Experimental and theoretical investigations on micro-scale multi-morph cantilever piezoelectric vibrational
energy harvesters (PZEHs) of the MicroElectroMechanical Systems (MEMS) 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 multi-layer 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
≤
0.5%). Experimentally, MEMS PZEHs were constructed using
the standard micro-fabrication technique. Calculated fundamental resonance frequencies, output electric
voltage amplitude V and output power amplitude 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
±
2.0 Hz under 0.7 g (g = 9.81 m/s2) external excitations, corresponding
peak power reaches 63 W with an output load impedance Z of 85 k. This micro-power
generator enabled successfully a wireless sensor node with the integrated sensor, radio frequency (RF)
radio, power management electronics, and an advanced thin-film lithium-ion rechargeable battery for
power storage at the 2011 Sensors Expo and Conference held in Chicago, IL. In addition, at 58 Hz and 0.5,
1.0 g excitations power levels of 32, and 128 W were also obtained, and all these three power levels
demonstrated to be 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-level, reached the highest
“Figure of Merit” [power density
×
(bandwidth/resonant frequency)] achieved amongst those reported
in the up-to-date literature for high quality factor Qf MEMS PZEH devices.