A porous elastomer with a cavity array for three-dimensional plantar force sensing

•A new method of sensitive and accurate detection of flexible three-dimensional contact forces in human gait by a porous elastomer with a cubic cavity array (PECA) is reported.•The PECA elastomer features with micro-sized pores and uniform millimeter-sized cavities. It demonstrates a high device sensitivity of 0.41 N−1 in the normal direction and 0.23 N−1 in the tangential direction, which are nearly three-times higher compared to those of the sensor without the cavity structure.•This method solves this problem of force deconvolution from the four-channel capacitance signals by utilizing a back propagation (BP) neural network. It brings a time-efficient and accurate solution to the signal coupling problem.•Different from most foot-wear sensing devices which only detect the normal stresses/forces, the PECA sensor comfortably detects the three-dimensional contact forces in various gait cycles, revealing more complete information in gait analysis. Human gait is an important indicator for diagnosis of various movement-related disorders. Three-dimensional (3D) plantar force monitoring enables real-time recording of contact forces in both the normal and tangential directions in each step, providing useful clues for identification of irregular gait patterns or gait-related health issues. Most flexible sensors for gait monitoring focus on contact forces in the normal direction, being limited to detect forces in the tangential direction. Herein we have developed a porous elastomer with a cavity array (PECA) to measure 3D contact forces for gait analysis. The sensor consists of two fabric electrodes and a dielectric layer of porous Ecoflex elastomer containing a 5 × 5 cavity array, forming four parallel-plate capacitor units in a soft construction. Therefore, a 3D force in any arbitrary direction generates four unique capacitive electrical signals. Importantly, the PECA includes a well-designed combination of micrometer-scale pores and millimeter-sized cavities, dramatically improving the detection sensitivity and linear elasticity range. We have demonstrated high sensitivities of 0.41 N−1 and 0.23 N−1 in the normal and tangential directions, respectively. The flexible PECA-based sensors have been tested to sensitively distinguish various standing postures and different stride lengths for gait analysis, promising reliable translation into areas such as healthcare monitoring, sports training, and rehabilitation engineering.