FEM and experimental studies of flexible pressure sensors with micro-structured dielectric layers

E-skin (electronic skin) is a key component for use ranging from wearable electronic devices to human-machine interactions. Previous studies proposed that a parallel plate capacitor with a PDMS dielectric layer of micro-pyramids showed good pressure sensing abilities, but overlooked effects of the flat PDMS layers at the top and bottom of these microstructures induced by fabrication processes of soft imprinting. In this work, these effects were firstly studied by the finite element method. The second-order Ogden model was employed to describe the nonlinear mechanical behaviors of the PDMS. We found that the E-skin sensing unit showed increased sensitivity but decreased linearity with the increase of the pyramid height ratio. 48% pyramid height ratio was therefore applied for experimental studies for compromising the performances. We demonstrated an easy accessible and cost-effective method of fabricating the sensing unit, by using a commercial precision abrasive sheet as the mold of the microstructured dielectric film. We introduced a prefilling step to control the pyramid height ratio. Experimental results proved that the sensitivity, pressure resolution and time response of the sensor unit with pyramid height ratio of 45% were better than that with 0. We further demonstrated its applications as a wearable health monitoring device and an approaching and touch sensing unit for a 3D-printed soft hand, showing its great potentials in continuous health monitoring sensors, as well as large area human-machine interactions.