The interest in modeling and prototyping the so-called Vibration Energy Harvesters (VEHs) has increased significantly in the last decades, given the growing demand for energy sources that can capture energy from the vibration of a machine, for example, to power small sensors and vibration monitoring devices. In this work, the design and optimization of a commercial Electromagnetic Vibration Energy Harvester (EMVEH) are presented. Such a device contains in its interior a resonant-type electromagnetic transducer, the latter composed basically by a seismic mass, a mechanical spring and a multi-turn coil. The complete set weighs about 90 g and occupies a total volume of approximately 50.97 cm3, being able to generate up 45mW at its resonance frequency of 60 Hz, with a bandwidth of 2.5 Hz. Furthermore, the linear generator presented in this paper reaches a maximum Normalized Power Density (NPD) of 1.8018mW/(cm3g2) at an acceleration amplitude of 0.7 g (∼ 6.67m/s2). To proceed with electromechanical modeling and further optimization, a numerical model was developed via commercial software COMSOL Multiphysics, from which it was possible to optimize its geometry in order to maximize its NPD and power output. A Surrogate optimization algorithm was then implemented in MATLAB, in which both volume and mechanical stress were considered as project constraints.
With smaller, cheaper, and more energy-efficient electrical components, energy harvesting systems have been a more attractive source of energy supply for wireless sensors, transducers, and other devices. One great example of mostly unused energy is the vibration of industrial machines. Along with the rise of predictive maintenance, more wireless sensors have been used to monitor those machines. Where the vibration energy present in those machines can be used to extend the sensor’s life constrained by the battery. This work presents two fabrication approaches to design these devices using the piezoelectric principle: MEMS fabrication and micro-machined devices. MEMS are widely investigated for harvesting purposes for their capability of building complex microscale structures (< 0.1 cm3). However, it can be difficult to designing MEMS energy harvesting systems for the low frequency range (40 Hz to 200 Hz), which is the operating range for standard industrial machines. The adapted micro-machined harvesters from off-the-shelf piezoelectric components mostly used in macro-scale applications (> 10 cm3), can be an alternative in this situation. Numerical models were developed to simulate the dynamic behavior of the piezoelectric device and used as input for design optimization. The models were improved using a differential evolution algorithm optimizing in terms of the Normalized Power Density (NPD) and Mechanical stress. In order to validate these models, prototypes were built ns tested, with the results compared considering the NPD and frequency bandwidth. The optimization process raised key design aspects of meso-scale low-frequency piezoelectric devices, including stress limits of thin-film piezoelectric and fabrication complexity, Overall, these aspects suggest that there is an advantage of micro-machined designs over MEMS devices for these applications.
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