With the advancement in the technologies around the world over the past few years, the microelectromechanical systems (MEMS) have gained much attention in harvesting the energy for wireless, self-powered and MEMS devices. In the present era, many devices are available for energy harnessing such as electromagnetic, electrostatic and piezoelectric generator and these devices are designed based on its ability to capture the different form of environment energy such as solar energy, wind energy, thermal energy and convert it into the useful energy form. Out of these devices, the use of a piezoelectric generator for energy harvesting is very attractive for MEMS applications. There are various sources of harvestable energy including waste heat, solar energy, wind energy, energy in floating water and mechanical vibrations which are used by the researchers for energy harvesting purposes. This paper reviews the state-of-the-art in harvesting mechanical vibrations as an energy source by various generators (such as electromagnetic, electrostatic and piezoelectric generators). Also, the design and characteristics of piezoelectric generators, using vibrations of cantilevered bimorphs, for MEMS have also been reviewed here. Electromagnetic, electrostatic and piezoelectric generators presented in the literature are reviewed by taking into an account the power output, frequency, acceleration, dimension and application of each generator and the coupling factor of each transduction mechanism has also been discussed for all the devices.

No abstract

No abstract

Periodic finite element/boundary element modeling of capacitive micromachined ultrasonic transducers J. Appl. Phys. 97, 034901 (2005); 10.1063/1.1839634The effects of membrane metallization in capacitive microfabricated ultrasonic transducers ABSTRACT. This paper presents a comparison of three Finite Element approaches for modeling the behavior of a Capacitive Micromachined Ultrasonic Transducer (CMUT). CMUTs have become very popular over the last decade because of the comparable bandwidth, sensitivity and dynamic range with its piezoelectric counterparts. The ease of fabrication is an added advantage. Modeling of CMUTs is a coupled physics problem, which involves solving Electrostatics and Structural interactions simultaneous. Finite Element models of the CMUT are constructed using the commercial code ANSYS (9.0). Three different approaches of solving the coupled field problem are discussed and the results are compared for resonance frequency, collapse voltage, capacitance and electromechanical coupling coefficient. The approaches discussed involve sequentially coupled-field analysis, direct coupled-field analysis and reduced order modeling. Detailed results have been presented for the effect of variation in geometrical factors as predicted by the three models.