Hybrid Photovoltaic/Flexoelectric Actuation of Beams with New Spiropyran-Polyvinylidene Fluoride (SpPVDF) Patches

A new hybrid photovoltaic/flexoelectric actuation mechanism by using a newly laboratory-made material, named spiropyran-polyvinylidene fluoride (SpPVDF), is studied. The classic photovoltaic effect and the flexoelectric effect of the new SpPVDF are, respectively, evaluated theoretically and experimentally. The photovoltaic model of the material is established through the ultraviolet (UV) light ON/OFF strategy. The relationship between the excitation voltage and the beam tip displacement is determined based on the converse flexoelectric effect of SpPVDF. Then, a hybrid actuation mechanism that combines the advantages of a wireless photovoltaic generator and a flexoelectric precision actuator is proposed. Two SpPVDF patches are placed above and below a cantilever beam. The patch below the beam generates photovoltage under UV light irradiation via the photovoltaic effect. As a voltage source, it provides actuation voltage to the patch above the beam. Based on the converse flexoelectric effect of the material, the patch above the beam generates internal stresses and consequently a bending control moment, which finally realizes noncontact precise actuation control of the structure. In addition, the influences of SpPVDF patch thickness, beam thickness, SpPVDF patch length, and line-electrode position on the hybrid actuation performance are also evaluated.