Energy harvesting using vibrating honeycomb sandwich panels with auxetic core and carbon nanotube-reinforced face sheets

The literature on energy harvesting using piezoelectric materials is firmly concentrated on structures like cantilever beams with piezoelectric layers. In the present research, a piezo harvester made of a honeycomb sandwich panel is studied. The modeled sandwich panel is made of an auxetic core and two carbon nanotube-reinforced face sheets. It will be shown that this harvester offers more flexibility in its stiffness, leading to better performance in harvested energy. The displacement field of the panel is formulated in a general form, which includes different types of shear deformable plate theories. Within these plate models, transverse shear stresses and rotary inertias are taken into account. A piezoelectric layer is integrated at the top of the honeycomb substructure, and vibrations are originated from an external harmonic source. The material properties of the carbon nanotubes vary lineally in the thickness direction. Hamilton's principle is adopted to derive governing equations of motion, and then weighted residual method is applied to discretize the coupled differential electro-mechanical equations of motions. After validating the model, a detailed parametric study is carried out to investigate the impacts of different parameters such as auxetic cell characteristics, carbon nanotube volume fraction, carbon nanotube configuration, and geometrical dimensions on the electrical power and voltage of the harvester.