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Format:
Print
Author:
Andosca, Robert George
Dept./Program:
Materials Science Program
Year:
2012
Degree:
Ph. D.
Abstract:
Experimental and theoretical investigations on MicroElectroMechanical Systems (MEMS) based piezoelectric vibrational energy harvesters (PZEHs) with mass loading are presented. The core body of a PZEH is a "multi-morph" cantilever, where one end is clamped to a base and the other end is free. This "fixed-free" cantilever system including a proof-mass (also called the end-mass) on the free-end that can oscillate with the multilayer cantilever under continuous sinusoidal excitations of the base motion. A partial differential equation (PDE) describing the flexural wave propagating in the multi-morph cantilever is reviewed. The resonance frequencies of the lowest mode of a multi-morph cantilever PZEH for some ratios of the proof-mass to cantilever mass are calculated by either solving the PDE numerically or using a lumped-element model as a damped simple harmonic oscillator; their results are in good agreement (disparity [equal or less than] 0.5 %).
Experimentally, MEMS PZEHs were constructed using standard micro-fabrication techniques at the Cornell NanoScale Science and Technology Facility at Cornell University in Ithaca, NY. The piezoelectric transduction material chosen was aluminum nitride (AIN) based upon its 8.6X higher piezoelectric coefficient/dielectric constant (d₃₁/Kp) ratio as compared to sol-gel lead zirconate titanate Pb[ZrxTi₁-x]O₃ 0[equal or less than]x[equal or less than]1 (PZT). Based upon the derived analytical model the electric voltage amplitude V and output power amplitude P are proportional to the (d₃₁/Kp) and (d₃₁/Kp)², respectively. Calculated fundamental resonance frequencies f₁, V and P with an optimum load compared favorably with their corresponding measured values; the differences are all less than 4%. Furthermore, a MEMS PZEH prototype was shown resonating at 58.0 Hz under external acceleration G =0.7 9 (g =9.81 m/s²) external excitations, corresponding peak power reaches 63 [Greek mu]Watts with an output load impedance Z of 82.6 k[Greek omega].
This micro-power generator enabled a wireless sensor node with integrated sensor, radio frequency (RF) radio, power management electronics, and an advanced thin-film lithium-ion rechargeable battery for power storage. In addition, at 58 Hz and 0.5, 1.0 g excitations power levels of 32, and 128 [Greek mu]Watts were also obtained, and these power levels are proportional to the square of the acceleration amplitude as predicted by the theory. The reported P at the fundamental resonance frequency f₁ and acceleration G-Ievel, reached the highest "Figure of Merit" [power density x (bandwidth/resonant frequency)] achieved amongst those reported in current literature for high quality factor Qf MEMS PZEH devices.