Experimental studies on carbon nanotube strain sensors

Abstract

Conventional metal foil strain sensors only measure strain on the structural surface in predetermined directions and locations. These are made of Nichrome (Ni-Cr alloy) and Constantan (Cu-Ni alloy) and have gauge factor of 2. A carbon nanotube (CNT) as a strain sensing material is gaining research interest due to its outstanding electrical and mechanical properties. These sensors apart from multidirectional sensing are capable of making additional contributions such as structure strengthening or structure damping. Bucky paper (BP) alternatively called CNT film or CNT network made from single-walled carbon nanotube or multiwalled carbon nanotubes (SWCNT or MWCNT) has been used by some researchers in the past as strain sensor. However, they have observed nonlinear relationship between strain and change in resistance, and lower gauge factor. Literature review in the field indicates that there is scope for improvement in the performance of Bucky paper-based strain sensors. The objective of this experimental work is to investigate effect of CNT film constituents (MWCNT, SWCNT and mix of both), purification of CNTs and effect of preparation method on sensitivity. The work involves preparation of film from CNTs by vacuum filtration method and preparing the strain sensors from the same. These sensors are loaded along with conventional foil strain gauges on opposite side. The change in resistance of sensor due to applied load is measured to evaluate sensitivity or gauge factor of sensor for various cases. It was observed that the sensitivity of CNT strain sensor is dependent on the preparation and purification methods as well as on the aspect ratio.