Vibration energy harvesting: testing & prototyping

26Nov07

I’ve been interesting in energy harvesting for a few years and knew at the beginning of this semester that it was something i wanted to explore – little did i know how frustrating it would be. Solar seemed limiting and after much research I narrowed it down to either mems or piezo transducers. I latched onto piezo since the past research pointed to the fact that it was possible to harvest 3 to 5 volts for low power devices such as zigbee transceivers, micro-controllers or just battery recharging stations. I thought about appliances that waist much energy on excess mechanical motion because they have motors for cooling fans or compressors for refrigeration that run all day every day; even useful in trains, cars or trucks. I thought I could make three or five of these modules, simply bridge rectifiers and bucket capacitor to store the charge, and have their storage data logged into a mySQL data base and graphed on line using php or flash. I’ve even proposed making a flashlite phone app that would depict the different charge states of each module on a cell phone. Now three weeks into testing the feasibility of the piezo transducer with Evrim Sahin and Rory Nuget, on 3 different piezo’s from MSI and Smart Materials, we’ve pretty much concluded that its not effective as we initially thought. See our wiki page documenting our initial testing.

Due to their nature, piezo transducer put out high voltage spikes each time they are deflected, but very low current. Thus, it take quite a while for the the stored charge to reach any significant level. But it does work! One solution has been to use three piezos in parallel so the output current and charging rate is tripled. We are also testing a piezo made from micro-fiber composite, which alone produces as much as the tripled regular piezos. The hard part now is finding optimal environments to place these modules where they can store the electricity produced. That means significant vibration for deflection at a relatively hight frequency.

piezotest1.jpg

We have the xbee sensor network set up and working – checking the capacitor charges at regular intervals as analog values and sending them to a base station where they are stored in a mysql database via processing. We have the values pulled from the database via a php script and graphed online: example bellow

graph1.png

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