• Journal of Sensor Science and Technology
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• v.28 no.1
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• pp.36-40
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• 2019

Energy harvesting is an advantageous technology for wireless sensor networks (WSNs) that dispenses with the need for periodic replacement of batteries. WSNs are composed of numerous sensors for the collection of data and communication; hence, they are important in the Internet of Things (IoT). However, due to low power generation and energy conversion efficiency, harvesting technologies have so far been utilized in limited applications. In this study, a piezoelectric energy harvester was modeled in a vibration environment. This harvester has an oval-shaped configuration as compared to the conventional cantilever-type piezoelectric energy harvester. An analytical model based on an equivalent circuit was developed to appraise the advantages of the oval-shaped piezoelectric energy harvester in which several structural parameters were optimized for higher output performance in given vibration environments. As a result, an oval-shaped energy harvester with an average output power of 2.58 mW at 0.5 g and 60 Hz vibration conditions was developed. These technical approaches provided an opportunity to appreciate the significance of autonomous sensor networks.

• Journal of Power Electronics
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• v.19 no.1
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• pp.211-219
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• 2019

In magnetically coupled resonant (MCR) wireless power transfer (WPT) systems, the introduction of additional intermediate coils is an effective means of improving transmission characteristics, including output power and transmission efficiency, when the transmission distance is increased. However, the position of intermediate coils in practice influences system performance significantly. In this research, a three-coil MCR WPT system is adopted as an exemplification for determining how the spatial position of coils affects transmission characteristics. With use of the fundamental harmonic analysis method, an equivalent circuit model of the system is built to reveal the relationship between the output power, the transmission efficiency, and the spatial scales, including the axial, lateral, and angular misalignments of the intermediate and receiving coils. Three cases of transmission characteristics versus different spatial scales are evaluated. Results indicate that the system can achieve relatively stable transmission characteristics with deliberate adjustments in the position of the intermediate and receiving coils. A prototype of the three-coil MCR WPT system is built and analyzed, and the experimental results are consistent with those of the theoretical analysis.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1365-1381
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• 2023

In this paper, a procedure for evaluating the structural integrity of the PCSG (Printed Circuit Steam Generator) unit block is presented with a simplified FE (finite element) analysis technique by applying the homogenization method. The homogenization method converts an inhomogeneous elastic body into a homogeneous elastic body with same mechanical behaviour. This method is effective when the inhomogeneous elastic body has repetitive microstructures, and thus the method was applied to the sheet assembly among the PCSG unit block components. From the method, the homogenized equivalent elastic constants of the sheet assembly were derived. The validity of the determined material properties was verified by comparing the mechanical behaviour with the reference model. Thermo-mechanical analysis was then performed to evaluate the structural integrity of the PCSG unit block, and it was found that the contact region between the steam header and the sheet assembly is a critical point where large bending stress occurs due to the temperature difference.

• Journal of Power Electronics
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• v.13 no.4
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• pp.679-691
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• 2013

High-power electromagnetic transmitter power supplies are an important part of deep geophysical exploration equipment. This is especially true in complex environments, where the ability to produce a highly accurate and stable output and safety through redundancy have become the key issues in the design of high-power electromagnetic transmitter power supplies. To solve these issues, a high-frequency switching power cascade based emission power supply is designed. By combining the circuit averaged model and the equivalent controlled source method, a modular mathematical model is established with the on-state loss and transformer induction loss being taken into account. A triple-loop control including an inner current loop, an outer voltage loop and a load current forward feedback, and a digitalized voltage/current sharing control method are proposed for the realization of the rapid, stable and highly accurate output of the system. By using a new algorithm referred to as GAPSO, which integrates a genetic algorithm and a particle swarm algorithm, the parameters of the controller are tuned. A multi-module cascade helps to achieve system redundancy. A simulation analysis of the open-loop system proves the accuracy of the established system and provides a better reflection of the characteristics of the power supply. A parameter tuning simulation proves the effectiveness of the GAPSO algorithm. A closed-loop simulation of the system and field geological exploration experiments demonstrate the effectiveness of the control method. This ensures both the system's excellent stability and the output's accuracy. It also ensures the accuracy of the established mathematical model as well as its ability to meet the requirements of practical field deep exploration.

• The Journal of the Acoustical Society of Korea
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• v.14 no.4
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• pp.29-37
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• 1995

A resonant frequency of piezoelectric transducer depends remarkably on the electric impedance connected to the vibrator. In this paper, using this effect of frequency controllable two layered PZT ultrasonic transducer is designed and its acoustic characteristics are analyzed by a new transmission model equivalent circuit. The theoretical and the experimental results of the electric impedance effect on the resonant frequency variation were compared and both results showed a good consistency each other. The resonant frequency has been controlled continuously in the wide frequency range of 180kHz~580kHz and the effective attenuations were less than 7dB in the frequency range of 330kHz~470kHz.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.907-913
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• 1998

Corrosion behavior of steel reinforcements embedded in concrete containing various chloride ion concentrations was investigated by an electrochemical impedance spectroscopy(EIS). Chloride ions were introduced into the concrete by dissolving the NaCl and $CaCl_2$ in the water with a given weight of cement. Based on the impedance parameters measured by EIS, more complete equivalent circuit, a schematic physical model, and the mechanism of concrete reinforcement corrosion were suggested. By the implement of experimental impedance parameters obtained from the model with corresponding CNLS-fitting data, the corrosion rate of steel reinforcement with chloride ions could be predicted.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1297-1300
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• 2008

A conventional linear accelerator system requires a flat-topped pulse with less than ${\pm}$ 0.5% ripple to meet the beam energy spread requirements and to improve pulse efficiency of RF systems. A pulse transformer is one of main determinants on the output pulse voltage shape. The pulse transformer was investigated and analyzed with the pulse response characteristics using a simplified equivalent circuit model. The damping factor ${\sigma}$ must be >0.86 to limit the overshoot to less than 0.5% during the flat-top phase. The low leakage inductance and distributed capacitance are often limiting factors to obtain a fast rise time. These parameters are largely controlled by the physical geometry and winding configuration of the transformer. A rise time can be improved by reducing the number of turns, but it produces larger pulse droop and requires a larger core size. By tradeoffs among these parameters, the high-voltage pulse transformer with a pulse width of 10 ${\mu}s$, a rise time of 0.84 ${\mu}s$, and a pulse droop of 2.9% has been designed and fabricated to drive a klystron which has an output voltage of 284 kV, 30-MW peak and 60-kW average RF output power. This paper describes design optimization of a high-voltage pulse transformer for high-power pulsed applications. The experimental results were analyzed and compared with the design. The design and optimal tuning parameter of the system was identified using the model simulation.

• Journal of Chest Surgery
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• v.38 no.10 s.255
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• pp.661-668
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• 2005

Background: We have hypothesized that, if a low resistant gravity-flow membrane oxygenator is used, then the twin blood sacs of TPLS can be located at downstream of the membrane oxyenator, which may double the pulse rate at a given pump rate and increase the pump output. The purpose of this study was to determine the optimal configuration for the ECLS circuits by using the concept of pulse energy and pump output. Material and Method: Animals were randomly assigned to 2 groups in a total cardiopulmonary bypass model. In the serial group, a conventional membrane oxygenator was located between the twin blood sacs. In the parallel group, the twin blood sacs were placed downstream of the gravity-flow membrane oxygenator. Energy equivalent pressure (EEP) and pump output were collected at pump-setting rates of 30, 40, and 50 BPM. Result: At the given pump-setting rate, the pulse rate was doubled in the parallel group. Percent changes of mean arterial pressure to EEP were $13.0\pm1.7,\; 12.0\pm1.9\;and\;7.6\pm0.9\%$ in the parallel group, and $22.5\pm2.4,\; 23.2\pm1.9,\;and\;21.8\pm1.4\%$ in the serial group at 30, 40, and 50 BPM of pump-setting rates. Pump output was higher in the parallel circuit at 40 and 50 BPM of pump-setting rates $(3.1\pm0.2,\;3.7\pm0.2L/min\;vs.\;2.2\pm0.1\;and\;2.5\pm0.1L/min,\;respectively,\;p=0.01)$. Conclusion: Either parallel or serial circuit configuration of the ECLS generates effective pulsatility. As for the pump out, the parallel circuit configuration provides higher flow than the serial circuit configuration.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.1-8
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• 2005

The gate length-dependence of cutoff frequency is modeled by using scaling parameter equations of equivalent circuit parameters extracted from measured S-parameters of Nano-scale MOSFETs. It is observed that the modeled cutoff frequency initially increases with decreasing gate length and then the rate of increase becomes degraded at further scale-down. This is because the extrinsic charging time slightly decreases, although the intrinsic transit time greatly decreases with gate length reduction. The new gate length-dependent model will be very helpful to optimize RF performances of Nano-scale MOSFETs.

• 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.