• Electrical & Electronic Materials
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• v.8 no.6
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• pp.744-751
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• 1995

This paper describes a study on absorption properties of electromagnetic wave by the composition ratio of Ni-Zn ferrite. Ni-Zn ferrite was composed of 48-52mol% Fe$\_$2/O$\_$3/, 18-22mol% NiO and 26-34mol% ZnO. The sintering of the composition was carried out at 1200.deg. C for 2 hours. Through the experiments, it was found that the resonance phenomenon occured at low frequency range for high permeability and vice versa. In the case of the composition of 49mol% Fe$\_$2/O$\_$3/, 20mol% NiO and 31mol% ZnO, the bandwidth ranged from 0.35GHz to 0.95GHz with the absorption thickness of 10mm. Also, in the case of the composition 51mol% Fe$\_$2/O$\_$3/, 22mol% NiO and 27mol% ZnO, the bandwidth ranged from 0.48GHz to 1.2GHz with the absorption thickness of 6mm.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.960-966
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• 2018

Communication antennas used at sea have been developed remarkably. However, the speed of this development is insufficient when compared with user demands. Therefore, we developed an antenna for UWB/Bluetooth that operates on 3 [GHz] and 5.72 [GHz] bands in order to use the high-speed communication network system which improved antenna miniaturization, gain and radiation patterns. To improve bandwidth, a microstrip patch antenna was selected and CST Microwave Studio 2014 program was used. Through the program, we calculated the slot width, length, transmission line width, etc. using a theoretical formula at each step. These figures were checked through simulation to see if they meet production standards. UWB for high-speed wireless communication for short-range communication at sea, Bluetooth for exchanging information at a short distance by connecting each device, and corresponding technology can be easily utilized.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.630-639
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• 1998

In this paper, a T-shaped microstrip feed line is proposed for a better impedance matching to the microstrip slot antenna in a various range of slot widths. It was found that the bandwidth of this antenna is proportional to the slot width. It was also found that the radiation resistance of this feed line structure is quite constant and low regardless to the slot width. A slot antenna with T-shaped microstrip feed line is analyzed by using the FDTD method. At first, the propagation process of the reflected wave and the electric field distribution in the time domain is calculated respectively. The antenna parameters also are optimized to get maximum band width, return loss, input impedance, and radiation pattern in the frquency domain by Fourier transforming the time domain results. From the computed results, the optimum slot antenna is designed and fabricated. When the slot width is 16 mm, approximately 35% of bandwidths are obtained without a matching circuit. These computed results using FDTD method were in relatively good accordance with the measured values.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.253-258
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• 2012

A computationally efficient interpolation filter with a low-distortion performance is a key component to utilize the naturally-sampled pulse width modulation (NPWM) in a digital domain. To realize the efficient interpolation filter, we propose a novel design based on the recently-proposed modified Farrow filter. The proposed filter shows a better pass-band distortion performance maintaining similar degree of complexity compared with the conventional Lagrange interpolation filter. We achieve the maximum distortion deviation of 10-3 dB to 20-kHz audible frequency range and distortion reduction of 1/6 times compared with the Lagrange interpolation filter.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.4
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• pp.285-289
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• 2009

Small RFID tag antenna were fabricated on Si substrate and their physical and electrical properties were evaluated. With decreasing the size of tag antenna on Si substrate, small SMD-type RFID tags could be fabricated, which is very useful for various applications including PCB tracking. Firstly, electromagnetic properties on tag antenna pattern were simulated with HFSS. The setup frequency was 13.56 MHz of HF-band RFID. The line-width and line-gap were modeled in the range of $50{\sim}200{\mu}m$. S parameters, SRF, and Q value were calculated from the model. When the line-width and line-gap were 100 urn and the loop-turn was 10, the SRF was 80 MHz and the Q value was ca. 9. When the microstrip antenna pattern of aluminum was fabricated by using DC sputtering, Vpp of ca. 1.6 V was obtained when the reader-tag distance was 40 mm.

• Journal of the Korean Institute of Landscape Architecture
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• v.28 no.1
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• pp.11-18
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• 2000

Taegu is notorious as hot and dry summer among Korea cities. One of the most important goals of the open space planning is to ameliorate urban climate of the city. The objective of this research is to evaluate the thermal mitigation effect of the cool islands in Taegu metropolitan city. Cool islands of this paper includes parks and rivers surrounded by or adjacent to urbanized areas. Based on the analysis of the thermal band of Landsat TM at May 17, 1997, the thermal mitigation effect of open spaces in the city could be summarized as follows ; Kumho river showed the largest mitigation effect in terms of the width of mitigation zone and temperature difference. Evaporation from wide water surface and evapo-transpiration from riparian grass land could bring into results. Significant mitigation effect of parks covered with forest can be observed. The temperature range of such parks were between 19.05$^{\circ}C$ and 19.44$^{\circ}C$ However, the thermal mitigation effect of Dalsung park and Apsan park was insignificant. The small size and high percentage of hard paving of the former and the relative low density of the residential areas adjacent to the latter could be the main reason. In conclusion, the thermal mitigation effect in urban ope spaces could be detectedby the employment of thermal band data of Landsat TM and GIS buffering technique.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.733-734
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• 2017

Ultrasonic, infrared, and CCD cameras are typically used to obtain location information, but the error range is large depending on the surrounding environment. However, IR-UWB can be used for distance and location measurement both indoors and outdoors, Technology. It is possible to determine the existence and distance of an object by emitting a short signal width in units of 1 ns and using a reflected signal and a time delay. It is also possible to measure the exact position within the cm error irrespective of the environmental conditions. Since it processes a large number of reflection signals, we try to measure three-dimensional spatial coordinates by improving the noise by using the mean value of the signal, the band pass filter and the FFT.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.857-871
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• 1994

In this paper, six kinds of spiral antenna, a combination of two types of spiral arm-width and three types of spiral curvature are analyzed by using moment method. Dividing spiral arms into N sections, the current distribution is calculated by Galerkin`s method. The radiation pattern and the antenna gain are derived from antenna currents. All os the six spiral antenna have amni-dirctional and wide-band characteristics, although the antenna gain changes within +_ 5dB bound for operating range(600MHz-2GHz). The variation of antenna`s gain is caused by the return loss in connection the Balun to the antenna. Simulation and experimental results on the radiation pattern also show spiral antennas have omni-directional and wide-band characteristics.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.69.2-69.2
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• 2021

We present the discovery of rare active galactic nuclei (AGNs) in nearby (z<0.05) compact elliptical galaxies (cEs) located in isolated environments. Using spectroscopic data from the Sloan Digital Sky Survey (SDSS) Data Release 12, four AGNs were identified based on the optical emission-line diagnostic diagram. SDSS optical spectra of AGNs show the presence of distinct narrow-line emissions. Utilizing the black hole (BH) mass-stellar velocity dispersion scaling relation and the correlation between the narrow L([OIII])/L(Hβ) line ratio and the width of the broad Hα emission line, we estimated the BH masses of the cEs to be in the range of 7×10⁵-8×10⁷ solar mass. The observed surface brightness profiles of the cEs were fitted with a double Sérsic function using the Dark Energy Camera Legacy Survey r-band imaging data. Assuming the inner component as the bulge, the K-band bulge luminosity was also estimated from the corresponding Two Micron All Sky Survey images. We found that our cEs follow the observed BH mass-stellar velocity dispersion and BH mass-bulge luminosity scaling relations, albeit there was a large uncertainty in the derived BH mass of one cE. In view of the observational properties of BHs and those of the stellar populations of cEs, we discuss the proposition that cEs in isolated environments are bona fide low-mass early-type galaxies (i.e., a nature origin).

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.65-80
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• 2014

This study conducted Trapdoor tests with actual tunnel shape, investigated the mechanical behavior of ground and loosening load on tunnels, and evaluated the mechanism of progressive failure by numerical simulation. The loosening load sharply decreased initially, but it generally increased and reached the stabilized level exhibiting the arching effect, and loose sand showed relatively higher values than those of dense sand. The shear band started from the tunnel shoulder with $63^{\circ}$ (loose sand) to $69^{\circ}$ (dense sand), and gently curved inward to the ground surface. The widths of shear band formation above the tunnel showed a range from 1.8b to 1.9b (b=Tunnel width), which are similar to those values calculated from existing formular. The vertical height of this shear band for deep tunnel was turned out to be a bit lower than that from existing studies (3.0*Tunnel Height).