Self-Powered Synchronized Switching Interfacing Circuits for Micro-Piezoelectric Energy Harvesters

In this work, we have combined a micro-piezoelectric energy harvester with a dedicated interfacing circuit using the non-linear switch harvesting techniques based on the concept of SSH (synchronized switch harvesting). We especially focused on the power enhancement effect of the switching technique on micro-power generators. The micro-piezoelectric energy harvester that was used in this work is based on a stainless steel substrate, which largely improved the power output capability of the device. The resonant frequency of the energy harvesting device is 117 Hz, giving a voltage output of 3.85 V under the acceleration of 0.05 g. The overall size of the harvesting device is merely 8*6*0.5 mm³, including the proof mass. In order to further enhance the power generation abilities of the micro-generator, non-linear electrical interface circuits have also been designed and tested on two devices. According to the value of the figure of merit given by the product of the squared coupling coefficient k² by the mechanical quality factor Q_M, a significant power gain compared to standard energy harvesting interface up to 3.13 has been tested for the device featuring a k²Q_M value of 0.17. A gain of 1.85 for a device with a k²Q_M value of 0.42 was also found. All of which were in good agreement with theoretical predictions. Furthermore, in order to be as close as possible to the realistic implementation of the micro-generators, the above mentioned nonlinear interface circuit were implemented in a self-powered design (i.e., without requiring an external energy source) using a very small part of the energy available generated from the piezoelectric energy harvester. Using the self powered technique, the overall system was available to provide 91.4 μW, with accelerations around 0.75 g, under the condition of k²Q_M = 0.72, and the power gain of 2.03.