• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.8 s.99
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• pp.815-824
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• 2005

In this paper, we proposed a new DGS(Defected Ground Structure) Doherty amplifier for IMT-2000 band. Originally, active load-pull analysis of a Doherty amplifier assumes ideal harmonic termination condition. However, there have been no papers considering this ideal harmonic termination condition. We obtained excellent improvements of efficiency, gain, maximum output power as well as superior size reduction of a Doherly amplifier by satisfying the overlooked assumption of ideal harmonic termination through the adaptation of DGS at the output transmission line of carrier and peaking amplifier that is essential for Doherty operation. The amount of both the 2nd and the 3rd harmonic rejection of the proposed DGS Doherty amplifier over the conventional one are 44.92 dB and over 23.77 dB, respectively. The acquired improvement in Pl dB, gain, drain efficiency, and ACPR to WCDMA 1FA signal were 0.42 dB, 0.33 dB, $6.4\%$ and 5.4 dBc, respectively. Moreover, electrical length of $90{\circ}$ is reduced at each of the DGS carrier amplifier path and DGS peaking amplifier path, therefore the whole amplifier circuit size is considerably reduced.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.3
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• pp.179-184
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• 2019

In many countries, such as developing countries where electricity is scarce, small wind turbines in the form of Off Grid are an effective solution to solve power supply problems. In some countries, the expansion of power systems and the decline of electricity-intensive areas have led to the use of small wind power in urban road lighting, mobile communications base stations, aquaculture and seawater desalination. With this change, the size of the small wind power industry is expected to have greater potential than large-scale wind power. In the case of small wind power generators, the generator is controlled at a variable speed, and the voltage and current generated by the generator have many harmonic components. To solve this problem, the AC to DC converter to be studied in this paper is a three-phase step-up type converter with a single switch. The inductor current is controlled in discontinuous mode, and has a characteristic of having a unit power factor by eliminating the harmonic of the input current. The proposed converter is composed of LCL filter and three phase rectification boost converter at the input stage and a single phase full bridge for grid connection. It is a control system with energy storage system(ESS) that the system stabilization can be pursued against the electric power.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.16-27
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• 2017

IEEE 802.15.6 standard, a Wireless Body Area Network, aims to transfer not only medical data but also non-medical data, such as physical activity, streaming, multimedia game, living information, and entertainment. Services which transfer those data have very various data rates, intervals and frequencies of continuous access to a medium. Therefore, an efficient anti-collision operations and medium assigning operation have to be carried out when multiple nodes with different data rates are accessing shared medium. IEEE 802.15.6 standard for CSMA/CA medium access control method distributes access to the shared medium, transmits a control packet to avoid collision and checks status of the channel. This method is energy inefficient and causes overhead. These disadvantages conflict with the low power, low cost calculation requirement of wireless body area network, shall minimize such overhead for efficient wireless body area network operations. Therefore, in this paper, we propose a medium access scheduling scheme, which adjusts the time interval for accessing to the shared transmission medium according to the amount of data for generating respective sensor node, and a priority control algorithm, which temporarily adjusts the priority of the sensor node that causes transmission concession due to the data priority until next successful transmission to ensure fairness.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.565-568
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• 2014

This paper presents a 0.2V DC/DC boost converter with regulated output for thermoelectric energy harvesting. To use low voltages from a thermoelectric device, a start-up circuit consisting of native NMOS transistors and resistors boosts an internal VDD, and the boosted VDD is used to operate the internal control block. When the VDD reaches a predefined value, a detector circuit makes the start-up block turn off to minimize current consumption. The final boosted VSTO is achieved by alternately operating the sub-boost converter for VDD and the main boost converter for VSTO according to the comparator outputs. When the VSTO reaches 2.4V, a buck converter starts to operate to generate a stabilized output VOUT. Simulation results shows that the designed converter generates a regulated 1.8V output from an input voltage of 0.2V, and its maximum power efficiency is 60%. The chip designed using a $0.35{\mu}m$ CMOS process occupies $1.1mm{\times}1.0mm$ including pads.

• Korean Chemical Engineering Research
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• v.62 no.2
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• pp.163-172
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• 2024

In this study, two different scenarios for ammonia liquefaction in the green ammonia manufacturing process were proposed, and the economic-feasibility and environmental impact of each scenario were analyzed. The two liquefaction processes involved gas-liquid separation before cooling at high pressure (high pressure cooling process) or after decompression without the gas-liquid separation (low pressure cooling process). The high-pressure cooling process requires higher capital costs due to the required installation of separation units and heat exchangers, but it offers relatively lower total utility costs of 91.03 $/hr and a reduced duty of 2.81 Gcal/hr. In contrast, although the low-pressure cooling process is simpler and cost-effective, it may encounter operational instability due to rapid pressure drops in the system. Environmental impact assessment revealed that the high-pressure cooling process is more environmentally friendly than the low-pressure cooling process, with an emission factor of 0.83 tCO₂eq less than the low-pressure cooling process, calculated based on power usage. Consequently, the outcomes of this study provide relevant scenario and a database for green ammonia synthesis process adaptable to various process conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.10
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• pp.90-99
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• 2009

In this paper, we proposed the new class-E frequency multiplier design that include the highest efficient characteristics. The proposed frequency multiplier is designed for 5.8[GHz] output using the frequency multiplier about 2.9[GHz] input signal. And studying in this paper is for the design and the implementation of the class E frequency multiplier. For the result, the maximum highest efficient characteristics 32[%] which is with output power 24.5[dBm] and 8.5[dB], is shown with frequency multiplier for the 2.9/5.8[GHz] class E. And we applied the linear method to the implemented class E frequency multiplier. As a result, the output spectrum for the linear is upgrade to 12[dB], 12[dB], 13[dB] of the ACPR characteristics on the +11[MHz], +20[MHz], +30[MHz] offset frequency in the center frequency. The result is satisfied with the 3.83[%] of the lineared EVM for the 64-QAM modulated method with the 54[Mbps] transmission velocity. In this paper, we show that the good compensation result of the linearity and the efficiency through the digital pre-linear method of the distortion with the frequency multiplier. Therefore, we suggested the frequency multiplier method are applying to WLAN, cellular, PCS, WCDMA, and etc.

• Journal of IKEEE
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• v.23 no.4
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• pp.1461-1464
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• 2019

In this paper, we propose the development of embedded board for integrated radiation exposure protection fireman's life-saving alarm capable of location tracking and radiation measurement. The proposed techniques consist of signal processing unit, communication unit, power unit, main control unit. Signal processing units apply shielding design, noise reduction technology and electromagnetic wave subtraction technology. The communication unit is designed to communicate using the wifi method. In the main control unit, power consumption is reduced to a minimum, and a high performance system is formed through small, high density and low heat generation. The proposed techniques are equipment operated by exposure to poor conditions, such as disaster and fire sites, so they are designed and manufactured for external appearance considering waterproof and thermal endurance. The proposed techniques were tested by an authorized testing agency to determine the effectiveness of embedded board. The waterproof grade has achieved the IP67 rating, which can maintain stable performance even when flooded with water at the disaster site due to the nature of the fireman's equipment. The operating temperature was measured in the range of -10℃ to 50℃ to cope with a wide range of environmental changes at the disaster site. The battery life was measured to be available 144 hours after a single charge to cope with emergency disasters such as a collapse accident. The maximum communication distance, including the PCB, was measured to operate at 54.2 meters, a range wider than the existing 50 meters, at a straight line with the command-and-control vehicle in the event of a disaster. Therefore, the effectiveness of embedded board for embedded board for integrated radiation exposure protection fireman's life-saving alarm has been demonstrated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.1
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• pp.79-84
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• 2013

DC/DC switching power converters are commonly used to generate a regulated DC output voltage with high efficiency. The DC/DC converter is composed of a PWM-IC (pulse width modulation-integrated circuit) controller, a MOSFET (metal-oxide semiconductor field effect transistor), inductor, capacitor, etc. It is shown that the variation of threshold voltage and the offset voltage in the electrical characteristics of PWM-IC increase by radiation effects in TID (Total Ionizing Dose) testing at the low energy ${\gamma}$ rays using $^{60}Co$, and 4 heavy ions applied for SEL (Single Event Latch-up) make the PWM pulse unstable. Also, the output waveform for the given input in the DC/DC converter is observed by the simulation program with integrated circuit emphasis (SPICE). TID testing on PWM-IC is accomplished up to the total dose of 30 krad, and the cross section($cm^2$) versus LET($MeV/mg/cm^2$) in the PWM operation is studied at SEL testing after implementation of the controller board.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.309-313
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• 2013

Silicon carbide (SiC) has recently drawn an enormous industrial interest because of its useful mechanical properties such as thermal resistance, abrasion resistance and thermal conductivity at high temperature. Especially, high purity SiC is applicable to the fields of power semiconductor and lighting emitting diode (LED). In this work, high purity carbon powders as raw material for high purity SiC were prepared by a RF induction thermal plasma. Dodecane ($C_{12}H_{26}$) as hydrocarbon liquid precursor has been utilized for synthesis of high purity carbon powders. It is found that the filtercollected carbon powders showed smaller particle size (10~20 nm) and low crystallinity compared to the reactor-collected carbon powders. The purities of reactor-collected and filter-collected carbon powders were 99.9997 % (5N7) and 99.9993 % (5N3), respectively. In addition, the impurities of carbon powders synthesized by RF induction thermal plasma were mainly originated from the surrounding environment.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.3
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• pp.50-55
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• 1999

Brushless DC Motor(BLDCM) has high efficiency. But this type of motor needs a rotor sensor which complicates the motor configuration. Rotor position sensor degrades system reliability in the severe environmental condition. In this paper, we study a controller which permits the determination of the rotor position by the back EMF to eliminate the rotor position sensor Also, since the back EMF is zero at standstill, a starting technique which permits the starting of an asynchronous motor without a sensor is described. The controller is implemented using microcontroller for minimal external component.