• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권9호
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• pp.611-615
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• 1999

Piezoelectric properties of PMN-PZT ceramics with $CeO_2$ impurity were investigated. Mechanical quality factor, $Q_m$ of 1792, 1285 and the electromechanical coupling coefficient, $k_p$ of 0.52, 0.54 were obtained from the specimen with 0.25 and 0.5 mole % $CeO_2$ respectively. Curie temperature was decreased with the addition of $CeO_2$ while the electric coercive field was proportional to the amount of impurity. Based on the system ceramics with 0.5 mole % cerium oxide, a Rosen type piezoelectric transformer was fabricated and tested. Voltage step-up ratios of 230 and 13 were obtained from the transformer at no load and $100 k\Omega$ resistance, respectively. Experimental results showed a potential of the transformer for the practical use coupled with the expected strength increase by the grain size refinement.

• 한국전기전자재료학회논문지
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• 제18권11호
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• pp.1007-1013
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• 2005

In this study, a step-down piezoelectric transformer was fabricated to utilize as an adapter for charging batteries of mobile electronic appliances. The ceramic part of the transformer is $Pb[(Mn_{1/3}Sb_{2/3})_{_0.05}Zr_{0.475}Ti_{0.475}]O_3$ with mechanical quality factor of 1600, electromechanical coupling coefficient $59\%$, and piezoelectric constant $d_{33}$ 1300, which can be utilized as a piezoelectric transformer. A simply fabricated disk-typed test pattern of diameter 28 mm and thickness 2 mm was used to characterize output voltage, step-down ratio as a function of electrode area with the input remained constant, and power, efficiency as a function of input voltage, and temperature-dependent electric characteristics were evaluated. The sample APT1 showed the best properties. The highest admittance, effective electromechanical coupling coefficient and an appropriate mechanical quality factor were obtained at the sample with the input/output area ratio of 1:1.5 at the common electrode, and the condition of 20 $V_{rms}$, $50\;\Omega$ made the maximum efficiency of $95\%$. The temperature was increased by 14.7'E as the input voltage was increased for $50\;V_{rms},\;50\;\Omega$.

• Smart Structures and Systems
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• 제11권4호
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• pp.349-364
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• 2013

Recently, researchers in the field of structural health monitoring (SHM) have been rigorously striving to replace the conventional NDE techniques with the smart material based SHM techniques, employing smart materials such as piezoelectric materials. For instance, the electromechanical impedance (EMI) technique employing piezo-impedance (lead zirconate titanate, PZT) transducer is known for its sensitivity in detecting local damage. For practical applications, various external factors such as fluctuations of temperature and loading, affecting the effectiveness of the EMI technique ought to be understood and compensated. This paper aims at investigating the damage monitoring capability of EMI technique in the presence of axial stress with fixed boundary condition. A compensation technique using effective frequency shift (EFS) by cross-correlation analysis was incorporated to compensate the effect of loading and boundary stiffening. Experimental tests were conducted by inducing damages on lab-sized aluminium beams in the presence of tensile and compressive forces. Two types of damages, crack propagation and bolts loosening were simulated. With EFS for compensation, both cross-correlation coefficient (CC) index and reduction in peak frequency were found to be efficient in characterizing damages in the presence of varying axial loading.

• 한국세라믹학회지
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• 제28권5호
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• pp.347-352
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• 1991

The effects of Ta2O3 doping on the microstructure, electrical properties and thermal expansion in Pb(Zr0.525Ti0.475)O3 ceramics were studied. Density, average grain size, electromechanical coupling factor kp and thermal expansion coefficient of unpoled and poled samples were measured as a function of Ta2O5 content. Average grain size was decreased and density increased above 0.6 mol% Ta2O5 addition. In case of 0.2 mol% addition, density showed minimum according to grain growth. Dielectric constant and electromechanical coupling factor kp were the lowest in 0.2 mol% addition increased with Ta2O5 addition.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2172-2179
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• 2002

In this paper, we examine the dynamic electromechanical behavior of an edge crack in a piezoelectric ceramic layer bonded between two elastic layers under the combined anti-plane mechanical shear and in-plane electric transient loadings. We adopted both the permeable and impermeable crack boundary conditions. Fourier transforms are used to reduce the problem to the solution of two pairs of dual integral equations, which are then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate are presented to show the dependences upon the geometry, material combination, electromechanical coupling coefficient and electric field.

• Advances in nano research
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• 제16권2호
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• pp.175-186
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• 2024

Dynamical behaviors of one-dimensional (1D) nano-sized structures are of great importance in nanotechnology applications. Therefore, the torsional dynamic response of functionally graded nanorods which could be used to model the nano electromechanical systems or micro electromechanical systems with torsional motion about the center of twist is examined based on the theory of strain gradient nonlocal elasticity in this work. The mathematical background is constructed based on both strain gradient theory and Eringen's nonlocal elasticity theory. The equation of motions and boundary conditions of radially functionally graded nanorods are derived using Hamilton's principle and then transformed into the eigenvalue analysis by using Fourier sine series. A general coefficient matrix is obtained to assemble the Stokes' transformation. The case of a restrained functionally graded nanorod embedded in two elastic springs against torsional rotation is then deeply investigated. The effect of changing the functionally graded index, the stiffness of elastic boundary conditions, the length scale parameter and nonlocal parameter are investigated in detail.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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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 Magnetics
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• 제19권3호
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• pp.215-220
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• 2014

This study investigates the dynamic magneto-mechanical behavior of magnetization-graded ferromagnetic materials Terfenol-D/FeCuNbSiB (MF). We measure the dynamic magneto-mechanical properties as a function of the DC bias magnetic field ($H_{dc}$). Our experimental results show that these dynamic magneto-mechanical properties are strongly dependent on the DC bias magnetic field. Furthermore, the dynamic strain coefficient, electromechanical resonance frequency, Young's moduli, and mechanical quality factor of Terfenol-D/FeCuNbSiB are greater than those of Terfenol-D under a lower DC bias magnetic field. The dynamic strain coefficient increases by a factor of between one and three, under the same DC bias magnetic field. In particular, the dynamic strain coefficient of Terfenol-D/FeCuNbSiB at zero bias achieves 48.6 nm/A, which is about 3.05 times larger than that of Terfenol-D. These good performances indicate that magnetization-graded ferromagnetic materials show promise for application in magnetic sensors.

• International Journal of Fluid Machinery and Systems
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• 제10권2호
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• pp.176-188
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• 2017

The nozzle-flapper valves are widely applied as a pilot stage in aerospace and military system. A subject of the analysis presented in this work is to find out a reasonable range of null clearance between the nozzle and flapper. This paper has presented a numerical flow coefficient simulation. In every design point, a parameterized model is created for flow coefficient simulation and cavitation under different conditions with varying gap width and inlet pressure. Moreover, a new test device has been designed to measure the flow coefficient and for visualized cavitation. The numerical simulation and test results both indicate that cavitation intensity gets fierce initially and shrinks finally as the gap width varies from small to large. From the curve, the flow coefficient mostly has experienced three stages: linear throttle section, transition section and saturation section. The appropriate deflection of flapper is recommended to make the gap width drop into the linear throttle section. The flapper-nozzle null clearance is optionally recommended near the range of $D_N/16$. Finally through simulation it is also concluded that the inlet pressure plays a little role in the influence on the flow coefficient.

• E2M - 전기 전자와 첨단 소재
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• 제10권1호
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• pp.20-25
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• 1997

In this study, piezoelectric actuator samples were fabricated using 0.375PMN-0.37OPT-0.255PZ system ceramics with Barium substitution and the strain properties of them were investigated. Dielectric constant of the specimens increased with the increase of Ba content up to 5mol% and decreased with futher addition of Ba. The largest piezoelectric coefficient and electromechanical coupling coefficient were observed at the sintering temperature of 1250'C and Barium content of 5mol%. The characteristics of strain hysteresis was found largely with varing the sintering temperature on the single round type, and the strain is proportional to piezoelectric coefficient.