• Smart Structures and Systems
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• v.11 no.2
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• pp.217-240
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• 2013

In this paper, practical methods to utilize PZT's dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material's dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.

• Smart Structures and Systems
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• v.2 no.2
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• pp.101-113
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• 2006

Structural health monitoring results obtained with the electro-mechanical (E/M) impedance techniqueand Lamb wave transmission methods during fatigue crack propagation of an Arcan specimen instrumented with piezoelectric wafer active sensors (PWAS) are presented. The specimen was subjected in mixed-mode fatigue loading and a crack was propagated in stages. At each stage, an image of the crack and the location of the crack tip were recorded and the PWAS readings were taken. Hence, the crack-growth in the specimen could be correlated with the PWAS readings. The E/M impedance signature was recorded in the 100 - 500 kHz frequency range. The Lamb-wave transmission method used the pitch-catch approach with a 3-count sine tone burst of 474 kHz transmitted and received between various PWAS pairs. Fatigue loading was applied to initiate and propagate the crack damage of controlled magnitude. As damage progressed, the E/M impedance signatures and the waveforms received by receivers were recorded at predetermined intervals and compared. Data analysis indicated that both the E/M impedance signatures and the Lamb-wave transmission signatures are modified by the crack progression. Damage index values were observed to increase as the crack damage increases. These experiments demonstrated that the use of PWAS in conjunction with the E/M impedance and the Lamb-wave transmission is a potentially powerful tool for crack damage detection and monitoring in structural elements.

• Structural Monitoring and Maintenance
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• v.1 no.3
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• pp.339-356
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• 2014

This study has been motivated to evaluate the practicality of numerical simulation of impedance monitoring for damage detection in steel column connection. In order to achieve the objective, the following approaches are implemented. Firstly, the theory of electro-mechanical (E/M) impedance responses and impedance-based damage monitoring method are outlined. Secondly, the feasibility of numerical simulation of impedance monitoring is verified for several pre-published experimental examples on steel beams, cracked aluminum beams, and aluminum round plates. Undamaged and damaged steel and aluminum beams are simulated to compare to experimental impedance responses. An aluminum round plate with PZT patch in center is simulated to investigate sensitive range of impedance responses. Finally, numerical simulation of the impedance-based damage monitoring is performed for a steel column connection in which connection bolts are damaged. From the numerical simulation test, the applicability of the impedance-based monitoring to the target steel column connection can be evaluated.

• Smart Structures and Systems
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• v.4 no.1
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• pp.35-46
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• 2008

In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.

• Journal of the Korean Electrochemical Society
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• v.2 no.1
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• pp.23-26
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• 1999

The Langmuir adsorption isotherm at the $(Pt)/0.1M\;H_2SO_4$ electrolyte interface has been qualitatively analyzed using the ac impedance measurement and phase-shift method. The phase shift $(\phi)$ depends on both the cathode potential (E<0) and frequency (f) and is inversely proportional to the factional surface coverage $(\theta)$. At an intermediate frequency band (ca. $1\~100$ Hz), the phase-shift profile $(\phi\;vs.\;E)$ can be related to the fractional surface coverage $(\theta\;vs.\;E)$. The phase-shift profile $(\phi\;vs.\;E)$ can be used as an experimental method to estimate and analyze the Langmuir adsorption isotherm $(\theta\;vs.\;E)$. The equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the adsorbed hydrogen atom $(H_{ads})\;and\;3\times10^{-4}$ and 20.1 kJ/mol, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.814-815
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• 2009

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.548-551
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• 2000

Spinel phase LiF $e_{y}$M $n_{2-y}$ $O_4$samples are synthesized by calcining a LiOH.$H_2O$, Mn $O_2$and F $e_2$ $O_3$mixture at 80$0^{\circ}C$ for 36h in air. Preparing LiF $e_{y}$M $n_{2-y}$ $O_4$showed spinel phase with cubic phase. The ununiform distortion of the crystallite of the spinel LiF $e_{y}$M $n_{2-y}$ $O_4$was more stable than that of the pure. The discharge capacity of the cathode for the Li/LiF $e_{0.1}$M $n_{1.9}$ $O_4$cell at the first than that of the pure. The discharge capacity of the cathode for the Li/LiF $e_{0.1}$M $n_{1.9}$ $O_4$cell at the first cycle and at the 70th cycle was about 113 and 90mAh/g, respectively. This cell capacity was retained about 82% of the first cycle after 70th cycle. Impedance profile of this cell was more stable than that pure. The resistance, the capacitance and chemical diffusion coefficients of lithium ion showed approximately 80$\Omega$, 36133.87$\mu$F ; 1.4$\times$10$^{-8}$ c $m^2$ $s^{-1}$ , respectively. , respectively.ely.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.949-955
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• 2009

In this study, we investigated the effects of Cr dopant (1.0 at% $Cr_2O_3$ sintered at $1000^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and interface state levels of ZnO using dielectric functions ($Z^*$, $M^*$, $Y^*$, $\varepsilon^*$, and $tan{\delta}$), admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). For the identification of the bulk trap levels, we examine the zero-biased admittance spectroscopy and dielectric functions as a function of frequency and temperature. Impedance and electric modulus spectroscopy is a powerful technique to characterize grain boundaries of electronic ceramic materials as well. As a result, three kinds of bulk defect trap levels were found below the conduction band edge of ZnO in 1.0 at% Cr-doped ZnO (Cr-ZnO) as 0.11 eV, 0.21 eV, and 0.31 eV. The overlapped defect levels ($Zn^{..}_i$ and $V^{\cdot}_0$) in admittance spectra were successfully separated by the combination of dielectric function such as $M^*$, $\varepsilon^*$, and $tan{\delta}$. In Cr-ZnO, the interfacial state level was about 1.17 eV by IS and MS. Also we measured the resistance ($R_{gb}$) and capacitance ($C_{gb}$) of grain boundaries with temperature using impedance-modulus spectroscopy. It have discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z"-logf plots with temperature.

• Journal of Industrial Technology
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• v.27 no.B
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• pp.129-135
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• 2007

In this paper, an modal analysis based on the distribution of the electromagnetic fields on the UWB elliptical patch-slot antenna is presented. We designed the UWB antenna by iterating the dimensional parameters of the antenna as the traditional design method. Then the antenna was carefully analyzed using 3D E-M simulator. The result of the analysis shows that the slot antenna operates on a series of the multi-pole radiations based on TE modes matched to the system impedance. This result gives us an easier method to design the similar antennas, which is the impedance matching to the system impedance after once constructing a proper structure with a series of multi-mode resonances.

• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.2
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• pp.7-16
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• 1987

Eddy Current Examination is expected as the effective technique for nondestructive inspection of steam generator and various kinds of heat exchanging tubes made of STS - 304. In Case of E. C. T, a study on the various factors which have an effect on coil impedance is very important to the sensitivity of defect detection and the ratio of signal to noise. Therefore, this study analyzed coil impedance by means of the variational principle, the minimized theory of energy functional and the application of Finite Element Method. Really by using E. C. T, the relationship between the size of defects and the intensity of Eddy Current Signals can be obtained. Signal intensity becomes maximum at certain frequency. This frequency is affected by the characteristics and the position of signal sources.