• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.537-540
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• 2008

This paper reviews the operation standards and manuals of earthquake monitoring system for Gyungbu high speed railroad. The domestic earthquake monitoring system detects the acceleration data at the locations of lower part of pier and deck of viaducts and bridges, not like foreign system to do the surface ground accelerations. For the purpose of evaluating the behaviors of the domestic earthquake monitoring system, measured acceleration data on the Odaesan earthquake at Iwon viaduct were analysed. The values of maximum acceleration level of the viaduct were increased from 0.0089g(EW component) of the lower part of pier to 0.014g(EW component) on the deck of the viaduct. And also the predominant periods and frequencies were analysed by the frequency domain analysis.

• Computers and Concrete
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• v.20 no.5
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• pp.595-603
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• 2017

Piezoceramic transducers have been widely used in the health monitoring of civil structures. However, in most cases, they are used as sensors either to measure strain or receive stress waves. This paper proposes a method of using piezoelectric transducers as strain gauges and acoustic emission (AE) sensors simultaneously. The signals received by piezoceramic transducers are decomposed into different frequency components for various analysis purposes. The low-frequency signals are used to measure strain, whereas the high-frequency signals are used as acoustic emission signal associated with local damage. The b-value theory is used to process the AE signal in piezoceramic transducers. The proposed method was applied in the bending failure experiments of two reinforced concrete beams to verify its feasibility. The results showed that the extracted low-frequency signals from the piezoceramic transducers had good agreement with that from the strain gauge, and the processed high-frequency signal from piezoceramic transducers as AE could indicate the local damage to concrete. The experimental results verified the feasibly of structural health monitoring using piezoceramic transducers as strain gauges and AE sensors simultaneously, which can advance their application in civil engineering.

• ETRI Journal
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• v.30 no.3
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• pp.461-468
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• 2008

This paper presents a chromatic dispersion monitoring technique using a clock-frequency component for carrier-suppressed return-to-zero (CSRZ) signal. The clock-frequency component is extracted by a clock-extraction (CE) process. To discover which CE methods are most efficient for dispersion monitoring, we evaluate the monitoring performance of each extracted clock signal. We also evaluate the monitoring ability to detect the optimum amount of dispersion compensation when optical nonlinearity exists, since it is more important in nonlinear transmission systems. We demonstrate efficient CE methods of CSRZ signal to monitor chromatic dispersion for optimum compensation in high-speed optical communication systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.523-523
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• 2012

As the wafer geometric requirements continuously complicated and minutes in tens of nanometers, the expectation of real-time add-on sensors for in-situ plasma process monitoring is rapidly increasing. Various industry applications, utilizing plasma impedance monitor (PIM) and optical emission spectroscopy (OES), on etch end point detection, etch chemistry investigation, health monitoring, fault detection and classification, and advanced process control are good examples. However, process monitoring in semiconductor manufacturing industry requires non-invasiveness. The hypothesis behind the optical monitoring of plasma induced ion current is for the monitoring of plasma induced charging damage in non-invasive optical way. In plasma dielectric via etching, the bombardment of reactive ions on exposed conductor patterns may induce electrical current. Induced electrical charge can further flow down to device level, and accumulated charges in the consecutive plasma processes during back-end metallization can create plasma induced charging damage to shift the threshold voltage of device. As a preliminary research for the hypothesis, we performed two phases experiment to measure the plasma induced current in etch environmental condition. We fabricated electrical test circuits to convert induced current to flickering frequency of LED output, and the flickering frequency was measured by high speed optical plasma monitoring system (OPMS) in 10 kHz. Current-frequency calibration was done in offline by applying stepwise current increase while LED flickering was measured. Once the performance of the test circuits was evaluated, a metal pad for collecting ion bombardment during plasma etch condition was placed inside etch chamber, and the LED output frequency was measured in real-time. It was successful to acquire high speed optical emission data acquisition in 10 kHz. Offline measurement with the test circuitry was satisfactory, and we are continuously investigating the potential of real-time in-situ plasma induce current measurement via OPMS.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.661-673
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• 2010

This paper presents recent developments in an extremely compact, wireless impedance sensor node (the WID3, $\underline{W}$ireless $\underline{I}$mpedance $\underline{D}$evice) for use in high-frequency impedance-based structural health monitoring (SHM), sensor diagnostics and validation, and low-frequency (< ~1 kHz) vibration data acquisition. The WID3 is equipped with an impedance chip that can resolve measurements up to 100 kHz, a frequency range ideal for many SHM applications. An integrated set of multiplexers allows the end user to monitor seven piezoelectric sensors from a single sensor node. The WID3 combines on-board processing using a microcontroller, data storage using flash memory, wireless communications capabilities, and a series of internal and external triggering options into a single package to realize a truly comprehensive, self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency analog-to-digital and digital-to-analog converters so that the same device can measure structural vibration data. The compact sensor node collects relatively low-frequency acceleration measurements to estimate natural frequencies and operational deflection shapes, as well as relatively high-frequency impedance measurements to detect structural damage. Experimental results with application to SHM, sensor diagnostics and low-frequency vibration data acquisition are presented.

• Journal of Power Electronics
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• v.19 no.1
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• pp.307-315
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• 2019

Condition monitoring has been recognized as an effective and low-cost method to enhance the reliability and improve the maintainability of power electronic converters. In power electronic converters, high-frequency oscillation occurs during the switching transients of power transistors, which is known as ringing. The ringing frequency mainly depends on the values of the parasitic capacitance and stray inductance in the oscillation loop. Although circuit stray inductance is an important factor that leads to the ringing, it does not change with transistor aging. A shift in either the inside inductance or junction capacitance is an important failure precursor for power transistors. Therefore, ringing frequency can be used to monitor the health of power transistors. However, the switching actions of power transistors usually result in a dynamic behavior that can generate oscillation signals mixed with background noise, which makes it hard to directly extract the ringing frequency. A frequency extraction method based on empirical mode decomposition (EMD) and Fast Fourier transformation (FFT) is proposed in this paper. The proposed method is simple and has a high precision. Simulation results are given to verify the ringing analysis and experimental results are given to verify the effectiveness of the proposed method.

• Structural Engineering and Mechanics
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• v.66 no.2
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• pp.185-193
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• 2018

In this study, low- and high-frequency structure behaviors were identified and a systematic analysis procedure was proposed using noisy GPS data from a 165-m-high tower in ${\dot{I}}stanbul$, Turkey. The raw GPS data contained long- and short-periodic position changes and noisy signals at different frequencies. To extract the significant results from this complex dataset, the general structure and components of the GPS signal were modeled and analyzed in the time and frequency domains. Uncontrolled jumps and deviations involving the signal in the time domain were pre-filtered. Then, the signal was converted to the frequency domain after applying low- and high-pass filters, and the frequency and periodic component values were calculated. The spectrum of the tower motion obtained from the filtered GPS data had dominant peaks at a low frequency of $1.15572{\times}10-4Hz$ and a high frequency of 0.16624 Hz, consistent with two equivalent GPS datasets. Then, the signal was reconstructed using inverse Fourier transform with the dominant low frequency values to obtain filtered and interpretable clean signals. With the proposed sequence, processing of noisy data collected from the GPS receivers mounted very close to the structure is effective in revealing the basic behaviors and features of buildings.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.409-417
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• 2009

This paper is focused on a relationship between the noise and vibration of a wheelset and the railway irregularity of a high speed railway using a time-varying frequency transform for a preliminary research of the railway condition monitoring by an in-service high-speed railway vehicle. Generally, the monitoring has been performed by a special railway inspection vehicle or industrial engineers for railway maintenance. However, they have been limited at night due to the in-service high-speed railway vehicles, and too slow to monitor all of the section. To solve this problem, the monitoring should be performed by an in-service high-speed railway vehicle. For the research, the noise and vibration of a wheelset are utilized, because they are closely related to the railway condition. They are measured by using some microphones and accelerometers, and stored in an on-board data acquisition system. The signals are post-processed by a time-varying frequency analysis and compared with the result of a railway geometry and profile measurement system. From the comparison, it is able to observe the relationship between the noise and vibration of a wheelset and the irregularity of a high-speed railway. Also, some distinct frequency components are observed, which are not observed in the railway geometry and profile.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8A
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• pp.846-851
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• 2008

With rapid development of communication industry, the kinds of communication service vary. According to the increasing use of radio waves, the intelligent and effective radio monitoring system needs to be developed, which is replaced for previous radio monitoring system. Next-generation intelligent radio monitoring system based on ITU-R, Rule of wireless facilities, and Radio Waves Act is used, and which can accurately and effectively function as effective radio monitoring system through spectrum analysis of channel power, frequency deviation, offset, and an occupied frequency bandwidth(99% or x-dB), about the analog and digital signal in On-Air of V/UHF bandwidth. Main function of the system has an radio quality measurement, unwanted electromagnetic signals (spurious, harmonic) measurement, high-speed spectrum measurement, frequency usage efficiency investigation, illegal radio exploration, working monitoring, In this paper, we proposes radio quality measurement, high-speed spectrum measurement of next-generation intelligent radio monitoring system.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.185-189
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• 2005

For the simultaneous measurement of strain and vibration signal, a fiber Bragg grating sensor system with a dual demodulator was proposed. One demodulator using a tunable Fabry-Perot filter could measure low-frequency signal such as strain and the other demodulator using a coarse wavelength division multiplexer could detect high-frequency signal such as vibration signal using intensity demodulation method. In order to measure strain and vibration of the composite main wing model under static loading a real time monitoring program was developed. Also using intensity demodulation of CWDM, sensitivity and resolution at high frequency vibration were evaluated.