摘要：A novel approach for battery-free food freshness monitoring is proposed and demonstrated in this study. The aim is to track the freshness of different sorts of food such as pork, chicken, and fish during storage. To eliminate the drawbacks of conventional food monitoring methods, which are normally based on measuring gas concentration emitted from food in a container, this approach measures the gradual increase in air pressure caused by the gas emission during storage. Additionally, we aim to design a smart sensor tag that can operate in fully passive mode without an external power source. To achieve this goal, near-field communication (NFC)-based energy harvesting is utilized in this work to achieve a self-powered operation of the sensor tag. To demonstrate the feasibility of the proposed method, experiments with the above-mentioned food were tested at room and refrigerated temperatures in 2 and 4 days, respectively. For each experiment, 200 g of the target food was placed in a 2-L container with the smart sensor tag. The experiments were conducted with both rigid and flexible containers to consider real food packaging environments. The air pressure inside the container was monitored as an indicator of food freshness by a sensitive pressure sensor on the smart sensor tag. The experimental results showed a remarkable increase in air pressure, which was able to be detected with high accuracy by the pressure sensor. The fabricated battery-free smart sensor tag is small (2.5 cm × 2.5 cm) and is capable of less than 1 mW of power consumption, which is ultra-low relative to other ordinary approaches that have a power consumption that normally surpasses 10 mW. The pressure value was used to classify food freshness into different levels on a mobile display to provide food freshness status using an NFC-enabled smartphone.
