Abstract
Proof mass can adjust the natural frequency of a cantilevered energy harvester to fit the vibration source frequency and, hence, improve energy efficiency. In this paper, a cantilevered energy harvesting model including a proof mass is presented based on the flexoelectric theory. The electromechanical coupling responses at steady state are obtained for harmonic excitations and then reduced to single-mode expressions for modal excitations. The flexoelectric coupling coefficient, which represents conversion of energy, is investigated. The numerical results reveal that the flexoelectric coupling coefficient can be improved by adjusting the proof mass to make the vibration frequency of the microbeam adapt to that of the ambient vibration source. The adjusting strategies have also been formulated. In addition, the flexoelectric coupling coefficient increases with the decrease in the thickness of the microbeam. As expected, the flexoelectric coupling coefficient can further be enhanced when the beam thickness reaches nanometer scale. For the beam thickness h = 0.3 μm, the current output decreases and the voltage output increases with the increase in the electrical load resistance. When the electrical load resistance is around 100 MΩ, the power output arrives at its maximum. The resonance frequency shifts from 34 693 Hz to 35 350 Hz with the increase in the load resistance from short- to open-circuit conditions, and the flexoelectric coupling coefficient for this thickness lever is kr ≈ 0.19.
Highlights
Since the development of micro-electro-mechanical-system, harvesting ambient mechanical energy into electrical energy holds great promise for powering the low-powered electronic devices, replacing the batteries, and achieving self-powered electronic devices in a variety of applications, such as personal electronics, wireless sensing, implantable medical devices, and so on.1,2 Until now, many energy harvesters have been developed based on piezoelectricity.3,4 piezoelectricity is inherent only in noncentrosymmetric materials
In centrosymmetric dielectrics, a polarization can be induced by the strain gradient or inhomogeneous strain field, known as flexoelectricity, which can broaden the choice of materials that can be used for electromechanical coupling
The electromechanical coupling responses at steady state are obtained for harmonic excitations and reduced to single-mode expressions for modal excitations in Sec
Summary
Since the development of micro-electro-mechanical-system, harvesting ambient mechanical energy into electrical energy holds great promise for powering the low-powered electronic devices, replacing the batteries, and achieving self-powered electronic devices in a variety of applications, such as personal electronics, wireless sensing, implantable medical devices, and so on. Until now, many energy harvesters have been developed based on piezoelectricity. piezoelectricity is inherent only in noncentrosymmetric materials. Nguyen et al developed a model to capture the Maxwell-Wagner polarization effect in a bilayer structure and established the equations of motion to investigate the role of dynamic flexoelectricity in piezoelectric nanobeams.. Yan further introduced the surface effect and proposed a flexoelectric energy harvester model.. Considering the strain gradient and flexoelectric effects, Managheb et al studied the energy harvesting from a Timoshenko beam.. The natural frequency of the cantilevered energy harvester can be adjusted by a proof mass to fit that of vibration source effectively. In this paper, based on the flexoelectric theory of Li et al, a cantilever beam model with a proof mass is proposed for energy harvesting.
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