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As worldwide awareness about global climate change spreads, green electronics are becoming increasingly popular as an alternative to diminish pollution. Thus, nowadays energy efficiency is a paramount characteristic in electronics systems to obtain such a goal. Harvesting wasted energy from human activities and world physical phenomena is an alternative to deal with the aforementioned problem. Energy harvesters constitute a feasible solution to harvesting part of the energy being spared. The present research work provides the tools for characterizing, designing and implementing such devices in electronic systems through their equivalent structural models.

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Low power electronic systems, whenever feasible, use supercapacitors to store energy instead of batteries due to their fast charging capability, low maintenance and low environmental footprint. To decide if supercapacitors are feasible requires characterising their behaviour and performance for the load profiles and conditions of the target. Traditional supercapacitor models are electromechanical, require complex equations and knowledge of the physics and chemical processes involved. Models based on equivalent circuits and mathematical equations are less complex and could provide enough accuracy. The present work uses the latter techniques to characterize supercapacitors. The data required to parametrize the mathematical model is obtained through tests that provide the capacitors charge and discharge profiles under different conditions. The parameters identified are life cycle, voltage, time, temperature, moisture, Equivalent Series Resistance (ESR) and leakage resistance. The accuracy of this electro-mathematical model is improved with a remodelling based on artificial neuronal networks. The experimental data and the results obtained with both models are compared to verify and weigh their accuracy. Results show that the models presented determine the behaviour of supercapacitors with similar accuracy and less complexity than electromechanical ones, thus, helping scaling low power systems for given conditions.

Discontinuous loads frequently compromise the performance of their power source and electronics. They cause the voltage and current ripple at the source and load, and introduce electromagnetic interferences. Also, they affect the efficiency of the power source. The aforementioned issues are particularly relevant in battery powered electronics. In order to minimise these unwanted effects, it is necessary to introduce a power supply architecture between the load and the source that should filter and/or regulate the currents and voltages. This architecture could be made solely of passive components or could use DC-DC regulators. The present work classifies and characterises the most relevant architectures available. A novel switched power supply architecture for pulsed loads with adaptive input current is also introduced. A mathematical analysis of the conditions and characteristics that the regulated architectures should fulfil to obtain the maximum performance in terms of efficiency and green electronics is provided. The simulation and experimental results shown in this study demonstrate the theoretical analysis.

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