Wireless strain sensing using carbon nanotube composite film

Carbon nanotubes in polymer matrix form a complex network which consists of resistors, inductors, and capacitors. The present research focuses on wireless strain sensing using multi-walled carbon nanotube/epoxy resin films. Following a specific process, the nanocomposite strain gauges with different multi-walled carbon nanotube concentrations were fabricated. The test on these prototypes shows that the multi-walled carbon nanotube/epoxy resin films can respond to wireless electromagnetic excitation by means of generating induced voltage. Experimental measurement also proves that mechanical strain affects the resonant frequencies of the multi-walled carbon nanotube/epoxy resin strain gauges. Therefore, the nanocomposite films can be used to detect mechanical strain wirelessly by calculating the shift of the resonant frequency. Aiming to reveal the working mechanism of the wireless sensing, this study hypothesizes that the nanocomposite strain gauges can be modelled by an equivalent RLC circuit. The subsequent theoretical analysis, and the comparison between the analytical predictions and the experimental results both indicate that the hypothesis is reasonable, since the RLC model can successfully explain the phenomenon of the strain-induced shift of the resonant frequency. The current work provides a promising method to make tag-type wireless strain sensors.