Architectures for vibration-driven micropower generators

• Published in: Journal of microelectromechanical systems Vol. 13; no. 3; pp. 429 - 440
• Main Authors: Mitcheson, P.D., Green, T.C., Yeatman, E.M., Holmes, A.S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-06-2004; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplitudes; Analytical models; Computational modeling; Computer architecture; Density; Design engineering; Displacement; Frequency; Generators; Mathematical analysis; Microelectromechanical systems; Micromechanical devices; Power generation; Resonance; Studies; Time domain analysis; Ubiquitous computing; Vibration; Vibrations
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2004.830151

Several forms of vibration-driven MEMS microgenerator are possible and are reported in the literature, with potential application areas including distributed sensing and ubiquitous computing. This paper sets out an analytical basis for their design and comparison, verified against full time-domain simulations. Most reported microgenerators are classified as either velocity-damped resonant generators (VDRGs) or Coulomb-damped resonant generators (CDRGs) and a unified analytical structure is provided for these generator types. Reported generators are shown to have operated at well below achievable power densities and design guides are given for optimising future devices. The paper also describes a new class-the Coulomb-force parametric generator (CFPG)-which does not operate in a resonant manner. For all three generators, expressions and graphs are provided showing the dependence of output power on key operating parameters. The optimization also considers physical generator constraints such as voltage limitation or maximum or minimum damping ratios. The sensitivity of each generator architecture to the source vibration frequency is analyzed and this shows that the CFPG can be better suited than the resonant generators to applications where the source frequency is likely to vary. It is demonstrated that mechanical resonance is particularly useful when the vibration source amplitude is small compared to the allowable mass-to-frame displacement. The CDRG and the VDRG generate the same power at resonance but give better performance below and above resonance respectively. Both resonant generator types are unable to operate when the allowable mass frame displacement is small compared to the vibration source amplitude, as is likely to be the case in some MEMS applications. The CFPG is, therefore, required for such applications.