Piezoelectric effect, as an electromechanical coupling effect, has been widely used for in-situ sensors and actuators in sensing and control applications. Flexoelectric effect, linear couplings between the electric polarization and strain gradient and between polarization gradient and strain of a solid, is newly developed as complementary to piezoelectric effect. Although the magnitude of the flexoelectric effect is generally small, its contribution to the overall dynamics of a solid can become significant or even dominant when the scale diminishes from macro to micro. The flexoelectric and piezoelectric effect on the actuating of a cantilever beam were compared in this study to explore how the size-dependent effect could affect the application of the flexoelectric effect. An AFM (atomic force microscopy) probe was used to generate the electric field in the flexoelectric patch, significant electric field gradient was induced. The electric field, distribution of control moment, induced modal force and the vibration control efficiency in terms of transverse displacements were analyzed in case studies.

Analytical results showed that the control moment of flexoelectric effect highly concentrated at the location of the AFM probe due to the inhomogeneous electric field, which shrunk the effect area of flexoelectric patch size. The distribution of the flexoelectric control moment was an impulse function and the distribution of the piezoelectric control moment was a step function, which resulted to the flexoelectric modal force strongly affected by the electric field gradient while the piezoelectric modal force highly depended on the patch size. For the flexoelectric actuating, decreasing the AFM probe radius could increase the electric field gradient and induce larger modal force. The thickness effect of flexoelectric patch depended on the electric field gradient and the control moment arm, and in the current study, increasing the patch size, the induced flexoelectric modal force increased slightly. Case studies on vibration control found that both the flexoelectric actuating and piezoelectric actuating could generate larger transverse tip displacement with increasing the patch size. However, when the patch sizes were in millimeter and below (i.e., 0.001), the flexoelectric actuator could accelerate the damping process faster than the piezoelectric actuator with identical electric input, but when the patches were in larger scales (i.e., 0.01m), the piezoelectric patch had better vibration control effect. Overall, this study proved that the flexoelectric actuating can provide effectively actuating and control effect to engineering structures when the size decreases. Considering the flexoelectric effect literally existing in all insulating materials while piezoelectricity is limited to non-centrosymmetric materials, and with specific structure designs, the gradient effect of flexoelectric effect can be further enhanced, it is still worth to put more effort in research on flexoelectric effect and its applications.


Comparison of Flexoelectric and Piezoelectric Actuating of Beams

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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