A MEMS Device Harvests Vibrations to Power the IoT

#News(IoTStack) [ via IoTForIndiaGroup ]

Scientists in Japan have developed a MEMS energy harvester charged by an off-chip electret
Vibration-based energy harvesting has long promised to provide perpetual power for small electronic components such as tiny sensors used in monitoring systems. If this potential can be realized, external energy sources such as batteries would no longer be needed to power these components.

Scientists at the Tokyo Institute of Technology and the University of Tokyo in Japan believe they have taken a step toward achieving self-powered components by developing a new type of micro-electromechanical system (MEMS) energy harvester. Their approach enables far more flexible designs than are currently possible—something, they say, that is crucial if such systems are to be used for the Internet of Things (IoT) and wireless sensor networks.

There are three basic ways to convert vibrations to electricity in a manner suitable to power miniature components: electromagnetic, electrostatic, and piezoelectric mechanisms. The Tokyo Tech scientists favor the electrostatic method because it provides a wider choice of frequencies at the low-frequency range, and because the output power density is relatively larger.

A MEMS electrostatic energy harvester uses an electret (the electrical equivalent of a permanent magnet with a permanently stored charge) and a MEMS variable capacitor. The capacitor employs a movable electrode attached to a spring, which moves with ambient vibration.

The capacitance of the electret circuit is fixed, whereas the variable capacitor changes according to the stretching of the spring. When the amount of variable capacitor charge is larger than the fixed charge, a movement of charges between the two electrodes is induced and the variable capacitor gains charge. Likewise, when the amount of charge in the fixed capacitor on the electret is larger, there is a movement of charges in the opposite direction and its electrode gains charge. It is this movement of charges that can be harvested as electricity, according to the principle of electrostatics.

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