Electromagnetic energy harvester with high efficiency using micro-machining Si springs

The direct force input type of electromagnetic energy harvester with significantly high generating efficiency over 40% has been developed. This high efficiency was realized by using the 1mm-thick uniquely-structured Si springs in the harvester, which was fabricated by D-RIE (deep reactive ion etching) from both sides of a 1mm-thick Si wafer. The harvester showed that the peak voltage was 3.7 V and the output energy on the most adequate load resistance was over 1 mJ at an input energy of 2.7 mJ, resulting in a generating efficiency of 41%.