Model-based approach for indentation on soft electronic skin

The primary objective of this research is to develop a model-based framework for the indentation on the surface of a soft electronic skin. In the current paper, the model has been applied to a soft electronic skin embedding piezoelectric polymer (PVDF, polyvinylidene fluoride) transducers. We revisit in a dimensionless fashion an analytical solution of the problem presented in a previous contribution for a normal force (frictionless case) and extend the analysis to account for a tangential component of the contact force (frictional case). First, the transmission of Hertzian distributed forces through the skin elastomer layer to a PVDF transducer is analyzed, assuming a half-space model for the elastomer. Then, the above mathematical formulation has been employed to perform extensive FEM simulations such to extend the analytical solutions for the half-space case to the real configuration where the elastomer layer has finite thickness and the transducer is not necessarily vertically aligned with the indenter. The model is applied to the case of a dragon skin, a well-known soft alternative to the silicone-based PDMS e-skin discussed in the previous paper. The model can be easily extended to other sensor types, provided the transducer is integrated on a rigid substrate and converts the pressure acting on its upper surface into a proportional electrical signal. The present framework is a first step towards the construction of a general design tool for soft electronic skins based on pressure transducers, regardless of the specific transducer type and material employed for the soft cover.