Abstract
With the emergence of the Internet of Things (IoT), connected devices are gaining a significant impact on our daily lives and the advancement of technology is revolutionizing the way we live, work, and communicate. For example, in the near future, the IoT aims to connect approximately 50 billion devices to facilitate the exchange and analysis of data among a range of autonomous modules. IoT devices are made up of sensors and antennas that enable remote monitoring, which can help improve efficiency, lower costs, and enhance safety in various sectors, such as Industry 4.0 and smart agriculture. For the widespread adoption of IoT technology on a large scale, cost and sustainability are important factors to consider. In the contemporary world, it is essential to develop technologies that are environmentally sustainable in order to enhance operational performance while also decreasing costs, energy consumption, waste, and negative impacts on the environment. The objective of green technology is to safeguard the environment, remediate past environmental damage, and conserve natural resources. For this reason, the goal of this PhD project is to develop a low-cost, sustainable printed antenna. To achieve this, eco-friendly paper substrate and printing techniques have been utilized for the manufacturing process. In this thesis, the design and optimization of green printed antennas for IoT applications is investigated. As a proof of concept, a microstrip patch antenna has been designed, optimized and fabricated on a cellulose-based paper substrate, using low-cost printing techniques such as screen-printing, dispense printing, inkjet printing and direct laser writing. Furthermore, the concept of a reconfigurable antenna for sensing applications has been explored, is in order to reduce the number of active components on the sensor nodes while also reducing system-level complexity. This approach holds the promising potential to facilitate the advancement of sensor nodes that are more sustainable in nature. First, different printing techniques (inkjet, screen, and dispense) have been explored for the fabrication of a patch antenna on a low-cost eco-friendly paper substrate. The above-cited manufacturing processes have been investigated in terms of the induced performance variability on the printed antenna. The research focused on three main areas related to the performance of printed antennas: the printing process itself, the impact of the ink carrier, and the effect of climatic variance (i.e., change in environmental temperature) on antenna performance. In the second part of the work, the use of laser-induced graphitization techniques (LIG) is explored. A patch antenna was fabricated using this method, which involves using laser pulses to transform a cellulose based paper substrate surface into a highly conductive carbon-rich precursor such as graphite or graphene structure. One benefit of LIG is that it does not require the use of conductive inks, unlike traditional printing techniques such as screen printing, rollto-roll printing, and inkjet printing. The fabricated antenna using this technique showed good performance in terms of its measured reflection coefficient S11 (-25dB). However, the sheet resistance of the lased structures was higher than that achieved with typical printing techniques. Despite this, LIG can be a good alternative to other printing techniques due to its eco-friendly and sustainable nature, as it allows for the fabrication of antennas on a food-derived cellulosebased paper substrate. in addition, development of green electronics devices using direct laser writing on the copper-coated paper substrate. An extensive optimization of the direct laser writing process was carried out, to sinter low-cost copper ink on a normal office printer paper substrate. The minimum achieved sheet resistance on a paper substrate was around 18 mΩ/sq, which is only 5 times higher than bulk copper. Using the optimized laser writing parameters, a microstrip patch antenna is fabricated and characterized. In third part this work, the computational simulation of a varactor-based reconfigurable antenna was carried out. The aim of this simulation was to explore the potential of a reconfigurable antenna for sensing applications. To this end, a model of a varactor-loaded reconfigurable antenna was created using Ansys HFSS software. The simulated model was then fabricated and tested with various biased voltages. It was found that the resonant frequency of the antenna could be varied by approximately 500 MHz by varying the voltage from 0 to 1 V. This demonstrated the potential of a varactor-based reconfigurable antenna as a sensor node, as the antenna’s resonant frequency could be varied in response to the output voltage of a potentiometric sensor. This ability to vary the resonant frequency allows the antenna to function as a transducer.