• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1062-1065
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• 2002

We demonstrate the MMIC(monolithic microwave integrated circuit) frequency doublers generating stable and low-cost 29 ㎓ local oscillator signals from 14.5 ㎓ input signals. These devices were designed and fabricated by using the MMIC integration process of 0.1 $\mu\textrm{m}$ gate-length PHEMTs (pseudomorphic high electron mobility transistors). The measurements showed S$\_$11/ of -9.2 dB at 14.5 ㎓, S/sub22/ of -18.6 dB at 29 ㎓ and a minimum conversion loss of 18.2 dB at 14.5 ㎓ with an input power of 6 dBm. The fundamental signal of 14.5㎓ was suppressed below 15.2 dBc compared with the second harmonic signal at the output port, and the isolation characteristics of the fundamental signal between the input and the output port were maintained above 30 dB in the frequency range of 10.5 ㎓ to 18.5 ㎓.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.1931-1939
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• 2000

Operating excitation forces of the linear vibratory system are normally determined by direct measurement techniques using load cells, strain gauges, etc. But, hydraulic forces of the rotating turbomachinery such as centrifugal pumps are exerted on an impeller due to asymmety of the flow by the interaction between pump impeller and volute. So, investigations of wide range of hydraulic designs and geometric deviations are difficult by direct method. This paper presents a hybrid approach for fourier transformed operational excitation forces, which uses pseudo-inverse matrix of the transfer matrix for the system and the measured vibrational data with standard installed pump. The determination of the transfer function matrix is based on a linear rotor/stationary system and steady state harmonic response in finite element analysis. And, vibrational data is collected in both vertical and horizontal directions at inboard and outboard bearing housings. The results of the process may be enhanced by making acceleration measurements at many more locations than there are forces to be determined.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.5
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• pp.407-417
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• 2015

For the more accurate prediction on manoeuvring performance of a ship at initial design phase, bare hull manoeuvring coefficients were estimated by RANS(Reynolds Averaged Navier-Stokes) based virtual captive model tests. Hydrodynamic forces and moment acting on the hull during static drift and harmonic oscillatory motions were computed with a commercial RANS code STAR-CCM+. Automatic and consistent mesh generation could be implemented by using macro functions of the code and user dependency could be greatly reduced. Computed forces and moments on KCS and KVLCC 1&2 were compared with the corresponding measurements from PMM(Planar Motion Mechanism) tests. Quite good agreement can be observed between the CFD and EFD results. Manoeuvring coefficients and IMO standard manoeuvres estimated from the computed data also showed reasonable agreement with those from the experimental data. Based on these results, we could confirm that the developed virtual captive manoeuvring model test process could be applied to evaluate manoeuvrability of a ship at the initial hull design phase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.396-401
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• 1999

In the present paper, potassium lithium niobate(KLN) crystals have been grown along <001>, <100> and <110> directions by the top seeded solution growth (TSSG) method from Li-richer melts with different compositions. The morphologies of KLN crystals grown along different directions have been studied, and the well-developed facets have been unambiguously indexed using X-ray goniometer and stereographic projection analysis. The growth mechanism and defects such as cracks and inclusions were discussed on the basis of observations of facets on the crystal-solution interfaces. The crystal compositions were determined by a chemical analysis method. The structure and lattice constants of KLN crystals were determined and calculated on the basis of XRD data by using TREOR90 and PIRUM programs. The Curie temperature and optical absorption were determined by dielectric constant peak and spectrum measurements. respectively. The blue second harmonic generation (SHG) characteristics of KLN sample were also investigated using a pulsed dye laser.

• Journal of electromagnetic engineering and science
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• v.17 no.4
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• pp.191-196
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• 2017

Microwave wireless power transmission (MWPT) is a promising technique for low and medium power applications such as wireless charging for sensor network or for biomedical chips in case with long ranges or in dispersive media such. A key factor of the MWPT technique is its efficiency, which includes the wireless power transmission efficiency and the radio frequency (RF) to direct current (DC) voltage efficiency of RF-DC converter (which transforms RF energy to DC supply voltage). The main problem in designing an RF-DC converter is the nonlinear characteristic of Schottky diodes; this characteristic causes low efficiency, higher harmonics frequency and a change in the input impedance value when the RF input power changes. In this paper, rather than using harmonic termination techniques of class E or class F power amplifiers, which are usually used to improve the efficiency of RF-DC converters, we propose a new method called "optimal input impedance" to enhance the performance of our design. The results of simulations and measurements are presented in this paper along with a discussion of our design concerning its practical applications.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.109-121
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• 2001

This paper describes results of an experimental study to examine the effect of a submerged horizontal breakwater to sea water exchange. Flow measurements were taken by using a PIV(Particie Image Velocimetry) system, and mean currents and wave ellipses extracted through the harmonic analysis are presented. As results, the rates of circulating flow were closely connected with the volume flux of incident waves and the counter-rotating vortex pair was observed at the onshore side of a plate. The dye study showed that incoming sea water and polluted water body mixed up significantly due to turbulent motions induced by a jet-like flow.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.446-456
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• 2007

Numerical analyses of stem waves, the interaction between incident and reflected waves of obliquely incident regular waves along a vertical wall in a constant water depth, are presented. For the numerical model of the analysis, the two-layer Boussinesq equations developed by Lynett and Liu(2004a,b) are employed. Numerical results are compared with both laboratory measurements and those obtained using parabolic approximation model. The overall comparisons between the results from the two numerical models and the experiments are good. However, the two-layer Boussinesq model is more accurate than the parabolic approximation model as the angle of incident waves increases. In particular, the higher harmonic generation due to the wave nonlinearity is captured only in the Boussinesq model.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.107-114
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• 2014

This paper applies a compensated low pass filter (LPF) to current measurements for permanent magnet synchronous motor (PMSM) drives. The noise limits the bandwidth of current controllers and has more adverse influences on control performances under the light load condition because of the low signal-to-noise ratio. In order to eliminate the noise sensitivity, this paper proposes a digital LPF with a compensator of gain attenuation and phase delay which are unacceptable in current information for PMSM drives. Characteristics of the proposed LPF are analyzed in comparison with the general LPFs. The compensated LPF is basically designed by the orthogonal property of the measured currents in the ${\alpha}{\beta}$ stationary reference frame. In addition, an implementation issue of the proposed method is discussed. Experimental results using the proposed method show improvements of the current control performance from two perspectives, rapid step responses and reductions of harmonic distortion.

• Journal of Broadcast Engineering
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• v.18 no.5
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• pp.771-774
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• 2013

This study investigates the relationship between voice quality measurements and emotional states, in addition to conventional prosodic and cepstral features. Open quotient, harmonics-to-noise ratio, spectral tilt, spectral sharpness, and band energy were analyzed as voice quality features, and prosodic features related to fundamental frequency and energy are also examined. ANOVA tests and Sequential Forward Selection are used to evaluate significance and verify performance. Classification experiments show that using the proposed features increases overall accuracy, and in particular, errors between happy and angry decrease. Results also show that adding voice quality features to conventional cepstral features leads to increase in performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.2
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• pp.13-18
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• 2001

In this paper, a four-pole quasi-elliptic function bandpass filter of 1.95GHz center frequency with 60 MHz bandwidth for IMT-2000 using miniaturized square SIR(Stepped Impedance Resonator) is designed and fabricated. The simulation of NUFDTD(Nonuniform Finite Difference Time Domain) is used to design the resonator and to calculate the coupling coefficient of three basic structures. The size reduction of miniaturized square SIR resonator is about more than 50% compare with a square open loop resonator. Bandpass filter using this resonator shows good microwave characteristic with the harmonic suppression of about 19dB. The results of measurements are almost similar to those of simulation.