Battery-less pork freshness real-time monitoring system with high efficient RF energy scavenging

摘要

The public has become more conscious of the importance of food quality and its effects on the human health. Consuming the expired food may lead to serious health problems, thus, a food freshness real-time monitoring system that is safe, inexpensive, and highly accurate is needed to ensure that customers can choose food packages with the best quality. In this paper, we demonstrate a method to monitor and indicate the quality of the food packages using a small smart sensor tag that consists of three ultra-low power consumption sensors. The freshness is monitored and assessed by various factors including temperature, humidity, as well as the gas concentration of ammonia and hydrogen sulfide. These low-consumption power sensors consume less than 4 mW of power. Therefore, an RF energy scavenging circuit integrated on the smart sensor tag can harvest energy from radio waves at a high frequency of 13.56 MHz to supply the power for the operation of all tag components. The energy harvester can obtain energy efficiently at a distance of around 40 cm from a reader that has transmitted an approximate 4 W of power. This design allows the smart sensor tag to operate without any batteries, as batteries cause the increase in cost due to frequent battery replacement. In this study, the freshness of reserved pork is monitored continuously in two different conditions: room temperature and refrigerator temperature, which are both the most usual places to store food during a one-week period the proposed battery-less tag. Based on the experimental results, the food assessment is classified into four categories: fresh, normal, low and spoilt.