Highly Efficient Battery-less Smart Sensor Tag with Relay Resonator for Wireless Food Monitoring

Abstract

Recently, RF (Radio Frequency) Energy Harvesting (RFEH) has become a promising technology. In this technique, the ambient RF radiation is captured by receiver antennas and converted to electrical energy which is used to supply to smart sensor modules. In this thesis, we propose a novel method to improve the efficiency of RFEH systems using strongly coupled electromagnetic resonance technology. A relay resonator, which receives the magnetic field from the reader and then relays to the tag antenna, is added between the reader and the smart sensor tag. The design of relay resonator based on resonant technique and near-field magnetic coupling concept would easily to improve the communication distance as well as the supplied power to the sensor module at longer distance. It is designed such that the self-resonant frequencies of the reader antenna, tag antenna and the relay resonator are synchronous at HF frequency (13.56MHz). The proposed method was analyzed using Thevenin equivalent circuit, simulated and validated in experiments to evaluate its performance. The experimental results show that the proposed harvesting method is able to generate approximate 10 times higher power than that provided by typical harvesting methods without a relay resonator. This thesis also presents a smart sensor module which is placed inside a meat sealed container. It is utilized to collect the vital data, including temperature, relative humidity, and gas concentration. These sensing data were carried out and used to evaluate the freshness of food. Overall, by exploiting the relay resonator, the smart sensor tag can continuously monitor food freshness without any batteries at the maximum distance of approximately 50 cm.