Signal-amplified stretchable PVDF kirigami sensor via neutral axis modification

Abstract

Stretchable sensors with smart materials now open up diversity opportunities by suggesting ways to overcome the limitations of conventional rigid sensors. The performance of piezoelectric devices is highly dependent on piezoelectric constants. Hence, materials with low piezoelectric constants hinder users to obtain signals induced by stimuli. To rectify this problem, there have been numerous efforts to increase piezoelectricity by doping additional materials or through chemical synthesis methods. These two methods have common limitations: low cost-effectiveness and inferior accessibility by scientists from diversity of fields. In this study, we suggest methods to amplify the response of a polyvinylidene fluoride (PVDF) kirigami sensor with a structural approach: neutral axis modification with a backing layer. We introduce two sensor models with a backing layer: single side and both sides backing layer models. In the former model, the backing layer is attached to the outward area of the concave bending section for stress increment; thereby the response of the sensor can be ameliorated. For the latter model, backing layers are attached on both sides; this synchronizes stress types in the concave and convex bending sections. Consequently, it aligns current movement within the sensor. These two methods are simple and the expected results are intuitive as the voltage amplitude changes proportionally to the backing layer thickness. Also, the modified sensor exhibits stable and identical responses during and after 1000 cyclic motions of stretching and releasing with an applied strain of 80%. The maximum voltage amplitude gap between the pristine and modified sensor is marked as 8.36 V, which is a 48% amplified response from the sensor without a backing layer. This method allows users to adjust the voltage response to their demands in a simple way. This modification also has the potential to be applied as a piezoelectric energy harvesting system.