• Smart Structures and Systems
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• 제16권4호
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• pp.623-640
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• 2015

This paper presents techniques to harvest higher voltage from piezoelectric cantilever energy harvester by structural alteration. Three different energy harvesting structures are considered namely, stepped cantilever beam, stepped cantilever beam with rectangular and trapezoidal cavity. The analytical model of three energy harvesting structures are developed using Euler-Bernoulli beam theory. The thickness, position of the rectangular cavity and the taper angle of the trapezoidal cavity is found to shift the neutral axis away from the surface of the piezoelectric element which in turn increases the generated voltage. The performance of the energy harvesters is evaluated experimentally and is compared with regular piezoelectric cantilever energy harvester. The analytical and experimental investigations reveal that, the proposed energy harvesting structures generate higher output voltage as compared to the regular piezoelectric cantilever energy harvesting structure. This work suggests that through simple structural modifications higher energy can be harvested from the widely reported piezoelectric cantilever energy harvester.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.495-501
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• 2000

This paper presents a method to minimize the initial deflection of a multi-layer piezoelectric microactuator without loosing its piezoelectric deflection performance required for light modulating micromirror devices. The multi-layer piezoelectric actuator composed of PZT silicon nitride and platinum layers deflects or buckles due to the gradient of residual stress. Based on the structural analysis results and relationship between process conditions and mechanical properties we have modified the fabrication process and the thickness of thin film layers to reduce the initial residual stress deflection without decreasing its piezoelectric deflection performance. The modified designs fabricated by surface-micromachining process achieved the 77% reduction of the initial deflection compared with that of the conventional method based on the measured micromechanical material properties is applicable to the design refinement of multi-layer MEMS devices and micromechanical structures.

• 한국도로학회논문집
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• 제19권5호
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• pp.107-115
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• 2017

PURPOSES : The piezoelectric energy road analysis technology using a three-dimensional finite element method was developed to investigate pavement behaviors when piezoelectric energy harvesters and a new polyurethane surface layer were installed in field conditions. The main purpose of this study is to predict the long-term performance of the piezoelectric energy road through the proposed analytical steps. METHODS : To predict the stresses and strains of the piezoelectric energy road, the developed energy harvesters were embedded into the polyurethane surface layer (50 mm from the top surface). The typical type of triaxial dump truck loading was applied to the top of each energy harvester. In this paper, a general purpose finite element analysis program called ABAQUS was used and it was assumed that a harvester is installed in the cross section of a typical asphalt pavement structure. RESULTS : The maximum tensile stress of the polyurethane surface layer in the initial fatigue model occurred up to 0.035 MPa in the transverse direction when the truck tire load was loaded on the top of each harvester. The maximum tensile stresses were 0.025 MPa in the intermediate fatigue model and 0.013 MPa in the final fatigue model, which were 72% and 37% lower than that of the initial stage model, respectively. CONCLUSIONS : The main critical damage locations can be estimated between the base layer and the surface layer. If the crack propagates, bottom-up cracking from the base layer is the main cracking pattern where the tensile stress is higher than in other locations. It is also considered that the possibility of cracking in the top-down direction at the edge of energy harvester is more likely to occur because the material strength of the energy harvester is much higher and plays a role in the supporting points. In terms of long-term performance, all tensile stresses in the energy harvester and polyurethane layer are less than 1% of the maximum tensile strength and the possibility of fatigue damage was very low. Since the harvester is embedded in the surface layer of the polyurethane, which has higher tensile strength and toughness, it can assure a good, long-term performance.

• 한국전기전자재료학회논문지
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• 제22권8호
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• pp.665-670
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• 2009

Lead-free piezoelectric ($Na_{1/2}K_{1/2}$)$NbO_3$ ceramics doped with CuO and $MnO_2$ were fabricated using the conventional oxide-mixing technique. With increasing content of CuO and $MnO_2$, the dielectric constant(${\varepsilon}_{33}$) and mechanical quality factor($Q_m$) value increased, while electromechanical coupling factor($K_p$) and piezoelectric constant($d_{33}$) decreased. The piezoelectric and dielectric properties ($Na_{1/2}K_{1/2}$)$NbO_3$ ceramics doped with CuO 2.461 wt% and $MnO_2$ 0.538 wt% at sintered temperature $1050\;^{\circ}C$ were attained ${\varepsilon}_{33}$ = 403, $K_p$ = 15, $Q_m$ = 122 and $d_{33}$ = 36 pC/N. Based on response surface methodology results using design of experiment, it was concluded that ($Na_{1/2}K_{1/2}$)$NbO_3$ doped with CuO 0.477 wt% and $MnO_2$ 0.269 wt% has possibility composition of being used for piezoelectric transformer.

• Journal of Periodontal and Implant Science
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• 제39권4호
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• pp.385-390
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• 2009

Purpose: In this study we evaluated the morphologic aspects of defects created by a piezoelectric ultrasonic scaler with scaler tip on casting gold alloy using scanning electron microscope (SEM) images and defect surface profiles. Methods: 54 blocks of type III casting gold alloy (Firmilay, Jellenko Inc, CA, USA) were scaled by a piezoelectric ultrasonic scaler (P-MAX, Satelec, France) with scaler tip (No. 1 tip) on a sledge device. 2-dimensional profiles of defects on all samples were investigated by a surface profilometer (a-Step 500, KLA-Tencor, CA, USA). The selected working parameters were lateral force (0.5 N, 1.0 N, 2.0 N), mode (P mode, S mode), and power setting (2, 4, 8). SEM images were obtained. Defect surface profiles were made on Microsoft Excel program using data obtained by a surface profilometer. Results: Among P mode samples, there were similarities on defect surface profiles and SEM images regardless of lateral force. The defects created in P mode were narrow and shallow although the depth and the width increased as power setting changed low (2) to high (8). In P mode samples, the defect depth was the greatest when lateral force of 0.5 N was applied. However all the depths were smaller than 1 m. SEM images of Lateral force of 0.5 N, S mode, power setting 2 and 4 were similar to that of P mode, but the other SEM images of S mode showed discernible changes. Defect depth of S mode samples was the greatest when lateral force of 1.0 N was applied. Conclusions: Within the limitations of this study, it can be concoluded that removing capability of piezoelectric scaler with scaler tip becomes maximized as power level becomes higher but the capability is restricted when excessive lateral force is applied on scaler tip.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.5-8
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• 2000

This paper proposes GaN film as a piezoelectric material for SAW(surface acoustic wave) filters. The fabricated GaN SAW filter exhibited a very high velocity of 5800 ㎧and relatively low insertion loss of -9.9 dB without matching circuit. From Smith's equivalent circuit model, the calculated electromechanical coupling factor (K$^2$) was about 4.$\pm$03％. which is larger than those obtained from other thin film piezoelectric materials and allows the realization of wider filter fractional bandwidths.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.869-872
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• 2001

A new in-pipe locomotive mechanism is developed using piezoelectric bimorphs. Two bimorphs are linked serially and produce an ellipsoidal motion at the end of bimorph. The device moves by the friction force between the rubber attached at the bimorph end and the inner surface of the pipe. The developed mechanism is very simple and need relatively small power compared to a conventional multi-layer piezoelectric motor.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.46-49
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• 2000

A decoupled thermo-~lezoelectric-mechanical model of composite laminates with surface bonded piezoelectric actuators, subjected to externally applied load, temperature change load, electric field load is developed. The governing differential equations are obtained by applying the principle of free energy and variational techniques. A higher order zigzag theory displacement field is employed to accurately capture the transverse shear and normal effects in laminated composite plates of arbitrary thickness.

• Advances in materials Research
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• 제8권4호
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• pp.259-274
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• 2019

Flexoelectric effect has a major role on mechanical responses of piezoelectric materials when their dimensions become submicron. Applying differential quadrature (DQ) method, the present article studies dynamic characteristics of a small scale beam made of piezoelectric material considering flexoelectric effect. In order to capture scale-dependency of such piezoelectric beams, nonlocal elasticity theory is utilized and also surface effects are included for better structural modeling. Governing equations have been derived by utilizing Hamilton's rule with the assumption that the scale-dependent beam is subjected to thermal environment leading to uniform temperature variation across the thickness. Obtained results based on DQ method are in good agreement with previous data on pizo-flexoelectric beams. Finally, it would be indicated that dynamic response characteristics and vibration frequencies of the nano-size beam depends on the existence of flexoelectric influence and the magnitude of scale factors.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.675-693
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• 2017

In this paper, based on the first-order shear deformation plate theory, buckling analysis of piezoelectric coupled transversely isotropic rectangular plates is investigated. By assuming the transverse distribution of electric potential to be a combination of a parabolic and a linear function of thickness coordinate, the equilibrium equations for buckling analysis of plate with surface bonded piezoelectric layers are established. The Maxwell's equation and all boundary conditions including the conditions on the top and bottom surfaces of the plate for closed and open circuited are satisfied. The analytical solution is obtained for Levy type of boundary conditions. The accurate buckling load of laminated plate is presented for both open and closed circuit conditions. From the numerical results it is found that, the critical buckling load for open circuit is more than that of closed circuit in all boundary and loading conditions. Furthermore, the critical buckling loads and the buckling mode number increase by increasing the thickness of piezoelectric layers for both open and closed circuit conditions.