Wide Bandwidth Piezoelectric MEMS Energy Harvesting
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Wide Bandwidth Piezoelectric MEMS Energy Harvesting
Ruize Xu1 and Sang-Gook Kim1 1 Mechanical Engineering, MIT, Cambridge, MA, United States.
ABSTRACT Piezoelectric Microelectromechanical Systems (MEMS) has been proven to be an attractive technology for harvesting small energy from the ambient vibration. Recent advancements in piezoelectric materials and harvester structural design, individually or in combination, have improved MEMS energy harvesters to achieve high enough power density, compactness and ultra wide bandwidth, bringing us closer towards battery-less autonomous sensors systems and networks in near future. Among the breakthroughs, non-linear resonating beam for wide bandwidth resonance is the key development to enable robust operation of MEMS energy harvesters over the unpredictable and uncontrollable frequency spectra of ambient vibration. We expect that a coin size harvester will be able to harvest about 100µW continuous power at below 100 Hz and less than 0.5 g input vibration and at reasonable cost. INTRODUCTION Increasing number of applications of sensor networks in monitoring civil structures’ health, air pollution etc. have prompted the need of power sources which require no regularly replacement and provide enough power to the sensors. Parasitic energy harvesters on vibrating systems converting kinetic energy into electrical energy through piezoelectric effect have shown tremendous potential as a perpetual power source. With no external power sources needed, experiments showed thin film piezoelectric energy harvesters have a decent output voltage (3V), a high power density (2W/cm3), a compact size (quarter coin size), which all indicate a desirable power source to be integrated on board to enable autonomous, self-powered sensor networks [1]. In the process of developing the desirable energy generators, however, it has been realized that the typical cantilever based energy harvesters have a linear resonance feature and thus an unfeasibly small bandwidth, which makes the harvesters useless in an environment with unpredictable frequency spectrum [2]. Much effort has been dedicated in improving the bandwidth of energy harvesters, and three main mechanisms are turning frequency, multiple beams and nonlinear resonance. The natural frequency of the resonator can be tuned by changing the axial tension of a beam through manipulating magnets [3, 4]. Beam dimensions [5], proof mass [6] have also been tuned mechanically to widen the bandwidth. However, frequency tuning consumes power, the tuning efficiency is low and the tuning range is limited [7]. Another approach to widen bandwidth is based on multiple beams. The device consists of multiple cantilever beams with various lengths
and end masses [8]. The combination of the cantilevers, which have different resonant frequencies, created a so-called ‘mechanical band pass filter.’ By selecting the length and end mass of each beam, the device had a wide band of resonant frequencies. This method increases the size and the cost, a more complex electric circui
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