Design of SOI MEMS-based Bennet’s doubler kinetic energy harvester

Abstract

Background: Design of microelectromechanical system based Bennet’s doubler kinetic energy harvester (KEH) is tricky as it has to satisfy the operating criteria of doubler circuit along with the harvester’s design constraints for its operation. Aim: Design guidelines for an electrostatic KEH using Bennet’s doubler circuit along with its experimental validation are presented. Approach: Bennet’s doubler circuit can work as a KEH only for a specific range of capacitance ratio across interdigitated electrodes of the harvester. The constraints on the resonant frequency of Bennet’s doubler harvester have been deduced to achieve operational capacitance ratio at both low and high vibrational frequencies. Finally, a test structure is fabricated, using silicon-on-insulator multiuser MEMS processes, and tested for capacitance ratio η greater than 1.366, a prerequisite for the operation of Bennet’s doubler circuit. Results: Resonant operation of the test structure achieves capacitance ratio of 1.39 with a capability of harvesting energy density of 4.63 μJ/cm3. Further, an improved harvester design is also presented for η = 1.5, based on the discussed guidelines that increase the energy density to 19.6 μJ/cm3. Conclusions: We will present an insight into the design of Bennet’s doubler harvester for different vibrational frequencies, which is being widely explored for electrostatic energy harvesting.