Energy Harvesting with Micro Machines
Abstract
A device that harvests heat into usable electrical power would increase overall power efficiency and reduce costs in the armed forces. Traditional combustion engines and moving fluid systems are too bulky and expensive to be placed in many conventional systems or places. Ferroelectric materials can generate power, but only if moved from a cold sink to a hot source using a mechanical device. MEMS devices are mechanical devices made with specialized techniques with feature sizes on the micrometer scale. A MEMS device that moves in response to heat is fabricated, and is used as a mechanical base for developing an energy harvesting device. Membranes with device layers as thin as 2 micrometers are fabricated. Simulation is used to determine resonance frequencies near 100 kHz. Simulations also show the time to reach thermal equilibrium is 1 millisecond. The voltage generated on such devices is shown to be 3 volts in simulations. The ideal thickness of oxide is examined, and is equal to the thickness of the silicon layer. The completed devices show deflections from 1 to 3 microns. Applied voltage produces a deflection of .2 microns. The optimal frequency for harvesting energy is 5 hertz and produces -60 dbV.