Fraunhofer Develops Tiny, Affordable Devices That Generate Their Own Energy

There's an increasing demand from industry and medicine for ever-smaller electronic devices to serve as mechanical gauges and human implants, so the German research institute Fraunhofer has come up with an affordable way to make miniature instruments that generate their own electricity through ambient movement.

The devices are based on piezoelectric materials, which work through what's known as "energy harvesting," gathering energy from pressure and vibrations. They are less bulky than mechanisms that require batteries and wiring, such as those used for implants. Fraunhofer will demonstrate a preliminary model at the annual Electronica trade show in Munich from Nov. 11-14.

Piezoelectric devices work this way: Ambient vibrations create a mechanical force that generates electricity by applying pressure to certain materials. The source of the vibrations can be just about anything, and the vibrations don't need to be at a constant frequency.

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Therefore these devices work not only in aircraft engines or other machinery but also the human body which, even at rest, is a riot of subtle motion, from blood pressure, heartbeat and breathing.

So far the material used in such devices has been lead zirconium-titanium composites (PZT). But another effective candidate is aluminum nitride (AIN). It not only has better mechanical properties than PZT, it's more stable and contains no lead, which makes safe to use in medical implants. And AIN is easy to include in the devices without altering the manufacturing process.

So why have piezoelectric devices so far relied on PZT instead of AIN? Because AIN can be miniaturized only so much. If devices using AIN are too small, they can't produce enough energy to operate.

Now, though, Fraunhofer scientists have established a process to break that barrier. What's more, the institute said, the new process produces more devices more quickly and is less costly than previous techniques. The process was developed at the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology (FEP).

The Fraunhofer researchers used exotic techniques and machinery to produce wafer-shaped layers that are tiled onto a sheet of silicon to create a flexible but strong layer containing AIN that can be shaped for use in increasingly miniaturized piezoelectric devices.

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The FEP researchers worked with colleagues at the Technical University of Dresden and Oulu University in Finland to test the new AIN coatings. They managed to harvest energy on small strips of the layered silicon and achieved yields of several hundred microwatts - millionths of a watt - of electricity.

Fraunhofer's project manager, Stephan Barth, conceded that this wasn't a great amount of electricity, but it's enough for low-power sensors in certain industrial applications and even in heart pacemakers.

Where more power is needed, Fraunhofer says, its researchers are adding layers of aluminum-scandium-nitrite, which, with AIN, has a higher potential for generating electricity.

By Andy Tully of Oilprice.com

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