Ali, Amjad
(2024)
Passive RFID tag for biomass tracking and monitoring
of temperature and humidity level.
PhD thesis, University of Nottingham.
Abstract
The last few decades have seen the United Kingdom (UK) being strongly supportive of renewable energy (RE) resources to reduce the use of depleting fossil fuels and its resultant greenhouse gas (GHG) emissions. For this purpose, one of the strategies is to utilise biomass energy as an alternate source of fossil fuel in various sectors such as house heating, electric power generation and industrial usage. In order to use biomass in all these sectors, it is crucial to monitor local humidity and temperature levels to ensure quality, reduce the self-ignition risk and enable supply chain tracking. Some of these important parameters are currently monitored at a very high cost with the use of expensive and complicated battery-based devices. Due to fire risks, sensors cannot have batteries, and it is difficult to recover sensors before combustion. Thus, any whole life monitoring system must minimise the risk of fire, not pose a blocking hazard, and be combustible while also being low-cost to produce. To date, no such sensor tag has been demonstrated.
This work provides a low-cost, flexible, miniaturised and high code density chipless RFID tag for biomass tracking and monitoring humidity and temperature levels. An extensive research study of various chipless RFID tags was performed, followed by the simulation of different tag geometries with U, square, spiral, and hexagonal shapes. This led to the conclusion that a high code density could be achieved with the combination of hexagonal and spiral-shaped tag geometry. The proposed tag is simulated on various substrates such as Rogers RT 6002, Polyethylene terephthalate (PET) and Taconic TLX-0 substrate in a compact size of 1x1 cm2 to 3x4 cm2. Copper, Silver and Gold were used as conducting layers. The tag consists of 17 nested concentric hexagons and a central spiral resonator for IDs encoding. The numerous closely spaced resonators cause increased mutual coupling and spectral signature interference, which is reduced by fine-tuning the design variables, iterative simulations and synthesising resonant frequencies. The overall structure and results have been significantly improved as compared to the latest research. The proposed tag geometry was selected due to its distinctive outcomes of high code density of 6.92 bits/cm2, regular geometry, high magnitude frequency dips, 360º angular stability, high radar cross-section, low cost, and compact size. The performance of the tag is presented, demonstrating the applicability of the design for different material systems whilst maintaining a compact size. The proposed tag is realised over FR4, Rogers and poly(ethylene naphthalate) (PEN) substrate. The tag geometry was manufactured by using PCB engraving with the help of a milling machine, silver paste deposition with the help of Voltera printing, inkjet printing by using DMP-2850 and Fujifilm printer, and laser printing. The various printed tags' RCS performance was measured by using a vector network analyser with a bi-static antenna setup. Where the measured and simulated RCS response shows a strong agreement.
The design of a low-cost, flexible, miniaturised and high code density chipless RFID tag is presented as a solution for tracking the transportation of biomass fuel pellets. In the next step, the tag performance was checked with six different biomasses for trace and tracking purposes. The reported results show that the tag could respond to most of the biomasses when the tag is attached to the front side. Due to the absorbing and scattering nature of biomass, the tag response is highly effected when measured from the back side or at a depth reading. Additionally, the high amount of present humidity could also effect the tag response. The tag's best response was achieved with 5kg rice husk from the front as well as from the back side reading. All these measurements and results of the suggested chipless RFID tag provide a pioneer pathway for a real-time biomass tracking application.
The reported incidents and literature show that the rise in temperature caused explosions in the biomass supply chain. Therefore, it is vital that the tag also has humidity and temperature monitoring capabilities. To incorporate temperature and humidity sensing capabilities, various smart materials were studied. Dry Polyvinyl Alcohol (PVA) tends to absorb humidity, which causes variations in electrical properties. Similarly, BaTiO3 also shows electrical properties variations with rise or fall in temperature. These two smart materials films were created on a single U-shape tag with the help of K-bar coating. The simulated and measured results show that the coated PVA-coated tag responds to humidity variations, while BaTiO3 coated tag actively responds to temperature variations. Thus, a temperature or humidity sensor could be created by putting either BaTiO3 or PVA to monitor biomass temperatures or humidity, respectively. Additionally, this tag has robustness, grindable, and combustible properties. All these properties of the suggested novel chipless RFID tag provide a pathway for biomass tracking.
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