• Transactions on Electrical and Electronic Materials
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• v.9 no.5
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• pp.181-185
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• 2008

Using the extensional vibration mode of PZT ring, a piezopump is successfully made. The PZT ring is polarized with thickness direction. The traveling extensional wave along the circumference of the ring is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. The proposed piezopump is consisted of coaxial cylindrical shells that are bonded piezoelectric ceramic ring. The pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving parts. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump is about 580 ${\mu}l/min$ in flow rate with the highest pressure level of 0.85 kPa, when the driving voltage is 150 $V_p$, 57 kHz.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.379-379
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• 2010

Recent technical advances in OLEDs (organic light emitting devices) requires more and more the improvement in low operation voltage, long lifetime, and high luminance efficiency. Inverted top emission OLEDs (ITOLED) appeared to overcome these problems. This evolved to operate better luminance efficiency from conventional OLEDs. First, it has large open area so to be brighter than conventional OLEDs. Also easy integration is possible with Si-based driving circuits for active matrix OLED. But, a proper buffer layer for carrier injection is needed in order to get a good performance. The buffer layer protects underlying organic materials against destructive particles during the electrode deposition and improves their charge transport efficiency by reducing the charge injection barrier. Hexaazatriphenylene-hexacarbonitrile (HAT-CN), a discoid organic molecule, has been used successfully in tandem OLEDs due to its high workfunction more than 6.1 eV. And it has the lowest unoccupied molecular orbital (LUMO) level near to Fermi level. So it plays like a strong electron acceptor. In this experiment, we measured energy level alignment and hole current density on inverted OLED structures for hole injection. The normal film structure of Al/NPB/ITO showed bad characteristics while the HAT-CN insertion between Al and NPB greatly improved hole current density. The behavior can be explained by charge generation at the HAT-CN/NPB interface and gap state formation at Al/HAT-CN interface, respectively. This result indicates that a proper organic buffer layer can be successfully utilized to enhance hole injection efficiency even with low work function Al anode.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.11
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• pp.2100-2106
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• 2007

Multi-stage folding A/D converter circuit with $0.25{\mu}m$ N-well CMOS technology is designed. This A/D converter consists of a transconductance circuit, linear folder circuit and 1bit A/D converter circuit. In H-spice simulation results, linear folder circuits having high linearity can be obtained when the current mode is used instead of voltage mode. And in case of 6bit, the delay time is limited about 40ns. From this results, 6bit 25MSPS A/D converter circuit can be realized.

• Journal of Magnetics
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• v.16 no.1
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• pp.71-73
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• 2011

Hybrid electric vehicles have attracted much attention of late, emphasizing the necessity of developing traction motors with a high input current and a wide speed range. Among such traction motors, various researches have been conducted on interior permanent-magnet synchronous motors (IPMSMs) with high power density and mechanical solidity. Due to the complexity of its parameters, however, with nonlinear motor characteristics and current vector control, it is actually difficult to accurately estimate the base speed within an actual operating speed range or a voltage limit. Moreover, it is impossible to construct an efficiency map as the efficiency differs according to the control mode. In this study, a simulation method for operation performance considering the nonlinearity of IPMSM was proposed. For this, datasets of various nonlinear parameters were made via the finite-element method and interpolation. Maximum torque-per-ampere and flux-weakening control were accurately simulated using the datasets, and an IPMSM efficiency map was accurately constructed based on the simulation. Lastly, the validity of the simulation was verified through tests.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.2
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• pp.110-115
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• 2019

$Pb(Sb_{0.5}Nb_{0.5})_x(Zr_{0.51}Ti_{0.49})_{1-x}O_3$ (abbreviation: PSN-PZT) ceramics were synthesized, using conventional bulk ceramic processing technology, with various PSN doping contents. The maximum density of PSN-PZT was 97% of the theoretical density in the samples sintered at $1,250^{\circ}C$. The maximum values of the piezoelectric properties achieved using the conventional processes were: $k_p$ of 0.625, $d_{33}$ of 531 pC/N, and $g_{33}$ of $33mV{\cdot}m/N$. Finally, we fabricated a piezo-speaker with the optimized PSN-PZT ceramics. The SPL of the speaker was measured at a distance of 1 m, with a driving voltage of $40V_{rms}$ in the frequency range of ~300 Hz to 9 kHz. The measured $SPL_{max}$ was at a very high level (95 dB), which was superior in quality in comparison with those of other commercial products.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.105-111
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• 2019

The TADF (Thermally Activated Delayed Fluorescence)-based OLED patents were analyzed and 4410 of patents were selected at the first step. And 975 patents were screened at second step. Finally, 39 key patents were selected. Patent qualitative analysis was performed in these patents to find which of the four property (lifetime, efficiency, color purity, driving voltage) of TADF was improved. Also, the variation of the hosts and dopants in patented TADF material were surveyed and their combination was analyzed. According to the analysis of the variation and the combination, some of TADF compounds were used as an assistant dopant to transfer energy. In addition, it tended to transfer energy by forming exciplex that shows TADF characteristics. These were similar to the mechanism of the introduced hyper fluorescence and could solve the inherent TADF problems. Finally, patent citation network was illustrated to visualize the patent citations and citations relationship of the major applicants in the current TADF-based OLED technology. The leading patent applicant organization was revealed as Idemitsu Kosan, Semiconductor Energy Laboratory, UDC, Princeton University, Merck and Nippon Steel & Sumikin Chemical, which had lots of reference patents 559, 524, 477, 310, 258, and 167, respectively.

• Journal of Korean Port Research
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• v.11 no.2
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• pp.273-280
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• 1997

Recently the importance of the cargo handling equipments in a port has been increasing to get strong competition from other ports. Many ports are making efforts to modernize their cargo handling equipments. The kernel technology of such equipments is the speed control of DC motor which is used as an essential part of them. In this paper, we discuss the speed control of a DC motor as a basic work for building cargo handling equipments in a port. DC Motors are still widely used in industrial fields, as driving power motor for electrical fields. DC drives, being easy to control, are widely used in many variable-speed and position control drive system. Traditional analog control circuits used in such applications have many disadvantages. Complex control schemes are difficult to implement with analog components. All these factor and invention of the microprocessor has made it possible to use digital control circuits, using microprocessing system. These digital circuits have been found to be reliable, flexible, and also immune to noise. In this paper it presents the speed control of a SCR DC motor driver which using dual converter by 80c196kc microprocessor. We developed a thyristor power amplifier which does not cause damage thyristor because it is designed to prevent triggering the two SCRs in the same arm simultaneously. And it was analyzed voltage and currents wave at reactive load.

• Composites Research
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• v.22 no.6
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• pp.7-12
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• 2009

This paper deals with a fabrication method of composite hinge mechanisms for flapping-wing micro air vehicles. The fabrication process includes curing process of Graphite/Epoxyprepregs, laser cutting for high fabrication repeatability, laminating of Graphite/Epoxy prepregs with Kapton film which is used for flexure, and so on. The fabricated hinge mechanism was attached with PUMPS actuators and the measured flapping angle was $173^{\circ}$ when driving voltage was 300V 170Hz.

• Journal of Sensor Science and Technology
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• v.32 no.6
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• pp.455-461
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• 2023

We investigated the electrical characteristics of ZnO nanoparticles (NPs) with air exposure that is a widely used electron transport layer for quantum dot light-emitting diodes (QLEDs). Upon air exposure, we observed changes in the density of states (DOS) of the trap levels of ZnO NPs. In particular, with air exposure, the concentration of deep trap energy levels in ZnO NPs decreased and electron mobility significantly improved. Consequently, the air-exposed ZnO reduced leakage current by approximately one order of magnitude and enhanced the external quantum efficiency at the low driving voltage region of the QLED. In addition, based on the excellent conductivity properties, high-brightness QLEDs could be achieved.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.620-626
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• 2023

Energy harvesting technology, which converts wasted energy sources in everyday life into usable electric energy, is gaining attention as a solution to the challenges of charging and managing batteries for the driving of IoT sensors, which are one of the key technologies in the era of the fourth industrial revolution. Hybrid energy harvesting technology involves integrating two or more energy harvesting technologies to generate electric energy from multiple energy conversion mechanisms. In this study, a hybrid energy harvesting device called TMPPEG (thermo-magneto-piezoelectric-pyroelectric energy generator), which utilizes low-grade waste heat, was developed by incorporating PVDF polymer piezoelectric components and optimizing the system. The variations in piezoelectric output and thermoelectric output were examined based on the spacing of the clamps, and it was found that the device exhibited the highest energy output when the clamp spacing was 2 mm. The voltage and energy output characteristics of the TMPPEG were evaluated, demonstrating its potential as an efficient hybrid energy harvesting component that effectively harnesses low-grade waste heat.