Design and analysis of novel microelectromechanical systems for energy harvesting and nanopositioning applications

Microelectromechanical systems (MEMS) continue to transform many areas of modern science and engineering, with an increasing number of applications enjoying the benefits of miniaturisation, low-cost volume fabrication and streamlined system integration. This thesis presents the design and analysis of novel MEMS-based devices that have been developed within the context of two areas that remain highly active within current microscale research: energy harvesting and nanopositioning. Energy harvesting involves the generation of electrical power using energy captured from environmental sources. This energy can be used to power a standalone electrical load, reducing its reliance on conventional electrical energy sources such as batteries. Implanted biomedical devices are an example of an application that stands to benefit significantly from the use of energy harvesting devices, with surgical procedures currently being needed to replace the batteries of implanted systems on a periodic basis. In this work, the harvesting of electrical energy from an external source of ultrasonic waves is explored via a number of novel MEMS-based energy harvesters. Through the use of innovative multi-degree-of-freedom harvesting structures, the generation of electrical energy from vibrations induced by an external ultrasonic transmitter is demonstrated. This concept can be applied to biomedical systems, with an integrated MEMS ultrasonic energy harvester potentially being able to supply electrical power to an implanted device. As the second application explored in this thesis, nanopositioning involves mechanically displacing a stage or other structure using high-precision motion with nanometre resolution. This is conventionally done using macroscale nanopositioning devices, however increasing interest is being shown in MEMS-based alternatives. This work demonstrates the implementation of novel microscale nanopositioners that feature MEMS-based actuation and sensing mechanisms. This research culminates in the demonstration of a feedback-controlled MEMS nanopositioner as the scanning stage for a commercial atomic force microscope, with a 3D image of gold features on the stage successfully being obtained by the microscope.