Characterization of a Soft Pressure Sensor on the Basis of Ionic Liquid Concentration and Thickness of the Piezoresistive Layer

A stretchable pressure sensitive piezoresistive film was fabricated through the polymerization of a mixture containing an ionic liquid (IL, 1-ethyl-3-methyl-imidazolium tetrafluoroborate) and a commercially available 3D printable photopolymer. This piezoresistive layer was placed between two carbon-nanotube (CNT)-based stretchable electrodes and was encapsulated with stretchable top and bottom insulating layers to form a multilayer piezoresistive pressure sensor. The intersecting electrodes create a sensing unit, referred to as a taxel. The sensor was connected to a Wheatstone half-bridge circuit, and a normal force was applied on the taxel to evaluate the sensor in terms of change in electrical resistance as the sensor underwent deformation. Sensor performance was investigated for various concentrations of IL and the thicknesses of the intermediate piezoresistive layer. The experimental results showed that the IL concentration and the thickness of the intermediate layer affect the sensitivity of the sensor. Next, various forces were applied to a sensor that was fabricated using reasonable values for IL concentration and layer thickness to determine the reliability and responsiveness. The proposed IL-based sensor displayed superior performance with high sensitivity and reliability. While the sensors for these experiments were manufactured using screen printing and molding processes, the materials used for sensor fabrication are 3D printable, as 3D printing is the target manufacturing technique for stretchable pressure sensors in the future.