• Progress in Superconductivity and Cryogenics
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• v.19 no.4
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• pp.26-30
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• 2017

The promising characteristics of 2G high-temperature superconductor (HTS) coated conductor (CC) tapes have made it possible to apply to various electrical device applications. In this study, the mechanical and electromechanical properties of Sn-Cu double layer stabilized GdBCO CC tapes have been characterized. The stress and strain tolerances of $I_c$ in GdBCO CC tapes adopting stainless steel substrate were evaluated using $I_c$-strain measurement at 77 K under both uniaxial tension and monotonic bending conditions. The results were compared to the conventional single Cu layer stabilized CC tape. As a result, the Sn-Cu double layer stabilized GdBCO CC tapes showed somehow lower or comparable electromechanical properties as compared to the Cu stabilized CC tape ones.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.35-39
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• 2008

In this study, electromechanical properties of carbon nanotube (CNT) thin film on flexible substrates were measured using a micro-tensile machine with functionality of simultaneous measurements of displacement, load and electrical resistance. The CNT thin film of about 100 nm thick was deposited on flexible substrates, polyethylene terephthalate (PET) using spraying and ink-jetting techniques. To investigate the effect of process condition on the electromechanical properties of CNT thin film, sets of CNT samples were fabricated under various heat treatments and microwave process. The microstructures of the CNT thin film before and after tensile test were investigated using Scanning Electron Microscope (SEM), and the failure modes of the CNT thin films were identified to understand their electromechanical behaviors and interaction with the flexible substrates. Based on the experimental results, the use of CNT thin film as flexible electrodes and strain gages is discussed.

• Progress in Superconductivity and Cryogenics
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• v.18 no.3
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• pp.6-9
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• 2016

The enhancement of mechanical properties of coated conductor (CC) tapes in practical application are usually achieved by reinforcing through lamination or electroplating metal layers on either sides of the CC tape. Mechanical or electromechanical properties of the CC tapes have been largely affected by the lamination structure under various loading modes such as tension, bending or even cyclic. In this study, the influence of brass laminate volume fraction on electromechanical properties of RCE-DR processed Gadolinium-barium-copper-oxide (GdBCO) CC tapes was investigated. The samples used were composed of single-side and both-side laminate of brass layer to the Cu-stabilized CC tape and their $I_c$ behaviors were compared to those of the Cu-stabilized CC tape without external lamination. The stress/strain dependences of $I_c$ in laminated CC tapes under uniaxial tension were analyzed and the irreversible stress/strain limits were determined. As a result, the increase of brass laminate volume fraction initially increased the irreversible strain limit and became gradual. The corresponding irreversible stress limit, however, showed no difference even though the brass laminate volume fraction increased to 3.4. But the irreversible load limit linearly increased with the brass laminate volume fraction.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.13-13
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• 2011

Graphene based nano-electronic and nano-electromechanical devices will be introduced in this presentation. The first part of the presentation will be covered by our recent results on the fabrication and physical properties of artificially twisted bilayer graphene. Thanks to the recently developed contact transfer printing method, a single layer graphene sheet is stacked on various substrates/nano-structures in a controlled manner for fabricating e.g. a suspended graphene device, and single-bilayer hybrid junction. The Raman and electrical transport results of the artificially twisted bilayer indicates the decoupling of the two graphene sheets. The graphene based electromechanical devices will be presented in the second part of the presentation. Carbon nanotube based nanorelay and A new concept of non-volatile memory based on the carbon nanotube field effect transistor together with microelectromechanical switch will be briefly introduced at first. Recent progress on the graphene based nano structures of our group will be presented. The array of graphene resonators was fabricated and their mechanical resonance properties are discussed. A novel device structures using carbon nanotube field effect transistor combined with suspended graphene gate will be introduced in the end of this presentation.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.321-328
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• 1988

The sintering phenomena, electrical resistivity, dielectric and piezoelectric properties of lead titanate ceramics modified by the partial substitution of La for Pb and Mn for Ti, (Pb1-1.5xLax)(Ti1-yMny)O3 ceramics, have been investigated. In (Pb1-1.5xLax)(Ti1-yMny)O3 system, with increasing lanthanum content, the realtive bulk density increased, but the Curie point and tetragonality (c/a) decreased. The tetragonal-to-cubic phase transition boundary existed in the range of 0.20

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.2
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• pp.116-122
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• 2004

A micromachined self-exited piezoelectric cantilever has been fabricated using PZT(52/48) thin film. For the application to biosensor using antigen-antibody interaction, electromechanical properties such as resonant frequency and quality factor of micromachined piezoelectric cantilever were important factors. Electromechanical properties and resonant behaviors of microfabricated cantilever were simulated by FEA (Finite Element Analysis) using Coventorware$^{TM}$2003. And these characterization of microcantilever were measured by using LDV(Laser Doppler Vibrometer) to compare with FEA data. We present the resonant frequency shift of micromachined piezoelectric cantilevers due to combination of mass loading and change of spring constant by gold deposition. Experimental mass sensitivities of microcantilever were characterized by Au deposition on the backside of microcantilever. Mass sensitivities with $100{\times}300$ ${\mu}{\textrm}{m}$ dimension cantilever from simulation and experimental were 5.56 Hz/ng and 16.8 Hz/ng respectively.y.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.303-304
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• 2003

Conducting polymers show several unique features, wherein electrical and optical properties change drastically during electrochemical reaction. By making use of these phenomena, several electronic devices have been fabricated, for instance, electrochromic displays, rechargeable batteries and electroplasticity memory devices. Electromechanical actuators using conducting polymers have been proposed by Baughman et. al [1]. (omitted)

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1723-1725
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• 1999

This paper is the study for piezoelectric properties of PMN-PT-PZ composition for high power piezoelectric device. It needs the properties such as high mechanical quality factor(Qm), high electromechanical coupling coefficient(kp) and high dielectric strain constant$(d_31)$, and the stable electromechanical properties under high vibration level. For acquiring this results, the value of x is changed in 0.1Pb$(Mn_{1/3}Nb_{2/3})O_3$+(0.9-x)$PbZrO_3+xPbTiO_3$ composition to find MPB(morphotropic phase boundary), and the piezoelectric constants is measured by resonance-antiresonance frequency method, based on IRE Standard. Also, it is measured as a function of the amount of additive, $Nb_2O_5$. When the composition is applied to high power device, the electromechanical properties is measured by laser vibrometer to confirm the reliablity under high vibration level. From these results, PMN-PT-PZ composition is shown excellent properties and capacity of application to high power device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.457-463
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• 2024

(Bi_1/2Na_1/2)TiO₃(BNT) piezoelectric ceramics are one of the promising materials that can replace Pb(Zr, Ti)O₃(PZT) piezoelectric ceramics due to the high electromechanical strain properties. However, it is still difficult to use practical applications because the required electric field for inducing electromechanical strain is relatively higher than that of PZT ceramics. To overcome this problem, it has been intensively studied on doping impurity or modifying other ABO₃ for BNT-based piezoelectric ceramics. Therefore, this study investigated the effects of La₂O₃ doping on the phase transition behavior and electromechanical strain properties in BNT-SrTiO₃ (BNT-ST) lead-free piezoelectric ceramics. In the case of the temperature-dependent dielectric properties, it was confirmed that a phase transition from ferroelectrics to relaxors is induced with increasing La₂O₃ content. As a result, the electromechanical strain properties of BNT-ST ceramics were improved. The highest S_max/E_max value corresponding to 300 pm/V was obtained at 2 mol% La₂O₃-dopped BNT-ST ceramics. Accordingly, this study successfully demonstrated that La₂O₃ doping is effective on the inducing phase transition from ferroelectrics to relaxors and the improving electromechanical strain properties of BNT-ST lead-free piezoelectric ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.930-934
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• 2009

In this study, in order to develop excellent lead-free composition ceramics for piezoelectric transformer, ($K_4CuNb_8O_{23}$) added $(K_{0.5}Na_{0.5})(Nb_{0.96}Sb_{0.04})O_3$ ceramics were fabricated using conventional mixed oxide method and their piezoelectric and dielectric properties were investigated as a fu+EY50nction of the amount of KCN addition. With increasing the amount of KCN addition, density and mechanical quality factor(Qm), electromechanical coupling factor (Kp) were increased up to 1.2 mol% and then decreased. At the 1.2 mol% KCN added specimen, mechanical quality factor (Qm), electromechanical coupling factor (Kp), density and dielectric constant (${\varepsilon}r$) showed the optimal values of 781, 0.445, $4.42\;g/cm^3$ and 443, respectively, for piezoelectric transformer application.