Photosensitive chipless radio-frequency tag for low-cost monitoring of light-sensitive goods

simple approach to develop a novel photosensitive radio-frequency (RF) tag to be used as non-volatile wireless light exposure detector is presented. This chipless tag is based on the coupling of a standard high frequency (HF) inductor-capacitor (LC) resonator with an interdigitated planar sensor featuring a micrometric inter-electrode gap optimized for a thin acrylamide photosensitive polymer layer. Exposure to ambient light within the absorbance band of the photosensitizer (~530 nm) triggers polymerization, which irreversibly modifies the electrical properties of the film, producing a significant decrease of the dielectric constant of 27%, thereby changing the resonance frequency (540 kHz shift) of the resonator. This allows the straightforward wireless detection of the light exposure event as demonstrated here. The sensor fabrication is fully compatible with high-throughput printing processes, therefore fostering a dramatic reduction of tag production costs and enabling mass application of disposable tags that can, for instance, be embedded into the packaging of light-sensitive goods.