Electromagnetic Generators for Portable Power Applications

The power source that is common to almost all electrically powered portable devices— the electrochemical battery — has failed to shrink at the same rate as circuits and sensors. While this growing disparity has been partially mitigated by the decreasing power requirements of many electronic circuits, the size and weight of portable electronic devices are increasingly dominated by electrochemical batteries. An obvious set of candidates for energy storage with higher levels of specific energy are hydrocarbon fuels, long used in transportation applications for just this reason. Several recent research efforts have sought to capitalize on the high specific energy of chemical fuels through the use of MEMS engines or turbines paired with electrical generators. Producing such a system to run efficiently on the milli- or microscale, however, poses considerable challenges in thermal and fluid management, combustion processes, and electromechanical energy conversion.

The contribution of the research presented in this dissertationis in the area of electromechanical energy conversion. The design, construction and testing of an electrical generator intended for interface with a MEMS–scale IC engine are presented.The majority of the generator structure is built at the millimeter scale from discrete parts, with only the rotor being microfabricated. We believe that this approach offers superior performance as compared to purely microfabricated generators for power outputs on the order of milliWatts and above, with only a modest penalty in massand volume.

Some of the design ideas from this millimeter scale generator are then extended to the macro scale, with focus on a power range of tens to hundreds of Watts. The application of interest is a generator for combustion-based portable power systems,and hence power density is a key metric. However, there are an enormous number of applications over a wide range of power levels — from implantable medical devices topower tools to electric vehicle drives to wind power generation — that would benefit from high-density motor or generator technology.