Power generation is limited by the generator's internal and external capacitances. Consequently, it's necessary to minimize those effects through modeling to achieve higher levels of power. Nevertheless, the researchers feel their development holds lots of promise.
POWER FROM LIQUID DROPLETS
In a novel approach to producing tiny power-generation systems, researchers at the California Institute of Technology reported on using MEMS arrays of liquid rotor electret power generators (LEPGs) to produce power.
These LEPGs are essentially fixed-charge, Teflon-coated capacitors with air-filled gaps and liquid droplets that move by vibration. As the liquid moves into and out of the gaps, a net voltage generates across the capacitor while image charges on the electrode redistribute themselves according to the position of the droplets.
Researchers studied series and parallel arrays to increase power output. They noticed that the power output from parallel arrays scales linearly, as expected, with the number of devices used. This should lead to outputs of up to 10 ±W. Researchers also noted that series arrays require further study, as they involve more complicated impedance-matching issues.
MEMS also has shown promise for making tools that will assist in creating miniature fuel cells and catalytic chemical microreactors. One such tool is a passive micro gas regulator for hydrogen flow control in miniature fuel cells. This joint development from Canon and the University of Tokyo is claimed to be the first of its kind.
According to the microregulator's developers, unlike previously reported active microregulators, this passive device makes it possible to achieve miniaturization. Its total size of just 8 by 8 by 1 mm suits it well for portable appliances.
Another important tool is a MEMS-based high-temperature-compatible nickel-silicide thermometer and heater for catalytic chemical microreactors. Developed at the Technical University of Denmark, it can operate at up to 800°C, a temperature limited only by the integrity of the Pyrex lid it uses.
What new applications will MEMS scientists think of next? Heard around the conference corridors was one comment from a Swiss MEMS researcher: "We're ready to replace all those steel precision-made gears in Swiss watches using MEMS gears." Switzerland is world-renowned for making millions if not billions of steel watch gears for the last two centuries. It remains to be seen if MEMS gears can replace them cost-effectively.