• Journal of Conservation Science
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• v.27 no.3
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• pp.277-290
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• 2011

The aim of this study is to examine the efficiency of ethylsilicate consolidants on sandstone according to its weathering state for an appropriate application to stone cultural heritage in Yeongyang area. Yeongyang area had sandstone and conglomeratic sandstone cultural heritages which needed conservation intervention due to granular disintegration and scaling on their surface. Hyeonri Three-storied Pagoda having typical stone materials in this area was investigated for the analyses of the material and deterioration. And both in-situ and laboratory applications of consolidants were conducted to the outcrop which had the same characteristics of rock type and weathering grade. As a result of the application, it was concluded that Wacker OH 100 and Remmers 300 showed the most appropriate consolidating effect, and Remmers 300 was the most effective to strengthen the loosen and granular-disintegrated surface of the sandstone.

• Korean Journal of Materials Research
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• v.27 no.3
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• pp.137-143
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• 2017

Boron-doped diamond (BDD) electrode has an extremely wide potential window in aqueous and non-aqueous electrolytes, very low and stable background current and high resistance to surface fouling due to weak adsorption. These features endow the BDD electrode with potentially wide electrochemical applications, in such areas as wastewater treatment, electrosynthesis and electrochemical sensors. In this study, the characteristics of the BDD electrode were examined by scanning electron microscopy (SEM) and evaluated by accelerated life test. The effects of manufacturing conditions on the BDD electrode were determined and remedies for negative effects were noted in order to improve the electrode lifetime in wastewater treatment. The lifetime of the BDD electrode was influenced by manufacturing conditions, such as surface roughness, seeding method and rate of introduction of gases into the reaction chamber. The results of this study showed that BDD electrodes manufactured using sanding media of different sizes resulted in the most effective electrode lifetime when the particle size of alumina used was from $75{\sim}106{\mu}m$ (#150). Ultrasonic treatment was found to be more effective than polishing treatment in the test of seeding processes. In addition to this, BDD electrodes manufactured by introducing gases at different rates resulted in the most effective electrode lifetime when the introduced gas had a composition of hydrogen gas 94.5 vol.% carbon source gas 1.6 vol.% and boron source gas 3.9 vol.%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.525-532
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• 2017

The development of an inkjet-based manufacturing machine for the production of next-generation displays using organic and quantum-dot light emitting diodes at a low cost has been conducted. To employ inkjet printing in production lines of displays, the development of a high-speed inkjet-monitoring device to verify the reliable droplet jetting status from multiple nozzles is required. In this study, an inkjet monitoring device using a rotatable mirror with rotary and linear ultrasonic motors is developed in place of a conventional, linear reciprocating, motion-based inkjet monitoring device. Its performance is also demonstrated. The measurements of circular patterns with diameters of $10{\mu}m$, $30{\mu}m$, and $50{\mu}m$ are performed with the accuracies of $0.5{\pm}1.0{\mu}m$, $-1.2{\pm}0.3{\mu}m$, and $0.2{\pm}0.5{\mu}m$, respectively, within 17 sec. By optimizing the control program, the takt time can be reduced to as short as 8.6 sec.

• Journal of the Korean Ceramic Society
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• v.54 no.2
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• pp.150-157
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• 2017

Three types of piezoelectric single crystals [PMN-PT (Generation I $[Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3]$), PMN-PZT (Generation II $[Pb(Mg_{1/3}Nb_{2/3})O_3-Pb(Zr,Ti)O_3]$), PMN-PZT-Mn (Generation III)] were grown by the solid-state single crystal growth (SSCG) method, and their dielectric and piezoelectric properties were measured and compared. Compared to (001) PMN-PT and PMN-PZT single crystals, the (001) PMN-PZT-Mn single crystals exhibited a higher transition temperature between the rhombohedral and tetragonal phases ($T_{RT}=144^{\circ}C$), as well as a higher coercive electric field ($E_C=6.3kV/cm$) and internal bias field ($E_I=1.6kV/cm$). The (011) PMN-PZT-Mn single crystals showed the highest coercive electric field ($E_C=7.0kV/cm$), and the highest stability of $E_C$ and $E_I$ during 60 cycles of polarization measurement. These results demonstrate that both Mn doping (for higher electromechanical quality factor ($Q_m$)) and a (011) crystallographic orientation (for higher coercive electric field and stability) are necessary for high power transducer applications of these piezoelectric single crystals. Specifically, the (011) PMN-PZT-Mn single crystal (Gen. III) had the highest potential for application in the fields of SONAR transducers, high intensity focused ultrasound (HIFU), ultrasonic motors, and others.

• Korean journal of food and cookery science
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• v.33 no.3
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• pp.256-263
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• 2017

Purpose: Essential oils are secondary metabolites of herbs and have antibacterial activities against foodborne pathogens. However, their applications for food protection are limited due to the hydrophobic and volatile natures of essential oils. Methods: In this study, essential oil nanoemulsions of rosemary and lavender were formulated with non-ionic surfactant Tween 80 and water using ultrasonic emulsification, and their antibacterial effects were determined. Results: The antibacterial activities of nanoemulsions were evaluated against 12 strains of 10 bacterial species, and significant antibacterial effects were observed against four Gram-positive and four Gram-negative bacteria but not against Streptococcus mutans and Shigella sonnei. In the disc diffusion test, the diameter of the inhibition zone proportionally increased with the concentration of nanoemulsions. Using cell turbidity measurement, minimum bactericidal concentration (MBC) of the nanoemulsions, which is the lowest concentration reducing viability of the initial bacterial inoculum by ${\geq}99.9%$, was significantly higher than the minimum inhibitory concentration (MIC) of the nanoemulsions. The largest bactericidal effects of lavender and rosemary essential oil nanoemulsions were observed against S. enterica and S. aureus, respectively. Conclusion: Nanoemulsion technique could improve antibacterial activity of essential oil nanoemulsions by increasing the solubility and stability of essential oils. Our findings shed light on the potential use of essential oil nanoemulsions as an alternative to chemical sanitizers in food protection.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1809-1811
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• 2000

High power piezoelectric materials are presently being extensively developed for applications such as ultrasonic motors and piezoelectric transformer In this study, the piezoelectric and dielectric properties of $MnO_2$ doped $0.36Pb(Sc_{1/2}Nb_{1/2})O_{3}-0.25Pb(Ni_{1/3}Nb_{2/3})O_{3}-0.39PbTiO_3$ (hereafter PSNNT), which is the morphotropic phase boundary composition of the PSN-PNN-PT system were investigated. $MnO_2$-addition into the $0.36Pb(Sc_{1/2}Nb_{1/2})O_{3}-0.25Pb(Ni_{1/3}Nb_{2/3})O_{3}-0.39PbTiO_3$ composition increases the piezoelectric coefficient up to $k_{p}{\fallingdotseq}$55.6[%] and $Q_{m}{\fallingdotseq}$252. Moreover, $MnO_2$ addition makes tetragonal phase more stable with respect to rhombohedral phase.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.217-222
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• 2006

To find a location, GPS has been wildly used. But, it is hard to use in indoor because of very weak signal level. To meet indoor requirements, there have been many studies applying wireless communication networks such as WLAN, UWB and ZigBee. Among these, ZigBee is widely adopted in many WSN applications because it has an advantage of low-power and low-cost. In ZigBee, the RSSI is used as range measurement for ad-hoc network. The RSSI are converted to ranges using the signal attenuation model and these ranges become inputs of positioning methods. The obtained position with RSSI has large error because of its poor accuracy. To overcome this problem, ultrasonic sensors are added in many researches. By measuring the arrival time difference of ZigBee and ultrasound as a range measurement, the precise position can be found. However, there are still many problems: scheduling of beacons to transmit signals in a correct order, addition and synchronization of beacons and low-rate positioning rate. At this paper, an efficient method to solve these problems is proposed. In the proposed method, a node transmits ZigBee and ultrasound signal simultaneously. And beacons find the range with the received signals and send it back to a node with ZigBee. The position is computed in a node with the received ranges. In addition, a new positioning algorithm to solve the risk of the divergence in the linearization method and the singularity problem in the Savarese method is presented. Both static and dynamic experimental results show 0.02m RMS errors with high output rate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.280-280
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• 2007

Lead oxide-based ferroelectrics are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is great interest in developing lead-free piezoelectric materials, which are biocompatible and environmentally friendlier. Recently alkali oxide materials, including sodium - potassium niobate (NKN), have been given attention in view of their ultrasonic application and also as promising candidates for piezoelectric lead-free system. However, it is difficult to sinter such NKN-based materials via conventional sintering process. In this reason, many researchers have investigated hot press, hot isostatic press or spark-plasma sintering of NKN-based ceramics. In this study, as candidates for lead-free piezoelectric materials, dense (Na,K,Li)(Nb,Sb)$O_3$ systems were developed by conventional sintering process. The microstructures and piezoelectric properties of the (Na,K,Li)(Nb,Sb)$O_3$ systems were investigated as a function of variable compositions. The excellent piezoelectric and electromechanical properties indicate that this system is potentially good candidate as lead-free material for a wide range of electro-mechanical transducer applications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.329-330
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• 2006

본연구에서는 초음파 모터 등의 고출력 액츄에이터에 응용 가능한 $0.4Pb(Ni_{1/3}Nb_{2/3})O_3$-$0.6Pb(Zr_{0.405}Ti_{0.595})O_3$ + 0.25wt% $Fe_2O_3$ 조성시스템에 $MnO_2$ (0~1 wt.%)첨가하여 압전, 유전특성 및 미세구조에 관해 고찰하였다. 본조성을 $1125{\sim}1175^{\circ}C$ 온도에서 2시간 소결하여 시편을 제조하였으며 이의 결정구조 및 미세조직을 분석하였다. $MnO_2$ 첨가량 증가에 따라 압전 상수와 전기기계결함계수는 감소하였으며, 기계적 품질계수는 0.5 wt% 첨가시까지 증가하였으나 첨가량이 그 이상 증가함에 따라 감소하였다. 압전특성은 $1125^{\circ}C$에서 소결한 $MnO_2$ 0.5wt%조성에서 ${\varepsilon}r$ = 2040, kp = 0.66, $d_{33}$ = 504, Qm=438의 우수한 특성을 나타내었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.521-537
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• 2000

Ultrasonic imaging is the most widely used modality among modern imaging device for medical diagnosis and the system performance has been improved dramatically since early 90's due to the rapid advances in DSP performance and VLSI technology that made it possible to employ more sophisticated algorithms. This paper describes "main stream" digital signal processing functions along with the associated implementation considerations in modern medical ultrasound imaging systems. Topics covered include signal processing methods for resolution improvement, ultrasound imaging system architectures, roles and necessity of the applications of DSP and VLSI technology in the development of the medical ultrasound imaging systems, and array signal processing techniques for ultrasound focusing.