A Plantar Pressure Sensing System with Balancing Sensitivity Based on Tailored MWCNTs/PDMS Composites

This paper presents a flexible plantar pressure sensor with a simple structure and easy accessibility, suitable for everyday use. In this study, the design, fabrication, and characteristics of both the composite and the sensor were involved. By using the solution method, the piezoresistive composite was fabricated by uniform dispersion of multiwall carbon nanotubes (MWCNTs) into the polydimethylsiloxane (PDMS) matrix. The proposed sensor consists of eight sensing elements with a laminated structure. The upper layer is a sensing layer made of the piezoresistive composite, and the lower layer is a flexible printed circuit-board working as electrodes. A particular design of sensing elements was carried out by using different doping concentrations according to arrangement positions under the feet to obtain balancing sensitivity. A signal processing system to convert the variable resistance signal into voltages by the current-to-voltage method was designed. Experimental results prove that the designed sensor shows a repeatable response with a sensitivity of 11.5 mV/kPa within the range of 265 kPa. Also, an actual application verifies that the designed plantar pressure sensor can measure the pressure under the foot and can be used for gait detection and disease diagnosis purposes.