• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.5
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• pp.226-231
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• 2001

The $Mg_{1-x}Sr_xTiO_3\;(x=0.02{\sim}0.08)$ ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were $1250^{\circ}C{\sim}1350^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite $SrTiO_3$ and ilmenite $MgTiO_3$ structures were coexisted in the $Mg_{1-x}Sr_xTiO_3\;(x=0.02{\sim}0.08)$ ceramics. The dielectric constant( ${\epsilon}_r$) was increased with addition of $SrTiO_3$. The temperature coefficient of resonant frequency( ${\tau}_f$) was gradually varied from negative value to the positive value with increasing the $SrTiO_3$. The temperature coefficient of resonant frequency of the $Mg_{1-x}Sr_xTiO_3(x=0.036)$ ceramics was near zero, where the dielectric constant, quality factor, and ${\tau}_f$ were 20.65, 95120 and +1.3ppm/$^{\circ}C$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.547-550
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• 2000

The (1-x)MgTiO$_3$-xSrTiO$_3$(x=0.03~0.04) ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 125$0^{\circ}C$~135$0^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite SrTiO$_3$ and ilmenite MgTiO$_3$ structures coexisted in the (1-x)MgTiO$_3$-xSrTiO$_3$(x=0.03~0.04) ceramics. The dielectric constant($\varepsilon$$_{r}$) was increased with addition of SrTiO$_3$. The temperature coefficient of resonant frequency($\tau$$_{f}$) was gradually varied from negative value to the positive value with increasing the SrTiO$_3$. The negative temperature coefficient of resonant frequency of the magnesium titanate was adjusted to near zero at x=0.036, where the dielectric constant, quality factor, and $\tau$$_{f}$ were 20.65, 95120, and +1.3ppm/$^{\circ}C$, respectively. The temperature stability of qualify factor in (1-x)MgTiO$_3$-xSrTiO$_3$(x=0.03~0.04) ceramics increased as the amount of MgTiO$_3$./TEX>.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.284-284
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• 2007

In this study, the microwave dielectric property variations of (1-x)$BiNbO_4-(x)ZnNb_2O_6$ composites (x=0.3, 0.5 and 0.7) with 10wt% zinc borosilicate(ZBS) glass was investigated as a function of the substitution of $ZnNb_2O_6$ with a view to applying thes system to LTCC technology. The all composition addition of 10wt% ZBS glass ensured a successful sintering below $900^{\circ}C$. In addition, a small amount of $Bi_2SiO_5$ as the secondary phase was observed in the all composition. The substitution of $ZnNb_2O_6$ on the $BiNbO_4$ composites increased the $Q{\times}f$ values, but it decreased the sinterability and dielectric constant due to the high sintering temperature and low dielectric constant of $ZnNb_2O_6\;than\;BiNbO_4$ ceramics. The increasing of $ZnNb_2O_6$ content from 0.3 to 0.7 in the (1-x)$BiNbO_4-(x)ZnNb_2O_6$ composites with 10wt% ZBS glass sintered at $900^{\circ}C$ demonstrated 28.1~15.6 in the dielectric constant$({\varepsilon}_r)$, 5,500~8,700GHz in the $Q{\times}f$ value.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.105-105
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• 2000

현재 급격히발전하는 이동통신기술로 미루어 보아 앞으로는 모든 정보통신이 무선통신으로 이루어질 것이다. 그런데 무선통신은 이동성과 대용량의 정보전송에 초점을 맞추어 발전하고 있다. 많은 정보량을 전달하기 위해서 현재 사용되는 주파수 대역보다 고주파의 전파가 사용되어야 한다. 또한 이동성을 향상시키기 위해서는 통신기기의 소형화를 이루어야 하고 그러기 위해서 궁극적으로 모든 소자를 하나의 칩(chip)으로 집적화하는 것이 필요하다. 따라서 벌크상태로 사용되고 있는 유전체 공진기를 소형화, 즉 박막화해야만 한다. 결국 유전체 박막의 마이크로파 대역에서의 유전특성을 연구하고 그 특성을 향상시켜야만 한다. 통신기기에서 사용되는 유전체 공진기는 소형화를 위해 높은 유전율과 낮은 유전손실(tan$\delta$), 즉 높은 품질계수 (Q)를 가져야 한다. 마이크로파 대역에서 사용되고 있는 유전체 중에서 TiO2는 벌크 상태의 rutile 상에서 100정도의 높은 유전율과, 4 GHz에서 10,000 정도의 높은 품질계수를 나타낸다고 보고되어 있다. 따라서 본 연궁서는 TiO2 박막의 마이크로파 유전특성을 연구하였고 anatase 박막의 유전특성도 측정하였다. TiO2 박막을 RF magnetron reactive sputtering 방법으로 Ar (15 sccm)과 O2 (1.5 sccm) 기체를 사용하여 상온에서 증착하였다. 4mTorr의 증착압력에서 안정한 rutile 박막을 얻었고, 15 mTorrdo서 준안정한 anatase 박막을 얻을 수 있었다. 그리고 그 중간의 압력에서 두 상이 혼합된 박막이 증착되었다. 위와 같은 방법으로 형성한 TiO2 박막의 마이크로파 유전특성을 측정하기 위해 마이크로스트립 링공진기 (microstrip ring resonator)를 제작하였다. 마이크로스트립 링 공진기는 링의 원주길이가 전자기파 파장길이의 정수배가 되면 공진이 일어나는 구조이다. Fused quartz를 기판으로 하여 증착압력을 변수로 하여 TiO2 박막을 증착하였다. 그리고 그 위에 은 (silver)을 사용하여 링 패턴을 형성하였다. 이와 같이 공진기를 제작하여 network analyzer (HP 8510C)로 마이크로파 대역에서의 공진특서을 측정하였다. 공진특성으로부터 전체 품질계수와 유효유전율, 그리고 TiO2 박막의 품질계수를 얻어내었다. 측정결과 rutile에서 anatase로 박막의 상이 변할수록 유전율은 감소하고 유전손실은 증가하는 결과를 나타내었다.

• Journal of the Korean Society of Food Culture
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• v.30 no.1
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• pp.1-7
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• 2015

Traditional cuisine reflects cooking traditions shaped by political, economic, social, cultural, and environmental conditions characterized by authenticity and uniqueness. Traditional food is not only a part of our cultural heritage but also a knowledge resource. Application of food science and technology in Korean traditional foods was reviewed from six points of view, including food preservation, fermentation, changes in food materials, utilization of food functionality, and packaging and development of cooking appliances. Books from disparate times were chosen in order to cover a wide range of materials from the past to the present. Food preservation and fermentation techniques were applied to various food materials. Combination of science and skills contributes to the accessibility of diverse food materials and better quality foods. Koreans use assorted and resilient plants, which have an abundance of functional substances such as food materials. Among cooking appliances, microwave oven and refrigerator are the most innovative products with huge influences on food eating patterns as well as lifestyle. Packaging effectively reduces post-harvest preservation losses, and better packaging has technical improvements for storage and distribution. Kimchi was chosen as an example in order to study technology from the past to the present. Availability of Kimchi cabbage, enrichment of functional ingredients, identification of useful microbial species, standardization of recipe for commercialization, prevention of texture softening, introduction of salted Kimchi cabbage and Kimchi refrigerators, and packaging were reviewed. The future of traditional foods in the market will be competitive. First, traditional foods market should be maintained to protect the diversity of food materials. Secondly, tailored foods for individuals should be considered using foods with functional properties. Information on health benefits would provide insights into health and traditional food products. Third, speedy transfer of new technology to the traditional food industry is needed to ensure food quality production and new opportunities in the market. Fourth, safety of traditional foods should be ensured without sacrificing the essential characteristics of culturally important foods. Improvement of logistics, distribution, and facility should be carried out. As demand for convenience foods increases, traditional foods should be developed into products.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.679-683
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• 2004

[ $BaO-Sm_2O_3-4TiO_2$ ] 세라믹을 LTCC용 재료로 사용하기 위해 $B_2O_3$와 CuO를 소결조제로 첨가하여 소결온도를 낮추었다. 10.0 mol%의 $B_2O_3$만을 첨가하였을 경우 $1000^{\circ}C$에서 2시간 소결시 er=72.23, Qf=4,050GHz, ${\tau}f=-0.574ppm/^{\circ}C$의 우수한 유전 특성값을 얻을 수 있었지만, $960^{\circ}C$이하에서는 소결이 잘 이루어지지 않았다. $B_2O_3$와 CuO를 동시에 소결조제로 첨가하였을 경우에는 $900^{\circ}C$에서 2시간 소결시 10.0 mol% $B_2O_3$, 15.0 mol% CuO의 첨가조성에서 ${\varepsilon}r$=70.09, Qf=4,728GHz의 우수한 유전특성을 보여 고유전율을 가진 저온 동시 소결용 재료로서의 가능성을 보여주었다. 이처럼 BaO-$Sm_2O_3-4TiO_2$ 세라믹의 소결온도를 낮출 수 있었던 요인은 소결온도보다 용융점이 낮은 2차상들이 액상을 형성하여 액상소결이 진행되었기 때문이며 이때 소결에 기여한 이차상들은 결정화되지 못하고 비정질 상태로 남아있는 것으로 추정된다.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.5
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• pp.239-244
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• 2021

Following Silicon Carbide, single crystal diamond continues to attract attention as a next-generation semiconductor substrate material. In addition to excellent physical properties, large area and productivity are very important for semiconductor substrate materials. Research on the increase in area and productivity of single crystal diamonds has been carried out using various devices such as HPHT (High Pressure High Temperature) and MPECVD (Microwave Plasma Enhanced Chemical Vapor Deposition). We hit the limits of growth rate and internal defects. However, HFCVD (Hot Filament Chemical Vapor Deposition) can be replaced due to the previous problem. In this study, HFCVD confirmed the distance between the substrate and the filament, the accompanying growth rate, the surface shape, and the Raman shift of the substrate after vapor deposition according to the vapor deposition temperature change. As a result, it was confirmed that the difference in the growth rate of the single crystal substrate due to the change in the vapor deposition temperature was gained up to 5 times, and that as the vapor deposition temperature increased, a large amount of polycrystalline diamond tended to be generated on the surface.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.271-276
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• 2020

In this study, an amorphous SiC block was manufactured using polycarbosilane (PCS), an organosilicon polymer. The dense SiC blocks were easily fabricated in various shapes via pyrolysis at 1100℃, 1200℃, 1300℃, 1400℃ after manufacturing a PCS molded body using cured PCS powder. Physical and chemical properties were analyzed using a thermogravimetric analyzer (TGA), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and universal testing machine (UTM). The prepared SiC block was decomposed into SiO and CO gas as the temperature increased, and β-SiC crystal grains were grown in an amorphous structure. In addition, the density and flexural strength were the highest at 1.9038 g/㎤ and 6.189 MPa of SiC prepared at 1100℃. The manufactured amorphous silicon carbide block is expected to be applicable to other fields, such as the previously reported microwave assisted heating element.

• Composites Research
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• v.34 no.1
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• pp.23-29
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• 2021

Commercialized carbon fiber obtained from polyacrylonitrile(PAN) precursor is subjected to oxidation stabilization at 180 to 300℃ in air atmosphere and carbonization process at 1600℃ or lower in inert gas atmosphere. Both of these processes use a lot of time and high energy, but are essential and important for producing high-performance carbon fibers. Therefore, in recent years, an alternative stabilization technology by being assisted with various other energy sources such as plasma, electron beam and microwave which can shorten the process time and lower energy consumption has been studied. In this study, the PAN precursor was stabilized by using plasma treatment and heat treatment continuously. The morphology, structural changes, thermal and physical properties were analyzed using Field emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), Fourier transform infrared(FT-IR), Thermogravimetric analysis(TGA) and Favimat.

• Composites Research
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• v.19 no.3
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• pp.1-6
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• 2006

As the structures of the high performance electronic equipments and devices recently become more complex, the electromagnetic interference (EMI) and compatibility (EMC) have been very essential for commercial and military purposes. Thus, sensitive electrical devices and densely packed systems need to be protected from electromagnetic wave. In this research, glass fabric/epoxy composites containing conductive multi-walled carbon nanotube (MWNT) and carbon fiber/epoxy composites as electrical shielding materials were fabricated and electrical properties of the composites were measured. The concerning frequency band is from 300 MHz to 1 GHz. The performances of composite shielding enclosures were predicted using electromagnetic wave 3-D simulation tool, CST Microwave Studio. The shielding enclosure made of carbon fiber/epoxy composites were fabricated and the shielding effectiveness (SE) was measured in the anechoic chamber.