Compact passive wireless UHF sensors for packaged food monitoring
Package to package monitoring of food commodities using printed RFID-based sensors offers a low-cost, environmentally friendly and bio-compatible alternative to traditional electronic sensors. The lack of batteries and expensive electronic components enable their integration into a sustainable food production and distribution model easily. Some of the essential properties essential for the practical implementation of such sensors include small size, easy detectability, and long detection range. Though a vast amount of research has been demonstrated towards the development of chipless and passive RFIDs little work has been carried out in literature for their application in food monitoring applications. This thesis presents the study of compact passive wireless sensors operating in the giga-hertz range for application in packaged food monitoring. Firstly, a radar-cross-section (RCS) based compact wireless humidity sensor with a built-in reference signature and time-gated measurement is presented. This novel approach of integrated reference in the same scattering element gives the differential sensing ability and thereby immunity to frequency detuning effects from the dielectric loading in the immediate environment of the sensor without an increase in the size of the tag. Environmental clutter is one of the biggest problems towards the practical implementation of RCS-based tags. The thesis thus further focuses on tackling this problem. One of the solutions to this is a polarimetry-based depolarizing tag that scatters orthogonally polarized fields. The next part of the thesis thereby presents the first of its kind compact depolarization-based sensing tag for acidic/basic volatile sensing. Further improvement in the clutter performance can be achieved using frequency diversity between the interrogator transmitted and sensor retransmitted signal. In the final part of the thesis a novel compact harmonic sensor with integrated transmit, receive antennas and non-linear doubling circuit integrated on an annular slot antenna is demonstrated for the first time. The sensor is suitable for monitoring of high-value food items like fish and meat. The non-linear sensor has the advantage of not needing background calibration for practical applications commonly needed for detection of chipless sensors passive sensors. Milk and ammonia monitoring are demonstrated using the presented sensors.
Passive Sensors, Food Monitoring, Chipless sensor, RFID, Milk Monitoring, Ammonia Sensing