Wireless Material Identification in the Recycling Chain Using Chipless RFID Tags

The utility of chipless radio frequency identification (RFID) technology for the identification of eight materials (seven plastic types and glass) in the recycling chain is examined. We first demonstrate how the frequency response of eight circular ring resonators (CRRs), designed to operate in the 1.5–6-GHz band, is used to encode eight unique material IDs. Tagged items are inserted one at a time in front of a chipless RFID reader and the speed and accuracy of material identification, based on the ability to decode the tag’s frequency response, is determined. We demonstrate the ability to correctly identify the material type using a random forest classifier with up to 93% accuracy while being 3–
$16\times $
faster than other methods reported in the literature. A technique to further improve the detection speed, taking measurements with lower resolution, at the cost of accuracy is then presented. Finally, future directions of exploration are discussed.