• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.912-918
• /
• 2011

This research simulates the ultrasonic wave propagation in multi-layered media using generalized formular of system response function. We made the artificial defect specimen of a rocket motor and compared with experimental wave forms. The simulation results are coinciede with mesuared waves and we found that the pulse echo method is able to detect disbond at liner-propellant interface.

• Structural Engineering and Mechanics
• /
• v.51 no.6
• /
• pp.1047-1065
• /
• 2014

The article presents the methodology for finding material damping capacity at higher frequency and at relatively lower amplitudes. The Lamb wave dispersion theory and loss less finite element model is used to find the damping capacity of composite materials. The research has been focused on high frequency applications materials. The method was implemented on carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) plates. The Lamb waves were generated using ultrasonic pulse generator setup. The hybrid method has been explored in this article and the results have been compared with bandwidth methods available in the literature.

• Proceedings of the KIEE Conference
• /
• 1998.11c
• /
• pp.904-906
• /
• 1998

PD pulses have about one nanosecond rise time in the $SF_6$ gas insulation. These pulses propagate in the apparatus to PD sensors in the form of the voltage oscillation, high frequency current and the electromagnetic radiation. In this paper, we investigated the characteristics of two types of PD sensors, by putting high frequency signals in the form of sine waves and pulse into the test apparatus in air. Also, we measured PD quantity from the needle electrode and the sensitivity of the sensors. We found that PD of 70pC could be detected with this method and the study in $SF_6$ gas should be carried out for application to $SF_6$ GIS.

• Journal of international Conference on Electrical Machines and Systems
• /
• v.1 no.2
• /
• pp.64-69
• /
• 2012

This paper presents a hybrid pulse width modulation (PWM) method under low switching frequency conditions based on space vector PWM (SVPWM) and selective harmonic eliminated PWM (SHEPWM), which use asynchronous carrier modulation SVPWM at low frequency, and SHEPWM at high frequency, a square wave after rated conditions. A transitive strategy is proposed to realize a smooth transition of individual modes including SVPWM, SHEPWM and square waves. Experimental results confirm this hybrid modulation method and their transition are reasonable and proper.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.1
• /
• pp.108-113
• /
• 2011

There are a lot of PDP TV for a plasma discharge pulse voltage generated by the use of electromagnetic waves. EMI mesh film is near Infrared ray caused by malfunction of the remote control intended to prevent this phenomenon. In this study, the formation of fine pattern by making the mold is imprinted on the film sheet. EMI mesh film has been granted by filling in the conductive material region imprinted with electroforming in the manufacture of resistance. The fine patterns fabricated with electroforming facility thickness of homogenization process technology were established to optimize the working conditions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.121-126
• /
• 2001

This paper presents the experimental study for the reduction of transmitted shock waves in smart structures incorporating MR insert. MR fluid is filled within the two aluminum layers and two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of the shock wave. Pulse wave generated by the transmitter is transmitted to the receiver through the MR insert and the plate. By applying magnetic field to the MR insert, the amplitude of the transmitted shock wave is reduced remarkably. The attenuation performance is tested by changing the applied magnetic field on MR inserts in two ways: by changing angle of permanent rubber magnet from 90 to 5 with 5 decrements, by using electromagnet in which magnetic field is controllable. The propagating wave speed of MR insert is also investigated.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.403-408
• /
• 1999

In this paper, ultrasonic tomography by the Mode-Converted Rayleigh wave (MCRW) in the back-scattered direction is presented. When a beam with a short pulse and narrow beam width enters a reflector with smooth surface, in general, two major arrivals can be observed in the output waveform: the specular reflection and the radiation of the MCRW from the reflector surface. The time-delay between the two waves is relatively large and thus can be measured easily. This large time-delay is due to the fact that the MCRW is slower than incident wave. In our method, this large time- delay is used for ultrasonic image reconstruction. To effectively detect the MCRW, the arrayed-receiving transducers are circularly arranged around the transmitter. In addition, a deconvolution method is employed to remove specular echo signals for reconstructing the MCRW image.

• Journal of Electrical Engineering and Technology
• /
• v.9 no.1
• /
• pp.154-161
• /
• 2014

To study and locate partial discharge(PD) and analyze the transient state of power transformer, there is a need for a high frequency model of transformer winding and calculation of its parameters. Due to the high frequency nature of partial discharge phenomenon, there is a need for an accurate model for this frequency range. To attain this goal, a Multi-Conductor Transmission Line (MTL) model is used in this paper for modeling this transformer winding. In order that the MTL model can properly simulate the transformer behavior within a frequency range it is required that its parameters be accurately calculated. In this paper, all the basic parameters of this model are calculated by the use of Finite Element Method (FEM) for a 20kV winding of a distribution transformer. The comparison of the results obtained from this model with the obtained shape of the waves by the application of PD pulse to the winding in laboratory environment shows the validity and accuracy of this model.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.30 no.3
• /
• pp.227-236
• /
• 1994

The characteristics of the P(VDF-TrFE) acoustic microscope transducer were evaluated theoretically and experimentally by comparison with those of the PVDF and the ZnO acoustic microscope transducers. It was found that its insertion loss was about 5dB lower than that of the PVDF and about 13$\textbf{dB}$ higher than that of the ZnO. And its relative bandwidth was 20% which could produce the effective acoustic pulse waves having about 4 periods duration into water. Another finding was that the effective horizontal focusing resolution and the focal depth were $120\mu m and $1.5mm$, respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.29 no.3
• /
• pp.229-235
• /
• 1993

In this paper, a method of ghost cancelling for the television signals using complex adaptive filter is studied. The sin(x)/x signal is used as the reference signal a complex adaptive filter. The ghost cancelling characteristics considering the delay time, the attenuation, and the phase difference of multipath waves are investigated using horizontal sync pulse and color burst signal in composite video waveform. The influences of phase difference in ghost cancelling are investigated and the performances between the real processing and the complex processing are compared by the computer simulation. It was found that influences in ghost by phase difference are remarkably reduced by the complex adaptive filtering.