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Flexoelectric effects hold promising applications in sensing, actuating, and energy capturing, and thus it is demanded to measure the flexoelectric coefficient tensors of dielectric materials accurately. In this work, an approach to measuring the effective flexoelectric coefficient tensor component μ 2312 of polymeric materials is developed by imposing a torque load upon a half cylindrical specimen. It is proven that μ 2312 can be calculated by assessing the electric charge on the axial plane and the strain gradient along the radial direction, both induced by the torque. To overcome the difficulty in experimental measurements, the relationship between the strain gradient and torque is deduced theoretically and further verified with finite element analysis. This approach is applied to testing bars machined from bulk polyvinylidene fluoride (PVDF). Potential errors from the piezoelectric effects and the non-uniform strain gradient are discussed to verify the validity of the measurement. The experimental results show good reproducibility and agreement with other measured effective flexoelectric tensor components of PVDF. This work indicates a potential application of PVDF-based mechanical sensors and provides a method to investigate the effective flexoelectric coefficient component of polymers.

Flexoelectricity describes the strain gradient-induced electric polarization. Due to the restrictions of experiment technologies, some of the components of flexoelectric coefficient have not been experimentally obtained. In this letter, an experimental method for the measurement of the shear flexoelectric response along 3121 direction of polyvinylidene fluoride (PVDF) is presented. An experiment is conducted on various unpolarized specimens, where shear strain gradient is generated along the radial direction by applying torque to 3 specially designed specimens. The generated shear strain gradient is calculated via finite element analysis and the corresponding induced electrical response is measured. Dynamic torque is exerted on the specimens with a static bias value and at different frequencies. The shear flexoelectric coefficient μ3121 is found to have an average value of 1.037 × 10−8 C/m. With this method, the shear flexoelectric response along 3121 direction of PVDF is experimentally obtained. The experimental results show good agreement with the current research results and indicate the potential value of this material property for electromechanical device fabrication.

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Mirror-scanning mechanisms are a key component in optical systems for diverse applications. However, the applications of existing piezoelectric scanners are limited due to their small angular travels. To overcome this problem, a novel two-axis mirror-scanning mechanism, which consists of a two-axis tip-tilt flexure mechanism and a set of piezoelectric actuators, is proposed in this paper. The focus of this research is on the design, theoretical modeling, and optimization of the piezoelectric-driven mechanism, with the goal of achieving large angular travels in a compact size. The design of the two-axis tip-tilt flexure mechanism is based on two nonuniform beams, which translate the limited linear output displacements of the piezoelectric actuators into large output angles. To exactly predict the angular travels, we built a voltage-angle model that characterizes the relationship between the input voltages to the piezoelectric actuators and the output angles of the piezoelectric-driven mechanism. Using this analytical model, the optimization is performed to improve the angular travels. A prototype of the mirror-scanning mechanism is fabricated based on the optimization results, and experiments are implemented to test the two-axis output angles. The experimental result shows that the angular travels of the scanner achieve more than 50 mrad, and the error between the analytical model and the experiment is about 11%. This error is much smaller than the error for the model built using the previous method because the influence of the stiffness of the mechanical structure on the deformation of the piezoelectric stack is considered in the voltageangle model.

This study proposes a novel hybrid piezo-electromagnetic actuator (HPEA) which can keep output displacement without power supply. The actuator consists of an electromagnetic driving actuator and a piezoelectric clamping actuator. The electromagnetic driving actuator generates displacement and force, which can be hold by the piezoelectric clamping actuator. The theoretical model of HPEA is established, the corresponding governing equation is derived. The static and dynamic output characteristics are simulated. Moreover, a controller is designed and the corresponding experimental system is set up to verify the theoretical analysis and simulation of the HPEA. The experimental results agree well with the simulation. Furthermore, the HPEA is used in indentation experiments of a soft material, polydimethylsiloxane. The results demonstrate that the HPEA has a good performance in soft material indentation test.

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