Système CGS

Résumé

Le système CGS est un système d'unités de mesure des grandeurs physiques, où les unités de base de la mécanique sont le centimètre (pour les longueurs), le gramme (pour les masses) et la seconde (pour les temps). Pour les unités électriques et magnétiques, il existe plusieurs variantes, dont le système CGS-UES (électrostatique), le système CGS-UEM (électromagnétique), le système d'unités de Gauss et le . Fondement et usage Le système CGS est proposé par la British Association for the Advancement of Science en 1874. Il est utilisé en science jusqu'au milieu du . En 1946 le Comité international des poids et mesures approuve le système MKSA (mètre, kilogramme, seconde, ampère). De nos jours le Système international d'unités retient sept unités de base. Par exemple, en conductimétrie, les constantes de cellules sont données en cm−1. En spectroscopie infrarouge ou UV-visible, l'unité la plus couramment utilisée est également le cm−1. Dans la classification périodique, les u

Source officielle

https://fr.wikipedia.org/wiki/Syst%C3%A8me_CGS

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Development of a Hybrid MEMS BLDC Micromotor

Sebastiano Merzaghi, Yves Perriard

This paper addresses the design of a new hybrid MEMS micromotor. It is a small 3-phases axial flux BLDC motor. The stator is realized following the almost CMOS technology rules used for MEMS manufacture and the coils have two copper layers. The rotor is made of a standard ring permanent magnet assembled over the stator chip. The stator design has been performed using an analytical model also presented in the paper. The microfabrication of the first prototypes is discussed before their characterization. With a Joule efficiency of about 31% for an input power lower then 400 nW, this MEMS micromotor has very good performances and demonstrates the potential of electromagnetic systems at this scale.

2009

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This paper addresses the design of a new hybrid microelectromechanical systems (MEMS) micromotor. It is a small three-phase axial flux brushless dc (BLDC) motor. The stator is developed following the almost-standard CMOS technology rules used for MEMS manufacturing, and the coils have two copper layers. The rotor is made of a ring permanent magnet assembled over the stator chip. The stator design has been performed using an analytical model also presented in this paper. The microfabrication of the first prototypes is presented, followed by their characterization. With an efficiency of about 42% for an input power of 310 nW, this MEMS micromotor has very good performance and demonstrates the potential of electromagnetic systems at this scale.

Institute of Electrical and Electronics Engineers2011

Chargement

Modeling the Photostability of Solar Water-Splitting Devices and Stabilization Strategies

Sophia Haussener, Fredy Intelligent Nandjou Dongmeza

The practical implementation of photoelectrochemical devices for hydrogen generation is limited by their short lifetimes. Understanding the factors affecting the stability of the heterogeneous photoelectrodes is required to formulate degradation mitigation strategies. We developed a multiscale and multiphysics model to investigate and quantify the photostability of photoelectrodes. The model considers the photophysical processes in an electrocatalyst-coated semiconductor immersed in electrolyte, and the kinetics of the competing water-splitting and photocorrosion reactions. When applied to 12 promising compound semiconductors for use as photoanodes (GaAs, GaP, InP, GaN, SiC, AlP, AlAs, CdTe, CdS, CdSe, ZnS, and ZnSe), the semiconductor–electrocatalyst interfacial charge transfer rate constant was found to be the most significant parameter for stabilizing the photoelectrodes. Its increase induced a sigmoid-like increase in photostability, and its optimization made it possible to stabilize nine semiconductors. The semiconductor surface back-bond energy also increased the photostability in a sigmoid-like response, and its optimization allowed to stabilize five semiconductors. The increase of irradiance induced a logarithmic drop in photostability, and limiting it to 100 W/m2 could stabilize three semiconductors. We further observed that the photostability in a device of centimeter-scale can vary by more than 50%, showing stable zones and photocorrosion hotspots. The photoelectrode’s length as well as the electrocatalyst and electrolyte conductivities were found to be relevant parameters to impact this heterogeneity in the photostability. Thus, the photostability is not only defined by material properties but also by the specific combination of materials and by the device architecture. The model presented in this study can also be applied to photocathodes and other PEC designs, and can serve as a design tool for understanding, quantifying, and improving the stability.

2022

Chargement

Modeling the Photostability of Solar Water-Splitting Devices and Stabilization Strategies

Sophia Haussener, Fredy Intelligent Nandjou Dongmeza

2022