Novel proximal fish freshness monitoring using batteryless smart sensor tag

Abstract Fish is the most perishable of fresh foods, but it is held in high regard for its flavor, taste and nutrition for the human body. Until now, most studies on monitoring the freshness of fish have used semiconducting metal oxide sensors that consume much power in sensing operation. To supply the operational sensing power and the power for wireless communication, any wireless sensor module needs a battery attached, and this entails extra effort for a regular battery change. Therefore, we developed a novel fish monitoring system in which no battery is needed for the sensing module. This study proposes a novel proximal fish freshness monitoring system. The novel smart sensing tag module has been developed as a self-powered device by using an additional energy harvesting circuit that operates at a frequency of 13.56 MHz. The harvester can collect sufficient radio frequency (RF) energy from the reader by using RF energy coupling within a maximum distance of 30 cm; then, the received power is stored in a single energy chip for supplying to the sensing circuit. The fish freshness is monitored by sensor modules for temperature and either hydrogen sulfide (H 2 S) or ammonia (NH 3 ) gas concentration measurement in the fish packaging. The sensing module is designed using ultra-low-power sensors that consume less than ∼10 mW, enabling us to extend the distance between the RF reader and the smart sensor tag for effective RF energy coupling and sensing data transmission. The results of freshness monitoring of a seafish package are classified into four grades to indicate the food quality: good, normal, caution, and bad. The proposed sensor tag can be used to predict the quality of packaged fish by accurate monitoring of temperature and the concentration of H 2 S or NH 3 in range of −40 to 105 °C, 0–200 ppm, and 0–100 ppm, respectively.