Design of a piezoresistive pressure sensor using topology optimization

Flexible pressure sensors are used commonly in applications ranging from smart per- sonal equipment to medical devices. Different applications require sensors designed specific to the application. In this thesis, a piezoresistive pressure sensor is designed via topology optimization for bedsore prevention (most sensitive at 4.6 kPa). The main objective is to develop a TO design framework for designing a sensor with maximum sensitivity, i.e. change in relative resistance over pressure. TO has been applied to many applications including mechanical, thermal, electromagnetic and piezoelectric devices. Although conductive material topologies have been designed for thermal or electric applications including use of TPMS structures, piezoresistive material design based TO has not been much explored. Here, we develop a TO framework based on modified SIMP material models constructed using numerical homogenization of piezoresistive gyroid unit cells. These material models are used during optimization and are needed during the reconstruction phase of the tapered gyroid sensor topology. The sensor design was envisioned as a PDMS-Polypyrrole composite material and its properties were taken from earlier measurements. A sheet type gyroid geometry is chosen due to its advantages such as volume fraction tunability that is easily linked to density based TO and its manufacturability using additive manufacturing. Simulation models were built and analyzed using FEM in COMSOL Multiphysics 6.2 and the TO framework was applied to three different design categories targeting: 1) mechanical performance, 2) electrical performance, and 3), both criteria simultaneously via multi-criteria design studies. CAD models where generated by a MATLAB script.