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Towards improved insect monitoring systems using UHF RFID and other passive asymmetric digital radio technologies
thesisposted on 2023-05-28, 09:27 authored by Hirsch, P
Radio technology has been used as a tool to gain insights into animal behaviour since the 1960s when it was first used to monitor animal locations using animal-mounted transmitters. Since then, ongoing miniaturisation accompanied by cost reduction has enabled new applications in this area, e.g. detecting large numbers of individually tagged insects in a few selected locations using RFID technology or tracking the location of a small number of tagged insects (typically less than 10) over distances of more than 100m using harmonic radar. It is however still impossible to track a large number of individually tagged small animals over distances exceeding a few cm. Yet exactly this combination would be required to gain more insight into the behaviour of honey bees (Apis mellifera), which are crucial for human food production but whose populations have declined steeply in many areas of the world. Presented in two parts, this thesis investigates different aspects of using asymmetric digital radio technology for automatically monitoring a large number of individually tagged small social animals such as honey bees (Apis mellifera). The first part focuses on the prospects and challenges of using UHF RFID as a cost effective automatic monitoring technology. The second part addresses the limitations in detection range inherent to UHF RFID as demonstrated in the first part. It presents a roadmap to developing a new class of digitally modulating passive radio tags combining ideas from harmonic radar and RFID, which allows to suppress unwanted reflections of the interrogation signal from the environment (also called 'clutter'), aiming to increase tag detection range. Below, I describe both parts in more detail. In the first part, as part of the research a very affordable first prototype monitoring system based on a compact off-the-shelf USB RFID reader module equipped with a single internal antenna was developed and built. Field trials testing this prototype on honey bees showed that this system is able to capture RFID tag detection data which allows to detect temporal variations in hive activity levels. This data also provides some information about tag recapture and tag reading longevity rates. However, it quickly became apparent that the data quality achievable by this system was limited. For example, with just a single antenna the system could not detect whether the tagged bees were entering or leaving the hive. This problem was addressed by another field trial using two of these RFID reader modules in tandem connected to a single control computer, operating alternatingly. Analysis of this data revealed that the reader modules only achieved low detection rates. Unfortunately, both trials frequently suffered from system failures due to overheating and some unknown technical issues, further reducing data quality. To better understand the low detection rates observed in the field experiments, a lab-based robotic measurement system to scan the spatial structure of the detectability range of our tags in the near field of a reader antenna was developed. Measurements performed with this system revealed that the detection range of the RFID reader modules in combination with our tags was limited to less than 10mm. These insights lead to the development of an improved detection system based on a more capable industrial RFID reader module supporting up to 4 antennas which addresses the needs of CSIRO's Global Initiative for Honeybee Health. Based on detection range measurements and electromagnetic simulations, an optimized arrangement of four commercially available RFID antennas was devised. Consisting of two opposing pairs of compact ceramic patch antennas, this arrangement lead to dramatically improved detection rates which were confirmed in further field trials using this new system in the course of an honours thesis within our group. The second part addresses the tight detection range limits inherent to UHF RFID while maintaining the ability to distinguish a large number of individual tag IDs by developing ideas for a new concept for passive transponders combining concepts from RFID technology and harmonic radar. As a first step towards this new development, a compact dual band parasitic dipole antenna was developed using electromagnetic simulations, manufactured as a prototype and tested in the laboratory.
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