Modeling, analysis and validation of a novel asymmetric cruciform harvester with d₁₅ mode

d ₃₁ mode piezoelectric property has been widely used in vibration-based energy harvester, however there are very few studies on fully utilizing maximum piezoelectric constant d ₁₅. In this study, a novel asymmetric cruciform harvester with d ₁₅ mode is proposed. The asymmetric cruciform beam is composed of one main beam and two asymmetric side beams. Under one directional excitation, the torsional vibration of the proposed harvester is easily induced by the asymmetry of side beams and added masses. A mathematical model of bending-torsional coupling is established and then verified by finite element method and experiments. The results indicate that, compared with the reference harvester with equal total mass, the resonant frequency of the proposed harvester can be significantly reduced. Furthermore, its output power can be highly enhanced. Based on the established theoretical model, the effects of design variables (side beam length, added mass thickness, and piezoelectric position) on performances (resonant frequency and output power) are analyzed in detail. The analytical results illustrate that the proposed harvester can output higher power at lower frequencies by increasing its asymmetry. The asymmetry can be enlarged by increasing the difference in added masses and length of the two side beams. More importantly, the proposed harvester can effectively reduce the performance deviations caused by piezoelectric position, which is beneficial to fabrication and applications. (paper)