Alternating current impedance measurement usefulness

The dielectric properties were measured by using an alternating current impedance analysis apparatus (HP-4294A). 

Electrochemical corrosion techniques are essential to predict service life in chemical and construction industries. The following direct current (dc) electrochemical methods are used in corrosion engineering practice linear polarization technique, Tafel extrapolation, and open circuit potential vs. time measurements. The alternating current (ac) technique is electrochemical impedance spectroscopy (EIS). This technique uses alternating current to measure frequency-dependent processes in corrosion and estimates the change of polarization resistance as a function of time. 

Ervin, E. N., H. S. White, L. A. Baker, and C. R. Martin, Alternating current impedance imaging of high-resistance membrane pores using a scanning electrochemical microscope. Application of membrane electrical shunts to increase measurement sensitivity and image contrast. Anal. Chem., Vol. 78, 2006 pp. 6535-6541. 

The IV measurements on molecules and monolayers have been carried out almost exclusively using direct current (DC) frequency-dependent alternating current (AC) impedance measurements have rarely been performed, even though a rich spectroscopy may reveal itself, if the IV measurements were followed as a function of frequency v. 

The two main techniques for measuring electrode losses are current interrupt and impedance spectroscopy. When applied between cathode and anode, these techniques allow one to separate the electrode losses from the electrolyte losses due to the fact that most of the electrode losses are time dependent, while the electrolyte loss is purely ohmic. The instantaneous change in cell potential when the load is removed, measured using current interrupt, can therefore be associated with the electrolyte. Alternatively, the electrolyte resistance is essentially equal to the impedance at high frequency, measured in impedance spectroscopy. Because current-interrupt is simply the pulse analogue to impedance spectroscopy, the two techniques, in theory, provide exactly the same information. However, because it is difficult to make a perfect step change in the load, we have found impedance spectroscopy much easier to use and interpret. 

An impedance measurement can be made either by applying an electrical potential and monitoring the current response or, conversely, by passing current and monitoring the potential response. Several decades of frequencies can be scanned rapidly and accurately using a frequency response analyzer [4]. An alternative approach applies multiple frequencies simultaneously (white noise) and deconvolutes the response with a lock-in amplifier. The use of an... 

There exist different methods for impedance measurement. Normally, a sine-wave current is injected and the voltage response is measured. In some special applications, it is possible to use an existing current ripple instead of the sine-wave current source. For example, the a.c. ripple from an alternator that is a part of the system can, perhaps, be used [11]. 

Electrochemical Measurements. Cyclic voltammetry and alternating current (ac) impedance spectroscopy were performed using an ac impedance system (EG G Princeton Applied Research model 378) that included a potentiostat-galvanostat (model 273), a two-phase lock-in analyzer (model 5208), and an IBM PS/2 computer. For ac impedance measurements, a 5-mV sine wave was superimposed on an applied voltage bias from the potentiostat. The reference electrodes were saturated calomel electrodes (SCE Fisher) for measurements in aqueous solution and silver electrodes... 

Electrochemical impedance spectroscopy An alternating current technique that measures the impedance of an electrochemical system. The resulting spectra can be used to estimate the various components of an equivalent circuit that represent an electrochemical cell. 

The measurements were conducted using a sinusoidal alternating current whose maximum amplitude was set at 100 mV. This value allows us to produce a current that is high enough for us to obtain precise impedance measures. 

Another interesting photoelectroanalytical method for the characterization of polymer films is a method which might be called photoimpedance spectrum. A small-amplitude sine-wave signal is applied to the working electrode and the resulting absorbance response is recorded at different frequencies. Alternatively, several frequencies are applied simultaneously and the response analyzed by using Fourier transform. The main advantage compared with the conventional electrical impedance measurements is naturally that only faradaic current... 

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