Session: 17-01-01: Research Posters

Paper Number: 149970

149970 - Investigation of Energy Exchange Between Coupled Mechanical-Electrical Conservative Oscillators 

Electrostatic vibration energy harvesters convert vibrational energy to electrical energy using variable capacitors. Research in this field focuses mainly on practical aspects related to demonstrating an increase in the power output of these systems through novel device designs or operation approaches. Fundamental studies dedicated to understanding the energy transfer in these systems are limited, which hinders efforts to improve power generation in systematic way. In modeling, these energy harvesters are represented as a mass spring- -dashpot system coupled with electrical components. The variable capacitor is formed by the spring-supported mass acting as an electrode that oscillates in the vicinity of a second, fixed electrode. This variable capacitor is also an integral part of the electrical circuit.   Stripping all dissipative components in both mechanical and electrical domains, this system can be idealized as a coupled, mechanical-electrical oscillators system. The objective of this  work is to study  theoretically this mechanical-electrical coupled conservative oscillators system aiming to gain insights on the effectiveness of harvesting energy from vibrational energy in a systematic way. As part of this study, mechanical, electrical and coupling energy are monitored to observe trends with changing different system parameters and initial conditions.This coupled mechanical-electrical system is governed by Newton’s second law and Kirchhoff’s law and the nondimensional form of these governing equations are solved numerically.

The preliminary results show that the coupled mechanical-electrical oscillators behave differently from purely electrical or purely mechanical coupled oscillators, due to the nonlinearity and one-way coupling. The mechanical-electrical coupled oscillator is uni-directional, meaning that it cannot be activated unless the initial condition on charge or current in the electrical oscillators is non-zero. This is due to the conservation of charge principle of the electrical system. In contrast, in purely mechanical or purely electrical oscillators, the energy transfer between oscillators is bi-directional.  It means the coupled system can be activated by one initial condition on  either of two of the coupled oscillators. The coupled mechanical-electrical system was investigated under equal natural frequency for both the mechanical and electrical subsystems.  It was found that all, mechanical, electrical and coupling energies, display a high-frequency oscillation, capturing the energy conversion within each oscillator (for example, from kinetic to potential energy), while the energy transfer between mechanical and electrical domains were captured with a low-frequency oscillation. It was also found that an increase in non-dimensional coupling energy rapidly leads to system crashing due to a large electrostatic force that cannot be overcome by spring forces. When increasing coupling energy, more energy is transferred between the two domains; however, the frequency of the large scale oscillation describing the energy transfer between the two domains also increases. This means that the power converted, which is of key interest in applications, is not necessarily higher with increased coupling energy. Finally, studies show that when the mechanical and electrical natural frequencies are not equal, the energy transfer between the two systems is not effective. These findings help establish coupling energy as a critical parameter to the effectiveness of energy transfer between mechanical and electrical domains.   

Presenting Author: Zahra Sotoudeh California State Polytechnic University

Presenting Author Biography: Dr. Zahra Sotoudeh’s is a professor with Aerospace Engineering Department at Cal Poly Pomona, which she joined on fall of 2016. Her areas of expertise are computational structural dynamics (CSD), aeroelasticity, and statistical energy analysis. She is an associate fellow of AIAA.

Authors:

Kairvi Lodhiya Rensselaer Polytechnic Institute
Zahra Sotoudeh California State Polytechnic University
Diana-Andra Borca-Tasciuc Rensselaer Polytechnic Institute