• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.491-491
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• 2011

Transparent and flexible electronic devices that are light-weight, unbreakable, low power consumption, optically transparent, and mechanical flexible possibly have great potential in new applications of digital gadgets. Potential applications include transparent displays, heads-up display, sensor, and artificial skin. Recent reports on transparent and flexible field-effect transistors (tf-FETs) have focused on improving mechanical properties, optical transmittance, and performances. Most of tf-FET devices were fabricated with transparent oxide semiconductors which mechanical flexibility is limited. And, there have been no reports of transparent and flexible all-organic tf-FETs fabricated with organic semiconductor channel, gate dielectric, gate electrode, source/drain electrode, and encapsulation for sensor applications. We present the first demonstration of transparent, flexible all-organic sensor based on multifunctional organic FETs with organic semiconductor channel, gate dielectric, and electrodes having a capability of sensing infrared (IR) radiation and mechanical strain. The key component of our device design is to integrate the poly(vinylidene fluoride-triflouroethylene) (P(VDF-TrFE) co-polymer directly into transparent and flexible OFETs as a multi-functional dielectric layer, which has both piezoelectric and pyroelectric properties. The P(VDF-TrFE) co-polumer gate dielectric has a high sensitivity to the wavelength regime over 800 nm. In particular, wavelength variations of P(VDF-TrFE) molecules coincide with wavelength range of IR radiation from human body (7000 nm ~14000 nm) so that the devices are highly sensitive with IR radiation of human body. Devices were examined by measuring IR light response at different powers. After that, we continued to measure IR response under various bending radius. AC (alternating current) gate biasing method was used to separate the response of direct pyroelectric gate dielectric and other electrical parameters such as mobility, capacitance, and contact resistance. Experiment results demonstrate that the tf-OTFT with high sensitivity to IR radiation can be applied for IR sensors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.218-224
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• 2007

Although piezoelectric materials such as PZT have been widely used as actuators in the field of active vibration suppression, the use of bare PZT as an actuator may cause some drawbacks such as critical breaks in the installation process, short circuits in the host material and low fatigue performance. The LIPCA-C2 (lightweight piezocomposite actuator) was developed to alleviate these problems. We implemented the LIPCA as an actuator to suppress the vibration of an aluminum cantilever beam with a tip mass. In our test, we used positive position feedback control algorithm. The filter frequency for this type of feedback should be tuned to the natural frequency of the target mode. The first three experimental natural frequencies of the aluminum cantilever beam agree well with the results of finite element analysis. The effectiveness of using the LIPCA as an actuator in active vibration suppression was investigated with respect to the time and frequency domains, and the experimental results show that LIPCAs with PPF control can significantly reduce the amplitude of forced vibrations and the settling time of free vibrations. For a case study, the forced vibration control of several beams with different thicknesses were performed.

• Polymer(Korea)
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• v.35 no.2
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• pp.130-135
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• 2011

Along with the fast development of electronics, the demands of portable electronics and wireless sensors are growing rapidly. The need for self-powering materials capable of powering the electrical devices attached to them is increasing, The piezoelectric effect of polyvinylidene fluoride (PVDF) can be used for this purpose. PVDF has a special crystal structure consisting of a ${\beta}$-phase that can produce piezoelectricity. In this paper, multilayer PVDF films were fabricated to increase the ${\beta}$-phase content. A solution of 10% concentration N;N-dimethylacetamide (DMAc) in PVDF (PVDF/DMAc) was used to fabricate the films via spin coating technique with the following optimum process parameters: a spin rate of 850 rpm, spin time of 60 s, drying temperature of $60^{\circ}C$, and drying time of 30 min, Compared with single-layer PVDF films, the multilayer films exhibited higher ${\beta}$-phase content. The ${\beta}$-phase content of the films increased gradually with increasing number of layers until 4, Maximum ratio of ${\beta}$-phase content was 7.72.

• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.67-74
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• 2009

Presently means of utilizing sensors such as Piezoelectric(PZT) Element for evaluating the affect of oscillator, strain gauge for analyzing physical changes and use of Fiber Bragg Grating(FBG) Sensor are widely practiced in the field. In this study, PZT and FBG sensors were used to tearing damage of cable systems in these sensors. Cable systems are a construction of elements carrying only tension and no compression or bending in membrane structure. But damage detection of cable systems by using existing safety diagnosis is difficult to detect the characteristic change of overall structural action. If cable snaps are occurred to cable release and tear in tension structures, these are set up a vibration. So, we used piezo-electric materials and result of experiment using this was compared with result of experiment using FBG sensors The purpose of this research is to develop of damage detection method of cable system in tensile stress.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.751-758
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• 2002

Boreholes that are drilled in soft or unconsolidated materials such as gravels and coals are prone to collapse. To maintain the hole, some kinds of casing pipes are needed. If thereby a plastic pipe e.g. PVC is used for the casing, Televiewer tool is still capable of detecting structural features such as fractures in the borehole wall behind the pipe, whereas other borehole-imaging logging devices such as BIPS (Borehole Image Processing System) and FMS(Formation Micro Scanner) won't provide any information about that. Televiewer's primary component is a piezoelectric transducer centered in the hole. It acts as both a transmitter and receiver, and sends an ultrasonic beam. That is reflected, in the same manner as the seismic wave propagation, from the both sides(inner and outer surfaces) of the casing pipe, transmits through the pipe and then reflected from the borehole wall. With an appropriate choice of time-windowing, it is possible to capture the returning signals from both the borehole wall and the outer side of casing pipe as well. A suite of laboratory tests were performed on various physical models composed of plastic pipes with different diameters. Although the amplitudes of returning signals were reduced to about half the usual value due to the transmission loss, the dynamic range of Televiewer tool was sufficient to observe the structural features behind the casing pipe. Besides, several representative case studies at various research areas in our country are presented. The results demonstrate the usefulness of the transmissivity of Televiewer acoustic km, which will assist in further structural interpretation.

• Transactions on Electrical and Electronic Materials
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• v.7 no.4
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• pp.196-203
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• 2006

An air-gap type FBAR was designed using Leach equivalent model for analyzing a vertical structure of the FBAR. For the top electrode, Pt, and the bottom electrode, Au, of $1.2{\mu}m$ thickness and the piezoelectric of 0.8,urn thickness, the resonance and anti-resonance occurred at 2.401 GHz and 2.460 GHz, respectively. $S_{11}$ was increased and $S_{21}$ was decreased as the resonance area of FBAR was widened. We observed the characteristics of insertion loss, bandwidth and out-of-band rejection of ladder-type FBAR BPF by changing resonance areas of series and shunt resonators and by adding stages. As the resonance area of series resonator was increased, insertion loss was improved but out-of-band rejection was degraded. And as the resonance area of shunt resonator was increased, insertion loss was degraded a little but out-of-band rejection was improved even without adding stages. We, also, changed the shape of the resonance area from square shape to rectangle shape to examine the effects of the resonator shape on the characteristics of the BPF. The best performances were observed when the sizes of series and shunt resonator are $150{\mu}m{\times}l50{\mu}m\;and\;5{\mu}m{\times}50{\mu}m$, respectively. Out-of-band rejection was improved about 10dB and bandwidth was broadened from 30MHz to 100MHz utilizing inductor tuning on $2{\times}2\;and\; 4{\times}2$ ladder-type BPFs.

• Smart Structures and Systems
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• v.21 no.3
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• pp.287-303
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• 2018

Applications of energy harvesting from mechanical vibrations is becoming popular but the full potential of such applications is yet to be explored. This paper addresses this issue by considering an application of energy harvesting for the dual objective of serving as an indicator of structural health monitoring (SHM) and extent of control. Variation of harvested energy from an undamaged baseline is employed for this purpose and the concept is illustrated by implementing it for active vibrations of a pipe structure. Theoretical and experimental analyses are carried out to determine the energy harvesting potential from undamaged and damaged conditions. The use of energy harvesting as indicator for control is subsequently investigated, considering the effect of the introduction of a tuned mass damper (TMD). It is found that energy harvesting can be used for the detection and monitoring of the location and magnitude of damage occurring within a pipe structure. Additionally, the harvested energy acts as an indicator of the extent of reduction of vibration of pipes when a TMD is attached. This paper extends the range of applications of energy harvesting devices for the monitoring of built infrastructure and illustrates the vast potential of energy harvesters as smart sensors.

• Electrical & Electronic Materials
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• v.3 no.3
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• pp.233-241
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• 1990

본 연구에서는 xPb(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$-yBa(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$-zPbTiO(0.50.leq.x.leq.0.60, 0.10.leq.y.leq.0.20, 0.20.leq.z.leq.0.40)세라믹을 1050.deg.C에서 2시간동안 유지시켜 일반소성법으로 제작하였다. 시편 제작시 조성은 조성변태 상경계부근을 선택하였으며 Ba(Zn$_{1}$3/ Nb$_{2}$3/)O$_{3}$ 고용량에 따른 purochlore상의 억제 및 그 영향을 조사하고 구조적, 유전적 및 압전적 특성을 측정하였다. X-선 회절분석 및 미세구조의 관찰 결과, Ba(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$의 고용량에 따라 pyrochlore상 및 미반응 물질등은 억제되어 0.20mol 고용된 시편에서는 균질한 perovskite상이 형성되었다. Ba(Zn$_{1}$3/Nb$_{2}$3/)O$_{3}$의 고용량이 증가함에 따라 유전상수는 증가하여 0.50PZN-0.20BZN-0.30PT시편의 경우 6880.9의 높은 값을 나타내었으며 정전용량의 온도계수는 감소하여 0.383[%/.deg.C]의 양호한 값을 나타내었다. 큐리온도는 PbTiO$_{3}$의 고용량이 0.20mol에서 0.40mol로 증가함에 따라 30.deg.C에서 170.deg.C로 증가하였다. 전기기계 결합계수 (K$_{p}$), 기계적 품질계수(Qm) 및 압전전하 계수 (d$_{33}$)는 조성변태 상경계 부근의 조성에서 크게 나타났으며 0.60PZN-0.15BZN-0.25PT 시편의 경우 각각 58.5%, 120.5, 150x$10^{-12}$[C/N]의 값을 나타내었다.다.다.

• Electrical & Electronic Materials
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• v.5 no.2
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• pp.198-206
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• 1992

(P $b_{1-x}$L $a_{x}$)[(S $b_{1}$2/S $n_{1}$2/) $Ti_{y}$ Z $r_{1-y}$] $O_{3}$(0.leq.x.leq.0.04, 0.25.leq.y.leq.0.40) 세라믹을 1250[.deg.C]에서 2시간동안 유지시켜 일반 소성법으로 제작하였으며 조성 및 L $a_{2}$ $O_{3}$첨가량에 따른 구조적, 압전적 특성을 관찰하였다. L $a_{2}$ $O_{3}$의 첨가량이 3-4[mol%]인 경우 La-rich의 pyrochlore상이 형성되었다. 시편의 평균결정립 크기는 1-2[.mu.n]의 크기를 나타내었으며 PbTi $O_{3}$조성이 증가함에 따라 다소 감소하는 경향을 나타내었다. 각 조성의 시편에 대해 PbTi $O_{3}$ 및 L $a_{2}$ $O_{3}$의 첨가량이 증가할수록 유전상수는 증가하는 경향을 나타내었으며 상전이 온도인 큐리온도는 PbTi $O_{3}$조성이 감소할수록 L $a_{2}$ $O_{3}$첨가량이 증가할수록 감소하는 경향을 나타내었다. 압전 전하계수 및 전기기계 결합계수는 L $a_{2}$ $O_{3}$첨가량 및 PbTi $O_{3}$조성에 따라 증가하였으며 L $a_{2}$ $O_{3}$가 4[mol%]첨가된 0.10PSS-0.40PT-0.50PZ 시편에서 각각 250x$10^{-12}$[C/N], 29.7[%]의 최대값을 나타내었다. 기계적 품질계수는 L $a_{2}$ $O_{3}$첨가량 및 PbTi $O_{3}$조성이 증가할수록 감소하는 경향을 나타내었으며 0.10PSS-0.25PT-0.65PZ 시편에서 138의 최대값을 나타내었다.다.

• Journal of Sensor Science and Technology
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• v.5 no.3
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• pp.25-31
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• 1996

Steel wires are made by elongating hot billets. If the billets have internal or surface defects, the wire can be broken during elongation process. After testing surface defect, we are testing internal defect by ultrasonic transducers. POSCO is producing two kinds of billets, hot rolled billet and cast billet. Hot rolled one is denser than cast billet. Because of the low density and rough surface, ultrasonic testing is difficult for the cast billet. Size of the transducer was related with the size and density of the billet. A transducer having 21mm long, 8.5mm wide and 0.95mm thick piezoelectric ceramic plate was best for $160mm\;{\times}\;160mm$ cast billet. Center frequency of the transducer was 2.25MHz and the focus distance was 70mm.