• Journal of the Korean Magnetics Society
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• v.16 no.2
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• pp.130-135
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• 2006

We theoretically demonstrate that the interlayer exchange coupling (IEC) energy can be manipulated by means of an external bias voltage in a $F_1/NM/F_2/S$$(F_1:ferromagnetic,\;NM:nonmagnetic\;metallic,\;F_2:ferromagnetic,\;S:semiconductor\;layers)$ four-layer system. It is well known that the IEC energy between two ferromagnetic layers separated by nanometer thick nonmagnetic layer depends on the spin-dependence of reflectivity to the $F_1/NM/F_2/S$ four-layer system, where the reflectivities at the interface in $NM/F_2$ interface also depends on $F_2/S$ interface due to the multiple reflection of an electron-like optics. Finally, the IEC energy depends on the spin-dependent electron reflectivity not only at the interfaces of $F_1/NM/F_2$, but also at the interface of $F_2/S$. Naturally the Schottky barrier is formed at the interface between metallic ferromagnetic layer and semiconductor, the Schottky barrier height and thickness can be tailored by an external bias voltage, which causes the change of the spin-dependent reflectivity at $F_2/S$ interface. We show that the IEC energy between two ferromagnetic layers can be controlled by an external bias voltage due ti the electron-optics nature using a simple free-electron-like one-dimensional model.

• ETRI Journal
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• v.26 no.6
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• pp.605-614
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• 2004

In this paper, we investigate array calibration algorithms to derive a further improved version for correcting antenna array errors and RF transceiver errors in CDMA smart antenna systems. The structure of a multi-channel RF transceiver with a digital calibration apparatus and its calibration techniques are presented, where we propose a new RF receiver calibration scheme to minimize interference of the calibration signal on the user signals. The calibration signal is injected into a multi-channel receiver through a calibration signal injector whose array response vector is controlled in order to have a low correlation with the antenna response vector of the receive signals. We suggest a model-based antenna array calibration to remove the antenna array errors including mutual coupling errors or to predict the element patterns from the array manifold measured at a small number of angles. Computer simulations and experiment results are shown to verify the calibration algorithms.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.3124-3132
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• 2011

Scott transformers have widely used to convert three phases into two phases and compensate the unbalance. Theoretically, the loads of the two secondary phases are same, no unbalance appears in the PCC(point of common coupling). But Due to the uncertainty of traction load, the unbalance are generally presented at the PCC. In this paper The amount of the voltage unbalance is expressed in the ratio of the negative sequence voltages to the positive sequence voltage. We tried to compensate the unbalance using SVC(Static Var Compensator）in an unbalance traction loads state by modeling. The SVC are installed and controlled to provide different amounts of reactive power compensation.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.539-545
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• 2001

This paper proposes a static synchronous series compensator based on multi-bridge inverter. The proposed system consists of 6 H-bridge modules per phase, which generate 13 pulses for each half period of power frequency. The dynamic characteristic was analyzed by simulations with EMTP code, assuming that it is inserted in the 154-kV transmission line of one-machine-infinite-bus power system. The feasibility of hardware implementation was verified through experimental works using a scaled model. The proposed system does not require a coupling transformer for voltage injection, and has flexibility in expanding the operation voltage by increasing the number of H-bridge modules.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.4
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• pp.1-11
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• 1995

Active suspension control for vehicles is developed to improve both ride comfort and steering stability which are in trade off relation. In this study, the modal sky-hook controller for 7 D. O. F. model is proposed to resolve the problems such as computaional power restriction and uncertainties in modeling of systems and environments. Modal sky-hook controller reduces the coupling between the modes to be controlled. The simulation result for ride comfort shows that the perform ance of the proposed controller matches that of the optimal controller. Systematic method of determining its gain is proposed. The model sky-hook controller shows the robustness to road irregularity and modeling error.

• Proceedings of the KIEE Conference
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• 2003.11b
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• pp.123-126
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• 2003

This paper presents an speed reference trajectory planning methods for vibration suppression in a t-mass resonant system which has a flexible coupling between a load and a driving motor. Due to this flexibility, the system often suffers vibration especially when the motor is controlled for higher speed command. The steady state conditions are utilized to derive desired load speed trajectory which does not cause the torsional vibration. And the desired motor speed trajectory is synthesized base on the relation between load and motor speed. The simulation and experiment result suggest that the proposed method effectively suppress the vibration.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.432-434
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• 1994

This paper describes a phase-shifter which can flexibly adjust the active and reactive power flow through an ac transmission line. The phase-shifter has two voltage-source converters sharing an energy storage capacitor. The magnitude of the injected voltage is controlled by the converter I connected in parallel with the sending terminal, while that of phase angle by the converter II in series with the line through the coupling transformer. In order to analyze the whole system operation, an equivalent circuit model was developed and verified by a computer simulation with EMTP code.