Browsing by Author "Struwig, Michael"

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    Modelling and optimization of linear-motion kinetic energy harvesters: two approaches
    (Stellenbosch : Stellenbosch University, 2023-03) Struwig, Michael; Niesler, Thomas; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Energy harvesting is a well-established method for extending the life of battery-powered devices, such as wildlife tracking collars. However, the operating conditions of these devices provide a number of challenges, such as size and weight constraints. They are also typically exposed to the non-harmonic forms of mechanical motion associated with animal footsteps. This renders much of the existing literature inapplicable, because it applies only to harmonic excitation. We propose a microgenerator architecture that consists of a variable number of evenly spaced magnets, forming a fixed assembly that is free to move through a series of evenly spaced coils, and is supported by a magnetic spring. Based on this architecture, we develop two microgenerator design approaches, each with their own electro-mechanical system model and optimization philosophy. The first approach assumes idealized (constant velocity) motion as a proxy for optimizing for the true, non-harmonic motion. We applied this method to design an optimal energy harvester for impulsive motion, resulting in a device with a length of approximately 125 mm and tube diameter of 11 mm that generated an average power of 3.01 mW in a 40 Ω test load from a 2.2 g impact force from a walking human test subject. The same method was applied to design a 85 mm length-constrained device, which was subsequently field-tested on a wild rhinoceros. When the animal walked slowly, this device generated an average of 0.342 mW. The second approach is based on an extended time-domain system model that, after an evolutionary parameter search, can predict the temporal behaviour of a microgenerator to within 25% of the measured load voltage RMS, for any chosen input excitation. Utilizing this model, we propose an enhanced optimization process that selects a set of energy harvester design parameters that maximizes the power delivered to a resistive load, resulting in an optimized device that is specific to any choice of input excitation. The resulting optimal design has a length of approximately 135 mm and a tube diameter of 11 mm and was found to deliver an average power of 1.526 mW to a 30 Ω load when driven by a less vigorous human footstep-like motion with a 1.5 g impact force. Finally, we introduce an open-source declarative energy harvester framework, FFS, and demonstrate how it can be used to design, simulate and optimize their energy harvester models.