• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.519-527
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• 2010

In this paper, we proposed a 13.56 MHz wireless power transfer system using loop antennas with tunable impedance matching circuits. In general, a wireless power transfer system shows an impedance mismatching due to a reflected impedance, because a coupling coefficient is varied with respect to separation distance between two resonating antennas. The proposed system can compensate the effect of this impedance mismatch owing to tunable impedance matching circuits using varactor diodes. Therefore, transmission efficiency is enhanced, moreover, the center frequency of the system is not changed, regardless of separation distance between two antennas. In order to demonstrate the performance of the proposed system, a wireless power transfer system with tunable impedance matching circuits is designed and implemented, which has a pair of loop antennas with a dimension of $30\;cm{\times}30\;cm$ cm. The input return loss, coupling coefficient, efficiency, and input impedance variation with respect to a distance between loop antennas were measured. From measured results, the proposed system shows enhanced performances than the case of the general fixed $50\;{\Omega}$ impedance matching circuits. Therefore, we verified that the proposed wireless power transfer system using the proposed impedance matching scheme will be able to ensure robust operation even when the separation distance of antennas is varied.

• Journal of Korean Association for Spatial Structures
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• v.6 no.4 s.22
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• pp.81-92
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• 2006

This paper presents exact solutions for the free vibrations and buckling of rectangular plates having two opposite, simply supported edges subjected to linearly varying normal stresses causing pure in-plane moments, the other two edges being free. Assuming displacement functions which are sinusoidal in the direction of loading (x), the simply supported edge conditions are satisfied exactly. With this the differential equation of motion for the plate is reduced to an ordinary one having variable coefficients (in y). This equation is solved exactly by assuming power series in y and obtaining its proper coefficients (the method of Frobenius). Applying the free edge boundary conditions at y=0, b yields a fourth order characteristic determinant for the critical buckling moments and vibration frequencies. Convergence of the series is studied carefully. Numerical results are obtained for the critical buckling moments and some of their associated mode shapes. Comparisons are made with known results from less accurate one-dimensional beam theory. Free vibration frequency and mode shape results are also presented. Because the buckling and frequency parameters depend upon Poisson's ratio ( V ), results are shown for $0{\leq}v{\leq}0.5$, valid for isotropic materials.

• KSBB Journal
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• v.16 no.5
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• pp.486-492
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• 2001

The antimutagenic mechanism of the fraction III(RG III)separated from the water extract of Rehmannia glutionosa was investigated by Escherichia. coli GW and B/r strains. RG-III treatment did not affect the ${\beta}$-galactosidase activity E. coli GW-1060, 1106, 1107 and 1105. These results indicated that RG-III did not induce RecA protein amplification and did not also prevent the proteolytic cleavage of LexA. The bio-antimutagenicity and survival effect of RG-III on 4-nitroquinoline 1-oxide(4NQO), N-methyl-N-nitor-N\`-nitrosoguanidine(MNING) were investigate by E. coli B/r strains with have different pathway of DNA repai. RG-III slightly increased the survival of 4NQO-treated WP2, WP2s, WP67, CM561, CM611 cells, but the reactivation of survival cannot ve explained by the repair mode. RG-III caused the decrease of mutagenicity and lethality treated with MNNG in ZA159 despite of the increase in WP2, WP2s, WP67, CW561, CM611. Compared with bio-antimutagenic effects of RG-III on 4NQO, greatly increased antimutagenic effects of RG-III were observed with all the E. coli B/r strains tested, but less active in ZA159. These results suggest that RG-III was identified as a blocking agent for preventing the 4NQO induced mutagenesis, and may act as chl-products.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.45-52
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• 2018

This paper deals with the analysis of the inner-loop algorithm of the Pixhawk which is a representative multi-copter open source. The algorithm is based on flight control-law structure. The inner-loop algorithm of the Pixhawk can be divided into a position controller and an attitude controller. The position controller generates the attitude of the multi-copter to move to the destination The position controller also generates the demand force and moment acting on each actuator. We confirm that the position controller saturates the desired acceleration and speed by using a proper relational expression. The expression can be used in order to prevent the sudden change in the attitude of a multi-copter.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.342-346
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• 2006

A polymeric ring resonator with electrically variable extinction ratio at resonant wavelengths has been proposed and demonstrated. It consists of a ring waveguide coupled to a straight bus waveguide and a modulating electrode, which is formed in the outer cladding region outside of the ring. When electrical power is applied to the electrode, the refractive index of the polymers underneath the electrode is lowered to strengthen the confinement of the guided mode of the ring and thus the equivalent effective refractive index felt by the mode is decreased. Therefore, the propagation loss of the guided mode is reduced with the applied electrical power Consequently the extinction ratio at resonant wavelengths is varied by the electrical power. For the achieved results, the extinction ratio was changed by about 9 dB for the electrical power of 12 mW, when the propagation loss of the ring was reduced by 80 dB/cm.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.354-360
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• 2002

The piezoelectric composites had many advantages in comparison with conventional piezoelectric ceramics and piezopolymers for ultrasonic transducers used in NDT and in medical ultrasionic imaging. The electromechanical coupling coefficient should be high and the acoustic impedance should be low in these applications. However, the cross-coupling with spurious oscillations caused by laterally running plate waves exhibited complex motions in the surface of piezoelectric composites with coarse lateral spatial scale. The thickness mode electromechanical coupling coefficient of 1-3type of piezoelectric compoistes were 0.36 to 0.64, and the acoustic impedance of them were 9.8 to 22.7 MRayl. The lateral resonance frequency of 1-3 type piezoelectric composites shifted to high frequency region with decreasing lateral spatial scale.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.9 no.1
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• pp.59-69
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• 2001

The rotor blade is modeled using a composite box beam with arbitrary wall. The active constrained damping layers are bonded to the upper and lower surfaces of the box beam to provide active and passive damping. A finite element model, based on a hybrid displacement theory, is used in the structural analysis. The theory is capable of accurately capturing the transverse shear effects in the composite primary structure, the viscoelastic and the piezoelectric layers within the ACLs. A reduced order model is derived based on the Hankel singular value. A linear quadratic Gaussian (LQG) controller is designed based on the reduced order model and the available measurement output. However, the LQG control system fails to stabilize the perturbed system although it shows good control performance at the nominal operating condition. To improve the robust stability of LQG controller, the loop transfer recovery (LTR) method is applied. Numerical results show that the proposed controller significantly improves rotor aeromechanical stability and suppresses rotor response over large variations in rotating speed by increasing lead-lag modal damping in the coupled rotor-body system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.2
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• pp.146-153
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• 1998

The optical near-field patterns, propagation loss and mode sizes of x-cut $Ti:LiNbO_3$ optical waveguide which was fabricated by Ti-diffusion varying with Ti strip thickness in wet oxygen atmosphere were discussed at optical wavelength 1550nm. As Ti thickness increased from $760{\AA}$, the insertion loss of waveguide was decreased. But at Ti thickness $1500{\AA}$, mode sizes are widely broadened. The Ti thickness of below $1100{\AA}$ and above $1500{\AA}$ showed negative effects to propagation loss and fiber coupling. The best Ti thickness for fabricating low propagation loss and good fiber coupling was inferred to be between $1100{\AA}-1500{\AA}$ in our conditions. And for Ti thickness $1150{\AA}$, its propagation loss, horizontal/vertical mode sizes were showed 1.61 dB/cm, $11.9/8.9{\mu}m$ for TM, 0.22 dB/cm, $12.0/9.1{\mu}m$ for TE respectively.

• Journal of Korea Water Resources Association
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• v.46 no.9
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• pp.909-919
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• 2013

This study examines the hydraulic characteristics, the channel changes, the behavior of bars, and bank stability by means of laboratory experiments. Three sets of laboratory experiments are conducted to elucidate the influence of riparian vegetation of the channels with erodible banks. Flow velocity is decreased in the vegetated zone, the mobility of lower channels is decreased. The double Fourier analysis of the bed waves shows that 1-1 mode (alternate bar) is dominant at the initial stage of the channel development. As time increases, 2-2 and 2-3 modes (central or multiple bars) are dominant due to the increased width to depth ratio. As the vegetation density is increased, the number of bars are increased, bank stability increases. The variation of sediment discharges is affected by vegetation density. The braided intensity is decreased with vegetation density. As the vegetation density is increased, the correlation coefficient of bed topography and bed relief index is increased.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.9
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• pp.779-788
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• 2014

The satellite should generate electric power efficiently to perform the mission successfully within limited power. For this reason, the electrical power system of LEO satellites usually regulates the power which is generated from the solar cells using MPPT (Maximum Power Point Tracking) method. This paper proposes advanced MPPT algorithm based on the fuzzy logic applied to small CubeSat satellite. The simulation has been performed to confirm the validity of the proposed method by interlocking between MATLAB/Simulink and STK (Systems Tool Kit). The EBA(Energy Balance Analysis) has also been performed at two different pointing modes of KAUSAT-5 for solar irradiation according to the satellite orbit and attitude, and load capacity varied with operation modes by Simulink and STK. The performance of fuzzy logic-based MPPT algorithm was verified through the EBA. The validity of the proposed MPPT algorithm based on the fuzzy logic was also confirmed by comparing with P&O (Perturbation & Observation) algorithm that is general in the MPPT.