• Proceedings of the IEEK Conference
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• 2004.06b
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• pp.335-338
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• 2004

We suggest Q-band MEMS MIMIC (Millimeter wave Monolithic Integrated Circuit) HEMT Oscillator using DAML (Dielectric-supported Airgapped Mcrostrip Line) structure. We elevated the signal lines from the substrate using dielectric post, in order to reduce the substrate dielectric loss and obtain low losses at millimeter-wave frequency. These DAML are composed with heist of $10\;{\mu}m$ and post size with $20\;{\mu}m\;{\times}\;20\;{\mu}m$. The MEMS oscillator was successfully integrated by the process of $0.1\;{\mu}m$ GaAs PHEMTs, CPW transmission line and DAML. The phase noise characteristic of the MEMS oscillator was improved more than 7.5 dBc/Hz at a 1 MHz offset frequency than that of the CPW oscillator And the high output power of 7.5 dBm was measured at 34.4 GHz.

• Journal of the Korea Convergence Society
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• v.6 no.1
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• pp.109-114
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• 2015

A circularly polarized small UHF RFID reader antenna is presented. The antenna is composed of four elements and printed on the plastic substrate(${\varepsilon}_r=2.2$, t=5mm). Each element is fed by a probe which is sequentially connected to the feed line. The feed line is manufactured on the FR-4 substrate(t=1.0mm, ${\varepsilon}_r=4.7$). The simulation results shows that the antenna can be achieved a return loss of 12dB, gain of 3.46dBic over the UHF band of 902-928MHz. According to our simulation results, two prototype antennas are manufactured and measured. The obtained antennas operate in UHF RFID bands and can be adapted for various portable applications. In addition, a parametric study is conducted to facilitate the design and optimization processes.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.317-328
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• 2017

This paper presents design and specific absorption rate analysis of a 2.4 GHz wearable patch antenna on a conventional and electromagnetic bandgap (EBG) ground planes, under normal and bent conditions. Wearable materials are used in the design of the antenna and EBG surfaces. A woven fabric (Zelt) is used as a conductive material and a 3 mm thicker Wash Cotton is used as a substrate. The dielectric constant and tangent loss of the substrate are 1.51 and 0.02 respectively. The volume of the proposed antenna is $113{\times}96.4{\times}3mm^3$. The metamaterial surface is used as a high impedance surface which shields the body from the hazards of electromagnetic radiations to reduce the Specific Absorption Rate (SAR). For on-body analysis a three layer model (containing skin, fats and muscles) of human arm is used. Antenna employing the EBG ground plane gives safe value of SAR (i.e. 1.77W/kg<2W/kg), when worn on human arm. This value is obtained using the safe limit of 2 W/kg, averaged over 10g of tissue, specified by the International Commission of Non Ionization Radiation Protection (ICNIRP). The SAR is reduced by 83.82 % as compare to the conventional antenna (8.16 W/kg>2W/kg). The efficiency of the EBG based antenna is improved from 52 to 74 %, relative to the conventional counterpart. The proposed antenna can be used in wearable electronics and smart clothing.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.760-767
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• 2005

In this paper, we proposed a new type SIR bandpass filter using DAMLs. This filter is consisted of 2 layers with MEMS resonator layer and CPW feed line. DAMLs ring resonator is elevated with $10{\mu}m$ height from GaAs substrate. Using MEMS processing, we are able to realize SIR bandpass filter easily. Furthermore it is useful to integrate on conventional MMICs because it has CPW interfaces and ring resonator is isolated from substrate by air-gap. We optimized and measured the results that $S_{21}$ attenuation at rejected band is over 15 dB, insertion loss is inside the limit of 3 dB, and relative bandwidth is about $10\%$ at 60 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1002-1008
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• 2001

The absorbing structure composed of multi-layered fiber reinforced composite materials was designed and microwave absorbing properties are investigated. On the basis of transmission line theory, the theoretical equations to predict the reflection loss and the appropriate composite material for each functional layer are suggested. The most significant result of this study is the successful design and fabrication of triple-layered composite laminates which has the superior microwave absorbing porperties (more than 10 dB in 4∼12 GHz range), without using the ferrite filler in the impedance transforming layer. In the two-layered composite laminate (absorber/substrate), however, the use of ferrite filler (about 40 wt %) in the absorbing layer is necessary to obtain the certain level of microwave absorbance. By combining the glass-fiber composite with ferrite filler and carbon-fiber composite substrate, the microwave absorbing properties more than 10 dB in 4∼12 GHz frequencies than be obtained.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.10-15
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• 1999

We have studied a method to design and fabricate the Intermediate Frequency(IF) band pass filter with low shape factor which is used for CDMA base station on the 35°Y-cut X-propagation Quartz substrate. In order to fabricate a device of the low shape factor for the IF SAW filter on this substrate, we employed apodization weighted type interdigital transducer(IDT) as an input and withdrawal weighted type IDT as an output by using impulse modelling method. Also, using the Kaiser-Bessel window function, we have adopted 2200pairs and 1000pairs of input and oueut IDT respectively to minimize the effect of ripple. Furthermore, the width and the space of IDT finger are 3.6 ㎛ and 3.5 ㎛ respectively. Thus, we can have optimal results when the IDT thickness is 6000Å in consideration of the ratio of SAW's wavelength while it's aperture is 2mm for impedance matching. The fabricated SAW filter for CDMA had the property of almost 115.2MHz of a center frequency, less then 1.27MHz of bandwidth, less than 1.3 of shape factor, - l5dB of out band attenuation insertion loss and -45dB of rejection band.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.28-28
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• 2010

This study realized low-temperature crystallization process of the $Ba_{0.6}Sr_{0.4}TiO_3$ (BST) thin films without thermal damage of substrate using excimer laser annealing (ELA) and structural and electrical characteristics were investigated. The amorphous BST thin films were prepared on Pt/Ti/$SiO_2$/Si substrate by sol-gel method at $250^{\circ}C$. The ELA was carried out using KrF excimer laser which provided excitation wavelength of 248 nm. The beam homogenizing system was used in order to homogenize beam shape of Gaussian fit. The XRD and SEM were used to analyze structural characteristics and the microwave capacitance, dielectric loss and tunability of the BST films were measured by a symmetrical stripline resonator method with shorted end. Consequently, the crystallinity of BST thin films were improved after ELA process and RF tunable capacitor was demonstrated at low temperature below $300^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.11
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• pp.1133-1136
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• 2011

In this paper, we proposed a collinear antenna with a stripline structure for IEEE 802.11b/g applications in ISM (Industrial, Scientific, Medical) band of 2.4~2.5 GHz, which supplements disadvantages of COCO(Coaxial Collinear) antenna and OMA(Omnidirectional planar Microstrip Antenna). By using the proposed 4-layer substrate, we obtained improved performances and advantages in production compared with the existing antenna. In order to get antenna arrays, the same phase structure is designed by alternatively connecting outer conductor to inner conductor with ${\lambda}$/2 antenna element, and the substrate of FR4 epoxy (${\epsilon}_r$=4.4, tan${\delta}$=0.02) was used for the actual implementation. The maximum gain of about 4.93 dBi was measured, which leaded to a little improved gain of 0.33 dBi in comparison to the existing OMA structure.

• Asian-Australasian Journal of Animal Sciences
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• v.20 no.9
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• pp.1444-1452
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• 2007

An in vitro experiment was conducted to evaluate the differences in microbial activity of five faecal inocula from weaned pigs and one faecal inoculum from unweaned pigs in combination with 6 substrates. The substrates tested were negative control diet, corn, soybean meal, oligofructose (OF), ground chicory roots and a mixture (60% chicory pulp and 40% OF). The inocula used were derived from pigs fed either a corn-soy based diet without antibiotics (NCON), the NCON diet supplemented with oligofructose (OF), a mixture of chicory pulp (40%) and OF (60%) (MIX), ground chicory roots (CHR) or the NCON diet supplemented with antibiotics (PCON). The cumulative gas production measured fermentation kinetics and end products, such as total gas production, ammonia and volatile fatty acids, were also determined. Both the substrate and the inoculum significantly affected the fermentation characteristics. The cumulative gas production curve showed that different substrates caused more differences in traits of fermentation kinetics than the different inocula. Inocula of weaned pigs gave a significantly higher VFA production compared to the inoculum from unweaned animals, whilst the rate of fermentation and the total gas produced did not differ. OF showed the highest fermentation kinetics and the lowest $NH_3$, pH and OM loss compared to other substrates. It was concluded that the microbial activity was significantly affected by substrate and inoculum. Inoculum from weaned pigs had more potential for microbial fermentation of the carbohydrate ingredients and oligofructose than that of unweaned pigs. A combination of high and low polymer inulin may be more beneficial to the gut ecosystem than using high- or low-polymer inulin alone.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.4
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• pp.200-207
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• 2006

In addition to the basic properties of the base and top coating agents, corrosion resistance of non-chrome magni 565 coating and characteristics of coating film when coated to steel substrate were studied. The system had a good wettability at room temperature. Moreover, both the contact angle and surface tension were affected little by the viscosity of coating agent and surface roughness of the steel substrate. And the samples coated with optimal conditions showed a great corrosion resistance in salt spray test with 1500 hours or longer of initial appearance time of rust. The coating film was composed of overlapping layer of zinc and aluminium flakes, and the thickness of base coat increased with an increase of base coat viscosity. Based on the C-F peaks of 1,1-Difluoroethaen homo-polymer, it was thought that the base coat was an inorganic polymer bond layer. Meanwhile, the top coat showed C-F peaks of polytetrafluoroethylene with C-H peaks of phenol in FT-IR analysis. From the lower weight loss of base coat in TG analysis, it was thought that cross linking density of base coat was larger than that of top coat. It was thought that the small exothermic reactions observed in DSC curves were due to the thermosetting resins contained in the coating agents. Compared to the non-coated specimen, the coated sample showed more higher polarization resistance and corrosion potential with lower corrosion current density.