• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.14 no.5
• /
• pp.472-485
• /
• 1989

This paper represents the occurrence structure of the timing variation of TV horizontal synchronizing pulse(H-sync pulse) in mobile TV reception. Fluttering ghost is caused by timing varations of the H-sync pulse and is due to frequency elective fading in a multipath propagation envoronment. H-sync timing fluctuations, and hence, fluttering ghost are directly correlated with the multipath parameters, i.e., H-sync timing fluctuations reflect well the severity of the multipath environment. The occurrence structure of H-sync timtng fluctuation is analysed theoretically in relation to the multipath environnment. The occurrence structure of H-sync timing fluctuation is analysed theoretically in relation to the multipath parameters, assuming the two-ray propagation model. The H-sync timing fluctuation occurs with the variation in relative phase and /or D/U variation of long-delayed multipath waves.

• Advances in aircraft and spacecraft science
• /
• v.10 no.3
• /
• pp.203-222
• /
• 2023

The detonation combustion is a supersonic combustion process follows on shock wave oscillations in detonation tube. In this paper numerical studies are carried out combined effect of blockage ratio and spacing of obstacle on detonation wave propagation of hydrogen-air mixture in pulse detonation combustor. The deflagration to detonation transition of stoichiometric (ϕ=1)fuel-air mixture in channel has been analyzed for effect of blockage ratio (BR)=0.39, 0.51, 0.59, 0.71 with spacing of 2D and 3D. The reactive Navier-Stokes equation is used to solve the detonation wave propagation mechanism in Ansys Fluent platform. The result shows that fully developed detonation wave initiation regime is observed near smaller vortex generator ratio of BR=0.39 inside the combustor. The turbulent rate of reaction has also a great significance role for shock wave structure. However, vortices of rapid detonation wave are appears near thin boundary layer of each obstacle. Finally, detonation combustor demonstrates the superiority of pressure gain combustor with turbulent rate of reaction of 0.6 kg mol/m3 -s inside the detonation tube with obstacle spacing of 12 cm, this blockage enhanced the turbulence intensity and propulsive thrust. The successful detonation wave propagation speed is achieved in shortest possible time of 0.031s with a significance magnitude of 2349 m/s, which is higher than Chapman-Jouguet (C-J) velocity of 1848 m/s. Furthermore, stronger propulsive thrust force of 36.82 N is generated in pulse time of 0.031s.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.50 no.1
• /
• pp.30-36
• /
• 2001

In this paper, propagation and damping characteristics of PD pulse in GIS are analyzed using SNM. These characteristics are very important to make a diagnosis and protection of accident in GIS. SNM is numerical method in time domain and very useful method to analyze 3-Dimensional structure such as GIS. GIS modeling is made simply as the form of coaxial cable and then spacers are inserted in it. The scattering and reflection in the GIS are appeared and damping characteristics of PD pulse are shown. When simulation using SNM compare to measurement, two results are similar.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.30A no.8
• /
• pp.27-33
• /
• 1993

This paper presents a mobile measurement technique of the ghost-flutter caused in mobile television reception. The ghost-flutter is caused by timing variation of the television horizontal synchronizing pulse due to frequency selective fading in a multipath propagation environment. The ghost-flutter can be detected by measuring the dynamic timing variation of horizontal synchronizing pulse. Especially, in this paper, a technique for measuring horizontal synchronizing timing fluctuations which cause the ghost-flutter is developed, using a Rubidium oscillator as a time standard with high stability.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.10
• /
• pp.39-47
• /
• 1994

In this paper, by modeling the Multilayer-Multiconductor Transmission Line(MMTL) with the characteristic parameters-effective dielectric constant, eigen modal voltages, characteristic impedances at each mode, pulse propagation characteristics of MMTL network are simulated. Transmission line modelling is performed in frequency domain, then time domain resposes are obtained by transforming the frequency domain response using fast Fourier transform.

• Proceedings of the IEEK Conference
• /
• 1999.06a
• /
• pp.869-872
• /
• 1999

As integrated circuits are developed, the crosstalk and the pulse distortion have been major problems in the design. In this paper. the PML and one-point resistive source are applied. This paper deal with the microstripline circuit which has the gap and three microstripline. Obtaining the Propagation pulse shape in microstripline, we prove that the use of the FDTD in the microstripline is valid.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• v.9 no.1
• /
• pp.431-434
• /
• 2005

LabVIEW를 사용하여 광섬유에서의 극초단 펄스 전파의 특성에 관한 연구를 수행하였다. 수치해석을 위해 1550nm의 극초단 광원을 Silica재질의 광섬유에 도파시키고 Split Step Fourier 방법을 이용하여 전파특성을 계산하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.5
• /
• pp.384-394
• /
• 1996

The propagation properties of square and Gaussian pulse signals on the microstrip line are investigated by using proper conventional models to meet the frequency range of a pulse, accuracy, and geometrical requirements of the microstrip line. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. The dispersion of pulse signals is analyzed regarding to the relative permittivity $\varepsilon_r$, substrate height h, strip width w of the microstrip line and pulse width $\tau$ of signal pulse. The simulation results show that small relative permittivity and small rationale of w/h are advantageous for the dispersion of the pulse signals, and that pulse signals with small bandwidth cause smaller dispersion. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.

• Smart Structures and Systems
• /
• v.29 no.2
• /
• pp.301-309
• /
• 2022

Protective coatings are most widely used anticorrosive structures for steel structures. The corrosion under the coating damages the host material, but this damage is completely hidden. Therefore, a field-applicable under-coating-corrosion visualization method has been desired for a long time. Laser ultrasonic technology has been studied in various fields as an in situ nondestructive inspection method. In this study, a comparative analysis was carried out between a guided-wave ultrasonic propagation imager (UPI) and pulse-echo UPI, which have the potential to be used in the field of under-coating-corrosion management. Both guided-wave UPI and pulse-echo UPI were able to successfully visualize the corrosion. Regarding the field application, the guided-wave UPI performing Q-switch laser scanning and piezoelectric sensing by magnetic attachment exhibited advantages owing to the larger distance and incident angle in the laser measurement than those of the pulse-echo UPI. Regarding the corrosion visualization methods, the combination of adjacent wave subtraction and variable time window amplitude mapping (VTWAM) provided acceptable results for the guided-wave UPI, while VTWAM was sufficient for the pule-echo UPI. In addition, the capability of multiple sensing in a single channel of the guided-wave UPI could improve the field applicability as well as the relatively smaller size of the system. Thus, we propose a guided-wave UPI as a tool for under-coating-corrosion management.

• Proceedings of the KIEE Conference
• /
• 2004.11a
• /
• pp.255-257
• /
• 2004

This paper was studied electromagnetic field distribution and damping of PD(Partial Discharge) signal in GIS(Gas Insulated Switchgear). Cut-off frequency of electromagnetic wave propagation modes were computed, electromagnetic field distribution of propagation modes in GIS by FEM(Finite Element Method) were simulated and simulated damping characteristic of electromagnetic waves in GIS by EMTP(Electromagnetic Transient Program) when generated PD pulse. Frequency band of $TE_{mn}/TM_{mn}$ modes were determinated by simulation results of electromagnetic field distribution and were discussed optimal position of UHF sensor from this results. Equivalent circuit was used to simulate signal damping of PD pulse in GIS by EMTP and compared with measured results in laboratory of KERI.