MEMS power generator with transverse mode thin film PZT
J.-h. Jeong, R. K. Sood, Y.B. Jeon, and S.-G. Kim
A thin film lead zirconate titanate Pb(Zr,Ti)O3 (PZT), MEMS power generating device is developed. It is designed to resonate at specific frequencies from an external vibrational energy source, thereby creating electrical energy via the piezoelectric effect. Our cantilever device is designed to have a flat structure with a proof mass added to the end. The Pt/Ti top electrode is patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d33 mode of the piezoelectric. This d33 mode design generates 20 times higher voltage than that of the d31mode design of the same beam dimension. The base-shaking experiments at the first resonant frequency generate charge proportional to the tip displacement of the cantilever with a linearity coefficient of 4.14 pC/mm. A PZT cantilever beam (170 mm´260 mm) generates 1 mW of continuous electrical power to a 5.2 MOhmresistive load at 2.4V DC. The corresponding energy density is 0.74 mW-h/cm2, which compares favorably to the values of lithium ion batteries. We expect the next generation design with lower resonant frequencies would harvest sufficient energy from the environmental vibration for wireless miniature sensor networks, so that the integrity of large-scale distributed complex systems will be effectively monitored.
Sensors and Actuators A: Physical 2005
Nonlinear Resonance-based Piezoelectric Vibration Energy Harvesting
Ultra-wide bandwidth piezoelectric energy harvesting
Arman Hajati and Sang-Gook Kim
We reported an ultra wide-bandwidth energy harvester by exploiting the nonlinear stiffness of a doubly clamped microelectromechanical systems (MEMSs) resonator. The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. This design has been fabricated into a compact MEMSdevice, which is about the size of a US quarter coin. Based on the open circuit voltage measurement, it is expected to have more than one order of magnitude improvement in both bandwidth (more than 20% of the peak frequency) and power density (up to 2 W/cm3) in comparison to the devices
Buckled MEMS Beams for Energy Harvesting from Low Frequency Vibrations
R. Xu, Haluk Akay, S. G. Kim
Linear resonance-based energy harvesters have been popular for vibration energy harvesting, due to their simplicity of micro-fabrication and high power efficiency at resonance. Nevertheless, the narrow frequency bandwidths that linear energy harvesters suffer prevent the technology from applying in the real frequency-changing ambient environment. As a promising potential solution, nonlinear resonance widens the power bandwidth by one order of magnitude, which shows the great potential of nonlinear designs. We built an electromechanically coupled, lumped model to provide a comprehensive analysis of nonlinear resonance-based energy harvesting. The model was based on the configuration of a doubly clamped beam with a thin film piezoelectric element working in d33 mode. The static indeterminate structure problem was solved with the Euler-Bernoulli beam theory and energy method. By considering the simple case of inputting a sinusoidal force and connecting the harvester to a resistor, we employed Kirchhoff’s laws and the Harmonic Balance Method (HBM) to build and solve the nonlinear differential equations. Closed form expressions of the system’s parameters were obtained from the analysis. The coupled, lumped model has verified varying electrical loads at each frequency to generate maximum power at that frequency by showing a power spectrum with a much wider bandwidth. Furthermore, the optimal electrical damping at each frequency was obtained; it shows that the electrical damping should be much higher than the mechanical damping to increase the power at low frequencies, and the maximum power is obtained when the electrical damping matches the mechanical damping.
