Electrode Polarization Impedance Research Articles

Sources of error in tetrapolar impedance measurements on biomaterials and other ionic conductors

Tetrapolar electrode systems are commonly used for impedance measurements on biomaterials and other ionic conductors. They are generally believed to be immune to the influence from electrode polarization impedance and little can be found in the literature about possible pitfalls or sources of error when using tetrapolar electrode systems. In this paper we show that electrode polarization impedance can indeed influence the measurements and that also other phenomena such as negative sensitivity regions, separate current paths and common-mode signals may seriously spoil the measured data.

Electrode Polarization Impedance in Weak NaCl Aqueous Solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.

Low-frequency dielectric spectroscopy of colloidal suspensions

The main difficulties related to low-frequency dielectric measurements of liquid conducting samples using impedance analyzers such as the HP 4192 A or HP 4284 A are presented and discussed. These include the small value of the phase angle and the electrode polarization impedance. We propose ways to overcome these difficulties in terms of cell design, choice of instrument settings, choice of electrode material, connection of the cell to the instrument. We also propose a new calibration method that allows a differential measurement of the dielectric properties with far higher precision than possible using the standard short–open calibration.

How epicardial electrodes influence the transmembrane potential during a strong shock.

This paper analyzes a possible artifact that may corrupt experiments studying defibrillation of the heart. Our hypothesis is that surface recording electrodes can influence the transmembrane potential during a shock. In the vicinity of an electrode, current leaves the intracellular space to take advantage of the low resistance of the extracellular path, thereby depolarizing the tissue. We calculate the transmembrane potential induced around a circular electrode when exposed to a uniform electric field. The bidomain model represents the electrical behavior of the cardiac tissue, and we account for electrode polarization impedance. Our results show that adjacent regions of depolarization and hyperpolarization exist around the electrode, and that the induced depolarization is greater than 100 mV for a 0.5 mm radius silver-silver chloride electrode in a 500 V/m electric field. We conclude that surface electrodes may produce artifacts during experiments designed to study defibrillation-strength electrical shocks.

Chronic electrical stimulation of the auditory nerve using high surface area (HiQ) platinum electrodes

High surface area cochlear implant electrodes with much smaller geometric surface areas than current designs might be used in the future to increase the number of stimulating electrodes along the carrier. Potential problems with an increase in charge density for a common stimulus resulting from decreasing the geometric surface area would be reduced by the enlarged real surface area of such electrodes. Electrochemically modified (HiQ) platinum (Pt) electrodes, with a real surface area ∼75 times greater than the current standard Pt electrodes of the same geometric size, had shown in vitro a low polarization ( Z pol) and electrode impedance ( Z e), as well as a low residual direct current (DC). In this study we examined the chronic performance of HiQ electrodes in cats, which were bilaterally implanted with a two-channel HiQ or standard Pt scala tympani electrode array and unilaterally stimulated for periods of up to 2390 h. Stimuli consisted of 50 μs/phase charge-balanced biphasic current pulses presented at 2000 pulses/s/channel with a 50% duty cycle. Electrode impedance ( Z e), access resistance ( R a) and polarization impedance ( Z pol) were calculated from current and voltage measurements obtained periodically throughout the implantation period. Immediately following implantation HiQ electrodes showed a significantly smaller Z pol, resulting in a reduced Z e ( P<0.0001) compared to standard electrodes, while there was no significant difference between R a of both electrode designs ( P=0.91). Subsequently, Z e generally increased mainly due to a rise in R a, which dominated Z e and obliterated the effect of a lower Z pol on Z e in HiQ electrodes. Peak R a levels correlated closely ( r=0.85) with the amount of intracochlear fibrous tissue found adjacent to the array. Following explantation of the array, voltage waveforms for both electrode designs recorded in saline were again very similar to those recorded immediately after implantation. Mean DC levels were consistently lower for HiQ electrodes compared with standard electrodes (22.45 nA vs 134.7 nA). Histopathological examination of corresponding cochlear sections comparing the stimulated test side with the unstimulated control side showed no significant difference ( P>0.05) for either animals implanted with HiQ electrodes ( n=6) or standard electrodes ( n=2). Nor were there any significant differences between the spiral ganglion cell density of the basal turn implanted with HiQ or standard electrodes for both the stimulated test ( P=0.31) and the unstimulated control side ( P=0.84). Although these findings are based on a small group of animals implanted with standard electrodes ( n=2), and those negative statistical results could potentially be due to the small sample size, similar spiral ganglion cell survival was found in a previous study of a larger group of animals using standard electrodes stimulated with the same stimulus paradigm as in the present study [Xu et al. (1997) Hear. Res. 105, 1–29]. Our data indicate that while some initial advantages of HiQ electrodes are lost during chronic implantation due to intracochlear fibrous tissue growth, low DC levels and the high surface area appear to be maintained, suggesting that HiQ electrodes may have important clinical applications.

Nonlinear system identification for cascaded block model: an application to electrode polarization impedance

A new algorithm has been developed to identify a system divided into cascaded blocks of dynamic linear (L), static nonlinear (N), and dynamic linear (L) subsystems based strictly on the input-output relationship. The nonlinear element is assumed to be equicontinuous, or must be satisfied by the Weierstrass criterion. Therefore, it could either be continuous type as represented by polynomial approximation or abrupt type as represented by piecewise-linear segments. The process uses a series of multilevel input to decouple the two linear subsystems from the nonlinear subsystem and then applies the predictor-corrector algorithm to minimize a cost function to obtain the parameter of the subsystem. The method does not restrict the type of input signal and no prior knowledge of the subsystems is necessary. Numerical example for a prescribed system is given and the results show almost identical values by any one of the three types of input, namely: step, sinusoidal, or white noise. Three computer programs have been developed for the identification of the system with odd, even, and piecewise abrupt types of nonlinearity. The method is applied to model the interfacial phenomenon of noble metal electrode (Pt) at the nonlinear range and the algorithm is verified by comparison with the result developed previously.

The polarization impedance of an ideally polarizable plane electrode

The theory of electrode polarization impedance is developed for a perfectly polarizable electrode in contact with a general electrolyte solution.An analytic expression for the electrode impedance is derived for the case when the electrode has zero zeta potential in the absence of an applied voltage. For finite zeta potential a numerical solution of the general problem is given. Numerical results showing the effect of electrolyte concentration and valency and electrode zeta potential are plotted. The frequency dependence of the electrode impedance is elucidated.

Linear AC electrode polarization impedance at smooth noble metal interfaces.

The linear A. C. electrode polarization impedance of polished platinum has been analyzed on the basis of the rate determining mechanism of the oxygen electrode. The impedance has been found to follow the frequency dependence predicted by an adsorption of the electroactive species. The effects of D. C. potential and specific adsorption of anions have been studied and their effect on the electrode polarization impedance is in agreement with the adsorption mechanism.

Measurement of Electrolytic Resistivity and Electrode-Electrolyte Impedance with a Variable-Length Conductivity Cell

ABSTRACT A variable-length conductivity cell is described which eliminates electrode polarization impedance errors in the measurement of electrolytic resistivity and does not require the use of an electrolyte of known resistivity for initial calibration. From the data obtained during the measurement of resistivity, the series-equivalent resistance and capacitance of the electrode-electrolyte interfaces can be determined.

A mathematical model for the polarization impedance of cardiac pacemaker electrodes: Jaron, D., Schwan, H. P. and Geselowitz, D. B. Biomed. Eng. 6: 579, 1968. (Biomed. Engin. Dept., Univ. of Pennsylvania, Philadelphia, Penna.)

A mathematical model for the polarization impedance of cardiac pacemaker electrodes: Jaron, D., Schwan, H. P. and Geselowitz, D. B. Biomed. Eng. 6: 579, 1968. (Biomed. Engin. Dept., Univ. of Pennsylvania, Philadelphia, Penna.)

Six-electrode method for the measurement of the passive electrical properties of brain envelopes.

In a previously-described four-terminal electrical model consisting of six branch impedances representing the passive electrical properties of the brain envelopes, alternating current signals were applied directly to two terminals of the tissue electrode system for determination of the lumped impedances of the model and for observation of transmission through the system. To obtain impedance values of the electrode-tissue system which would be representative of tissue impedance, electrode polarization impedance of the four electrodes of the model has been reduced by applying the signals to two additional electrodes inserted into the brain to form a dipole signal generator. An electronic half-bridge technique augments the sensitivity of the measurements.

A mathematical model for the polarization impedance of cardiac pacemaker electrodes.

A mathematical model for the linear properties of the polarization impedance of cardiac pacemaker electrodes is presented. This model reproduces frequency and time domain behavior of the electrodes in physiological saline.

Electrode polarization impedance and measurements in biological materials.

Electrode polarization impedance and measurements in biological materials.

Polarization impedance of stainless steel bipolar electrodes in brain

The polarization impedance of a stainless steel bipolar electrode, which is used for chronic implants in laboratory rats, has been measured across the frequency spectrum from 200 Hz to 100 kHz. The polarization impedance has been measured in various solutions which are used for perfusion fixation, and it has also been measured in brain before and after fixation for electron microscopy. For the electrodes in brain, a significant amount of polarization impedance remained at 100 kHz, and prevented an accurate determination of tissue capacitance. However, tissue resistance was estimated by measuring impedance at several frequencies.

Altenating current electrode polarization.

This article summarizes principles of alternating current electrode polarization. The importance of alternating current electrode polarization in biological impedance studies is discussed. The following topics are treated in detail: Definition of Electrode Polarization Impedance; Linearity and Superpositioning Principle; Frequency Dependence of Electrode Impedance; Preparation of Electrodes (Optimal current density for platinum black application, Stability of electrode impedance, Cell design for platinization purposes, Aging and cleaning of electrodes); Effect of Electrode Polarization on Biological Impedances; Effects of Biological Matter on Electrode Polarization; Techniques to Correct for Electrode Polarization (Electrode distance variation technique, Large electrode distance, Graphical technique, Substitution technique, Frequency variation technique, Four-electrode technique); Transient Response of Electrodes; Microelectrodes.

The electrical interaction between artificial pacemakers and patients, with applications to electrocardiography

Eleven artificial pacemakers were calibrated prior to surgery. The current delivered by these units to human hearts was then measured at surgery with a current probe. Body surface pacemaker voltages were recorded subsequently in nine cases. The amplitude and shape of the current pulse depends upon the patient load impedance. Patient load impedance consists of myocardial electrode polarization impedance and tissue resistance. For the pacemaker and myocardial electrodes employed, the patient load impedance is well represented by an equivalent circuit consisting of a series parallel arrangement of two capacitors and two resistors. Values of these circuit parameters were determined in nine cases. Tissue resistance is represented by a fraction of the series resistor in the equivalent circuit. The remainder of the equivalent circuit is attributable to polarization. The voltage pulse measured at the body surface is related to the current pulse delivered to the myocardium by a transfer impedance. Since details of the current pulse, which had a rise time of less than a microsecond, were present in surface voltages, the transfer impedance is approximately resistive and independent of frequency up to a megacycle per second. It is concluded that no significant frequency distortion of electrocardiograms is caused by the electrical characteristics of body tissues. The value of the maximal scalar transfer impedance from these studies has been cast into the vectorial form employed by others in torso model studies. Under the conditions discussed, the vectorial transfer impedance has comparable magnitude whether obtained from model studies or from the present pacemaker study.