Fig. 2: Eco-friendly chipless temperature-responsive tag concept, fabrication and testing setup.

a Image of the chipless tag and schematic of the monitoring concept for smart packaging application. b Schematic of the operation principle based on a chipless tag with pristine and melted PCM resulting in a resonance shift towards lower frequencies. c Exploded view of the multi-layered biodegradable tag and material thicknesses. d Cross-section view and 3D representation of the manufacturing process flow. e Optical image of the completed chipless tag before use. f Optical images of the reader antenna and chipless tag with PCM positioned over the antenna with a 2 mm spacer. g Climatic setup with a cold chamber and a camera, and a schematic showing the tag placed over the reader antenna inside the chamber at an inclination angle θ.