MEMS Generates Electricity from Body Heat and MEMS Device Harvests Enough Walking Energy to Power a GPS receiver

1. Fabrication and Characterization of CMOS-MEMS Thermoelectric Micro Generators (11 page pdf)

This work presents a thermoelectric micro generator fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 μV at the temperature difference of 1 K.

2.

A breakthrough in piezoelectric power generation is the new voltage regulation circuits that we developed at Louisiana Tech University that efficiently converts the piezoelectric charge into a usable voltage.

A conversion circuit coverts the high voltage to a regulated 3 V output for charging batteries or for directly powering electronics at better than 70% conversion efficiency. New voltage regulation circuits can convert the piezoelectric charge in a shoe into a usable voltage and combined with the polymer transducer give a time-averaged power of two milliwatts per shoe on an average walk – that’s comparable to lithium coin/button cells and enough to power running sensors, RF transponders and GPS receivers.

The generated power output can be compared to typical storage capacity of 30 mAh for lithium coin/button cells — with an average current consumption 0.5 mA, a miniature coin cell is depleted in less than three days whereas the shoe power generator gives power output as long as the user keeps walking. The total energy output can therefore easily surpass conventional batteries. In addition to running sensors and inertial navigation, the show power generator can be used to power RF transponders, GPS receivers, and locator tags that require a milliwatt power source.

FURTHER READING
Work from 2009 on energy harvesting from a knee brace.

Energy Harvesting rubber sheets

Wearable displays and the potential of harvesting energy from the body

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