• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.5
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• pp.1164-1171
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• 2008

The present study, which is about a ceramic waveguide filter for UMTS, designed a filer using a circuit and structure simulator, suggested a design method at a required frequency band, and developed a waveguide filter, which can be applied at a power of over 50W and be miniaturized, through implementing the design and examining related variables and characteristics. In the results of designing a waveguide filter with the center frequency of 1,950 MHz and 2,140 MHz and examining its characteristics, bandwidth was 60MHz, insertion loss was below 1.0dB, return loss was over 20dB, and attenuation at the relative frequency band was over 60dB. In the results of a power station test, the characteristics did not change and internal temperature was below $30^{\circ}C$ at 50.8W, and this confirmed that the filter is usable at over 50W.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.94-100
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• 2017

In this paper, we suggest a design method of a metamaterial-based low-profile antenna working at 425 MHz for LEO/Cube satellites. Satellites play an important role in linking th remote nodes in a wireless communication network and covering wide areas of the globe. Especially, an increasing number of universities or individuals aspire having their own satellites and build low-budget structures such as cube satellites in LEO and the ways to reduce the sizes of their satellites. Since the antenna occupies a major portion of the satellite surface, the antenna should be miniaturized for lighter weight. The proposed metamaterial low-profile antenna, unlike the conventional patch antenna, produces such a zeroth-order resonance to create an omnidirectional radiation pattern. Also, it is connected to a UHF waveguide bandpass filter as the feeding system to examine the possible change in the situation that the antenna is combined with the system. The performances of the monopole and proposed metamaterial antennas are compared to one another.

• Korean Journal of Materials Research
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• v.20 no.7
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• pp.374-378
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• 2010

$MgTiO_3$ thin films were prepared by r.f. magnetron sputtering in order to prepare miniaturized NPO type MLCCs. $MgTiO_3$ films showed a polycrystalline structure of ilmenite characterized by the appearance of (110) and (202) peaks. The intensity of the peaks decreased with an increase in the chamber pressure due to the decrease of crystallinity which resulted from the decrease of kinetic energy of the sputtered atoms. The films annealed at $600^{\circ}C$ for 60min. showed a fine grained microstructure without micro-cracks. The grain size and roughness of the $MgTiO_3$ films decreased with the increase of chamber pressure. The average surface roughness was 1.425~0.313 nm for $MgTiO_3$ films prepared at 10~70 mTorr. $MgTiO_3$ films showed a dielectric constant of 17~19.7 and a dissipation factor of 2.1~4.9% at 1MHz. The dielectric constant of the films is similar to that of bulk ceramics. The dielectric constant and the dissipation factor decreased with the increase of the chamber pressure due to the decrease of grain size and crystallinity. The leakage current density was $10^{-5}\sim10^{-7}A/cm^2$ at 200kV/cm and this value decreased with the increase of the chamber pressure. The small grain size and smooth surface microstructure of the films deposited at high chamber pressure resulted in a low leakage current density. $MgTiO_3$ films showed a near zero temperature coefficient and satisfied the specifications for NPO type materials. The dielectric properties of the $MgTiO_3$ thin films prepared by sputtering suggest the feasibility of their application for MLCCs.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.355-360
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• 2002

ElectroSlag Strip Overlaying (ESSO) process has been around since 1970. ESSO process had limited acceptance due to a few problems associated with the use of this process in its very early stage. Limited knowledge and, most significantly, poor quality of the equipment and welding flux gave the ESSO process a bad name. However, this process is well accepted today and used in North America, Europe and Japan. The ESSO process provides low dilution overlays at high deposition rates, excellent and consistent deposit chemistry with excellent surface quality, and virtually no defects. Capitan has taken this process one step further through extensive research and development of the process itself as well as the equipment. The improvement brought to the process warranted the issuance in May 2000 of an US patent. This study demonstrates the feasibility of this process with immediate positive production results. The main achievements of this work are as follows: $\textbullet$ Development of six various strip-flux combinations on three different base materials: carbon steel, $\frac{1}{4}$ Cr/.5 Mo and 2 $\frac{1}{4}$ Cr/l Mo, fully tested with: penetrant, ultrasound, bends, hardness, overlay chemistry, corrosion and hydrogen disbonding. $\textbullet$ 12" dia. 90 hot formed elbows from straight pipe electroslag overlayed with "1 layer" and "2 layer" Alloy 625 $\textbullet$ a very unique development of miniaturized overlaying equipment able to perform overlay in pipe with diameters as low as 10" (254 mm). This development has large applications in the field of offshore, petrochemical, refining, pulp and paper and power generation industries. The aftermath of this development was its immediate acceptance by major end users with the completion of four projects of overlayed pipe in the USA and Far East Asia.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.173-181
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• 2015

We developed a wireless gamma-ray probe based on radiation photon counting method to diagnose and detect remaining lesions after surgery, and its effectiveness was evaluated using calibration sources and a phantom. The probe was designed and miniaturized using a semi-conductor-based radiation sensor, and a Bluetooth remote communication module was used to implement the wireless diagnosis and detection system. Moreover, a remote monitoring system was implemented to monitor affected areas during diagnosis and surgery. To assess the effectiveness of the developed probe in this study, calibration sources $^{57}Co$, $^{133}Ba$, $^{22}Na$ and $^{137}Cs$ and a chicken breast phantom were used. Furthermore, the probe's detection response to gamma ray was confirmed through evaluation. Its clinical applicability was verified by assessing the response linearity and detection direction according to gamma-ray intensity, as well as the detection efficiency according to the depth of the gamma source in the phantom.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.2
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• pp.171-179
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• 2017

In this paper, microstrip antenna using multi-layer and folded structure for GPS application is presented for aircraft loading. Existing microstrip patch antenna used dielectric of high specific inductive capacity to miniaturize that cause smaller bandwidth and decline of efficiency due to dielectric loss. To compensate the existing flaws, Rogers TMM 10i(dielectric constant=9.8, loss tangent=0.002) is used for multi-layer dielectric miniaturization, and we construct folded radiating element on the surface of the dielectric applying perturbation effect. The antenna is designed in the bandwidth of GPS $L_1$ band, and the size of the antenna's radiating element is $20.3mm{\times}19.93mm$, and it gets 94.2% miniaturized characteristic of basic ${\lambda}/2$ microstrip patch antenna. Also the measured -10 dB bandwidth is 32.3 MHz(2.05%), 3 dB axial ratio bandwidth is 6.7 MHz(0.43%). Measured radiation patterns was maximum gain of 0.56 dBi at x axis polarization, 1.23 dBi at y axis polarization.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.12
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• pp.1007-1010
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• 2017

In this paper, a frequency selective surface(FSS) with bandstop operation for radio-frequency spectrum management is presented. The proposed FSS is composed of patterns of fractal-based miniaturized unit cells for stable performance for angles of incidence and polarizations. For practical applications requiring high productivity and environmental compatibility, we fabricated a film-type FSS by screen-printing using Ag ink, rather than a conventional manufacturing method using a printed circuit board. To validate this study, we measured the transmission characteristics of the proposed FSS using the free-space measurement method, and observed the received strength of signal penetrating the FSS film applied to a wall.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.1-7
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• 2017

In this paper, a design method for a compact stepped open slot antenna for an operation in the UWB band is studied. The proposed antenna is miniaturized by inserting L-shaped slots on the ground plane of the stepped open slot antenna through the creation of a resonance in the low frequency, and a strip director is appended to the antenna in order to increase the gain in the middle and high frequency regions. The effects of varying the length of the L-shaped slots, the distance between the director and the slot antenna, and the director length on input reflection coefficient and realized gain characteristics of the proposed antenna are analyzed. The optimized antenna with the size of $30mm{\times}30mm$ is fabricated on an FR4 substrate, and the experiment results show that the antenna has a frequency band of 3.02-11.04 GHz for a VSWR < 2, which assures the operation in the UWB band.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.6
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• pp.504-513
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• 2009

This paper proposes the new type LED driver modularization for illumination LED driver. The proposed LED driver circuit insulates a hot GND of AC input power and a cold GND of LED driver part by using a fly-back converter. In order to control easily the current of the LED, the fly-back converter is operated in the discontinuous mode with excellent dynamic characteristics, and the characteristics of the LED are verified after the closed loop control is performed using a KIA2431. The LED driver module allows the wide AC power input ranges and realizes the burst dimming function which directly regulates a PWM control IC. This paper describes the operation principle of the LED driver module and it is proved the usefulness through the real model with experimentation. Besides, this paper proposes the multi-channel LED driver which the miniaturized and modularized LED driver module are connected by parallel, and verified its propriety by experiments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.128-134
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• 2016

IoT devices including smart devices are connected with internet, thus they have security threats everytime. Particularly, IoT devices are composed of low performance MCU and small-capacity memory because they are miniaturized, so they are likely to be exposed to various security threats like DoS attacks. In addition, in case of IoT devices installed for a remote place, it's not easy for users to control continuously them and to install immediately security patch for them. For most of IoT devices connected directly with internet under user's intention, devices exposed to outside by setting IoT gateway, and devices exposed to outside by the DMZ function or Port Forwarding function of router, specific protocol for IoT services was used and the devices show a response when services about related protocol are required from outside. From internet search engine for IoT devices, IP addresses are inspected on the basis of protocol mainly used for IoT devices and then IP addresses showing a response are maintained as database, so that users can utilize related information. Specially, IoT devices using HTTP and HTTPS protocol, which are used at usual web server, are easily searched at usual search engines like Google as well as search engine for the sole IoT devices. Ill-intentioned attackers get the IP addresses of vulnerable devices from search engine and try to attack the devices. The purpose of this study is to find the problems arisen when HTTP, HTTPS, CoAP, SOAP, and RestFUL protocols used for IoT devices are detected by search engine and are maintained as database, and to seek the solution for the problems. In particular, when the user ID and password of IoT devices set by manufacturing factory are still same or the already known vulnerabilities of IoT devices are not patched, the dangerousness of the IoT devices and its related solution were found in this study.