" Fractional-order capacitors

Abstract: Equivalent circuit modeling stands as a cornerstone in the electrical characterization of real-world systems, from physics to biology, by offering important insights into their dynamic behavior and providing a physical interpretation of the responses. The existence of microdomain-type structural and/or energetic heterogeneities that influence the ionic motion and charge transfer in such physical systems causes an anomalous behavior of energy storage that deviates from the classical ideal capacitive behavior that seems so straightforward in elementary electrical engineering courses. This is the case, for instance, in electrochemical double-layers, space-charge accumulation zones or cell membranes. One of the most common features is found via Impedance Spectroscopy, where the Nyquist plots show "depressed" semicircles that reveal a capacitance distribution and are represented in circuit models as a "fractional-order capacitor". Translating this anomalous behaviour to transient dynamic responses poses a challenge in emerging research fields, such as photovoltaics or neuromorphic computing.

Bio: Enrique Hernández Balaguera is an assistant professor of Electronic Engineering at Universidad Rey Juan Carlos de Madrid. He obtained his Ph.D. degree from the Universidad de Castilla-La Mancha in 2019, where the research topics presented covered the challenges to characterize the non-ideal passive electrical properties of biological tissues using circuit theory, fractional calculus, and bioimpedance measurements. His research activity follows various areas within the field of physiological measurements, neuroscience, electrochemistry, third-generation photovoltaics, and advanced electronic devices. Unraveling the mechanisms of perovskite solar cells has established scientific work of high impact by Balaguera and coworkers in the last few years. He is currently conducting research in the context of multidisciplinary sciences from the perspective of the electrical equivalent circuits with collaborators from all over the world, in Spain, United Arab Emirates, Germany, France or Canada. He is author of around 30 articles published in refereed international bioelectrochemistry, physics, mathematics, and engineering journals with more than 350 citations and h-index 14.