Meta-Sticker: Sub-Terahertz Metamaterial Stickers for Non-Invasive Mobile Food Sensing

Food waste is one of the greatest economic and ethical challenges in the world. Empowering consumers with the ability to assess the quality of fruit can be a game changer for reducing waste and motivating a healthier diet. In this paper, we present Meta-Sticker a novel low-cost non-invasive solution for accurate fruit sensing via a sub-THz metamaterial sticker. The key idea is to exploit fruit as a substrate for resonating meta-atoms. Changes in the chemical composite of the fruit over time (e.g., sugar and water concentration) yield variation in the dielectric properties of the fruit (here substrate). Interestingly, this would affect the resonant frequency of the Meta-Sticker. We design Meta-Sticker to resonate in the sub-THz bands for their sensitivity to water, mm-scale penetration depth, and non-ionizing features that offer high-resolution inferences from the inner pulp of the fruit. We develop a model that translates the resonance of Meta-Sticker to well-known ripeness metrics, namely Dry Matter and Brix. We fabricate Meta-Sticker on paper and conduct extensive over-the-air experiments. We demonstrate that our system can estimate Brix and Dry Matter in three different types of fruits with an average Normalized RMSE value of 1.24%, an error that yields a negligible impact on taste and is imperceptible by the consumer. Our design is non-invasive, low-cost (less than a cent), passive, biodegradable, and conformal.