• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1514-1519
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• 2001

This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.346-346
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• 2007

압전세라믹 재료는 현재 압전 변압기, actuator, transducer, sensor, speaker 등에 광범위하게 이용이 되고 있다. 이 중에서 압전세라믹 소결체를 이용한 스피커의 제조는 가공이 까다롭고, 대형의 크기로 제작 시 소자가 깨지는 등의 많은 제약을 받고 있으며, 저음 특성이 떨어져 응용 범위가 한정되어 있다. 따라서 최근에는 이러한 단점을 극복하기 위하여 세라믹/고분자 복합체를 이용한 필름 스피커를 제작하고자 시도하고 있다. 이러한 세라믹/고분자 0-3형 압전 복합체를 이용할 경우, 제품의 경량화를 실현할 수 있고, 크기나 환경의 영향을 거의 받지 않으므로, 고기능성 스피커로의 응용에 적합할 것으로 보인다. 따라서 본 연구에서는 PZT계의 세라믹와 PVDF, PVDF-TrFE, Polyester, acrylic resin 등의 여러 고분자 물질과의 복합체를 제조하여 압전특성을 평가하였다. 본 실험은 먼저 $(Pb_{1-a-b}Ba_aCd_b)(Zr_xTi_{1-x})_{1-c-d}(Ni_{1/3}Nb_{2/3})_c(Zn_{1/3}Nb_{2/3})_dO_3$ (이하 PZT라 표기)의 최적화 조성을 선택하여, $1050^{\circ}C$에서 소결된 분말을 48시간 ball milling방법 로 약 $1{\mu}m$ 크기로 분쇄하였다. 고분자 물질들은 알맞은 용제들을 선택하여 녹였다. 그 다음 소결된 PZT분말과 고분자를 50:50, 60:40, 65:35, 70:30등의 무게 분율로 혼합하고, 분산제, 소포제 등을 첨가하여 3단 roll mill을 이용하여 충분히 분산시켜 페이스트 (Paste)를 제조하였다. 제조된 페이스트를 ITO가 코팅된 PET필름 위에 스크린 프린팅 법을 사용하여 인쇄하여 $120^{\circ}C$에서 5분간 건조하였다. 코팅된 복합체의 두께는 약 $80{\mu}m$ 정도로 측정되었다. Ag 페이스트를 이용한 상부 전극 형성에도 스크린 프린팅 법을 적용하였다. 이를 $120^{\circ}C$에서 4 kV/mm의 DC 전계로 분극 공정을 수행한 후 전기적 특성을 평가하였다. 유전특성을 조사하기 위해서 LCR meter (EDC-1620)를 사용하였고, 시편의 결정구조는 XRD (Rigaku; D/MAX-2500H)을 통해 분석하였으며, 전자현미경(SEM)을 이용하여 미세구조를 분석하였다. 압전 전하상수$(d_{33})$ 값은 APC 8000 모델을 이용하여 측정하였다. PZT의 혼합비가 증가할수록 비유전율 및 압전 전하 상수 등의 전기적 특성이 증가되었다. 또 여러 고분자 물질 중에서 PVDF-TrFE 수지가 가장 우수한 특성을 보였다. 이는 PVDF-TrFE 수지가 압전성을 나타내기 때문인 것으로 판단되었다.

• Advanced Composite Materials
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• v.18 no.4
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• pp.327-338
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• 2009

In this paper, through an evaluation process conducted on several designs of mini-LIPCA (Lightweight Piezo-Composite curved Actuator), an optimal design of a mini-LIPCA has been proposed. Comparing with the LIPCA-C2, the design of the mini-LIPCA comes with reduced overall size and a thinner active layer. Since a variation in the number and lay-up of fiber composite layers may strongly affect the performance of the device, one is able to configure several designs of mini-LIPCA. The evaluation process is then followed in order to determine a configuration which characterizes the possibly optimal performance. That is, a design of a mini-LIPCA is said to be optimal if it is capable of producing a maximum out-of-plane displacement. The size of the LIPCA to be investigated was selected to be $10\;mm\;{\times}\;20\;mm$ in which the thickness of PZT plate is about 0.1 mm. The thickness of glass/epoxy and carbon/epoxy are about 0.09 mm and 0.1 mm, respectively. The evaluation process has been conducted thoroughly, i.e., analytical estimation, numerical approximation and the experimental measurement are all involved. Firstly, the design equation was used to calculate essential parameters of proposed lay-up configurations. Secondly, ANSYS, a commercial FEA package, was utilized to estimate displacement outputs of the actuators upon being excited. Finally, experimental measurements were able to verify the predicted results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.191-194
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• 2002

In optical pick-up, optical components such as objective lens, collimator, mirror, laser diode and photo diode are mounted on the pick-up base. These components must keep their original position during operation for proper transmittance of information from laser diode to optical disk and back to photo diode. However, micro thermal deformation of pick-up base which is induced by thermal environment during operation can deteriorate the performance of optical pick-up. Therefore, it is important to measure and analyze the thermal deformation behavior of pick-up base under thermal environment. In the present study, a measurement system using holographic interferometry was designed to measure micro thermal deformation of pick up base. The measurement system was verified by using the deformation of cantilever with prescribed motion actuated by PZT with 1 nm resolution. Interferometric measurement was compared quantitatively with that induced by PZT actuator. Finally, micro thermal deformation of pick-up base under actual thermal environment was measured using the present holographic interferometry and the results were analysed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1219-1222
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• 2005

As the optical communication is introduced to the backbone network at first and becomes a general communication method of network, the demand of kernel parts of optical communication such as PLC(Planar Light Circuit), Coupler, and WDM(Wavelength Division Multiplexing) element increases. The alignment and the attachment technology are very important in the fabrication of optical elements. In this paper, the driving mechanism of ultra precision stage is studied with the aim of optimal design of stage. The travel and the resolution of stage are investigated. The hysteresis of the stage is generated because of PZT actuator. The hysteresis and the inverse hysteresis are modeled in X, Y, and Z-axis motion. The input data of desired displacement to the stage according to input voltage is obtained from the inverse hysteresis equation. In the result of experiments with the input data, the errors due to hysteresis are well compensated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.20-25
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• 2001

To develop the piezoelectric actuator, the structural, dielectric and piezoelectric properties and electric fieldinduced strain of the ceramics(Pb$\_$1-2/Ba$\_$x/)[Mg$\_$1/2/W$\_$1/2/)$\_$0.03/-Ni$\_$1/3/Nb$\_$2/3/)$\_$0.12/-(Zr$\_$0.5/Ti$\_$0.5/)$\_$0.85/]O$_3$(x=0, 0.01, 0.03, 0.05, 0.07, 0.1) were investigated with the substitution of Ba. The tetragonality of crystal structure and grain size decreased by the substitution of Ba. Curie temperature decreased due to the decrease of the tetragonality, and dielectric constants increased with the substitution of Ba. The coercive field, remnant polarization and electromechanical coupling factor also decreased, whereas the piezoelectric constatns d$\_$33/ and d$\_$31/ were showed the highest value of 430 and 209(x10$\^$-12/C/N), respectively, because of the increase of dielectric constant. The strain induced by 60Hz AC electric field had the maximum value of 204x10$\^$-6/Δℓ/ℓ at the substitution of Ba 3mol%. As the applied electric field approaches to the coercive field, the piezoelectric element is depolarized and the electric field induced strain revealed non-linearity.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.126-130
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• 2008

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 ${\mu}m$ graded index multimode fiber using a short cylindrical piezoelectric transducer(PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2834-2838
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• 2008

An free breathing proton exchange membrane fuel cell (PEMFC) was developed. This paper presents a study of the several effect on the performance of a fuel cell such as air flow rate, opening ratio, and cathode structures. Especially, an air flow rate is critical condition to improve the fuel cell performance. In this paper, we developed a synthetic jet micro air blower to supply high stoichiometric air. The synthetic jet actuation is usually generated by a traditional PZT-driven actuator, which consists of a small cylindrical cavity, orifices and PZT diaphragms. In comparison with free convection fuel cells, the forced-convection fuel cell which equipped synthetic jet micro air blower brings higher performance and stability for long term test. Also, power consumption of the synthetic jet micro air blower is under 0.3W. The results show that the maximum power density was $188mW/cm^2$ at $400mA/cm^2$. The maximum power density was higher 40% than power density of free convection fuel cell.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3131-3135
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• 2008

This paper presents an energy harvester using piezoelectric elements that is a kind of generator which converts the mechanical power to the electric one using windmill system with many PZT actuators. In this study, low frequency characteristics of the cantilever-type piezoelectric actuator are experimentally investigated. Advantages of the cantilever use are to take a very large displacement and to improve the endurance of the PZT element. The material of cantilever is an aluminum and three kinds of cantilever of which size is $150[mm]{\times}20[mm]{\times}1.5[mm]$, $170[mm]{\times}20[mm]{\times}1.5[mm]$ and $190[mm]{\times}20[mm]{\times}1.5[mm]$ were experimented, respectively. The cantilever was fixed on the vibrator. The characteristics of frequency and mass variation of cantilever end part such as 0[g], 5[g], 10[g] are investigated. Maximum voltage was outputted at the condition of $150[mm]{\times}20[mm]{\times}1.5[mm]$ and 10[g] of mass. It was confirmed that the lower natural frequency at the larger length of cantilever and at the bigger of mass is gotten.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.711-719
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• 2002

This paper presents the synchronous vibration control of a rotor system using an active air bearing(AAB). In order to suppress the synchronous vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by pivots containing piezoelectric actuators and their radial position can be actively controlled by applying voltage to the actuators. Thus, disturbances, i. e. various kinds of external force can cause shaft vibration as well as change of the air film thickness. The dynamic behavior of a rotary system supported by two tilting-pad gas bearings and its active stabilization using the tilting-pads as actuators are investigated numerically. The $\mu$ synthesis are applied to the AAB system with three pads, two of which contain piezoelectric actuators. To test the validity of the theoretical method, the performance of this control method is evaluated through experiments. The experimental results also show the effectiveness of the control system for suppressing the unbalanced response of the rigid modes.