• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2005.11a
• /
• pp.385-390
• /
• 2005

In this paper, we studied a new concept of wireless LAN service. Current service for wireless LAN has some weak points such as occuring a frequency shadowed area, high cost for setting a number of APs, electromagnetic interference by means of a large output transmission and weak security issues. To reduce those problems, we proposed setting antennas which are from one AP for each rooms, and designed a suitable antenna. After that we measured a PMA(Propagation Measurement & Analysis). Experimental results showed that a new concept of wireless LAN service is excellent to resolve interference and weak security issues by minimizing external propagation of a building.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.35.3-35.3
• /
• 2019

Blazars are a subclass of active galactic nuclei (AGNs) with relativistic jets aligned with our line of sight. The jet physics is yet to be understood, but can be studied with blazar variability (e.g., flares). The highly variable blazar 3C 279 has shown a general decline of its radio flux density since 2013, but the flux density has been increasing since 2017. To better understand physical properties of 3C 279 related with the flux variations, we analyze multi-frequency new radio data obtained with Korean VLBI Network (KVN), as well as archival data from Owens Valley Radio Observatory (OVRO) and Submillimeter Array (SMA). We measure the radio spectral variability and infer the relativistic jet properties of 3C 279. The high-cadence OVRO and SMA observations are used to construct detailed light curves of the source, and KVN data supplement the spectral coverage and allow us to locate the spectral break frequencies precisely. In this talk, we present our analysis results and interpret them using a blazar jet model.

• Ocean and Polar Research
• /
• v.44 no.4
• /
• pp.287-296
• /
• 2022

High-frequency (HF) radar measures sea surface currents from the radio waves transmitted and received by antenna on land. Since the data quality of HF radar measurements sensitively depend on the radio wave environment around antenna, Antenna Pattern Measurements (APM) plays an important role in evaluating the accuracy of measured surface currents. In this study, APM was performed by selecting the times when the background noise level around antenna was high and low, and radial data were generated by applying the ideal pattern and measured pattern. The measured antenna pattern for each case was verified with the current velocity data collected by drifters. The radial velocity to which the ideal pattern was applied was not affected by the background noise level around antenna. However, the radial velocity obtained with APM in the period of high background noise was significantly lower in quality than the radial velocity in a low noise environment. It is recomended that APM be carried out in consideration of the radio wave environment around antenna, and that the applied result be compared and verified with the current velocity measurements by drifters. If it is difficult to re-measure APM, we suggest using radial velocity in generating total vector with the ideal pattern through comparative verification, rather than poorly measured patterns, for better data quality.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.52.2-53
• /
• 2018

A stationary Type IV (IVs) radio burst was observed on September 24, 2011. Observations from the Nançay RadioHeliograph (NRH) show that the brightness temperature (TB ) of this burst is extremely high, over 10^11K at 150 MHz and over 10^8K in general. The degree of circular polarization (q ) is between -60%~-100%, which means that it is highly left-handed circularly polarized. The flux-frequency spectrum follows a power-law distribution, and the spectral index is considered to be roughly -3~-4 throughout the IVs. Radio sources of this event are located in the wake of the coronal mass ejection and are spatially dispersed. They line up to present a formation in which lower-frequency sources are higher. Based on these observations, it is suggested that the IVs was generated through electron cyclotron maser emission.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.14 no.3
• /
• pp.192-204
• /
• 2011

With the international increasing of the important of oceanic researches related to climate changes, resources conservation and development and the advanced application of oceanic researches, advanced countries in ocean have developed the systematic management systems for oceanographic instruments. Despite the increasing realization of need for the establishment of management system, no systematic management system has been built in KOREA. There is an ungently need to construct the efficient and professional maintenance and management system of oceanographic instruments that are extremely expensive for meeting the increasing demands of oceanographic observation and investigation. In this paper, the present possession of oceanographic instruments in KOREA and the need for the establishment of management systems for oceanographic instruments are discussed. In addition, we introduce the total management system for oceanographic instruments using a RFID(Radio Frequency IDentification) at KORDI and discuss the necessity of the introduction and establishment for producing high quality data in oceanic researches.

• Journal of the Korean Wood Science and Technology
• /
• v.39 no.2
• /
• pp.132-139
• /
• 2011

This study examined the characteristics of radio-frequency/vacuum dried Korean red pine ($Pinus$ $densoflora$) heavy timbers with 250 ${\times}$ 250 mm (S), 300 ${\times}$ 300 mm (L) in cross section and 300 mm in diameter, and 3,600 mm in length, which were subjected to compressive loading after a kerf pretreatment. The following results were obtained : The drying time was short and the drying rate was high in spite of the large cross section of specimens. The moisture gradient inall specimens was gentle in both longitudinal and transverse directions owing to dielectric heating. The shrinkage of the width in the direction perpendicular to was 21 percent ~ 76 percent of that of the thickness of square timbers in the direction parallel to the mechanical pressure. The casehardening for all specimens was very slight because of significantly reduced ratio of the tangential to radial shrinkage of specimens and kerfing. The surface checks somewhat severely occurred although the occurrence extent of the surface checks on the kerfed specimens was slight compared withthat on the control specimen.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.16 no.1 s.92
• /
• pp.92-101
• /
• 2005

In this paper, the Gunn diode mount is experimentally designed for use in a W-band waveguide voltage controlled oscillator(VCO). The role of the Gunn diode mount is to match the low impedance of the Gunn diode to the high impedance of waveguide. Computer simulations of VCO characteristics such as center frequency, frequency tuning range, and output power are carried out for various values of disc diameter, disc height, post diameter, and utilized in the experimental optimization of the Gunn diode mount. The designed VCO shows excellent characteristics; 93.9 GHz center fiequency, 600 MHz frequency tuning range with $2{\%}$ linearity, 16 dBm output power.

• Journal of the Korean Institute of Gas
• /
• v.2 no.3
• /
• pp.60-69
• /
• 1998

Methane, the major constituent of natural gas, had been converted to higher hydrocarbons by microwave and radio-frequency plasma in vacuum condition. Methane had been activated to plasma by suppling high energy then converted to ethane, ethylene, acetylene. The direct conversion process of methane had produced few by-products and demanded low-energy. The plasma sources were microwave and radio-frequency. Two types of reactor had been used to activate methane. One is common single tubular-type reactor and the other is series coil-type reactor which used for the first time in this study. To produce more C2 products, methane had been converted by a plasma and catalyst. The results of this study could be used to study mechanism of plasma reaction of methane, design the plant-scale reactor.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.11
• /
• pp.583-588
• /
• 2004

We stabilized the frequency and power of a high voltage excited CW CO2 laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The photoacoustic signal is directly coupled from an radio frequency discharge chamber via a capacitor microphone into a detector and a lock-in stabilizer. The frequency stability is estimated to be better then 1.2×10/sup -7/ at the transition P(20) line. The stabilized output power variation was reduced to from 77 % to 3.3 %.

• Applied Science and Convergence Technology
• /
• v.26 no.4
• /
• pp.74-78
• /
• 2017

The discharge characteristics of the radio frequency (RF) surface dielectric barrier discharge have been simulated for the investigation of the ratio of the ion transit time to the RF period. From one-dimensional particle-in-cell (PIC) simulation for a planar dielectric barrier discharge (DBD), it was observed that the high-frequency driving voltage confines the ions in the plasma because of a shorter RF period than the ion transit time. For two-dimensional surface dielectric barrier discharges, a fluid simulation is performed to investigate the characteristics of RF discharges from 1 MHz to 40 MHz. The ratio of the peak density to the average density decreases with the increasing frequency, and the spatiotemporal discharge patterns change abruptly with the change in the ratio of ion transit time to the RF period.