Working within the Holst Centre program on Micropower Generation and Storage, researchers have developed a small piezoelectric device capable of harvesting 85 microwatts of electricity from vibrations. Fabricated using MEMS technology, the fully autonomous temperature sensor generates enough power to wirelessly measure and transmit environmental data to a base station every 15 seconds.
The piezoelectric effect (from the Greek Piezo, meaning to press or squeeze) converts mechanical stress or pressure into electric current. It was first demonstrated in 1880 by Pierre and Jacques Curie using various crystals but remained somewhat of a laboratory curiosity until the development of sonar gave it its first practical application.
Probably the most familiar everyday example of the effect in action is the electric cigarette lighter, where depressing a button triggers a spring-loaded hammer to hit a crystal. The resulting electric current flows across a small spark gap and ignites the flowing gas. Other examples include ceramic cartridges on phonographs, pickups on acoustic guitars, ultrasonic transducers, quartz clocks (of course) and auto focus motors in reflex cameras.
The effect can also be used to harvest vibrational energy to power miniature devices like sensor nodes. The harvester built by IMEC (Europe’s largest independent research center in nano-electronics and nano-technology) has not only managed to generate a record 85 microwatts of power but the manufacturing process has been undertaken using cost-effective CMOS compatible micro-electro-mechanical systems (MEMS) technology.
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