A novel inkjet-printed wireless chipless strain and crack sensor on flexible laminates

We studied a low-cost chipless radio-frequency identification strain sensor tag operating at 2.45 GHz. The sensor is based on a 18.5 × 18.5 mm² single split ring resonator which is fully inkjet printed on a flexible substrate. For an applied strain of 20 %, a silver-based ink strip printed on a polyimide substrate showed an irreversible conductivity variation up to 700 %. Correspondingly, when illuminated by an incident plane wave, the printed sensor features an electromagnetic response with a magnitude strongly correlated with the strain applied on it. We recorded up to 15 dB variation in the radar cross section. Both, the simulations and wireless measurements in indoor environment validated the sensor operation.