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Abstract Flexoelectric effect refers to the strain gradient induced electric polarization, and it is a universal electromechanical coupling effect in all solid dielectrics due to the inversion symmetry breaking by the strain gradient. Since the strain gradients are inversely proportional to the characteristic dimensional of materials, flexoelectric effect is expected to beyond the piezoelectric effect to dominant the electromechanical coupling phenomenon of materials at the nano scale. Mechanical Energy harvesters based on flexoelectric effect are considered one of the most promising applications in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). In the present work, a theoretical model for the flexoelectric energy harvester is established. The governing equations and corresponding boundary conditions are derived from the energy variation principle. In addition, the performance of the flexoelectric unimorph cantilever beam based energy harvester are analyzed based on the theoretical model. The effects of the resonance frequency, the resistance of the circuit, the thickness of the flexoelectric layer, and the Young’s modulus of the elastic layer on the output voltage frequency response and the output power density frequency response are discussed. Particularly, numerical analysis for cantilever beam based flexoelectric energy harvester fabricated by PVDF polymer thin film and epoxy substrate are obtained. It is found that the maximum output voltage frequency response and output power density frequency response appear at the resonance frequencies of the cantilever energy harvester. The output voltage and the output power density increase with the increase of the resonance frequencies at each mode. The numerical results also showed that there is an optimum resistance. Furthermore, the output power density increases with the decrease of the thickness of the flexoelectric layer when the resistance near its optimum value. Moreover, it is found that the output voltage decreases with the increase of the Young’s modulus of the elastic layer. The numerical results in this paper is helpful in designing cantilever beam-based flexoelectric energy harvesters.
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Received: 13 January 2020
Published: 28 April 2020
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2020, Vol. 41 
