Electrical impedance spectroscopy is a technique used to determine the impedance of biological tissues. Typically, the impedance spectrum of a biological tissue consists of two components, the impedance modulus and the capacitive reactance. These are measured at different frequencies and plotted on a real or virtual axis. The result is a spectral trajectory of impedance values varying with frequency.
The resulting graphs represent the impedance of a system at a given frequency. The impedance is defined as the ratio between the current and voltage at that frequency. The main drawback of this method is the strong manipulation of equations. The graphs usually have multiple semicircles, but only a fraction of them are visible.
Another problem with empirical models is that there is no equivalent circuit for a spectral data. This means that the model cannot be taken as a perfect representation of the cell's internal dynamics. Hence, it is important to verify the model before putting it into practice. One way to check this is to make a change in one component of the cell. For example, increasing the thickness of a layer of paint may affect the impedance spectrum.
Another method is to fit the data using the CPE equation. This method fits the EIS data to a mathematical model. The model parameters control the shape of the model impedance spectrum, as well as the size of each feature. The model is then fit to the EIS spectrum using a nonlinear least-squares regression technique.
Electrical impedance in the lower frequency range is widely used in plant and medical research. Low frequency currents move along cell walls, whereas high frequency currents can penetrate cell membranes and intracellular fluids. In this way, EIS can identify the cellular state of the cell. This method is also useful for studying the composition of an electrode.
Another use of impedance spectroscopy is to understand the behavior of metal hydrides. This technique involves measuring the impedance of an electrode that is made from LaNi5. The results obtained from the experiments were compared with a mathematical model that took into account the effects of water reduction, hydrogen adsorption, and diffusion through the metal ingot.
However, it is important to understand that the impedance values of coated metals are complex, and interpreting impedance data from failed coatings is difficult. The equivalent circuit shown in Figure 22 is the subject of much debate in the literature, and researchers differ as to how to assign the impedances to various physical processes.
EIS can also be used to distinguish between kinetic and mass transport losses, and can be used to regress model parameters with reduced uncertainty. An EIS experiment involves perturbing the system's steady state operation with a small sinusoidal current perturbation, usually between 103 Hz and 10 Hz. The corresponding voltage response is then measured.
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