Fluids energy harvesting system with low cut-in velocity piezoelectric MEMS

Energy harvesting from environmental vibrations has established as an effective and green solution for electric energy production. In particular, fluid flows like the wind represent a steady and ubiquitous energy source. Traditional fluids harvesters are based on huge and bulky infrastructures like turbines, with a high environmental impact and a quite high cut-in speed (higher than 3÷4 m/s) for the fluids to be harvested. Transducers based on piezo-electric devices in the micrometric scale have pushed this value down by about one order of magnitude. The development of nanostructured piezo-electric transducers in the submicrometric scale offers a new generation of devices capable of converting the energy of very slow fluids (velocities lower than 1 m/s), like human breath, thanks to their high flexibility. The electronic interface circuit demanded of harvesting the energy from such a transducer is called to sense output signals of hundreds of millivolts with power equal to few microwatts or less. Active architectures must be employed even though they suffer for a start-up phase and the power demand. For building up the circuit supply voltage in few hundreds of milliseconds with the mentioned input power, we propose the employment of two storage devices so that the powering of interface circuit is decoupled from the energy storing. For harvesting all the peaks of the input waveform down to 50 mV, a detector based on current sensing and offset rejection through AC coupling is proposed.