Novel Multiaxial Force Decoupling Strategy in Vertically Stacked Force Sensors With Hybrid Fabrication Techniques

This study shows the development of a capacitive force sensor, which cannot only detect multi-axial forces but also differentiate the applied normal and shear force due to its innovative structural design. The sensor contains five capacitors arranged in a specific pattern as a sensing unit with vertically stacked three polyethylene terephthalate (PET) substrates, two polydimethylsiloxane (PDMS) dielectrics, and several silver electrodes in each capacitor. In addition, one and four capacitors were put to the upper (hard) and lower (soft) layer, respectively. Comprehensive structure design, numerical simulation, hybrid fabrication (photolithography and inkjet printing), and analysis were performed in this work. Under the normal force, the top capacitor showed a sensitivity of 0.501 pF/N, while the bottom capacitors showed a comparably negligible sensitivity of 5.267 fF/N. Meanwhile, under the shear force, the bottom capacitors showed a maximum sensitivity of 57.370 fF/N, and the top capacitor showed a comparably near-to-zero sensitivity of −11.743 fF/N, as expected. This sensitivity difference allows users to decouple the type of applied force and its orientation in the xy -plane through the proposed novel algorithm (workflow) for the first time.