• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.579-584
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• 2014

In this paper, we propose beamsapce MIMO(mulitple input multiple output) system using patch ESPAR(Electronically Steerable Parasitic Array Radiator) antenna. When using conventional monopole ESPAR antenna, we have advantages cost of hardware and power consumption of RF cirsuit because of single RF chian. But it is difficult to apply to small portable mobile device. Therefore we design patch ESPAR antenna in order to reducing volume and analyze performance of BS MIMO system that is able to MIMO communication with single RF chain. In This paper, we confirm beam pattern of designed patch ESPAR antenna is steered as ${\pm}15^{\circ}$ elevation angle. Furthermore, we design BS MIMO system using this ESPAR antenna and confirm BER performance of this system.

• Journal of the Korean Institute of Intelligent Systems
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• v.25 no.6
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• pp.571-577
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• 2015

In the paper, we propose a method for developing a physical training management module which sends physical data to smart devices using an wireless module attached to physical appliances. In the proposed stick-type physical appliance, the physical amount of data measured from sensors inside the appliance is sent to a smart device via wireless communication. And then the smart device records the physical amount of data categorized in person-based data and shows useful information about the user's physical training on the dedicated display. For the performance evaluation, indoor environment and electro magnetic wave tests are taken from national specialized organizations, and their results was very efficient. The proposed physical training management module is highly extensible since it is easily applicable to other physical appliances and useful to both Android and iOS platforms.

• Journal of IKEEE
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• v.22 no.4
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• pp.1068-1072
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• 2018

In underwater communications, there are many challenges due to energy limitations, long propagation delay, low data rate, and high power loss, unlike terrestrial RF communications. Especially, the propagation delay of underwater acoustic channel is five orders of magnitude higher than in electro-magnetic terrestrial channels due to the low speed of sound(1,500m/s). Thus, the MAC protocols for terrestrial communications are not suitable for underwater network. In this paper, we studied the considerations for MAC protocol in underwater acoustic channel. Here, we concentrated on CSMA based MAC protocols. From the results, we confirmed that the number of control packets has an important effect on the performance in underwater environment. These results would be useful in designing MAC protocols for underwater acoustic communications.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.1
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• pp.46-52
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• 2019

This work proposes a noncontact ultrasonic transducer for detecting wall-thinning of containment liner plates of nuclear power plants by measuring their thickness without physical contact. Because the containment liner plate is designed to prevent atmospheric leakage of radioactive substances under severe nuclear accident, its wall-thinning inspection is important for safety of nuclear power plants. Wall-thinning investigation of containment liner plates have been carried out by measuring their thickness with contact-type ultrasonic thickness gauge by inspectors and needs a lot of time and cost. As an alternative, an electromagnetic acoustic transducer measuring precisely thickness of containment liner plates without any physical contact or couplant was suggested in this research. A transducer generating and measuring shear ultrasonic waves in thickness direction was designed and wave field produced by the transducer was analyzed to verify the design. The working performance of the suggested transducer was tested with carbon steel plate specimens with various thicknesses. The test result shows that the proposed transducer can measure thickness of the specimens precisely without any couplant and implies that swift scanning of wall-thinning of containment liner plates will be possible with the proposed transducer.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.5
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• pp.548-558
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• 2014

EMP(Electromagnetic Pulse) protection facility was evaluated according to standard of shielding effectiveness. To comply with the standard, transmitting antenna was placed on outside of protection facility and receiving antenna was placed on inside of protection facility. However, measurement is impossible that place does not have enough space between protection facility and external concrete structure. In this paper, we performed a various of tests that put transmitting antenna inside the EMP protection facility in order to find out test method for measuring the shielding effectiveness of electromagnetic wave. Transmitting antenna was placed on inside of the EMP protection facility for measuring the shielding effectiveness to compare and analyze the impact of the position regarding to the transmitting and receiving antenna. As a result of test, in case that transmitting antenna was placed on inside of the EMP protection facility, it was found that test frequency range 10 kHz~1 GHz were occurred overall average difference of ${\pm}4$ dB level.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.80-85
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• 2017

In this paper, a mircrowave breakdown of X-band circular waveguide cavity filter, which occurred during ground test, was introduced, and electro-magnetic field simulation results to identify a root cause, and the analysis of possibility of its occurrence on orbit operation were presented. Filter modeling for simulation was conducted with a commercial tool (FEST3D), and electric fields inside the filter were monitored at the input of 1 W continuous wave. In our observation, strong electric field intensities were monitored on the tuning screws especially at the input of band-edge frequencies. The threshold power levels for the breakdown were also estimated and compared with the input power levels actually injected to the filter. From this estimation, we could figure out that the power exceeding the breakdown threshold was injected to the filter so that strong electric fields were generated and temperature increased high, and this became a root cause of the electrical short. Our further analysis showed that this kind of microwave breakdown is not likely to occur on orbit operation, and multipactor is expected not to occur at the input of band-edge frequencies. As a measure to prevent the microwave breakdown, we suggested to avoid the injection of band-edge frequencies and inject lower power levels to the filter.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.1
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• pp.60-71
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• 2019

Electrical power supply is needed to operate the radar system in the field. In addition, it should not cause performance deterioration under the environmental factors due to characteristics of military equipment, and should not cause malfunction due to electromagnetic waves generated in radar, and then should not cause malfunction in radar equipment. Therefore, By applying a permanent magnet to the rotor of the generator, light weighting and high efficiency of generator were achieved. As a result, electrical performance test of the generator, the rated output power was 80.8 kW, the maximum output power was 88.1 kW, and the output power efficiency was 98.1 % under the full load condition. When the load capacity of the generator was changed from no load to full load, the maximum voltage variation was 3.6 % and the frequency variation was 0.3 %. As a result of the transient response test for measuring the output power of the generator according to the load characteristics change, the maximum voltage variation of 7.9 %, frequency variation of 0.5 % were confirmed, and the transient response time was 2.1 seconds. Environmental tests were conducted in accordance with MIL-STD-810G and MIL-STD-461F to evaluate the operability of the generator groups. Normal operation of radar system generator group was confirmed under high temperature and low temperature environment conditions. Electromagnetic tests were conducted to check if electromagnetic wave generated from both radar system and generator group in operation caused any performance deterioration to each other. As a result, it was confirmed that the performance deterioration due to electromagnetic wave inflow, radiation, and conduction did not occur. It is expected that it should be possible to provide high efficiency power supply and stable power supply by applying to various military system as well as radar system.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.436-442
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• 2014

In this study, we developed an optical-fiber sensor using cobalt chloride solution to monitor temperature in real-time between long distance points unaffected by the electro-magnetic wave and the vibration. Cobalt chloride solutions were made using 10% water and 90% ethanol (v/v) solution. The transmittance of these solutions was analyzed on 655 nm using UV-Visible spectrometer regarding temperature change. Also 30.8 mM cobalt chloride solution was gelled by dissolving polyvinyl butyral and the transmittance of this was analyzed on 655 nm regarding temperature change. The results of transmittance and optical power measurement showed decrease of both transmittance and optical power with increase of temperature from 66.8% and 149.5 nW at $25^{\circ}C$ to 7.1% and 48 nW at $70^{\circ}C$, respectively. These results support the possibility of gelled cobalt chloride/polyvinyl butyral as an optical-fiber sensor to monitor temperature change.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.23-31
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• 2015

In this paper, we design a SSD(simultaneous single band duplex) system using RF cancellation and digital cancellation. And then, we analyze performance of the SSD system using pre-distorter with HPA non-linearity. Also, we analyze digital cancellation performance of the SSD system using pre-distorter with HPA non-linearity. Additionally, digital cancellation cancels residual self-interference. In linear conditions, digital cancellation can cancel self-interference of 40dB. Therefore, the SSD system has good BER performance because most of self-interference is canceled. But, in HPA non-linearity conditions, digital cancellation cancels residual self-interference of 25dB. In this conditions, self-interference is greater than desired signal. Therefore, bit informations of distant station can not be received. But, we confirm that if the proposed system uses pre-distorter then bit information of distant station can be received by HPA non-linearity compensation. Also, we confirm that even though the proposed system uses pre-distorter, if HPA non-linearity increases then digital cancellation performance is degraded by imperfect compensation of HPA non-linerity.