Tunable resonant frequency power harvesting devices

Over the past years, there has been growing interests in the field of power harvesting technologies for low-power electronic devices such as wireless sensor networks and biomedical sensor applications. Methodologies of using piezoelectricity to convert mechanical power to electric power with a cantilever beam excited by external environmental vibration were widely discussed and examined. Operating in resonant mode of the cantilever beam was found to be the most efficient power harvesting condition, but in most cases that the resonant frequencies of the cantilever beam are hardly matching with the frequency of external vibration sources. The mechanical resonant has relatively high Q factor, and thus the harvesting output will be significantly lower compared to the condition when resonant matching to external vibration frequency. A tunable resonant frequency power harvesting device in cantilever beam form which will shift its resonant frequency to match that of the external vibrations will be developed and verified in this paper. This system utilizes a variable capacitive load to shift the gain curve of the cantilever beam and a low power microcontroller will sampling the external frequency and adjust the capacitive load to match external vibration frequency in real-time. The underlying design thoughts, methods developed, and preliminary experimental results will be presented. Potential applications of this newly developed power harvesting to wireless sensor network will also be detailed.