Passive multi-source energy harvesting schemes

Mobile electronics have continually decreased in size; however, mobile power sources have not had comparable increases in energy density or specific energy. Researchers are considering energy harvesting technologies to reduce dependence on batteries, providing alternate sources of power. Combining multiple energy harvesters onto a single platform is a logical and practical method to increase energy output and system robustness. This study explored the dynamics of two passive, multi-source energy harvesting schemes: disparate sources of piezoelectric and photovoltaic, as well as an array of piezoelectrics. A series and a parallel topology were explored for each scheme. For both the schemes, the series topology lends itself to high-level, low-duty cycle load characteristics as it is able to achieve greater amounts of energy on a storage capacitor. The parallel topology lends itself to low-level, high-duty cycle load characteristics due to increased maximum power levels. Both the parallel and the series topologies of the array of piezoelectrics effectively combine the power from the two harvesters in the absence of differences between the two signals. The series topology is insensitive to amplitude differences, and the parallel topology is insensitive to a phase angle or a frequency difference.