Abstract
Energy harvesters withstanding high temperatures could provide potentially unlimited energy to sensor nodes placed in harsh environments, where manual maintenance is difficult and costly. Experimental results on a classical microcantilever show a 67% drop of the maximum power when the temperature is increased up to 160 °C. This decrease is investigated using a lumped-parameters model which takes into account variations in material parameters with temperature, damping increase and thermal stresses induced by mismatched thermal coefficients in a composite cantilever. The model allows a description of the maximum power evolution as a function of temperature and input acceleration. Simulation results further show that an increase in damping and the apparition of thermal stresses are contributing to the power drop at 59% and 13% respectively.
Highlights
Energy harvesting has become over the recent years the main focus to supply low-power miniaturized sensor nodes from on-site available energy
While most piezoelectric thin films lose piezoelectric properties when heated up, aluminum nitride (AlN) has been shown to be stable at high temperatures [2]
When the working temperature is increased to 160 ◦C, a power drop of almost 70% is experimentally measured
Summary
Energy harvesting has become over the recent years the main focus to supply low-power miniaturized sensor nodes from on-site available energy. While most piezoelectric thin films lose piezoelectric properties when heated up, AlN has been shown to be stable at high temperatures [2] When it integrated as a thin-film piezoelectric layer on a resonating silicon micro-. Cantilever, other mechanical or electrical effects induced by temperature can affect the harvested power, which are investigated in this study. Three frequency sweeps are performed at each temperature and fixed input acceleration: with the device in open circuit, in short circuit and on a matched 300 kΩ resistive load. The resonance frequency is decreasing from 217.7 Hz to 216.1 Hz, corresponding to a 0.7% drop and the mechanical quality factor is going from 726 to around 475 over the tested range, or a 35% decrease. For various acceleration levels the resonance frequency and quality factor show the same rate of decrease, whereas the power slope gets steeper for higher accelerations
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