Electrode polarization impedance

Shi, J. and Sun, H.H. 1990. Nonlinear system identification for cascade block model an application to electrode polarization impedance. IEEE Trans. Biomed. Eng. 37 574. 

There are sources of nonlinearity both in electrode polarization and tissue impedance (Schwan 1992). Onaral and Schwan (1982) studied electrode polarization impedance and found that the limit voltage of linearity was about 100 mV and frequency independent. The corresponding hmit current is of course impedance dependent and therefore frequency dependent, and may be about 5 pA/cm at a frequency of 1 Hz. 

Mirtaheri P, Grimnes S, Martinsen 0G. 2005. Electrode polarization impedance in weak NaCl aqueous solutions. IEEE Trans Biomed Eng. 52(12), 2093-2099. 

Schwan HP. 1968. Electrode polarization impedance and measurements in biological materials. Ann NY Acad Sci 148,191-208. 

Figure 8 Equivalent circuits for a conductive dielectric sample with electrode polarization impedance described by Cp and Rp.

Figure 11 Equivalent circuits for a conductive dielectric sample with electrode-polarization impedance described by recap Cy(s). (From Ref. 71. With permission from American Physical Society.)...

Living tissues are wet biomaterials and therefore electrolytic conductors, with ions free to migrate and therefore with DC conductivity. With living tissue, the situation is therefore complicated, and hydration, double-layer formation, and electrode polarization must be accounted for. A dry dielectric is much easier to handle. There is no galvanic contact with the electrodes and, accordingly, no electrode polarization impedance (see Section 7.9) in series with the dielectric. Complex dielectric theory is well adapted to both wet and dry systems if the necessary precautions because of water are taken. 

In a real case with a metal electrode in an electrolyte solution, the electrode polarization impedance resulting from the surface layer is physically in series with the electrolytic resistance given by Eq. (6.1). Equation (6.1) shows that the electrolytic resistance is inversely proportional to radius a (or circumference 2Tca) of the electrode. However, the electrode polarization impedance is inversely proportional to a (surface area 2Tca ). Therefore, the influence of the electrode polarization can be made as small as wanted by increasing the sphere radius. Alternatively, by reducing the electrode radius sufficiently, it... 

In some skin applications, the electrode polarization impedance may still he a source of error. With solid gel contact electrolytes, the series resistance of the contact medium may he disturbing at higher frequencies. When the stratum corneum is highly penetrated hy electrolytes (Figure 7.5), the skin impedance is so low (50 kO) that the electrode polarization impedance becomes important. 

In most cases, electrode polarization is a nuisance because it is only the tissue impedance that is of interest. Electrode polarization impedance introduces errors in tissue impedance... 

Polarization comprises both dynamic and static properties. An AC voltage u connected to a skin electrode pair generates an AC current in the electrode wires. The impedance is Z = uH and it comprises both the tissue impedance and the double electrode polarization impedances. They are physically coupled in series. Can we avoid the electrode... 

Figure 7.17 AgCI electrode polarization impedance with pregelled wet electrolyte. Two ECG commercial electrodes measured front to front, contribution of one electrode.

Figure 7.18 Equivalent circuits for the electrode polarization impedance found with one AgCI/wet-gel electrode, (a) with frequency-dependent CPE components (m = 0.47) (b) more simplified version with ideal components, valid around 10 Hz (ECG).

Figure 7.19 Electrode polarization impedance for 5 cm skin contact area hydrogel/aluminum electrode. Two ECG commercial electrodes front to front contribution of...

A polarization ratio can he defined as the ratio of polarization impedance to the bulk resistance of the electrolyte. Mirtaheri et al. (2005) measured the ratio as a function of frequency (10 —10 Hz) and NaCl concentration (2.4—77.0 mmol/L) and found that the polarization ratio diminished as a function of concentration regardless of electrode material. Medical stainless steel ratio was concentration independent hut had high electrode polarization impedance values compared with the other metals studied. Aluminum showed small ratio changes at low concentrations. However, the changes were more pronounced at higher concentrations. Gold, platinum, and silver showed a moderate concentration dependency at low concentrations. 

EA and according to Section 6.1, the total electrode impedance may be high and dominated by electrode polarization impedance. A needle tip may look bright and shining, but the magnified surfaces shown in Figure 7.35 shows fractal surface increase and debris from the manufacture. This may lead to unstable polarization impedance on the tip. 

Figure 7.37 shows the monopolar impedanee spectrum measured with a thin insulated needle inserted in porcine living tissue. The 90% sensitivity zone is roughly a sphere of about 3 mm centered at the exposed needle tip. Above = 10 kHz the data are dominated by tissue properties, below 1 kFlz by electrode polarization impedance. 

Measure electrode polarization impedance separately and subtract... 

Method numbers 2 and 3 are based on the assumption that the metal/liquid interphase and thus the polarization impedance is invariable. This is not always the case. Measuring on dry samples for instance implies poor control of the contact electrolyte. Also a sample may contain local regions of reduced conductivity near the electrode surface. The currents are then canalized with uneven current density at the metal surface (shielding effect). Electrode polarization impedance, in particular at low frequencies, is then dependent on the degree of shielding. An example of method 4 is Krizaj and Pecar (2012), who described such a method for removing the contribution from electrode polarization impedance on measured impedance data of a suspension of microcapsules. 

Electrode behavior in the nonlinear region may be studied by electrode polarization impedance Z = R + jX measured as a function of sinusoidal amplitude. The limit current of linearity iL may, for instance, be defined as the amplitude when the values of R or X deviate more than 10% from low current density values. Often 1l is increasing with frequency proportional to f (Schwan s law of nonlinearity) (Onaral and Schwan, 1982 McAdams and Jossinet, 1991a, 1994). m is the constant phase factor (as defined in this book) under the assumption that it is obeying Fricke s law and is frequency independent (Section 9.2.5). When the measuring current is kept limit current of linearity will usually be lower for X than for R. 

Many types of mammalian cells are dependent on attachment to a surface in order to grow and multiply. Exceptions are the different cells of the blood and cancer cells which may spread aggressively (metastases). To study cell attachment, a microelectrode is convenient as shown in Chapter 5.2, the half-cell impedance is more dominated by electrode polarization impedance the smaller the electrode surface is. Figure 10.25 shows the setup used by Giaevers group (Giaever and Keese, 1993) ... 

Hugo Fricke showed that, for example, the electrode polarization capacitance often varies as (in this book written as f ), and that there is a basic empirical relationship between the exponent m and the phase angle of the electrode polarization impedance (Fricke s law)

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At low frequencies, the determination of the electrical parameters of electrolytes is complicated by the appearance of an electrode polarization impedance. 

Figure 2.2. Basic model for ac electrode polarization impedance study.

Initial studies of the nonlinear behavior of ac electrode polarization impedance were reported by Schwan and Maczuk (1965). In summary, their... 

Electrode polarization impedance depends upon the electrode material and its surface treatment, the electrode area, the electrolyte, the temperature. 

Platinization of electrodes is not a panacea. It extends the lower frequency range over which electrolyte measurements can be made, and reduces the effects of ac electrode polarization impedance. The only way in which the polarization impedance can be eliminated is to make measurements in a manner that eliminates the current density at the electrode-electrolyte interface. 

Starting from the principles outlined above, Damaskin (1967) has developed a theoretical and experimental treatment of ac electrode polarization impedance. His circuit model (p. 73), developed on a series basis, is... 

Recent studies by DeRosa and Beard (1973) have indicated that ac electrode polarization impedance is sensitive to pH and PO2. In their... 

Schwan, H. P. and Maczuk, J. G., 1965, Electrode polarization impedance limits of linearity, Proc. I8th ACEMB, Philadelphia, p. 24. 

In Chapter 2, we approached alternating-current electrode polarization impedance from the phenomenological point of view, which parallels the historical development of this subject. Before we embark upon descriptions of electrochemical cells, ion-specific electrodes, and potentiometric techniques, it is necessary to discuss some of the electrochemical processes that occur at the interface between a solid electrode surface and a contacting electrolyte. 

The signal source pulse I (t) was simply a rectangular pulse of 1-msec duration. Pulse amplitude could be varied from 0 to 10 V peak without overloading the amplifier system or affecting the linear range of the electrode polarization impedance. In each of the photographic records which follow. 

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