Lithographic production of vertically aligned CNT strain sensors for integration in soft robotic microactuators

This paper reports on a piezoresistive strain sensor that uses vertically aligned carbon nanotube (CNT) filler elements which are embedded in a rubber matrix. Compared to previously used conductive filler elements, vertical CNTs can be patterned using lithography, making it possible to scale down the sensor footprint into the micrometer range. This technological advancement is instrumental for developing intelligent soft microrobots with embedded flexible sensors. We compare vertical CNTs and carbon black as filler elements, where newly developed lithographic production techniques are applied to shape a generic strain sensor topology that is compatible with the majority of planar inflatable microactuators. This research shows a significant improvement in sensor linearity by using vertical CNTs as filler elements over carbon black. Further, a lithographically fabricated strain sensor has been successfully embedded in an elastic inflatable bending microactuator with outer dimensions of 5.5×1×0.06mm3. The full lithographic production process to create this actuator is described in this paper, together with its characterization under a static pressure input.