MEMS Energy Harvesting from Low-frequency and Low-g Vibrations
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MEMS Energy Harvesting from Low-frequency and Low-g Vibrations Ruize Xu, Sang-Gook Kim Mechanical Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 02139, USA ABSTRACT MEMS vibration energy harvesting has been investigated to provide energy to low-power micro-electronic systems and potentially to enable batteryless autonomous systems. While enjoying the small footprint hence the ability to be embedded in other systems, MEMS vibration energy harvesters are working at much higher frequencies and input vibration amplitudes. The mechanical resonator based energy harvesters seem inherently have such high frequency due to the scaling of the device dimension. Lower the working frequency range and input vibration amplitude are possible by optimizing the dimensions of the device. However, we are viewing the problem from a different perspective and proposing a solution based on employing the common material property of the micro-fabricated thin film – residual stress. We found that by taking advantage of the compressive residual stress, a bi-stable mechanical resonator could be built and a new spectrum of dynamics can be brought into energy harvesting, which could lower the working frequency range and input g value. The concepts have been analytically simulated and experimentally verified by a meso-scale model. INTRODUCTION MEMS-scale vibration energy harvesting has been investigated for more than a decade to enable autonomous systems such as batteryless wireless sensor networks. Toward this goal, a fully assembled energy harvester at a size of a quarter dollar coin should be able to generate robustly about 100PW continuous power from ambient vibration (mostly less than 100Hz and 0.5g acceleration) with reasonably wide bandwidth (>20%). We are inching close toward this goal in terms of power density and bandwidth, but not in terms of low frequency operations. Most of the reported vibration energy harvesters use a linear cantilever resonator structure to amplify small ambient vibrations [1,2,3]. While such structures are easy to model, design and build, they typically have a narrow bandwidth. In contrast, nonlinear resonators have different dynamic response and greatly increase the bandwidth by hardening or softening the resonance characteristic of the beam structure. In addition, it has been found that non-linear resonating stretching beams can extract more electrical energy than linear resonating bending beams can. Our previous research with non-linear resonating stretching energy harvesters achieved 2.0 mW/mm3 power density with >50% power bandwidth [4]. But it was operated with input vibrations of >1 KHz and 4.0 g acceleration, which practically limits the use of this technology, 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 bi-stable nonlinear resonating buckled beam. Compared to mono-stable nonlinear resonance, we found bi-stable resonance could bring more dyn
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