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Micro/nano-actuation -- piezoelectric and graphene-based designs
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posted on 06.02.2017by Rogers, Geoffrey William
In recent times, there has been an immense push towards the miniaturisation of technologies for the purpose of micro-robotic minimally invasive surgery (MIS). The predominant factor limiting the further miniaturisation of these technologies is the existence of practical actuators that are small, powerful and versatile enough for the application at hand. This has prompted intense research into novel micro/nano-actuation techniques. However, the solutions proposed are far from optimal, particularly concerning the practical realisation of high-power sub-millimetre actuators. A complete survey of the actuation technologies available reveals piezoelectric actuators and graphene-based electro-active materials to be the most promising candidates for miniaturisation. As a result, this thesis investigates, develops and tests micro/nano-actuators based on piezoelectricity and graphene-based electro-activation. Comprehensive investigations into these two actuation technologies results in the development of new and useful micro/nano-actuators. Specifically, a diameter 350 μm three degree-of-freedom (DOF) piezoelectric micro- motor is numerically developed, and is experimentally shown to produce controlled, reversible rotation about three orthogonal axes. As this micro-motor operates via resonance, two micro-Bragg reflectors are designed and tested in order to isolate the acoustic energy of the micro-motor from its surroundings, thereby allowing it to be integrated with sensitive micro-electromechanical systems (MEMS), such as micro-guidewires. Attention then turns to the electromechanical actuation of graphene-based materials, where using a novel computational model it is shown that the high electromechanical responses (strains) of these materials in the presence of liquid electrolytes are primarily attributed to the electrostatic double-layer (EDL) effect. Given the significant response time constraints of EDL-based actuators (~1 s), this thesis presents graphene-based materials (highly-ordered compounds of graphene oxide (GO)), which are capable of producing strains as high as those of the EDL effect; but with very short response times (~1 ns), via the quantum mechanical effect alone. These GO actuators are shown to produce reversible and irreversible strains as high as 6.3% and 28.2%, respectively, with very unique responses such as electron-induced contraction, making them ideal building blocks for the development of artificial muscles. With the ever-increasing demand for smaller and more useful micro/nano-actuators, novel techniques and methods must be developed and adopted in order to pioneer the next generation of technological breakthroughs in all fields, including minimally invasive surgery.