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MEMS chip harvests energy from car tires

Posted: 09 Dec 2011 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS? energy harvester? pressure sensor? car tire?

A shock-induced MEMS device that can harvest energy from vibrations in car tires has been announced by Imec. According to the research center, the maximum output of the harvester that could power built-in sensors reached 489?W.

Imec's harvester includes a cantilever with a piezoelectric layer sandwiched between metallic electrodes, forming a capacitor. At the tip of the cantilever, a mass is attached that translates the macroscopic vibration into a vertical movementputting strain on the piezoelectric layer and generating a voltage across the capacitor. Aluminum nitride (AlN) was used as the piezoelectric material. The harvesters are packaged with a 6in wafer scale vacuum packaging process. The micromachining production process is compatible with low-cost mass-production fabrication.

MEMS energy harvester

MEMS energy harvester generates power from vibrations inside tires.

Together with an automotive partner, Imec validated the use of the harvester in car tires. These submit the harvester to regular shocks, depending on the car's speed and the characteristics and condition of the tire. Each shock will displace the mass, after which it will start to ring down at its natural resonance frequency. During this ring-down period, which depends on the quality factor Q of the harvester, part of the mechanical energy is harvested. It is shown that in this way, a constant power output as high as 42?W can be harvested at a speed of 70km/h.

Micromachined vibration harvesters such as these are ideal devices to generate electricity from machines, engines and other industrial appliances that vibrate or undergo repetitive shocks. In these environments, they will power miniaturized autonomous sensor nodes, in situations where battery replacement is inconvenient. The energy harvesters will allow sustainable monitoring on a massive scale, added Imec.

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