• Proceedings of the KSR Conference
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• 2006.11b
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• pp.522-529
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• 2006

Running train is one of the most main factor for railway bridge vibration. The repeated forces with equidistant axles cause the magnification of dynamic responses which relates with maintenance of the track structure and structure-borne noises. The noise problem is one of the most important issues in services of light rail transit system which usually passes through towns. The noise of railway bridges can be divided into the noise from track-vehicle system and structure-borne noises. In the present study, The vibration and noise of the LRT bridge will be investigated with utilizing dynamics responses from moving train as input data for noise analysis.

• Journal of Sensor Science and Technology
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• v.29 no.2
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• pp.75-81
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• 2020

We introduce a new visible light communication (VLC) method in which three-level return-to-zero (RZ) modulation is used for flicker-free transmission. In the VLC transmitter, the three-level RZ modulation ensures that the average optical power is constant; thus, a flicker-free light-emitting diode (LED) light is achieved. In the VLC receiver, a resistor-capacitor high-pass filter is used for generating spike signals, which are used for data recovery while eliminating the 120 Hz optical noise from adjacent lighting lamps. In transmission experiments, we applied this method for wireless transmission of an air quality sensor message using the visible light of an LED array. This configuration is useful for the construction of indoor wireless sensor networks for air pollution monitoring using LED lights.

• Journal of Sensor Science and Technology
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• v.28 no.3
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• pp.191-197
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• 2019

In this study, we propose a dimming control method for a visible light communication (VLC) system, in which the subcarrier on-off keying (OOK) modulation of Manchester code is used for data transmission. In the VLC transmitter, non-return-to-zero (NRZ) code data is transformed to Manchester code, which is OOK modulated with a subcarrier. Manchester code is used for flicker-free lighting; the duty factor is changed for dimming control, and the subcarrier is used for preventing the adjacent noise light interference. In the experiments, the dimming control was carried out from about 8%-92% of the continuous wave (CW) LED light. This configuration is simple and effective in constructing a VLC system for indoor wireless sensor networks with flicker-free illumination and dimming control capability without adjacent noise light interference.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.10
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• pp.1136-1142
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• 2010

In this paper, we reduced the optical noise interference using the ASK modulation with optoelectronic feedback in a wireless optical system in which a lighting LED is used as a light source. The carrier frequency of 70 kHz was generated internally by the oscillation in the optoelectronic feedback circuit, and the output light was ASK modulated at a data rate of 9.6 kbps by opening and shortening the feedback loop with the input signal. In an environment with adjacent noise lights, the ASK modulation with optoelectronic feedback improved the signal to noise ratio by about 25 dB.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.137-138
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• 2023

The floating floor is a structure which introduced to reduce the noise of apartment houses. This structure can decrease vibration energy through resilient materials. However, it is limited to completely construct resilient materials in South Korea due to floor heating structure and other reasons. And It is a controversial issue how well the resilient materials should be constructed to prevent floor impact noise. These resilient defect areas are typically found in wall corners, door sills, hot water dispenser in kitchen and areas where thermal insulation is attached. This study investigates the acoustical effect of the defect areas in two ways. First, it is analyzed by several assumption conditions and calculated how much deviation would occur. Then we researched the deviation of the 76 field test data about light-weight floor impact noise. This study could be useful for a constructor to determine how much should minimize resilient materials defect areas.

• Current Optics and Photonics
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• v.3 no.2
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• pp.105-110
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• 2019

The visible-light communication (VLC) system is a promising candidate to fulfill the present and future demands for a high-speed, cost-effective, and larger-bandwidth communication system. VLC modulates the visible-light signals from solid-state LEDs to transmit data between transmitter and receiver, but the broadcasting and the line-of-sight propagation nature of visible-light signals make VLC a communication system with a limited operating range. We present a novel architecture to increase the operating range of VLC. In our proposed architecture, we guide the visible-light signals through the fiber and amplify the dissipated signals using visible-light fiber amplifiers (VLFAs), which are the most important and the novel devices needed for the proposed architecture of the VLC. Therefore, we design, analyze, and apply a VLFA to VLC, to overcome the inherent drawbacks of VLC. Numerical results show that under given constant conditions, the VLFA can amplify the signal up to 35.0 dB. We have analyzed the effects of fiber length, active ion concentration, pump power, and input signal power on the gain and the noise figure (NF).

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.9
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• pp.850-857
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• 2011

Generally, sound-absorbing materials in vehicles are used for giving the comfort to passengers by reducing noise while driving. Materials of which targets are light weight, high performance, eco friendliness and recycling have been developed recently. In this study, sound-absorbing materials using PET(polyethylene terephthalate) hollow fibers to achieve the light weight and the high sound absorption performance are developed, and then evaluated to meet a requirement for the automotive components. The test results show that the acoustic performances of developed products having new fiber structure are better than those of the conventional product.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.175-179
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• 2008

In this study, computational structural vibration analysis of helicopter search light exposing unsteady buffet load have been conducted using combined advanced numerical methods. Unsteady CFD method based on Navier-Stokes equations is used to predict viscous buffet load due to flow separation effects. Full three-dimensional finite element model is constructed in order to conduct static and structural dynamic analyses of the search light model for two different typical flight speeds. Also, the correct performance of the search light can be physically estimated to examine the actual lighting area considering the effects of structural deformations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1083-1087
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• 2001

The purpose of this study is to obtain the basic data of existing light-weight Drywall through the evaluation and analysis of the light-weight drywall in reverberation chamber and to improve sound insulation performance of drywalls. Sound transmission loss of the total 11 types were analyzed in each frequency a-third octave band and evaluated sound insulation performance for each frequency. From data by analysis and calculation, STC value plotted on STC contour. We found that the improved light-weight drywall specimens ⓑ, ⓒ and ⓖ were satisfied with the domestic standard of sound transmission loss.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.9
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• pp.870-875
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• 2009

In this study, computational structural vibration analysis of helicopter search light exposing unsteady buffet load have been conducted using combined advanced numerical methods. Unsteady CFD method based on Navier-Stokes equations is used to predict viscous buffet load due to flow separation effects. Full three-dimensional finite element model is constructed in order to conduct static and structural dynamic analyses of the search light model for two different typical flight speeds. Also, the correct performance of the search light can be physically estimated to examine the actual lighting area considering the effects of structural deformations.