Equivalent Series Resistance | EPFL Graph Search

La résistance série équivalente ou ESR (pour en) est une représentation de la résistance électrique d'un composant électronique passif, mesurée en ohms. En l'absence de mentions contraires, l'ESR est toujours une résistance sur courant alternatif mesurée à des fréquences standards. Généralités La théorie de l'électronique manipule des résistances, des condensateurs et des bobines idéaux : ils sont dotés uniquement d'une résistance, d'une capacité ou d'une inductance. En pratique, tous ces composants sont conçus pour minimiser les deux autres paramètres : les comportements « parasites » sont suffisamment faibles pour ne pas affecter le fonctionnement du circuit. Cependant, dans certaines circonstances, ces parasites peuvent devenir importants, voire prédominants. Plus particulièrement, tout équipement physique est constitué de matériaux dotés d'une résistance finie qui contribue à la résistance électrique de l'équipement. Une manière de prendre en compte ces résistances

Ageing of porous carbon electrodes

Manxi Zhu

Ultracapacitors, also called electrochemical double layer capacitors (EDLC) or supercapacitors, may improve the performance of conventional electrolytic capacitors in terms of specific energy, or improve the performance of rechargeable batteries in terms of specific power when combined with respective device. However, the application of ultracapacitors faces the problem of ageing – the deterioration of capacity and increase of equivalent series resistance of the system. This thesis intends to elucidate ageing mechanisms of ultracapacitors based on activated carbon electrodes with tetrafluoroborate in acetonitrile as electrolyte. Multi-method experimental investigations are presented which allow to obtain a comprehensive picture of ageing. Ultracapacitors were electrochemically aged under various conditions by applying voltages and temperatures close to the actual operation conditions. The influences of ageing on the electrodes were investigated by structural and chemical characterization. Gas volumetric measurement (porosimetry) and Raman spectroscopy were applied to follow the structural changes; elemental analysis, electron spectroscopy for chemical analysis (ESCA, XPS) and attenuated total reflection infrared spectroscopy (ATR-IR) were applied for chemical composition analysis. It was found that the changes of both structure and chemical composition, which occur on aged anodes and cathodes, are asymmetric. Aged anodes showed more significant changes such as stronger decrease of pore volume and specific area, and more complex chemical species. Chemically bound nitrogen species were found only on aged anodes, but not on fresh electrodes and aged cathodes. Based on the experimental results, several mechanisms for ageing are suggested. The functionalities in activated carbons play an important role for ageing. Various oxygen-containing functional groups can take part in the reactions. A higher amount of functionalities means that more electroactive sites can be found on the graphene sheets in activated carbons to promote electrochemical reactions. Thus one can assume that less functional groups in activate carbons would be preferable for the stability of ultracapacitors. Ageing tests were carried out on individual components of the electrodes, mainly on activated carbon powders and conductive carbon additives. Observations are consistent with those on assembled electrodes. It turned out that the activated carbons from synthetic resin precursors, which have fewer oxygen functional groups, suffer less from ageing than those from natural precursors with more oxygen functional groups. A similar phenomenon was also observed on the conductive agents.

EPFL2006

Investigation of bias-dependent series resistances and barrier height in Double Gate Schottky MOSFETs

Jyotshna Bhandari, Mihai Adrian Ionescu, Jean-Michel Sallese

This work reports on gate voltage dependent source and drain series resistance and associated barrier height in modified Double Gate Schottky MOSFETs with dopant segregation. We show that in our devices the series resistances is significantly reduced by lowering the Schottky Barrier Height (SBH). The series resistance and the barrier have been extracted using an external series resistance method and Arrhenius plots, respectively. Series resistances as low as 400Ω.μm for VG>VT and SBH of 0.1eV at VG=VT, are reported Finally, this paper points our the correlation of RT(VG) and ΦB(VG) in DG Schottky MOSFETs and the importance of the simultaneous extraction and modeling. © 2009 IEEE.

2009

Investigation of bias-dependent series resistances and barrier height in Double Gate Schottky MOSFETs

Jyotshna Bhandari, Mihai Adrian Ionescu, Jean-Michel Sallese

This work reports on gate voltage dependent source and drain series resistance and associated barrier height in modified Double Gate Schottky MOSFETs with dopant segregation. We show that in our devices the series resistances is significantly reduced by lowering the Schottky Barrier Height (SBH). The series resistance and the barrier have been extracted using an external series resistance method and Arrhenius plots, respectively. Series resistances as low as 400 Omega.mu m for V-G>V-T and SBH of 0.1eV at V-G=V-T, are reported Finally, this paper points our the correlation of R-T(V-G) and Phi(B)(V-G) in DG Schottky MOSFETs and the importance of the simultaneous extraction and modeling.

IEEE2009

Ageing of porous carbon electrodes

Manxi Zhu

EPFL2006