MEMS Energy Harvesting from Low-Frequency and Low-Amplitude Vibrations

Vibration energy harvesting at the micro-electrito mono-stable nonlinear oscillations, we found cal-mechanical system (MEMS) scale will promisingly bi-stable oscillations could bring more dynamics advance exciting applications such as wireless sensor networks and the Internet of Things by eliminating troublesome battery-changing or power wiring. On-site energy generation could be an ideal solution to powering a vast number of distributed devices usually A meso-scale prototype verified the theoretical employed in these systems. To enable the envisioned battery-less systems, a fully assembled energy harvest- er at a size of a quarter-dollar coin should generate robustly 101~102μW of continuous power from ambient vibrations (mostly less than 100 Hz and 0.5 g accelera- tion) with wide bandwidth. We are inching close to this goal in terms of power density and bandwidth, but not in terms of low-frequency and low-amplitude operations. The previous research with nonlinear resonating bridge-structure-based energy harvesters achieved 2.0 mW/mm3 power density with >20% power bandwidth. However, they were operated with input vibrations of >1 kHz at 4 g, which practically limits the use of this technology for harvesting energy from real environmentally available vibrations. Many believed this is an inherent limitation imposed on the MEMS-scale structures.

We approached this problem with a buckled-beam-based bi-stable nonlinear oscillator. Compared to mono-stable nonlinear oscillations, we found bi-stable oscillations could bring more dynamics phenomena to help reduce the operation frequency. An electromechanical lumped model has been built to simulate the dynamics of the damped-damped buckled beam based piezoelectric energy harvesters.

A meso-scale prototype verified the theoretical prediction, showing that the same energy harvester in a bi-stable configuration generated more power than the mono-stable configuration at lower frequencies. Residual stress-induced buckling was proposed and implemented through micro-fabrication to build the MEMS energy harvester. The multi-layer bridge structure has employed compressive residual stress in the micro-fabricated thin-films to reach overall compression and balanced stress distribution with respect to the neutral axis. As a main control parameter, the total compression can be tuned to exceed the critical buckling load and induce buckling. The buckled beam oscillates nonlinearly at large amplitude to maintain a wide bandwidth at much lower frequencies. The MEMS prototype of a quarter-dollar coin size has been built and is being tested. The preliminary testing shows an order-of-magnitude-lower operating frequency range than the same sized mono-stable device we previously developed.