• Korean Journal of Materials Research
• /
• v.32 no.4
• /
• pp.181-185
• /
• 2022

In this study, phase-pure titanium dioxide TiO₂ ceramics are sintered using standard high-temperature solid-state reaction technique at different temperatures (1,000, 1,100, 1,200, 1,300, 1,400 ℃). The effect of sintering temperature on the densification and impedance properties of TiO₂ ceramics is investigated. The bulk density and average grain size increase with the increase of sintering temperature. Impedance spectroscopy analysis (complex impedance Z^* and complex modulus M^*), performed in a broad frequency range from 100 Hz to 10 MHz, indicates that the TiO₂ ceramics are dielectrically heterogeneous, consisting of grains and grain boundaries. The complex impedance Z^* -plane indicates the resistance of grains of the TiO₂ ceramics increases with increasing sintering temperature, while that of grain boundaries develops in the opposing direction. The complex modulus M^*-plane shows a grain capacitance that seems to be independent of the sintering temperature, while that of the grain boundaries decreases with increasing sintering temperature. These results suggest that different sintering temperatures have effects on the microstructure, leading to changes in the impedance properties of TiO₂ ceramics.

• Journal of Mechanical Science and Technology
• /
• v.19 no.3
• /
• pp.778-791
• /
• 2005

A novel pneumatic artificial muscle actuator (PAM actuator), which has achieved increased popularity to provide the advantages such as high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks, has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. Then it is not easy to realize the performance of transient response of pneumatic artificial muscle manipulator (PAM manipulator) due to the changes in the external inertia load with high speed. In order to realize satisfactory control performance, a variable damper-Magneto­Rheological Brake (MRB), is equipped to the joint of the manipulator. Superb mixture of conventional PID controller and a phase plane switching control method brings us a novel controller. This proposed controller is appropriate for a kind of plants with nonlinearity, uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control method and without regard for the changes of external inertia loads.

• Journal of the Korean Magnetics Society
• /
• v.13 no.6
• /
• pp.221-225
• /
• 2003

Effects of annealing temperature on the crystalline and magnetic properties of YIG films grown by solid phase epitaxy. The eptiaxy films were made by annealing Fe-Y-O amorphous films in the air at 550-1050 $^{\circ}C$ which were sputtered on GGG (111) substrates in a conventional rf sputtering system. Crystallization temperature of Fe-Y-O amorphous films on GGG (111) substrate was between 600 and 650 $^{\circ}C$ which is much lower than that Fe-Y-O powder prepared by sol-gel method. Excellent epitaxial growth of YIG films could be conformed by the facts that the diffraction intensity of YIG (888) plane was comparable with that of GGG (888) plane and full width at half maximum of YIG (888) rocking curve was smaller than 0.14$^{\circ}$ when films were annealed at 1050 $^{\circ}C$. It could be seen that it is necessary to anneal the films at higher temperature for an excellent epitaxy because lattice parameter of YIG films were smaller and the peak of YIG (888) plane is higher and narrower with increasing annealing temperature. Films annealed at higher temperature shows M-H loop with perpendicular anisotropy which was due to 0.15％ lattice mismatch between YIG and GGG.

• IEIE Transactions on Smart Processing and Computing
• /
• v.2 no.4
• /
• pp.240-247
• /
• 2013

The main aim of this study was to suppress the angular velocity against strong winds during storms and analyze the stability and performance of the phase plane method. The utilization of small-scale wind turbine system has become common in agriculture, houses, etc. Therefore, it is considered to be a scheme for preserving the natural energy or avoiding the use of fossil fuels. Moreover, settling small-scaled wind turbines is simpler and more acceptable compared to ordinary huge wind turbines. In addition, after converting the energy there is no requirement for distribution. Therefore, a much lower cost can be expected for small-scaled wind turbines. On the other hand, this system cannot be operated continuously because the small-scaled wind turbine consists of a small blade that has low inertia momentum. Therefore, it may exceed the boundary of angular velocity, which may cause a fault in the system due to the centrifugal force. The aim of this study was to reduce the angular velocity by controlling the stall factor. Stall factor control consists of two control methods. One is a shock absorber that is loaded in the junction of the axis of the blade of the wind turbine gear wheel and the other is pitch angle control. Basically, the stall factor itself exhibits nonlinear behavior. Therefore, this paper confirmed the feasibility of stall factor control in producing desirable performance whilst maintaining stability.

• Journal of the Optical Society of Korea
• /
• v.1 no.2
• /
• pp.81-89
• /
• 1997

The formation of phase singularities in optical fibers is theoretically and experimentally investigated. In particular, their structural characteristics and properties are discussed in relation to guided mode patterns. It is found that except for the fundamental linearly polarized(LP) modes, all the mixed modes displayed phase singularities in the transverse plane. The results in the few mode fiber show that superposition of the LP even and odd modes produces isolated dark points and phase singularities. Phase singularities are found to be of the screw type and of first order. The number of phase singularities linearly increases with the number of guided modes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.14 no.1
• /
• pp.48-53
• /
• 2001

The crystal structure of ZnS fabricated by gas-liquid phase reaction was refined by the Rietveld program using X-ray diffraction data. The R-weighted pattern (R$\sub$wp/) of ZnS powder was 10.85%. The fraction of HCP phase was closely related with extra amount of H$_2$S gas. The lattice parameters and crystalline size were changed by the relative ratio of multi-phase. The luminescence property of ZnS:Cu, Al green phosphors prepared by conventional methods was good in the range of 91∼94% and 150∼190${\AA}$, respectively. According to the maximum entropy electron density(MEED) methods, any defects in (001) plane of cubic phase were not found. We suggest that both the Rietveld and maximum entropy density methods may be useful tools for studying luminescence mechanism of other phosphors materials.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.2
• /
• pp.53-58
• /
• 2004

In this paper, the low-phase dual-band VCO, by adding switching circuit with PIN diode at feedback loop of the oscillation part having negative-resistance, is realized. In order to reduce the phase noise of the VCO, PBG structure applied to the ground plane of the resonator. When applying for PBG structure, output power is -9.17㏈m and phase noise is -102㏈c/Hz at 5.25㎓, output power is -5.17㏈m and phase noise is -101㏈c/Hz at 1.8㎓, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.6
• /
• pp.43-50
• /
• 2010

In this paper, we analyzed radiated emission generated by the split power/ground plane structures in order to reduce EMI in system modules. The magnetic fields and electric fields were simulated and measured on the test boards under various conditions. In order to reduce radiated emission, we have to determine spacing and location of the split ground gap so that input signal frequency does not coincide with the resonance frequency of the split power/ground plane structure and the phase of reflection coefficient is close to $0^{\circ}$ at input signal frequency. Moreover, we found that inserting a stitching capacitor could reduce the radiated emission. Low magnitude of reflection coefficient and the phase close to $0^{\circ}$ are required to reduce radiated emission. It is necessary to properly decide value and location of a stitching capacitor to fulfil those requirements.

• Journal of Positioning, Navigation, and Timing
• /
• v.7 no.1
• /
• pp.37-42
• /
• 2018

This paper proposed a microstrip antenna that can perform jamming of satellite signals from the GPS L5, GLONASS G3, BDS B2 frequency bands (1164 - 1217 MHz) that are employed mainly for military purposes among the GNSS frequencies using unmanned aircrafts over the enemy's sky in time of emergency. The single element in the proposed antenna can be easily mounted to unmanned aircrafts. This study analyzed the characteristics of miniaturization and beam of radiating elements by applying the image theories and perturbation effect to satisfy the uniform level at ${\pm}45^{\circ}$ of beam steering goal due to the phase delay after antenna array. The designed microstrip antenna had a miniaturized radiating element area (x-y plane), which was reduced by 76.3% compared to that of basic microstrip antenna, and its beam width was $190^{\circ}$ in the E-plane and $140^{\circ}$ in the H plane. In addition, the simulation was conducted to determine the characteristics due to the phase delay by arranging the designed single microstrip antenna by $1{\times}4$ array and the results showed that beam steering of ${\pm}45^{\circ}$ is possible in the H-plane on the basis of $0^{\circ}$. Thus, the proposed antenna was verified to be effective in satellite signal jamming in the air as it was attached to the lower end of unmanned aircrafts.

• Journal of The Korean Astronomical Society
• /
• v.48 no.1
• /
• pp.57-66
• /
• 2015

Monte-Carlo radiative models of the diffuse Galactic light (DGL) in our Galaxy are calculated using the dust radiative transfer code MoCafe, which is three-dimensional and takes full account of multiple scattering. The code is recently updated to use a fast voxel traversal algorithm, which has dramatically increased the computing speed. The radiative transfer models are calculated with the generally accepted dust scale-height of 0.1 kpc. The stellar scale-heights are assumed to be 0.1 or 0.35 kpc, appropriate for far-ultraviolet (FUV) and optical wavelengths, respectively. The face-on optical depth, measured perpendicular to the Galactic plane, is also varied from 0.2 to 0.6, suitable to the optical to FUV wavelengths, respectively. We find that the DGL at high Galactic latitudes is mostly due to backward or large-angle scattering of starlight originating from the local stars within a radial distance of r < 0.5 kpc from the Earth. On the other hand, the DGL measured in the Galactic plane is mostly due to stars at a distance range that corresponds to an optical depth of $${\sim_\sim}$$ 1 measured from the Earth. Therefore, the low-latitude DGL at the FUV wavelength band would be mostly caused by the stars located at a distance of $r{\leq}0.5$ kpc and the optical DGL near the Galactic plane mainly originates from stars within a distance range of $1{\leq}r{\leq}2kpc$. We also calculate the radiative transfer models in a clumpy two-phase medium. The clumpy two-phase models provide lower intensities at high Galactic latitudes compared to the uniform density models, because of the lower effective optical depth in clumpy media. However, no significant difference in the intensity at the Galactic plane is found.