• Title/Summary/Keyword: Impedance spectra

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Impedance Characteristics of Oxide Layers on Aluminium

  • 오한준;장경욱;치충수
    • Bulletin of the Korean Chemical Society
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    • v.20 no.11
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    • pp.1340-1344
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    • 1999
  • The electrochemical behavior of oxide layers on aluminium was studied using electrochemical impedance spectroscopy. Impedance spectra were taken at a compact and a porous oxide layer of Al. The anodic films on Al have a variable stoichiometry with gradual reduction of oxygen deficiency towards the oxide-electrolyte interface. Thus, the interpretation of impedance spectra for oxide layers is complicated, with the impedance of surface layers differing from those of ideal capacitors. This layer behavior with conductance gradients was caused by an inhomogeneous dielectric. The frequency response cannot be described by a single RC element. The oxide layers of Al are properly described by the Young model of dielectric constant with a vertical decay of conductivity.

The thermal impedance spectroscopy on Li-ion batteries using heat-pulse response analysis

  • Barsoukov Evgenij;Jang Jee Hwan;Lee Hosull
    • 한국전기화학회:학술대회논문집
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    • 2001.11a
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    • pp.145-161
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    • 2001
  • Novel characterization of thermal properties of a battery has been introduced by defining its frequency-dependent thermal impedance function. Thermal impedance function can be approximated as a thermal impedance spectrum by analyzing experimental temperature transient which is related to the thermal impedance function through Laplace transformation. In order to obtain temperature transient, a process has been devised to generate external heat pulse with heating wire and to measure the response of battery. This process is used to study several commercial Li-ion batteries of cylindrical type. The thermal impedance measurements have been performed using potentionstat/galvanostate controlled digital signal processor, which is more commonly available than flow-meter usually applied for thermal property measurements. Thermal impedance spectra obtained for batteries produced by different manufactures are found to differ considerably. Comparison of spectra at different states of charge indicates independence of thermal impedance on charging state of battery. It is shown that thermal impedance spectrum can be used to obtain simultaneously thermal capacity and thermal conductivity of battery by non-linear complex least-square fit of the spectrum to thermal impedance model. Obtained data is used to simulate a response of the battery to internal heating during discharge. It is found that temperature inside the battery is by one-third larger that on its surface. This observation has to be considered to prevent damage by overheating.

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Impedance spectroscopy for lifetime analysis of OLED

  • Yoon, Chul-Oh;Kim, Hyun-Chul;Yi, Seok-Kyung;Kong, Ung-Gul;Lee, Nam-Heon;Lee, Chang-Hee
    • 한국정보디스플레이학회:학술대회논문집
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    • 2002.08a
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    • pp.137-140
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    • 2002
  • The frequency response analysis of complex impedance spectra using small perturbation ac impedance spectroscopy is an informative method of OLED performance characterization and lifetime analysis. Using simple RC equivalent circuit mode,l macroscopic nonliniear transport properties of semiconductive emission/transport layers can be analyzed and parameterized. We present the bias voltage dependence and aging effect in impedance spectra measured from an ITO/CuPC/TPD/$Alq_3$/LiF/Al OLED device, and discuss possible failure mechanism based on impedance model parameters.

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Magneto-impedance and Magnetic Relaxation in Electrodeposited Cu/Ni80Fe20 Core/Shell Composite Wire (전기도금 된 Cu/Ni80Fe20 코어/쉘 복합 와이어에서 자기임피던스 및 자기완화)

  • Yoon, Seok Soo;Cho, Seong Eon;Kim, Dong Young
    • Journal of the Korean Magnetics Society
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    • v.25 no.1
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    • pp.10-15
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    • 2015
  • The model for the magneto-impedance of composite wires composed of highly conductive nonmagnetic metal core and soft magnetic shell was derived based on the Maxwell's equations. The Cu($100{\mu}m$ diameter)/$Ni_{80}Fe_{20}$($15{\mu}m$ thickness) core/shell composite wire was fabricated by electrodeposition. The impedance spectra for the $Cu/Ni_{80}Fe_{20}$ core/shell composite wire were measured in the frequency range of 10 kHz~10 MHz under longitudinal dc magnetic field in 0 Oe~200 Oe. The spectra of complex permeability in circumferential direction were extracted from the impedance spectra by using the derived model. The extracted spectra of complex permeability showed relaxation-type dispersion which is well curve-fitted with Debye equation with single relaxation frequency. By analyzing the magnetic field dependence of the complex permeability spectra, it has been verified that the composite wire has magnetic anisotropy in longitudinal direction and the origin of the single relaxation process is the magnetization rotation in circumferential direction.

THE TRANSFER OF CHLORIDE ION ACROSS ANION EXCHANGE MEMBRANE

  • Yu, Zemu;Wang, Hanming;Wang, Erkang
    • Analytical Science and Technology
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    • v.8 no.4
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    • pp.597-601
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    • 1995
  • The transfer of chloride ion across an anion exchange membrane (AEM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectra. In CV experiment, when the size of the hole in membrane was much smaller than the distance between membrane holes, the Cl anion transfer showed steady state voltammetric behavior. Each hole in membrane can be regarded as a microelectrode and the membrane was equivalent to a microelectrode array in this condition. When the hole in membrane was large or the distance between membrane holes was small, the CV curve of the Cl anion transfer across membrane showed peak shape, which attributed to linear diffusion. In ac impedance measurement, the impedance spectrum of the membrane system was composed of two semicircles at low de bias, corresponding to the bulk characteristics of the membrane and the kinetic process of ion transfer, respectively. The bulk membrane resistance increases with increasing dc bias and only one semicircle was observed at higher dc bias. The parameters related to kinetic and membrane properties were discussed.

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The Impedance Properties of Poly(p-phenylene)-based Carbon/Li cell (PPP-based Carbon/Li cell의 임피던스 특성)

  • 류현옥;홍성문;김주승;구할본
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1997.11a
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    • pp.283-285
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    • 1997
  • We have obtained disordered carbon by pyrolyzing PPP in a nitrogen atmosphere for 8 hour at 700$^{\circ}C$. AC impedance property was measured with the PPP-based carbon/EC-DEC/Li cell. The impedance spectra of the cell were measured during the 1st discharge proceed. As the result of measurement the cell resistance decreased in intial discharge, but increase in final discharge.

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A New Algorithm Design for the Real-time Electrochemical Impedance Monitoring System

  • Chang, Byoung-Yong
    • Journal of Electrochemical Science and Technology
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    • v.3 no.4
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    • pp.154-158
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    • 2012
  • It is generally known that electrochemical impedance spectroscopy is a powerful technique and its real-time application has been demanded for prompt observations on instantaneous electrochemical changes. Nevertheless, long measurement time and laborious analysis procedures have hindered development of it. Solving the problems, here I report of a new algorithm design for development of a real-time electrochemical impedance monitoring system, which potentially provides a guideline in developing monitoring systems of electric vehicles batteries and other electrochemical power plants. The significant progress in this report is employment of the parallel processing protocol which connects independent sub functions to successfully operate with avoiding mutual interruptions. Therefore, all the processes required to monitor electrochemical impedance changes in realtime are properly operated. To realize the conceptual scheme, a Labview program was coded with sub functions units which conduct their processes individually and only data are transferred between them through the parallel pipelines. Finally, measured impedance spectra and analysis results are displayed, which are synchronized according to the time of change.