• KIEE International Transactions on Electrophysics and Applications
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• 제5C권3호
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• pp.102-110
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• 2005

Piezoelectric transformers(PT) are expected to be small, thin and highly efficient, and which are attractive as a transformer with high power density for step down voltage. For these reasons, we have attempted to develop a step-down PT for the miniaturized adaptor. We propose a PT, operating in thickness extensional vibration mode for step-down voltage. This PT consists of a multi-layered construction in the thickness direction. In order to develop the step-down PT of 10 W class and turn ratio of 0.1 with high efficiency and miniaturization, the piezoelectric ceramics and PT designs are estimated with a variety of characteristics. The basic composition of piezoelectric ceramics consists of ternary yPb(Zr$_{x}$Ti$_{1-x}$)O$_{3}$-(1-y)Pb(Mn$_{1/3}$Nb1$_{1/3}$Sb$_{1/3}$)O$_{3}$. In the piezoelectric characteristics evaluations, at y=0.95 and x=0.505, the electromechanical coupling factor(K$_{p}$) is 58$\%$, piezoelectric strain constant(d$_{33}$) is 270 pC/N, mechanical quality factor(Qr$_{m}$) is 1520, permittivity($\varepsilon$/ 0) is 1500, and Curie temperature is 350 $^{\circ}C$. At y = 0.90 and x = 0.500, kp is 56$\%$, d33 is 250 pC/N, Q$_{m}$ is 1820, $\varepsilon$$_{33}$$^{T}$/$\varepsilon$$_{0}$ is 1120, and Curie temperature is 290 $^{\circ}C$. It shows the excellent properties at morphotropic phase boundary regions. PZT-PMNS ceramic may be available for high power piezoelectric devices such as PTs. The design of step-down PTs for adaptor proposes a multi-layer structure to overcome some structural defects of conventional PTs. In order to design PTs and analyze their performances, the finite element analysis and equivalent circuit analysis method are applied. The maximum peak of gain G as a first mode for thickness extensional vibration occurs near 0.85 MHz at load resistance of 10 .The peak of second mode at 1.7 MHz is 0.12 and the efficiency is 92$\%$.

• 한국전기전자재료학회논문지
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• 제24권11호
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• pp.859-864
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• 2011

An operation temperature of $Pb(Zr,Ti)O_3$ based piezoelectric ultrasonic flowmeter was generally restricted to below 200$^{\circ}C$ due to a low depoling temperature of its ceramic material. Thus, a new designed piezoelectric ultrasonic flowmeter was fabricated in order to protect from the extremely hot fluid. Its structure is optimized by a finite element method to effectively stop heat flowing along a waveguide. Various materials such as Cu, Al, SUS were examined as a multi-plate radiation shield to enhance the performance of piezoelectric ultrasonic flowmeter. The SUS was evaluated as the most effective material to enhance the performance of piezoelectric ultrasonic flowmeter. As the number of plates of the radiation shield increased, the temperature at piezoelectric transducer away from the hot fluid was constantly decreased with a ratio of 3.12$^{\circ}C$ per the plate number.

• 한국광물학회지
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• 제14권1호
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• pp.39-51
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• 2001

공주군 유구면 일대의 화강암질 편마암의 풍화작용에 따른 원소의 거동과 pH와 이차광물과의 관계를 XRF, ICP-AES, ICP-MS를 이용한 원소분석결과를 통하여 검토하였다. 이 지역의 암석은 pH6 내외의 산성환경, 침철석, 아나타제와 같은 다양한 이차광물을 생성하면서 심각한 화학조성의 변화를 초래했다. 주원소의 화학조성을 이용한 풍화지수는 토양층에서 79~88로 모암 중의 사장석이 용해되고 흑운모가 변질되어 캐올리광물의 생성이 활발한 방향으로 풍화작용이 진행되었다. 지표층으로 가면서 Al에 대한 주 원소의 거동은 Si, Ca, Na, K, P가 감소하고 Fe, Ti, Mn이 증가하는 경향을 보이며 pH가 낮은 풍화단면에서 주 원소의 변화량이 더 크다. 이 풍화대에서 Mg은 거의 일정하다. Li, As 모든 전이원소는 pH가 감소함에 따라 증가하며 특히 이들 원소는 Fe의 함량과 비례해서 증가해 침철석과 공침하였거나 표면에 흡착되어 있는 것으로 보인다. Ga은 Fe와 비례하기는 하지만 변화량은 전 풍화단면에서 일정하다. Zr, Mo, Sn, Cd은 pH에 변화에 상관없이 일정한 반면에 Rb, Sr, Ba, Y, Pb, Th, U 등은 감소하는 경향을 보인다. 특히 Rb 과 Sr은 Ca에 비례해서 감소한다. 희토류원소는 전 풍화단면에서 감소하는 경향을 보이는데 $Al_2$$O_3$에 대한 상대적인 변화량을 보면 경희토류원소는 사프롤라이트(saprolite)하부와 상부에서 부화되어 있고 중부 사프롤라이트와 토양층에서 감소하는 반면에 중희토류원소는 사프롤라이트 하부와 상부에서 감소하고 중부사프롤라이트 및 토양층에서 부화되는 경향을 보인다. 전반적으로 희토류원소의 원자번호가 클수록 손실율이 커진다. 이 풍화단면에서 원소의 거동은 각 풍화층의 pH와 생성된 이차광물의 조성에 지배를 받았다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.289-293
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• 2003

This study dealt with the characterization of $MoSi_2$ based composites containing three types of additive materials such as SiC, $NbSi_2\;and\;ZrO_2$ particles have been investigated, based on the detailed examination of their microstructures and fracture surfaces. The effects of reinforcing materials on the high temperature strength of $MoSi_2$ based composites have been also examined. $MoSi_2$ based composites were fabricated by the hot press process under the vacuum atmosphere. The volume fraction of reinforcing materials in the composite system was fixed as 20 %. The microstructures and the mechanical properties of $MoSi_2$ based composites were investigated by means of SEM, EDS, XRD and three point bending test.

• 한국전기전자재료학회논문지
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• 제35권1호
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• pp.72-79
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• 2022

Piezoelectric energy harvesting technologies, which can be used to convert the electricity from the mechanical energy, have been developed in order to assist or power the wearable electronics. To realize non-toxic and biocompatible electronics, the lead-free (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) nanoparticles (NPs) are being studied with a great attention as flexible energy harvesting device. Herein, piezoelectric hybrid nanocomposites were fabricated using BCTZ NPs-embedded poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] matrix to improve the performance of flexible energy harvester. Output performance of the fabricated energy device was investigated by the well-optimized measurement system during the periodically bending and releasing motions. The generated open-circuit voltage and the short-circuit current of the piezoelectric hybrid nanocomposite-based energy harvester reached up to ~15 V and ~1.1 ㎂, respectively; moreover, the instantaneous power of 3.5 ㎼ is determined from load voltage and current at the external load of 20 MΩ. This research is expected to cultivate a new approach to high-performance wearable self-powering electronics.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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• pp.23-28
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• 2002

This paper describes the machining characteristics of the $MoSi_2$ based composites by electric discharge drilling with various tubular electrodes, besides, Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $MoSi_2$ -based composites has been developed in new materials for jet engine of supersonic-speed airplanes and gas turbine for high- temperature generator. Achieving this objective may require new hard materials with high strength and high temperature-resistance. However, With the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. By combining a nonconducting ceramics with more conducting ceramic it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like (Nb, Mo)$SiO_2$ and $Nb_2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature. $MoSi_2$ composites which a hole drilling was not possible by the conventional machining process, enhanced the capacity of ED-drilling by adding $NbSi_2$ relative to that of SiC or $ZrO_2$ reinforcements.

• 대한치과보철학회지
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• 제44권5호
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• pp.654-664
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• 2006

Statement of problem: There has been a eat interest in the use of titanium for fixed and removable prostheses in recent because of its excellent biocompatibility. However, the melting temperature and chemical reactivity of titanium necessities casting system different from those used in conventional casting. The current titanium casting systems are based on an electric-arc design for melting the metal in an argon atmosphere and its exclusive investment. Despite the new development in Ti casting system, inadequate mold filling and internal porosity are frequently observed casting defects. Purpose : The purposes of this study were to compare the castibility and reaction layer of the casting titanium under the two casting machines and their investment condition. Material and method: coping and machine-milled titanium coping according to the casting methods and the marginal configurations. The total 28 specimens were used, and these are divided into 4 groups according to 2 casting machines and 2 investments. The castings were analyzed using x-ray microanalysis and microhardness testing. The reaction layer between margin of titanium casting and the investments was observed and analyzed with scanning electron microscope. Result: 1. Castabiliy of casting titanium specimen was best in the group of centrifugal casting machine and Selevest $CB^{\circledR}$ and good that of Selevest CB and pressure differential casting machine, Rematitan plus and centrifugal casting machine, Rematitan plus and pressure differential casting machine in order. 2. There was no significanct correlation in titanium castability in respect of casting machine. However ANOVA indicated that Selevest $CB^{\circledR}$ groups had significantly better castability than Rematitan $plus^{\circledR}$ groups.(p<0.05) 3. There was a significant microhardness difference between centrifugal casting machine groups and pressure differential groups.(p<0.05) Titanium castings in centifugal groups had significantly harder than those in pressure differential groups. 4. The addition of zirconia decreased interfacial reactivity. Conclusion: above result revealed that of the castability of titanium casting specimens had little correlation in casting machines and was better in magnesia-based investment contained ZrO2 groups. However in order to practice casting titanium in clininic, its castability should be improved, also there should be more research on factor of castability so that long-span prothesis and removable partial denture metla frame may be casted completly.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.58.1-58.1
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• 2010

In solar cell module manufacturing, single solar cells has to be joined electrically to strings. Copper stripes coated with tin-silver-copper alloy are joined on screen printed silver of solar cells which is called busbar. The bus bar collects the electrons generated in solar cell and it is connected to the next cell in the conventional module manufacturing by a metal stringer using conventional hot air or infrared lamp soldering systems. For thin solar cells, both soldering methods have disadvantages, which heats up the whole cell to high temperatures. Because of the different thermal expansion coefficient, mechanical stresses are induced in the solar cell. Recently, the trend of solar cell is toward thinner thickness below 180um and thus the risk of breakage of solar cells is increasing. This has led to the demand for new joining processes with high productivity and reduced error rates. In our project, we have developed a new method to solder solar cells with a laser heating source. The soldering process using diode laser with wavelength of 980nm was examined. The diode laser used has a maximum power of 60W and a scanner system is used to solder dimension of 6" solar cell and the beam travel speed is optimized. For clamping copper stripe to solar cell, zirconia(ZrO)coated iron pin-spring system is used to clamp both joining parts during a scanner system is traveled. The hot plate temperature that solar cell is positioned during lasersoldering process is optimized. Also, conventional solder joints after $180^{\circ}C$ peel tests are compared to the laser soldering methods. Microstructures in welded zone shows that the diffusion zone between solar cell and metal stripes is better formed than inIR soldering method. It is analyzed that the laser solder joints show no damages to the silicon wafer and no cracks beneath the contact. Peel strength between 4N and 5N are measured, with much shorter joining time than IR solder joints and it is shown that the use of laser soldering reduced the degree of bending of solar cell much less than IR soldering.

• 한국터널지하공간학회 논문집
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• 제9권4호
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• pp.403-413
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• 2007

터널과 같은 지하공간 구조물에 있어서 록볼트는 숏크리트와 함께 주요 지보재 중의 하나이며, 그러므로 록볼트 시공품질 정도에 따라 이러한 지중구조물의 안정성에 큰 영향을 미치게 된다. 본 연구의 목적은 록볼트를 따라 전파되는 유도파에 대하여 푸리에 및 웨이브렛 변환을 이용하여 록볼트의 건전도를 평가하는데 있다. 각기 다른 결함비율을 가진 다섯 개의 록볼트 시험체를 제작하여 콘크리트 블록에 매설한 후, PZT($Pb[Zr_xTi_{1-x}]O_3$: lead zirconate titanate) 엘리먼트로 유도파를 발생시키고 AE(acoustic emission) 센서를 이용하여 신호를 측정하였다. 수집된 신호는 푸리에 변환을 이용하여 주파수 영역에서 분석하였고, 가버 웨이브렛을 사용한 웨이브렛 변환을 이용하여 시간-주파수영역에서 분석하였다. 푸리에 변환을 이용하여 얻은 스펙트럼을 분석하면 록볼트의 결함비율이 증가함에 따라 고주파 대역 에너지의 비율이 증가하는 것을 알 수 있다. 또한, 시간-주파수 영역에서의 각 파군별 최대 에너지가 나타나는 지점의 시간차는 각 반사파군 간의 이동 시간차를 나타내며, 이를 통해 계산된 유도파의 에너지 속도는 록볼트의 공동결함비율이 증가함에 따라 증가하는 것으로 나타났다. 본 연구는 스펙트럼 비와 에너지 속도가 록볼트의 건전도 평가에 있어서 하나의 지표가 될 수 있음을 보여준다.

• 자원환경지질
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• 제22권1호
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• pp.35-63
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• 1989

구룡산(九龍山)(또는 옥천(沃川)) 함(含)우라늄 흑연질점판암(黑鉛質粘板岩)은 옥천대(沃川帶) 서북부(西北部)에 따라 증상(層狀) 또는 부딘상(狀)으로 90km이상(以上) 연장(延長) 분포(分布)한다. 함(含)우라늄점판암(粘板岩)의 오토레디오그라프에 나타나는 퇴적(堆積), 속성(續成), 변성구조(變成構造)는 우라늄과 동시퇴적물(同時堆積物)로서 속성작용과정(續成作用過程)에서 전혀 이동(移動)하지 않고 황성변성(廣域變成) 초기(初期)에 제자리에서 미립(微粒)우라니나이트로 재결정(再結晶)하였음을 보여준다. 동시(同時)에 유기물(有機物)은 미세환장흑연(微細環狀黑鉛)으로 되었다. 라미나구조(構造)의 발달(發達)과 평균(平均) 19.64% C, 2.32% S의 함유(含有)는 함(含)우라늄흑니(黑泥) 퇴적(堆積)의 일반조건(一般條件)으로서의 극(極)히 낮은 퇴적화(堆積比), 고유기물함유(高有機物含有), 염기성황경등을 충족(充足)하였으며 Th/U가 0.07로서 해수원(海水源)임을 뜻한다. 지역별(地域別) CaO, $P_2O_5$의 평균치(平均値)가 매우좁은 범위(範圍)의 일정치(一定値)이며 높은 CaO 평균치(平均値)를 나타내어 전퇴적(全堆積)분지를 통(通)하여 동일(同一) pH(7.8-8.0)조건(條件)의 환경(環境)에서 퇴적(堆積)하였음을 나타낸다. 함(含)우라늄점판암(粘板岩)은 같은 성인(成因)의 타산장(他産狀)에 비(比)하여 미량원소(微量元素) 부화도(富化度)가 매우 높다. 고부화(高富化)의 중요(重要)한 원인(原因)으로서 미량원소(微量元素)의 소스(source)인 해수(海水)의 주기적(週期的) 교체(交替)가 요구(要求)되는데 사이크릭퇴적구조(堆積構造)는 그러한 현상(現象)을 뒷받침하여 준다. 흑니(黑泥)의 성인별(成因別) 구성광물(構成鑛物)과 원소(元素)의 수반관계(隨伴關係)에서 쇄설성광물(鑛物)에는 Si, Al, K, Na, Ti, Zr, Th, Be, B, Li, 유기물(有機物)후락숀에, U, Ni, Cu, Co, Zn, Ag, Mo, Pb, Sn, Cd, S, Fe, V, Cr, Y, 탄산염광물(炭酸鹽鑛物)에 Ca, Mg, Mn, P, Ba가 높은 상관(相關)을 나타낸다. 유기물(有機物)의 우라늄고정심전능력(固定沈澱能力)에 있어 사프로페릭(Sapropelic)형(型)보다 휴믹(Humic)형(型)에서 더 높다. 육성식물(陸性植物)의 분해물(分解物)인 휴무스(Humus)는 고대성(古生代) 중기(中期)에 출현(出現)한다. 우라늄 함유(含有) 흑니(黑泥)는 이 시대(時代)의 형성물(形成物)로서 이런 형(型)의 광상(鑛床)은 생물상(生物相)의 진화(進化)에 규제(規制)된 광화작용(鑛化作用)의 산물(産物)이다.