• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.29A no.4
• /
• pp.7-13
• /
• 1992

Diffraction loss occurs when the propagation path is obstructed by mountains and hills between a base station antenna and a moving vehicle antenna in mobile-radio communication. In this paper an approximate mathematical model using Fresnel-Kirchhoff diffraction theory is considered to predict propogation attenuation by natural obstacles with lateral profiles having general shapes. Field tests are conducted using helical and crossed drooping dipole antenna at 820 MHz. The theoretical analysis used in estimating the effects of hills agrees reasonably with experimental data. The results seem to be useful for estimating the level of received power, the minimum allowable input power, the optimum site of base station and consequently, planning terrestrial microwave links.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2003.11a
• /
• pp.33-37
• /
• 2003

This paper presents the characteristics of large-scale fading in a tunnel environment. The Ray-Launching Method has been used to analyze the characteristics of the tunnel. For a curved tunnel, The concept of RDN (Ray Density Normalization) is introduced in order to obtain more accurate results. For our purposes, the structure of tunnel is assumed to be either a straight or curved tunnel having rectangular cross-section. A large scale fading has been presented shown in several tunnel cases.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.3
• /
• pp.427-432
• /
• 2012

In this paper, we have designed and fabricated 7-bands (GSM 850/900, DCS/PCS, and UMTS 3 bands) LTCC front end module (FEM) embedded LPF (low pass filter) to efficiently eliminate harmonics generated in TX path. The proposed FEM is composed of flip-chip typed CMOS SP9T switch to select transceiver signals, dual type SAW filters to receive Rx signals, and 0603 size chip components for the antenna matching and ESD protection. The whole size of FEM is $4.5{\times}3.2{\times}1.2mm^3$. The insertion loss of Tx and Rx ports are measured at 1.7 dB and 4.8 dB, respectively.

• Proceedings of the KIEE Conference
• /
• 2007.04a
• /
• pp.430-432
• /
• 2007

This paper proposes the possibility of SonicID system which is the active RFID based on the ultrasonic spectrum instead of using radio frequency. For the feasibility study, various performance indexes are measured in terms of power consumption and signal path loss onto the frequencies of 40KHz, 433MHz, and 2.4GHz. In addition to the line of sight condition, realistic situations are considered for diverse deploying environments. The results of these analyses demonstrate that the SonicID holds the potential to meet the needs of future advanced RFID system in a scalable fashion.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.12
• /
• pp.1719-1724
• /
• 2013

In this paper, a size-reduction technique is presented for the RFID reader antenna working at two UHF bands. To tackle the problem of size increase in multi-band applications, two resonance paths are made to occur in one geometry with a single feed. While one resonance path is combined with the other, the entire geometry is determined to guarantee the resonance at the target frequencies through the dual-band input impedance matching. The antenna performance is predicted by the full-wave simulation, and the design method is verified by observing the good agreement between the simulated and measured results. At the two frequencies, the satisfactory return loss as well as the antenna efficiency and peak gain of the far-field pattern is obtained.

• Journal of Korean Medical classics
• /
• v.23 no.1
• /
• pp.129-132
• /
• 2010

This article aims at clarifying the formation and accumulation of the "phlegm" in the body. If the phlegm can't be dispelled, it would do great harm to the body health in many aspects, even leading to various diseases which are complex and hard to cure. "phlegm blocking the orifices of the heart", "Gi(氣) activities blocking", "the blood vessels choking", "muscular striae[肌腠] overflowing", " tumor accumulated", "inveterate phlegm loss the path", are the outstanding pathogenic characteristics of the "phlegm". Ancient and modern physicians accumulated rich experiences on preventing and treating the phlegm diseases. Those are worth excavating, organizing and clarifying deeply for the prevention, diagnosis and treatment of the phlegm diseases efficiently.

• Journal of ILASS-Korea
• /
• v.19 no.3
• /
• pp.130-135
• /
• 2014

This study was performed to reveal the relationships between various gas supply conditions including inlet numbers and positions for Photobioreactor. To do that, this study was installed the experimental apparatus. All experiments were performed for the cases with 1, 2, 3, and 4 inlets and for gas flow rate of 4~8 lpm. Through the experiments, this study showed that the case with 3 or 4 inlets could reduce about 50% of the pressure loss head for all gas path than that of one inlet base case. So, these results can be used as basic data to design the gross or multiple photobioreactor.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.1
• /
• pp.214-230
• /
• 2014

This paper presents a high performance sensor less control four motorized wheels for electric vehicle. Firstly, we applied a sensor less master-slave DTC based control to both the two in wheel motors by using sliding mode observer for its quick response and its high reliability in electric vehicle application. Secondly, to overcome the possible loss of adherence of one of the four wheels which is likely to destabilize the vehicle a solution is proposed in this paper. Thirdly, a Fuzzy logic anti-skid control structure well adapted to the non-linear system is used to overcome the main problem of power train system in the wheel road adhesion characteristic. Various Simulation results have been include in this paper to show that the proposed control strategy can prevent vehicle sliding and show good vehicle stability on a curved path.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.5B no.4
• /
• pp.358-365
• /
• 2005

In induction machine drive without a speed sensor, the estimation of the motor flux and speed often becomes deteriorated at low speeds with low back EMF. Our analysis shows that, in addition to the state resistance variation, the estimated value of field orientation angle is often corrupted by accumulative errors from the integration of voltage variables at motor terminals that have low signal/noise ratio at low frequencies. A repetitive loop path of integration in the feedback can amplify this type of error, thus speeding up the degradation process. The control system runs into information starvation due to the loss of correct field orientation. The machine's spiral vectors are controlled only in a reduced dimension in this situation. A novel control scheme is developed to improve the control performance of motor's current, torque and speed at low frequencies. The scheme gains a full-dimensional vector control and is less sensitive to the combined effect of the error sources at the low frequencies. Experimental tests demonstrate promising performances are achievable even below 0.5 Hz.

• Journal of Korean Society for Atmospheric Environment
• /
• v.20 no.3
• /
• pp.361-369
• /
• 2004

A metal fiber bed has seldom been applied to the practical filtration process despite its excellent mechanical and chemical stability. The filter-bed used in this work was highly porous with open structure, of which apparent porosity was 80 ∼ 90%. Although pressure loss across the filter-bed was very low, separation efficiency was found to be quite high. This paper focuses on the basic filtration mechanisms of a metal filter-bed and a thin ceramic filter from fly ash for reference. The experimental parameters were face velocity, dust loading and porosity of filter-bed. Pressure drop increased with increasing face velocity and dust feeding load for both filters. It also showed that dust particles deposited in the deep flow path, finally resulting in clogging the pore channels. It thereby indicates that the dominating mechanism of the metal filter-bed would be depth filtration. Meanwhile, the thin fly ash composite filters trapped the aerated dust mainly on the surface of the filter medium, so that the instantaneously formed dust layer might cause a steep increase of pressure drop across the filtration system.