• 대한기계학회논문집A
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• 제39권6호
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• pp.589-596
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• 2015

횡등방성 압전재료에 대한 모서리경사균열 문제를 해석하였다. 두 기계적 집중 면외하중과 전기적 집중 면내하중이 표면과 균열면에 각각 작용하고, 균열면은 절연균열면이다. 일반화된 변위벡터를 도입하고 Mellin 변환을 사용하여 문제를 수식화하고, 이로부터 Wiener-Hopf 식을 유도하였다. 이식을 풀므로써 폐형으로 주어지는 해를 얻었다. 임의의 균열길이나 경사각에 대해서도 적용이 되는 응력 및 전기변위 강도계수와 에너지 방출율을 구하였다. 이 해는 중첩에 의하여 임의로 분포하는 전기기계하중 문제에 대한 해를 제공하는 기본해로 사용될 수 있다.

• The Journal of the Acoustical Society of Korea
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• 제13권1E호
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• pp.45-54
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• 1994

탄성표면파 소자용 압전재료의 특성을 평가하여 최적 절단명과 전파방형을 결정하였다. 압전단결정 $LiTaO_4$에 대하여 Rayleigh파의 속도, 결합계수, 표면유전상수, 주파수-온도계수, 감쇠계수, 퓨어모드 전하, 빔 산란, 그리고 정열오차 감도 등의 항목들을 평가하였다. 이론적 계산 결과 Y절단면상의 X축 방향이 최적치로 나타났고, 이결과는 시럼에 의해 확인되었다. 본 논문의 평가방법은 여타 다른 압전재료들에도 동일하게 적용이 가능하다.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1993-2001
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• 2006

The piezoelectric bimorph film, which, as an actuator, can generate more effective displacement than the usual PVDF film, is used to control the turbulent boundary-layer flow. The change of wall pressures inside the turbulent boundary layer is observed by using the multi-channel microphone array flush-mounted on the surface when actuation at the non-dimensional frequency $f_b^+$:=0.008 and 0.028 is applied to the turbulent boundary layer. The wall pressure characteristics by the actuation to produce local displacement are more dominantly influenced by the size of the actuator module than the actuation frequency. The movement of large-scale turbulent structures to the upper layer is found to be the main mechanism of the reduction in the wall- pressure energy spectrum when the 700$700{\nu}/u_{\tau}$-long bimorph film is periodically actuated at the non- dimensional frequency $f_b^+$:=0.008 and 0.028. The biomorph actuator is triggered with the time delay for the active forcing at a single frequency when a 1/8' pressure-type, pin-holed microphone sensor detects the large-amplitude pressure event by the turbulent spot. The wall-pressure energy in the late-transitional boundary layer is partially reduced near the convection wavenumber by the open-loop control based on the large amplitude event.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.20.2-20.2
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• 2010

Recently inkjet printing technology has been developed in the areas of low cost fabrication in environmentally friendly manufacturing processes. Although inkjet printing requires the interdisciplinary researches including development of materials, manufacturing processes and printing equipment and peripherals, manufacturing a printhead is still core of inkjet technology. In this study, a piezoelectric driven DOD (drop on demand) inkjet printhead has been fabricated on three layers of the silicon wafer in MEMS Technology because of its chemical resistance to industrial inks, strong mechanical properties and dimensional accuracy to meet the drop volume uniformity in printed electronics and display industries. The flow passage, filter and nozzles are precisely etched on the layers of the silicon wafers and assembled through silicon fusion bonding without additional adhesives. The piezoelectric is screen-printed on the top the pressure chamber and the nozzle plate surface is treated with non-wetting coating for jetting fluids. Printheads with nozzle number of 16 to 256 have been developed to get the drop volume range from 5 pL to 80 pL in various industrial applications. Currently our printheads are successfully utilized to fabricating color-filters and PI alignment layers in LCD Flat Panel Display and legend marking for PCB in Samsung Electronics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.347-352
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• 2013

Seoul National University Flap (SNUF) blade is a small-scaled rotor blade incorporating a small trailing-edge flap control surface driven by piezoelectric actuators at higher harmonics for vibration attenuation. Initially, the blade was designed using two-dimensional cross-section analysis and a geometrically exact one-dimensional beam analysis, and material configuration was finalized. Flap deflection angle of ${\pm}45^{\circ}$ was established as the criterion for better vibration reduction performance based on an earlier simulation. Flap linkage mechanism design is carried out and static bench tests are conducted to verify the flap actuation mechanism performance. Different versions of test beds are developed and tested with the flap and chosen APA 200M piezoelectric actuators. Through significant improvements, a maximum deflection of ${\pm}3.7^{\circ}$ was achieved. High frequency experiments are conducted to evaluate the performance and transfer function of the test bed is determined experimentally. As the static tests are almost completed, rotor power required for testing the blade in whirl tower (centrifugal environment) is calculated and further preparations are under way.

• Smart Structures and Systems
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• 제20권6호
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• pp.657-668
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• 2017

In this research, an active vibration suppression of a smart beam having piezoelectric sensor and actuators is investigated by designing separate controllers comprising a linear quadratic regulator and a neural network. Firstly, design of a smart beam which consists of a cantilever aluminum beam with surface bonded piezoelectric patches and a designed mechanism having a micro servomotor with a mass attached arm for obtaining variations in the frequency response function are presented. Secondly, the frequency response functions of the smart beam are investigated experimentally by using different piezoelectric patch combinations and the analytical models of the smart beam around its first resonance frequency region for various servomotor arm angle configurations are obtained. Then, a linear quadratic regulator controller is designed and used to simulate the suppression of free and forced vibrations which are performed both in time and frequency domain. In parallel to simulations, experiments are conducted to observe the closed loop behavior of the smart beam and the results are compared as well. Finally, active vibration suppression of the smart beam is investigated by using a linear controller with a neural network based adaptive element which is designed for the purpose of overcoming the undesired consequences due to variations in the real system.

• 센서학회지
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• 제22권6호
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• pp.400-403
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• 2013

The piezoelectric composite film of ferroelectric PZT ceramic ($PbZr_xTi_{1-x}O_3$) and polymer (PDMS, Polydimethylsiloxane) was prepared to improve the flexibility of piezoelectric material. The bar coating method was applied to fabricate flexible nanocomposite film with large surface area by low cost process. In the case of using metal electrode on the composite film, although there is no problem by bending process, the electrode is usually broken away from the film by stretching process. However, the well-attached, flexible CNT electrode on PZT/PDMS film improved flexibility, especially stretchability. PZT particles was usually settled down into polymer matrix due to gravity of the weighty particle, so to improve the dispersion of PZT powder in polymer matrix, small amount of additives (CNT powder, Carbon nanotube powder) was physically mixed with the matrix. By stretching the film, an output voltage of PZT(70 wt%)/PDMS with CNT (0.5 wt%) was measured.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.834-839
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• 2004

In this paper, we have studied on the active vibration control of an automotive roof in passenger car's structure using piezoelectric material as the actuator and sensor attached on the surface of the automotive roof, As a control algorithm, negative velocity feedback control method is used in the study and the position of the sensor is almost attached on the nearest position of maximum normal stresses occurring while the roof is vibrating due to disturbance or exciting, Also, the actuator is attached on the other side mostly collocated to the sensor. The optimum positions have the maximum stresses of the roof which have been found in the result of the finite element analysis using Nastran software, As the fundamental experiments, a beam and plate have also been implemented to verify the performance of vibration suppression. Finally the experiment of the roof has been carried out and The roof experiment has just given a possibility to an active vibration control of the automotive structure still not applied for passenger cars.

• Steel and Composite Structures
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• 제32권6호
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• pp.753-767
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• 2019

Vibration control in mechanical equipments is an important problem where unwanted vibrations are vanish or at least diminished. In this paper, free vibration active control of the porous sandwich piezoelectric polymeric nanocomposite microbeam with microsensor and microactuater layers are investigated. The aim of this research is to reduce amplitude of vibration in micro beam based on linear quadratic regulator (LQR). Modified couple stress theory (MCST) according to sinusoidal shear deformation theory is presented. The porous sandwich microbeam is rested on elastic foundation. The core and face sheet are made of porous and three-phase carbon nanotubes/resin/fiber nanocomposite materials. The equations of motion are extracted by Hamilton's principle and then Navier's type solution are employed for solving them. The governing equations of motion are written in space state form and linear quadratic regulator (LQR) is used for active control approach. The various parameters are conducted to investigate on the frequency response function (FRF) of the sandwich microbeam for vibration active control. The results indicate that the higher length scale to the thickness, the face sheet thickness to total thickness and the considering microsensor and microactutor significantly affect LQR and uncontrolled FRF. Also, the porosity coefficient increasing, Skempton coefficient and Winkler spring constant shift the frequency response to higher frequencies. The obtained results can be useful for micro-electro-mechanical (MEMS) and nano-electro-mechanical (NEMS) systems.

• Smart Structures and Systems
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• 제16권1호
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• pp.27-46
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• 2015

Active surface adjustment of cable net structures is becoming significant when large-size cable net structures are widely applied in various fields, especially in satellite antennas. A general-duty adjustment method based on active cables is proposed to achieve active surface adjustment or surface profile reconfiguration of cable net structures. Piezoelectric actuators and voice coil actuators are selected for constructing active cable structures and their simplified mechanical models are proposed. A bilevel optimization model of active surface adjustment is proposed based on the nonlinear static model established by the direct stiffness method. A pattern search algorithm combined with the trust region method is developed to solve this optimization problem. Numerical examples of a parabolic cable net reflector are analyzed and different distribution types of active cables are compared.