Range-extended wireless food spoilage monitoring with a high energy efficient battery-free sensor tag

In this study, we developed a smart sensor tag without a battery for monitoring spoilage in packaged foods. To give our smart sensor tag a compact structure for inserting into food packaging, we designed a double PCB structure with two 6-turn rectangular antennas. The first PCB includes several low power sensors for monitoring food spoilage, a transceiver IC for communication with a reader, a microcontroller for the smart sensor tag operations, and a 6-turn rectangular antenna at the edge of the PCB. The second relay PCB contains another 6-turn rectangular antenna (that is the same size as the first antenna) and is parallel to the first board. This second PCB is designed as a relay resonator to improve the RF energy harvesting efficiency from the reader side. The antenna on the first board transmits data to the reader and simultaneously operates as a receiver resonator for RF energy harvesting. To evaluate the food spoilage, the proposed smart sensor tag was designed to have several low power sensors that monitor factors including humidity, temperature, total volatile organic compounds, and equivalent carbon dioxide. Validation results showed that the proposed smart sensor tag with the sensor module is able to collect the sensing data on food spoilage without a battery, at a maximum distance of 50 cm from a reader. The collected sensing data were analyzed with a personal computer to evaluate spoilage level in food packages. (C) 2019 Elsevier B.V. All rights reserved.