Session: 08-02 Alternative Energy Conversion Techniques

Paper Number: 117129

117129 - Investigation of Non-Linear Coupled Oscillators Utilized by Electrostatic Vibrational Energy Harvesters 

The rise of IOT (Internet of Things) devices has increased the need for power sources at the microscale. One of the many possible ways to achieve these power needs is the conversion of ambient vibration to electrical energy. Many power harvesters achieve this through a variety of electro-phenomena, however, electrostatic vibrational energy harvesters (E-VEHS) remain of high interest due to their compatibility with CMOS microfabrication techniques and on-chip integration potential. One of the drawbacks of such devices is the limited bandwidth and power output. One of the methods being explored to improve these is frequency up-conversion. 

            The objective of this research is to explore the dynamics associated with E-VEH devices based on frequency up-conversion technique. These devices feature a central shuttle mass supported within an anchored frame by suspension springs. Such devices operate by translating vibrational stimuli into the oscillation of interdigitated electrodes of a capacitor formed between mobile electrodes attached to the mass and fixed electrodes attached to the anchor. Frequency up-conversion refers to a higher frequency response that occurs when electrode plates collide and produce individual oscillations higher than the excitation frequency.  In this work, electrode features are an important element to device operation and sport non-uniform geometry for two reasons: 1) preventing electrode pull-in and 2) providing greater mass distribution away from electrode base to encourage greater independent oscillation.

            The dynamics of such devices can be modeled via lumped capacitance as coupled oscillators. This system is highly non-linear with complex force relationships. Spring forces, damping forces, and electrostatic forces all play an important role and affect device operation. As electrodes oscillate, damping forces and electrostatic forces govern electrode interaction. The characteristics of their interplay trigger the frequency-up conversion. For instance, for otherwise identical conditions, the reduction in damping forces allows for electrode secondary oscillation following collision. However, when damping forces become too small, pull-in, where electrodes do not decouple following collision, may occur. The reverse condition referred here as “pull-centering” is also seen. This occurs when small amplitude excitations and high electrostatic forces dampen the mobile electrodes movement, forcing them to remain close to their rest position. Overall this study highlights the importance of the interplay between damping and electrostatic forces in relationship to external excitation characteristics and the effect of this interplay on secondary oscillation of the capacitor electrodes. This insight is needed to engineer devices that exhibits higher power output and increased bandwidths.   

Presenting Author: Matthew Galarza Rensselaer Polytechnic Institute

Presenting Author Biography: Matthew Galarza is a Ph.D. candidate studying Mechanical Engineering at Rensselaer Polytechnic Institute focusing on energy harvesting systems and the non-linear dynamics that they exhibit. Specifically, his research explores non-linear dynamics, mixing entropy of coupled mechanical and electrical oscillators, and device optimization/machine learning.