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Comparison of flexoelectric and piezoelectric dynamic signal responses on flexible rings

Piezoelectric materials have been widely used for structural sensing due to the linear electromechanical coupling effect. Flexoelectricity, generally existing in all dielectrics, describes the linear inhomogeneous electromechanical coupling phenomena. Previous studies have shown that the direct flexoelectric effect is sensitive to the bending deformation. This study focuses on comparison and differences between two sensing mechanisms, that is, the flexoelectric and the piezoelectric effects, and explores their distinctive characteristics and potential applications. Based on the direct flexoelectric/piezoelectric effects, flexoelectric/piezoelectric materials treated as flexoelectric/piezoelectric sensors are applied to two ring models with identical dimensions. The mathematical models of thin elastic rings laminated with flexoelectric/piezoelectric sensors are established. Open-circuit sensing signals are derived for further evaluation and comparison. Sensing capabilities of these two materials and mechanisms are compared with respect to ring thickness, sensor thickness, and ring radius in case studies. Results show that the piezoelectric sensing signal appears to be sensitive for both bending-dominant and membrane-dominant vibrations, while the flexoelectric signal is much more prominent than the piezoelectric one for sensing of bending-dominant vibrations. For a flexible structure performing transverse vibration, the bending behavior is usually dominant. Thus, the flexoelectric effect could provide an effective alternative for structural sensing.