Electrical impedance scanning

Malich, A., Boehm, T., Facius, M., Freesmeyer, M. G., Fleck, M., Anderson, R., and Kaiser, W. A. (2001). Differentiation of mammographically suspicious lesions evaluation of breast ultrasound. MRI mammography and electrical impedance scanning as adjunctive technologies in breast cancer detection. Clinical Radiology 56 278-283. 

Polar Cell Systems for Membrane Transport Studies Direct current electrical measurement in epithelia steady-state and transient analysis, 171, 607 impedance analysis in tight epithelia, 171, 628 electrical impedance analysis of leaky epithelia theory, techniques, and leak artifact problems, 171, 642 patch-clamp experiments in epithelia activation by hormones or neurotransmitters, 171, 663 ionic permeation mechanisms in epithelia biionic potentials, dilution potentials, conductances, and streaming potentials, 171, 678 use of ionophores in epithelia characterizing membrane properties, 171, 715 cultures as epithelial models porous-bottom culture dishes for studying transport and differentiation, 171, 736 volume regulation in epithelia experimental approaches, 171, 744 scanning electrode localization of transport pathways in epithelial tissues, 171, 792. 

The most widely used stream scanning technique employs the Coulter principle (Figure 9.1a) where the interrogating field is electrical and particle size (volume) is proportional to the change in electrical impedance as the particles pass through the field. 

Assenheimer, M., Laver-Moskovitz, O., Malonek, D., Manor, D., Nahaliel, U., Nitzan, R., and Saad, A. (2(K)1). The T-SCAN technology electrical impedance as a diagnostic tool for breast cancer detection, Physiological Measurement, 22 1-8. 

Depending upon the products, there might be very narrow margins to that exercise and the endpoint temperatures, velocities of cooling, and rewarming need to be known very accurately by previous laboratory determinations such as differential thermal analysis (DTA) or differential scanning calorimetry (DSC), low temperature electric impedance measurements, velocity of crystallization in the supercooled state, etc. 

The two preceding electroanalytical techniques, one in which the measured value was the current during imposition of a potential scan and the other a potential response under an imposed constant current, owe their electrical response to the change in impedance at the electrode-electrolyte interface. A more direct technique for studying electrode processes is to measure the change in the electrical impedance of an electrode by electrochemical impedance spectroscopy (EIS). To relate the impedance of the electrode-electrolyte interface to electrochemical parameters, it is necessary to establish an equivalent circuit to represent the dynamic characteristics of the interface. 

Fig. 17. a A scanning electron micrograph of square pores etched in a 3 micrometer thick silicon membrane. The pores were produced by anisotropic etching and their width on this side of the membrane is 6 pm. Cells (fibroblasts 3T3) attach to the surface and migrate over the pores, b Electrodes are placed on either side of the membrane and a constant current passed through it (mainly through the pores). The presence of cells is easily detected and movements of cell filopodia of less than 100 nm and the passive electric properties of the cell body can be determined by analysis of the signal fluctuations and impedance... 

Although electrochemical characterizations have recently been performed on single intercalation particles, in most cases composite powdery electrodes containing a mixture of intercalation particles, electrically conductive additives (e.g., carbon black) and PVDF binder have also been used. In order to obtain consistent results and to reach comprehensible intercalation mechanisms in these electrodes, basic electroanalytical characterizations such as slow-scan rate -> cyclic voltammetry (SSCV), -> potentiostatic intermittent titration (PITT) (or -> galvanostatic intermittent titration, GITT), and -> electrochemical impedance spectroscopy (EIS) should be applied in parallel or in a single study. 

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... 

Concerning the two-layer model, the thickness and properties of each layer depend on the nature of the electrolyte and the anodisation conditions. For the application, a permanent control of thickness and electrical properties is necessary. In the present chapter, electrochemical impedance spectroscopy (EIS) was used to study the film properties. The EIS measurements can provide accurate information on the dielectric properties and the thickness of the barrier layer [13-14]. The porous layer cannot be studied by impedance measurements because of the high conductivity of the electrolyte in the pores [15]. The total thickness of the aluminium oxide films was determined by scanning electron microscopy. The thickness of the single layers was then calculated. The information on the film properties was confirmed by electrical characterisation performed on metal/insulator/metal (MIM) structures. 

In contrast to the EIS method, the Tafel-extrapolation, Tafel-curve-modeling and polarization-resistance methods are conducted under essentially dc conditions. In these cases, in generating the appropriate Eexp versus log iex or iex curve, the potentiodynamic potential scan rate is very slow, or the time between potentiostatic potential steps is very long. The common practice is a potential scan rate of 600 mV/h or an equivalent step rate of 50 mV every 5 min. Underthese conditions, it is assumed that a steady-state, extemal-current-density results at every discrete potential. Consequently, every element in the electrical circuit is purely resistive in nature, and therefore, the applied potential and resultant extemal-current-density are exactly in phase. Since the impedance (normalized with respect to specimen area) is dEexp/diex, under these conditions, the impedance, Z, at Ecorr is given by (see Eq 6.29) ... 

Te and Cu monolayers on gold, as well as Ag and Bi monolayers on platinum were obtained by cathodic underpotential deposition and investigated in situ by the potentiodynamic electrochemical impedance spectroseopy (PDEIS). PDEIS gives the graphical representation of the real and imaginary interfacial impedance dependencies on ac frequency and electrode potential in real-time in the potential scan. The built-in analyzer of the virtual spectrometer decomposes the total electrochemical response into the responses of the constituents of the equivalent electric circuits (EEC). Dependencies of EEC parameters on potential, especially the variation of capacitance and pseudocapacitance of the double layer, appeared to be very sensitive indicators of the interfacial dynamics. 

In EIS, the impedance of the system is measured by applying a small ac signal and by the frequency scanned (typically between 10-100 kHz and 1 Hz or less). Stable impedance spectra can be obtained with electrically charged redox markers in solution. The data can be fitted with an equivalent electrical circuit, where the most important components are the charge transfer resistance Ret and the double layer/biolayer capacitance Cdi. 

S. J. Lin, On the Scan Impedance of an Array of V-Dipoles and the Effect of the Feedlines, Ph.D. Dissertation, Ohio State University, Department of Electrical Engineering, Columbns, OH, 1985. 

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