Signal amplitude monitoring system for in-plant communication based on multi-source energy harvesting: design and characterization

Environmental sustainability has become a significant topic, especially in recent years. The consequences of the increasingly frequent extreme natural phenomena (such as domestic and international mass migrations, food insecurity related to the rise of the world population, etc.) have further highlighted the environmental situation and increased interest in the relative research and publications. Within this framework, Smart Agriculture solutions may represent a viable answer to boost productivity, improve resilience, reduce emissions and waste, and optimize human labor through the utilization of several new technologies and techniques helping to speed up the change of route in the climate-change scenario due to the crucial impact on the environment of the agricultural sector. In this perspective, this thesis work proposes an energetically self-sufficient, low-cost, and low-power system capable of evaluating the plant health status by the stem electrical impedance developed to minimize the waste of energy and water resources and the eventual chemical utilization to what is strictly necessary for every single plant's maintenance. A Plant Microbial Fuel Cell (PMFC) has been chosen to work with a photovoltaic (PV) module to achieve the energy-related goal. Thus, a PMFC-based solution has been studied and characterized in this thesis work to inspect the most suitable electrode materials combination and to retrieve information on this still-not-so-exploited energy solution. Then, the system used for the electrical plant stem impedance evaluation has been designed and developed comprising a transmitting module, a receiving device, and a microcontroller unit (MCU). The transmitting module injects a signal with a known amplitude and a plant-stem-related frequency. The receiving device exploits a peak-detector-based solution to estimate the electrical plant stem impedance module by retrieving the peak voltage of the signal sent by the transmitter and proportionally attenuated by the distance traveled along the plant stem before being read by the receiver. The microcontroller unit (MCU) has been configured to properly manage the data from the transmitter, receiver, and other eventually exploited sensors and send the results via LoRa communication protocol. The developed system has been mounted and tested on a tobacco plant, reporting strong and promising results.