Stretchable RFID for Wireless Strain Sensing With Silver Nano Ink

Flexible and stretchable inductor-capacitor (LC) resonator-based chipless radio frequency identification (RFID) tags have been fabricated by the direct stamping with silver nano ink. The tags are optimized based on the sympathetic oscillation of LC circuit at specifically designed resonant frequencies ranged from 1.12 to 1.7 GHz by adjusting dimensions of the inductor and capacitor in a tag. Pressure applied to the layer of silver nano ink during the stamping procedure helps densification of silver nanoparticles inside trenches of the stamp before heat-annealing of them. Transfer stamping process is simulated to demonstrate stress distribution across the layer of silver nanoparticles. Compaction of silver nanoparticles, in turn, positively affects mechanical strength of the final silver electrode and enables RFID strain sensors on polydimethylsiloxane to be stretchable up to 7%. By the stretchable RFID strain sensors, wireless strain sensing is demonstrated with a gauge factor of 0.51. Multiple encoded identifications with combination of double tags and stretching behavior of fabricated tags are also demonstrated. This stretchable RFID sensor is promising for biomedical applications such as real-time monitoring of motion detection.