Centimetre–gram–second system of units

The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unambiguously derived from these three base units, but there are several different ways in which the CGS system was extended to cover electromagnetism. The CGS system has been largely supplanted by the MKS system based on the metre, kilogram, and second, which was in turn extended and replaced by the International System of Units (SI). In many fields of science and engineering, SI is the only system of units in use, but there remain certain subfields where CGS is prevalent. In measurements of purely mechanical systems (involving units of length, mass, force, energy, pressure, and so on), the differences between CGS and SI are straightforward and rather trivial; the unit-conversion factors are all powers of 10 as 100 cm =

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

Development of a Hybrid MEMS BLDC Micromotor

Sebastiano Merzaghi, Yves Perriard

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

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

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

Sophia Haussener, Fredy Intelligent Nandjou Dongmeza

2022