• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.51-59
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• 2012

Piezoelectric langasite crystals have superior properties such as high temperature performance and high quality Q and can be applied in combustion pressure sensors and surface acoustic wave (SAW) filters. Crystal growth, crystal structure and properties of langasite group are reviewed, and the mechanism of piezoelectricity of langasite is presented based on the crystal structure and deformation under high pressure. Finally, for the discovery of new piezoelectric materials, this paper presents the role of the framework, and recommends the search of framework crystal structure, because the characteristic of the mechanism exists on the framework of the crystal structure.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.1
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• pp.104-107
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• 2021

The orientation of trabeculae and porosity determine the wave propagation in cancellous bone. Wave propagation, as well as charge density and piezoelectricity, stimulate bone remodeling. Also, Charged ions in the fluid affect wave propagation in cancellous bone. But the trabecular struts' piezoelectricity does not change the waveform of cancellous bone. However, the underlying mechanism is unknown yet why trabecula struts' piezoelectricity does not change wave propagation through cancellous bone. Thus, we derived the governing equation indicating that trabecular struts' piezoelectric properties show that those do not affect wave propagation in cancellous bone.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.69-71
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• 2014

MLCCs are used broadly in electronic industry like smart phone and TV. Although they are fabricated in small size and have high capacitance, there are acoustic noise problems to reduce comfort of user. Acoustic noise results from linear piezoelectricity and nonlinear electrostriction of $BaTiO_3$ in MLCC and there are some researches on MLCC vibration under AC electric field. When only AC electric field without DC bias is applied to MLCC, fundamental frequency response is affected by piezoelectricity and second-harmonic frequency response shows electrostrictive vibration. In this study we get vibration shape of MLCC under AC electric field for each frequency and analysis on the mechanism of MLCC vibration affected by piezoelectricity and electrostriction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.462-465
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• 2009

Cellulose based electro-active paper (EAPap) is a new smart material that has a potential to be used in biomimetic actuator and sensor. Beside of the natural abundance, cellulose EAPap is fascinating with its biodegradability, lightweight, high mechanical strength and low actuation voltage. An actuating mechanism of EAPap is revealed to be the combination of ion migration effect and piezoelectricity. EAPap can generate the electrical current and voltage when the mechanical stress applied due to its electro-mechanical characteristics. In this paper, we investigated the feasibility of EAPap as a mechanical strain sensor.

• Journal of the Korean Vacuum Society
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• v.8 no.3A
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• pp.187-193
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• 1999

In this study, PVDF thin films which show the excellent piezoelectricity and pyroelectricity, are prepared by PVD (physical vapor deposition) method, and thir electrical conduction phenomena for analyses of the electrical conduction mechanism and TSC (Thermally Stimulated Current) for identification of the behavior of conductive carriers are investigated. As a result of FT-IR(Fourier Transform Infrared Spectroscopy) spectra, the crystalline phase transforms $\alpha$ type into $\beta$ type with increasing electric field. From XRD (X-Ray diffraction) analyses patterns, the degree of crystallinity increases from 49.8% to 67%, as the substrate temperature increases from $30^{\circ}C$ to $80^{\circ}C$. As a result of electrical conduction phenomena, the electrical conduction mechanism of PVDF thin films is identified as ionic conduction mechanism. From TSC analyses, there are three peaks as P1, P2, P3 with increasing temperature, and with increasing substrate temperature, the peak temperature of TSC increases and the peak intensity of TSC decreases.

• Vacuum Magazine
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• v.3 no.2
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• pp.17-20
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• 2016

Piezoelectric nanogenerators are energy harvesting device to convert a mechanical energy into an electric energy using nanostructured piezoelectric materials. This review summarizes works to date on piezoelectric nanogenerators, starting with a basic theory of piezoelectricity and working mechanism, and moving through the reports of numerous nanogenerators using nanorod arrays, flexible substrates and alternative materials. A sufficient power generated from nanogenerators suggests feasible applications for either power supplies or strain sensors of highly integratedl nano devices. Further development of nanogenerators holds promise for the development of self-powered implantable and wearable electronics.

• Transactions on Electrical and Electronic Materials
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• v.13 no.4
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• pp.171-176
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• 2012

As langasite $A_3BC_3D_2O_{14}$ compounds with piezoelectric properties exhibit no phase transition up to the melting point of 1,400-$1,500^{\circ}C$, many high temperature applications are expected for the SAW filter, temperature sensor, pressure sensor, and so on, based on the digital transformation of wider bandwidth and higher-bit rates. It has a larger electromechanical coupling factor compared to quartz and also nearly the same temperature stability as quartz. The $La_3Ga_5SiO_{14}$ (LGS) crystal with the $Ca_3Ga_2Ge_4O_{14}$-type crystal structure was synthesized and the crystal structure was analyzed by Mill et al. It is also an important feature that the growth of the single crystal is easy. In the case of three-element compounds such as $[R_3]_A[Ga]_B[Ga_3]_C[GaSi]_DO_{14}$ (R=La, Pr and Nd), the piezoelectric constant increases with the ionic radius of R. In this study, crystal structures of four-element compounds such as $[A_3]_A[B]_B[Ga_3]_C[Si_2]_DO_{14}$ (A = Ca or Sr, B = Ta or Nb) are analyzed by a single crystal X-ray diffraction, and the mechanism and properties of the piezoelectricity depending on the species of cation was clarified based on the crystal structure.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.256-256
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process. Charge accumulation and resulting electric field generation mechanism by spray coating method were shown in Fig. 1. The capacitance of the CNT/PVDF films increased by adding CNTs into the PVDF matrix, and finally saturated. However, the I-V curves didn't show any saturation effect in the CNT concentration range of 0~4 wt%. Therefore we can control the performance of the devices fabricated from the CNT/PVDF composite film by adjusting the current level resulted from the CNT concentration with the uniform capacitance value.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.11
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• pp.740-745
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• 2014

ZnO nanowires were grown by hydrothermal synthesis process and piezoelectric poly vinylidene fluoride (PVDF) was then coated on top of the ZnO-nanowires by spray-coating technique. The composite layer of ZnO-nanowires/PVDF was applied to an energy harvesting device based on piezoelectric-conversion mechanism. A defined mechanical force was given to the nanogenerator device to evaluate their electric power generation characteristics, where output current density and voltage were examined. Electric power generation property of the ZnO-nanowires/PVDF based nanogenerator device was compared to that of the nanogenerator device with ZnO-nanowires as single active layer. Effect of the ZnO-nanowires on improvement of power generation was discussed to examine its feasibility for the nanogenerator device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.7
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• pp.550-554
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process.