The analysis of the radiometric force for the development of an energy scavenging MEMS scale generator

The rapid integration of wireless devices into the lives and hands of nearly every citizen has created transformative change. Powering these devices remains a limiting factor prohibiting true autonomous operation. Energy scavenging, harnessing ambient energy to power a wireless device, will lead to true autonomy and provide for another level of disruptive technologies. As in any field a diverse approach to finding a solution ultimately provides the best outcome. In this work the radiometric force is investigated through experimental and numerical analysis to determine the feasibility of a MEMS scale, scavenging device supplementing the existing photovoltaic, vibrational and piezoelectric scavengers. This fluid dynamic phenomenon provides a force when a temperature gradient exists between the faces of a thin film within a rarefied gas, displacing the film, or vane, with the cold surface leading. The force is proportional to the magnitude of the temperature gradient which can be varied via incident electromagnetic energy or resistive heating. A prototype, macroscale, permanent-magnet induction generator based in the design of Crooke's radiometer serves as a test bed for the development of experimental characterization and mathematical verification providing proof-of-concept. Macroscale prototype generators are found to produce 1.96 x 10⁻² [mu]W/cm³. Dynamic analysis of kinematic and electrical behavior of the device is verified through the use of mathematical simulations. The Direct Simulation Monte Carlo method provides insight into the radiometric forces flow field characteristic, while finite element analysis determines vane temperature gradient and magnetic field intensities. A MEMS scale axial flux permanent-magnet generator driven by multiple radiometric vanes is proposed. Simulations investigating the output of various configurations through adjustments in number of poles, device dimensions, vane configuration are presented. Finally, case studies determining the performance of CPU integrated scavenging devices with 1 and 0.25 cm² die surface area designed to harness the 10 W/m² waste heat emitted by functioning integrated circuits are presented. Case study theoretical outputs' are used to provide insight into the position of radiometric generators within the energy-scavenging field. Results indicate that a device which scavenges waste heat does not produce substantial power for energy scavenging applications. However applications which seek to harness solar irradiance or electromagnetic sources of similar intensity provide enough impulse to theoretically produce a radiometric energy scavenging device.