Total harmonic distortion based method for linearity assessment in electrochemical systems in the context of EIS

Abstract

ElsevierGiner Sanz, JJ.; Ortega Navarro, EM.; Pérez-Herranz, V. (2015). Total harmonic distortion based method for linearity assessment in electrochemical systems in the context of EIS. Electrochimica Acta. 186:598-612. doi:10.1016Acta. 186:598-612. doi:10. /j.electacta.2015 Electrochemical Impedance Spectroscopy (EIS) is a widely used electrochemical measurement technique that has been used in a great spectrum of fields since it allows deconvolving the individual physic-chemical processes that take place in a given system. Ohm's generalized law, and thus the impedance concept, are only valid if 4 conditions are fulfilled: causality, finiteness, stationarity and linearity. In the case that any of these conditions is not achieved, the obtained impedance spectra will present distortions that may lead to biased or even erroneous results and conclusions. For this reason it is crucial to verify if the 4 conditions are fulfilled, before accepting the results extracted from impedance spectra. In this work, a linearity assessment quantitative method based in the total harmonic distortion (THD) parameter is presented and verified experimentally. The experimental validation of the implemented method showed that the implemented method is able to assess quantitatively the linearity of the system. In addition, it is also able to determine the threshold frequency above which the system will not present significant nonlinear effects even for large perturbation amplitudes. It was observed that the THD method is more sensitive to nonlinear effects than the spectra themselves.

Quantification of a Low-Cost Stretchable Conductive Sensor Using an Expansion/Contraction Simulator Machine: A Step towards Validation of a Noninvasive Cardiac and Respiration Monitoring Prototype

“…Assuming the bands were linear and the rig was perfect, we would have expected a perfect sine wave as the output voltage of the ERB during a complete expansion/contraction (one full cycle of the motor). This is because when a mono frequency sinusoidal wave is applied to a linear system, a sinusoidal wave with the same frequency component appears as the output [28]. In contrast, inputting a mono frequency sinusoidal wave to a nonlinear system results in generation of a multi-frequency wave, which contains the fundamental frequency component of the input signal and an associated range of harmonics.…”

“…The existence of harmonics at the output of a system with a mono frequency input may then be seen as representative of the system's nonlinearity. Total harmonic distortion (THD) is widely used for quantification of the level of nonlinearity due to its sensitivity to the level of harmonics and nonlinear effects in electromechanical systems [28]. Therefore, we calculated the THD of each ERB recording to determine the similarity of the output voltage to a perfect sine wave and so to quantify the level of nonlinearity.…”

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“…For this reason, validation is a fundamental part of the preliminary analysis of experimental EIS spectra. In this work, all the measured EIS spectra were double‐validated: on the one hand, they were validated using the linearity assessment methods developed in previous works; on the other hand, they were validated using the Kramers‐Kronig based quantitative validation technique described elsewhere . The EIS measurements were performed at 100 frequencies logarithmically spaced between 10 kHz and 10 MHz.…”

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“…[41,42] Its main strength is that it allows to deconvolve the different physic-chemical processes undergoing at different timescales in the system. In this work, all the measured EIS spectra were double-validated: on the one hand, they were validated using the linearity assessment methods developed in previous works; [45,46] and on the other hand, they were validated using the Kramers-Kronig based quantitative validation technique described in previous works. The main limitation of EIS is that its validity is restricted to situations in which causality, linearity and stability are achieved.…”

“…[44] For this reason, validation is a fundamental part of the preliminary analysis of experimental EIS spectra. In this work, all the measured EIS spectra were double-validated: on the one hand, they were validated using the linearity assessment methods developed in previous works; [45,46] and on the other hand, they were validated using the Kramers-Kronig based quantitative validation technique described in previous works. [47,48] In this work, the EIS measurements were performed at 100 frequencies logarithmically spaced between 10 kHz and 10 mHz.…”