| Summary: | All-textile capacitive sensor arrays made of a polyurethane foam, fabric and electrically-conducting yarn were fabricated for a ‘smart chair’. Polyurethane foam slab that functioned as a dielectric medium was encased between two pieces of commercially available fabric. The electrically-conducting yarn was used to embroider the capacitor electrodes on both fabric pieces. The completed sensor arrays were investigated under normal compressive load with the targeted pressure range of 2 to 30 kPa for the chair seat and 2 to 8 kPa for the backrest. The sensor capacitance versus normal compressive load exhibited a load/unload hysteresis for all sensor arrays. The hysteresis was modelled with sigmoid function and much narrower hysteresis was observed when all sensors were loaded simultaneously, as opposed to their individual loading, allowing development of a phenomenological model for the former. Among the studied sensor arrays, the array with dimensions of 30 cm <inline-formula> <tex-math notation="LaTeX">$\times 30$ </tex-math></inline-formula> cm made of a 10-mm-thick polyurethane foam with density of ~18.6 kg/m<sup>3</sup> was the most suitable for the following reasons: (a) unloaded sensor capacitance was ~2.7 pF, (b) the sensor location did not affect its response, (c) ~10 kg load applied across individual sensor raised its capacitance by ~12 pF, and (d) 60 kg load applied uniformly across the whole sensor array increased the capacitance by ~5 pF. During the compression of the individual sensors the top fabric affected the sensor’s electro-mechanical response and elastic fabric would be favored for applications with non-uniform pressure distribution.
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