December 8, 2011 — Imec and Holst Centre micromachined a vibration-energy harvester with 489µW output power, using piezoelectric material in a MEMS cantilever. The team presented results at IEEE’s International Electron Devices Meeting (IEDM) this week in Washington DC.
Also read: imec’s IEDM papers reach "record number"
Shock-induced energy, as well as vibration, is harvested by the micro electro mechanical systems (MEMS). One application is energy harvesting in car tires, where the device could power built-in sensors. At 70km/h, the energy harvesters were shown to deliver a constant 42µW.
The harvester design sandwiches a piezoelectric (aluminum nitride) layer between metallic electrodes in a cantilever structure, forming a capacitor. A mass is attached to the cantilever tip, translating the macroscopic vibration into a vertical movement and straining the piezoelectric layer. This generates a voltage across the capacitor.
The harvesters are packaged with a 6" wafer-scale vacuum packaging process. The micromachining production process is compatible with low-cost mass-production fabrication.
The harvester has a record output power of 489µW when the vibrations closely match the MEMS’ resonance vibration, which in this case is 1011Hz. An automotive partner joined with imec to validate the harvester for use in car tires. Depending on car speed and road conditions, the tires — and energy harvesters — receive regular shocks, diplacing the mass. When the mass rings down at its natural resonance frequency, part of the mechanical energy is harvested.
MEMS that harvest machine or vehicle vibration can be used to power miniaturized autonomous sensor nodes, in situations where battery replacement is not sustainable or practical. Harvesters will allow sustainable monitoring on a massive scale. One example is Tire Pressure Monitoring Systems (TPMS) and its successors: a car tire with built-in sensors that monitor e.g. the tire integrity and pressure, the road condition, or the driving style.
Imec performs world-leading research in nanoelectronics. Learn more at www.imec.be.
Holst Centre is an independent open-innovation R&D centre that develops generic technologies for Wireless Autonomous Transducer Solutions and for Systems-in-Foil. Visit www.holstcentre.com.