Nonlinear MEMS Piezoelectric Harvesters in the presence of geometric and structural variabilities

This paper investigates the use of an electrostatic device to improve the performance of MEMS piezoelectric harvesters in the presence of geometric and structural variabilities due to the manufacturing process. Different types of uncertain parameters including material and geometric uncertainties have been considered. The variability of these parameters are estimated based on available existing experimental data in the literature. Monte Carlo simulation (MCS) is used for uncertainty propagation and it is shown that the resonance frequencies of the majority of the samples are far away from the excitation frequency and consequently this results in less harvested power. This paper identifies these samples and uses electrostatic devices to improve the performance of the harvester. The proposed device is composed of an unsymmetric arrangement of two electrodes to decrease the resonance frequency of samples through a softening nonlinearity. The unsymmetric arrangement of two electrodes is inevitable and due to geometric variability of the harvester. There are also two arch shape electrodes which can be used to create a hardening effect to increase the resonance frequency of samples which have resonance frequencies smaller than the nominal value

Stochastic modelling and updating of a joint contact interface

Dynamic properties of the contact interfaces in joints and mechanical connections have a great influence on the overall dynamic properties of assembled structures. Uncertainty and nonlinearity are two major effects of contact interfaces which introduce challenges in accurate modeling. Randomness in surface roughness quality, surface finish and contact preload are the main sources of variability in the contact interfaces. On the other side, slip and slap are two mechanisms responsible for nonlinear behavior of joints. Stochastic linear/nonlinear models need to be developed for such uncertain structures to be used in dynamic response analysis or system parameter identification. In this paper, variability in linear behavior of an assembled structure containing a bolted lap-joint is investigated by using experimental results. A stochastic model is then constructed for the structure by employing a stochastic generic joint model and the uncertainty in the joint model parameters is identified by using a Bayesian identification approach

Design, analysis, and feedback control of a nonlinear micro-piezoelectric–electrostatic energy harvester

A nonlinear micro-piezoelectric–electrostatic energy harvester is designed and studied using mathematical and computational methods. The system consists of a cantilever beam substrate, a bimorph piezoelectric transducer, a pair of tuning parallel-plate capacitors, and a tip–mass. The governing nonlinear mathematical model of the electro-mechanical system including nonlinear material and quadratic air-damping is derived for the series connection of the piezoelectric layers. The static and modal frequency curves are computed to optimize the operating point, and a parametric study is performed using numerical methods. A bias DC voltage is used to adapt the system to resonate with respect to the frequency of external vibration. Furthermore, to improve the bandwidth and performance of the harvester (and achieve a high level of harvested power without sacrificing the bandwidth), a nonlinear feedback loop is integrated into the design

Improving Performance of MEMS Piezoelectric Harvesters in the Presence of Manufacturing Uncertainties

This paper investigates the use of a MEMS energy harvester with adjustable resonance frequency to improve the performance of MEMS harvesters in the presence of manufacturing uncertainties. Model parameters which are subject to considerable variability have been selected and standard Monte Carlo simulation (MCS) is used for uncertainty propagation. It is shown that the manufacturing uncertainty can have significant influence on the performance of the MEMS harvester. This paper proposes the use of an electrostatic device to adjust the resonance frequencies of the system to compensate for the model parameters variability. By applying DC voltages to the electrodes, the samples at which the resonance frequencies are greater than the nominal value can be modified due to the softening effect. On the other hand, applying a follower load to the harvester can create a hardening effect to compensate the effects of uncertainty in the harvester by increasing the resonance frequency

Design of MEMS piezoelectric harvesters with electrostatically adjustable resonance frequency

In this paper the analytical analysis of an adaptively tuned piezoelectric vibration based energy harvester is presented. A bimorph piezoelectric energy harvester is suspended between two electrodes, subjected to a same DC voltage. The resonance frequency of the system is controllable by the applied DC voltage, and the harvested power is maximized by controlling the natural frequency of the system to cope with vibration sources which have varying excitation frequencies. The nonlinear governing differential equation of motion is derived based on Euler Bernoulli theory, and due to the softening nonlinearity of the electrostatic force, the harvester is capable of working over a broad frequency range. The steady state harmonic solution is obtained using the harmonic balance method and results are verified numerically. The results show that the harvester can be tuned to give a resonance response over a wide range of frequencies, and shows the great potential of this hybrid system

A hybrid piezoelectric and electrostatic vibration energy harvester

Micro Electro Mechanical Systems for vibration energy harvesting have become popular over recent years. At these small length scales electrostatic forces become significant, and this paper proposes a hybrid cantilever beam harvester with piezoelectric and electrostatic transducers for narrow band base excitation. One approach would be to just combine the output from the different transducers; however, this would require accurate tuning of the mechanical system to the excitation frequency to ensure the beam is resonant. In contrast, this paper uses the applied DC voltage to the electrostatic electrodes as a control parameter to change the resonant frequency of the harvester to ensure resonance as the excitation frequency varies. The electrostatic forces are highly non-linear, leading to multiple solutions and jump phenomena. Hence, this paper analyses the non-linear response and proposes control solutions to ensure the response remains on the higher amplitude solution. The approach is demonstrated by simulating the response of a typical device using Euler Bernoulli beam theory and a Galerkin solution procedure