• Current Optics and Photonics
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• v.7 no.1
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• pp.1-14
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• 2023

Wavefront-coding imaging can achieve high-quality imaging along with a wide range of defocus. In this paper, the anti-laser detection and damage performance of wavefront-coding imaging systems using different asymmetric phase masks are studied, through modeling and simulation. Based on FresnelKirchhoff diffraction theory, the laser-propagation model of the wavefront-coding imaging system is established. The model uses defocus distance rather than wave aberration to characterize the degree of defocus of an imaging system. Then, based on a given defocus range, an optimization method based on Fisher information is used to determine the optimal phase-mask parameters. Finally, the anti-laser detection and damage performance of asymmetric phase masks at different defocus distances and propagation distances are simulated and analyzed. When studying the influence of defocus distance, compared to conventional imaging, the maximum single-pixel receiving power and echo-detection receiving power of asymmetric phase masks are reduced by about one and two orders of magnitude respectively. When exploring the influence of propagation distance, the maximum single-pixel receiving power of asymmetric phase masks decreases by about one order of magnitude and remains stable, and the echodetection receiving power gradually decreases with increasing propagation distance, until it approaches zero.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.157-166
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• 2016

In this paper, a new sag and peak voltage detector is proposed for a single-phase inverter using delta square operation. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on d-q transformations using an all-pass filter (APF). The d-q transformation is typically used in the three-phase coordinate system. The APF generates a virtual q-axis voltage component with a 90° phase delay, but this virtual phase cannot reflect a sudden change in the grid voltage at the instant the voltage sag occurs. As a result, the peak value is drastically distorted, and it settles down slowly. A modified APF generates the virtual q-axis voltage component from the difference between the current and the previous values of the d-axis voltage component in the stationary reference frame. However, the modified APF cannot detect the voltage sag and peak value when the sag occurs around the zero crossing points such as 0° and 180°, because the difference voltage is not sufficient to detect the voltage sag. The proposed algorithm detects the sag voltage through all regions including the zero crossing voltage. Moreover, the exact voltage drop can be acquired by calculating the q-axis component that is proportional to the d-axis component. To verify the feasibility of the proposed system, the conventional and proposed methods are compared using simulations and experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.10
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• pp.2619-2627
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• 2009

The ground fault is occupying 70% among the total number of faults in ungrounded distribution power system. When the ground fault occurs in ungrounded system, the fault current is so small that it is hard to detect. But fault handling is very important because to continue power supply during fault conditions may cause the fault spreading and the distribution device in trouble. This paper presents the fault line detection method by using GPT signal detecting zero sequence voltage, and the fault section detection method by detecting whether GPT signal is disappeared or not during shifting normally open switch, which is connecting switch between distribution lines with open state in order to restore the outage area under emergency situation, and during isolating each section one by one which belongs to the fault line. This method is efficient because there is no whole power interruption during the fault section detection, and it is possible to perform both the fault section detection and the service restoration for the outage area at the same time, and it can apply to various distribution system configuration. Program for the fault restoration was developed applying proposed method, and it has been validated by applying to the pilot project of distribution automation system in Vietnam which has the ungrounded distribution system.

• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.8-14
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• 2013

Although there are various factors that threaten the security of ships, one of the most harmful is corrosion. It is not easy to find corroding areas and the status of corrosion, even though corrosion causes serious problems such as submergence and marine pollution as a result of leaking oil and polluted water. To monitor the corrosion of ships, non-destructive inspection, weight loss coupons, electrical resistance, linear polarization resistance, zero resistance ammeter, and electrochemical impedance spectroscopy have been developed. However, these methods require much time to detect corrosion, and most are not appropriate for real time monitoring. Coating, sacrificial anode, and impressed current cathodic protection (ICCP) methods have been developed to control corrosion. The ICCP and sacrificial anode methods are the most popular ways to prevent ship corrosion. However, ICCP is only appropriate for the outside of a ship and cannot be used for complex structures such as ballast tanks because these are composed of many separate chambers. Sacrificial anodes have to be replaced periodically. This paper proposes an integrated corrosion monitoring and control system (ICMCS) that can detect corrosion in real time and is appropriate for complex structures such as ballast tanks. Because the system uses titanium for an anode, exhausted anodes do not need to be replaced.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1918-1927
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• 2016

This paper proposes active frequency drift (AFD) as an anti-islanding method applied to micro-inverters with uncontrollable reactive power. When using ordinary inverter topologies, such as full bridge inverters in photovoltaic systems, the islanding phenomenon can be detected with reactive power-based methods, such as reactive power variation. However, when the inverter topology cannot control the reactive power, conventional anti-islanding methods with reactive power cannot be utilized. In this work, the topology used in this paper cannot control the reactive power. Thus, an anti-islanding method that can be used in topologies that cannot control the reactive power is proposed. The conventional anti-islanding method of the topology that cannot control reactive power is introduced and analyzed. Unlike the conventional AFD method, the proposed method extends a zero current interval every predetermined cycle. The proposed method offers certain advantages over conventional AFD methods, such as total harmonic distortion. The proposed method is validated through simulation and experiment.

• Current Optics and Photonics
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• v.7 no.4
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• pp.345-353
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• 2023

We propose a turbulence-tolerant Manchester on-off keying (M-OOK) transmission for free-space optical (FSO) communication. At the transmitter end, a M-OOK signal featuring a spectrum with low-frequency components absent is modulated and transmitted into a turbulent channel. At the receiver end, a low-pass filter (LPF) -based adaptive-threshold decision (ATD) with LPF-extracted channel-state information (CSI) and a high-pass filter (HPF)-based fixed-threshold decision (FTD) are employed to compensate for the effects of turbulence, owing to the low-frequency spectral characteristics of the turbulent channel. The performance of LPF-based ATD and HPF-based FTD are evaluated for various cutoff frequencies for the LPF and HPF. Besides, the proposed M-OOK transmission is compared to conventional non-return-to-zero OOK (NRZ-OOK) for different data rates. The proposed technique is verified in simulation. The simulation results show that the proposed M-OOK detection with optimized cutoff frequencies of LPF and HPF has better bit-error-rate (BER) performance compared to NRZ-OOK, and it is close to the theoretical ATD with the knowledge of precise CSI under various degrees of turbulence effects.

• Journal of Sensor Science and Technology
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• v.26 no.1
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• pp.15-23
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• 2017

In this study, bioelectrical impedance analysis, which has been used to assess an alteration in intracellular fluid (ICF) of the body, was applied to detect intravenous infiltration. The experimental results are described as follows. Firstly, when infiltration occurred, the resistance gradually decreased with time and frequency i.e., the resistance decreased with increasing time, proportional to the amount of infiltrated intravenous (IV) solution. At each frequency, the resistance gradually decreased with time, indicating the IV solution (also blood) accumulated in the extracellular fluid (ECF) (including interstitial fluid). Secondly, the resistance ratio started to increase at infiltration, showing the highest value after 1.4 min of infiltration, and gradually decreased thereafter. Thirdly, the impedance ($Z_C$) of cell membrane decreased significantly (especially at 50 kHz) during infiltration and gradually decreased thereafter. Fourthly, Cole-Cole plot indicated that the positions of (R, $X_C$) shifted toward left owing to infiltration, reflecting the IV solution accumulated in the ECF. The resistance ($R_0$) at zero frequency decreased continuously over time, indicating that it is a vital impedance parameter capable of detecting early infiltration during IV infusion. Finally, the mechanism of the current flowing through the ECF, cell membrane, and ICF in the subcutaneous tissues was analyzed as a function of time before and after infiltration, using an equivalent circuit model of the human cell. In conclusion, it was confirmed that the infiltration could be detected early using these impedance parameters during the infusion of IV solution.

• Progress in Medical Physics
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• v.15 no.2
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• pp.105-111
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• 2004

The parallel plate detector with dielectric film for dosimetry was designed to measure detection characteristic of 6 MV X-ray with medical linear accelerator. PTFE film was inserted into FEP films that are made by two one-side metal coated materials for ion source. The thicknesses of PTFE dielectric film was 100 ${\mu}{\textrm}{m}$ and the thickness of FEP dielectric film was 100 ${\mu}{\textrm}{m}$, respectively. This detector was fixed by two acrylic plate for physical hardness ad geometrical consistency. The geometrical condition for measurement with parallel-plate for detector was below; SSD=100 cm and the 5 cm depth between detector and phantom surface The major parameter of detector characteristics such as zero drift current, leakage current, charge response by applied voltage, reproducibility, linearity, TMR measurement, dose rate effect were measured. The zero drift currents are 8.3 pA and leakage currents are 10 pA. The charge response of applied voltage is showing linearity in 414 voltage. The measurement deviation of reproducibility in this detector is within 1% for dose and the linearity of applied dose shows in this detector. The TMR curves in phantom between this parallel plate detector and reference detector are matched within 3% deviation from maximum dose depth to 7.5 cm depth. It is considered that this dosimetric system is satisfactory for the purpose of the constancy check of the 6 MV x-ray from medical linear accelerator.

• Journal of the Korean Society of Safety
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• v.33 no.1
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• pp.28-34
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• 2018

The purpose of this study is to fabricate a sensor module to detect the resistive leakage current (Igr) in real time that occurs to low voltage electric lines and to verify its reliability. In the case of the developed sensor module, wires are inserted into the zero current transformer (ZCT) and current transformer (CT) in advance and then the branch line is connected to the circuit breaker. The measurement result of the resistance of the distribution panel equipped with the developed sensor module shows that the resistance is $0.151m{\Omega}$ between the R and R phases, $0.169m{\Omega}$ between the S and S phases, and $0.178m{\Omega}$ between the T and T phases, respectively. The insulation resistance measured at AC 500 V and 1,000 V is $0.08m{\Omega}$ between the R, S, T and N phases, respectively. Then, the insulation resistance measured at DC 500 V is $83.3G{\Omega}$ between the R, S, T and G terminal, respectively. In addition, the applied withstanding voltage is AC 220 V/380 V/440 V and it was found that characteristics between all phases are good. This study measured the standby power by installing the developed sensor module at the rear of the MCCB and switching the circuit breaker on sequentially. The standby power is 1.350 W when one circuit breaker is turned on, 1.690 W when 2 circuit breakers are turned on, and 4.371 W when 10 circuit breakers are turned on. This study also verified the reliability of the standby power of the distribution panel equipped with the developed sensor module using the Minitab Program (Minitab PGM). Since the analysis shows the statistical average of 1.34627 in the reliable range of normal distribution, standard deviation of 0.001874, AD of 0.554, and P value of 0.140, it is found that the distribution panel equipped with the developed sensor module has high reliability.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.6
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• pp.64-72
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• 2000

This paper deals with the parallel operation of two PWM converters for auxiliary block of high speed train. The parallel operation of AC/DC PWM converter controlled by 3-level PWM switching method to operate switching devices to realize a high power factor and reduce the primary side of the transformer current harmonics is proposed. In this paper, it is presented the phase shift technique between two converters switching phase, solution to eliminate the coupling effects due to the transformer and zero crossing detection method for synchronized with the source and controller. Experimental results for laboratory system with TMS320C31 microprocessor and 10［kVA］PWM converter confirm the validity of the proposed algorithm.