• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1343-1350
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• 2012

This paper presents a new method for designing a dual-band WIFI antenna using the third-order harmonic mode of a monopole antenna whose first-order mode operates at the low frequency band of WIFI. As analysing the current distribution of the third-order mode of this monopole antenna, the strongest point of electric field can be found. Then by attaching a stub at this point, the resonant frequency of the stub radiator can be adjusted from the third-order mode of the monopole antenna into the high frequency band of WIFI and the input impedance at this resonant frequency can be controlled with the width of the branch, without affecting the low frequency band of WIFI (the first-order mode of the monopole antenna). The compact dual-band antenna is designed at the size of an USB(universal serial bus) dongle and the bandwidth covers 600 MHz(2.3~3 GHz) at 2 GHz and 1 GHz(4.9~5.9 GHz) at 5 GHz under -10 dB which is satisfied with WLAN frequency. Efficiency of proposed antenna achieves over 50 % at WLAN frequency.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.771-777
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• 2017

The applications of smartphones or other portable smart devices have dramatically changed people's lifestyle. Researchers have been investigating useage of smartphones for structural health monitoring, earthquake monitoring, vibration measurement and human posture recognition. Their results indicate a great potential of smartphones for measuring pedestrian-induced loads like walking, jumping and bouncing. Smartphone can catch the device's motion trail, which provides with a new method for pedestrain load measurement. Therefore, this study carried out a series of experiments to verify the application of the smartphone for measuring human-induced load. Shaking table tests were first conducted in order to compare the smartphones' measurements with the real input signals in both time and frequency domains. It is found that selected smartphones have a satisfied accuracy when measuring harmonic signals of low frequencies. Then, motion capture technology in conjunction with force plates were adopted in the second-stage experiment. The smartphone is used to record the acceleration of center-of-mass of a person. The human-induced loads are then reconstructed by a biomechanical model. Experimental results demonstrate that the loads measured by smartphone are good for bouncing and jumping, and reasonable for walking.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.737-742
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• 2007

The method of the reducing duct noise can be classified by passive and active control techniques. However, passive control has a limited effect of noise reduction at low frequencies (below 500Hz) and is limited by the space. On the other hand, active control can overcome these passive control limitations. The active control technique mostly uses the Least-Mean-Square (LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time particularly when the Filtered-X LMS (FXLMS) algorithm is applied to an active noise control (ANC) system. However, the convergence performance of the LMS algorithm decreases slightly so it may delay the convergence time when the FXLMS algorithm is applied to the active control of duct noise. Thus the Co-FXLMS algorithm was developed to improve the control performance in order to solve this problem. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Co-FXLMS algorithm is presented in comparison with the FXLMS algorithm. Simulation results show that active noise control using Co-FXLMS is effective in reducing duct noise.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.11
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• pp.1318-1326
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• 2007

Simple practical design method is proposed for the waffle-iron waveguide filter. The design procedure comprises two steps. The first step is to calculate the K-inverter based on the transformed ABCD parameter from the S parameter for the single window of waffle-iron structure by use of EM S/W tool. The second step is to optimize the size of the windows such that the calculated K inverters may be in accord with the distributed constant prototype filter. In order to validate the design method, a waffle-iron filter for satellite communications over the Ka band is designed and fabricated. The measured results are in good agreement with the calculated ones.

• Journal of Power Electronics
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• v.9 no.5
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• pp.757-771
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• 2009

This paper proposes a systematic approach to the modeling of the small-signal characteristics of three-phase bridge boost rectifiers under non-sinusoidal conditions. The main obstacle to the conventional synchronous d-q frame modeling approach is that it is unable to identify a steady-state under non-sinusoidal conditions. However, for most applications under non-sinusoidal conditions, the current loops of boost rectifiers are designed to have a bandwidth that is much higher than typical harmonics frequencies in order to achieve good current control for these harmonic components. Therefore a quasi-static method is applied to the proposed modeling approach. The converter small-signal characteristics developed from conventional synchronous frame modeling under different operating points are investigated and a worst case point is then located for the current loop design. Both qualitative and quantitative analyses are presented. It is observed that operating points influence the converter low frequency characteristics but hardly affect the dominant poles. The relationship between power stage parameters, system poles and zeroes is also presented which offers good support for the system design. Both the simulation and experimental results verified the analysis and proposed modeling approach. Finally, the practical case of a parallel active power filter is studied to present the modeling approach and the resultant regulator design procedure. The system performance further verifies the whole analysis.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.2
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• pp.79-84
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• 2012

In this paper, a three-phase high-voltage converter (HVC), in which the main structure of each phase is composed of a cascaded PWM rectifier (CPR) and cascaded inverter (CI), is studied. A high-voltage grid is the input of the HVC. In order to ensure proper operation of the HVC, the control method should achieve output voltage sharing (OVS) among the rectifiers in the CPR, OVS among the inverters in the CI, and high power factor. Master-slave direct-current control (MDCC) is used to control the CPR. The ability of the control system to prevent interference is strong when using MDCC. The CI is controlled by three-loop control, which is composed of an outer common-output-voltage loop, inner current loops and voltage sharing loops. Simulation results show low total harmonic distortion (THD) in the HVC input currents and good OVS in both the CPR and CI.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.5
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• pp.713-718
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• 2016

Predicting precise specifications of differential mixed-signal circuits is a difficult problem, because analytically derived correlation between process variations and conventional specifications exhibits the limited prediction accuracy due to the phase unbalance, for most self-tests. This paper proposes an efficient prediction technique to provide accurate specifications of differential mixed-signal circuits in a system-on-chip (SoC) based on a nonlinear statistical nonlinear regression technique. A spectrally pure sinusoidal signal is applied to a differential DUT, and its output is fed into another differential DUT through a weighting circuitry in the loopback configuration. The weighting circuitry, which is employed from the previous work [3], efficiently produces different weights on the harmonics of the loopback responses, i.e., the signatures. The correlation models, which map the signatures to the conventional specifications, are built based on the statistical nonlinear regression technique, in order to predict accurate nonlinearities of individual DUTs. In production testing, once the efficient signatures are measured, and plugged into the obtained correlation models, the harmonic coefficients of DUTs are readily identified. This work provides a practical test solution to overcome the serious test issue of differential mixed-signal circuits; the low accuracy of analytically derived model is much lower by the errors from the unbalance. Hardware measurement results showed less than 1.0 dB of the prediction error, validating that this approach can be used as production test.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.4
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• pp.499-504
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• 2017

A UHF CMOS variable gain low-noise amplifier (LNA) is designed for mobile digital TV tuners. The proposed LNA adopts a feedback topology to cover a wide frequency range from 474 to 868 MHz, and it supports the notch filter function for the interoperability with the GSM terminal. In order to handle harmonic distortion by strong interferers, the gain of the proposed LNA is step-controlled while keeping almost the same input impedance. The proposed LNA is implemented in a $0.11{\mu}m$ CMOS process and consumes 6 mA at a 1.5 V supply voltage. In the measurement, it shows the power gain of greater than 16 dB, NF of less than 1.7 dB, and IIP3 of greater than -1.7 dBm for the UHF band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1024-1029
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• 2003

This paper presents the complex antenna factor of a top-hat EMI monopole antenna for measuring time domain electromagnetic fields. The approach is facilitated by adding a artificial parallel ground plane above the monopole antenna. This allows use of cylindrical harmonic field expansions in each of three subregions enclosed by the two ground plane. The results show that the complex antenna factor of the top-hat monopole antenna does not diverge at low frequencies. When compared with a monopole antenna, the top-hat monopole antenna has broadband characteristics. In order to verify the availability of the mode-matching method, the input impedance of the antenna were compared with experiments.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.204-206
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• 2002

For small capacity rectifier circuits such as these for consumer electronics and appliances. capacitor input type rectifier circuits are generally used Consequently. various harmonics generated within the power system become a serious Problem. Various studies of this effect have been presented previously. However. most of these employ switching devices, such as FETs and the like. The absence of switching devices makes systems more tolerant to over -load, and brings low radio noise benefits. We propose a power factor correction scheme using a LC resonant in commercial frequency without switching devices. In this method. It makes a sinusoidal wave by widening conduction period using the current resonance in commercial frequency. Hence, the harmonic characteristics can be significantly improved. where the lower order harmonics. such as the fifth and seventh orders are much reduced. The result are confirmed by the theoretical and expermental implementations.