Design of flow based micro electro mechanical systems MEMS energy harvester

Aero elastic flutter as a means of harvesting energy from ambient fluid flow is a topic of active research. (1-3) Such a design is even more crucial for micro scale devices such as MEMS, where due to scaling effects, friction becomes prohibitively high to use successful macro scale designs involving sliding such as a rotary fan. MEMS sensors require miniscule energy and powering those using batteries, whose life is a function of their size, is counterproductive to their usage as tiny sensing units. Hence the energy harvested in the manner described above can be used to power continuously operating remote MEMS sensors with application in structural health monitoring, smart dust, body prosthetics etc. One of the measures taken for increasing the efficiency of this system is to increase the vorticity of the flow before it hits the vibrating elements. This is achieved by placing a bluff body in front of the flow to generate vortex trail (G. W. Taylor, et al., IEEE Journal of Oceanic Engineering 26, 539 (2001)). Properly designed device, e.g.: one with resonant frequency equal to vortex shedding frequency would flutter in this flow with high amplitude. With a piezoelectric strip attached to this fluttering device, the vibrational energy can be converted to electrical and can either be directly used or stored in tiny rechargeable batteries. We present a systematic design of this system, with a cantilever shaped vibrating element. Using CFD based numerical analysis we determine the best design for the bluff body in providing the most turbulent flow. Using the POD modes generated for the flow field, we also determine the best location for the placement of this device. The designs are validated using coupled Fluid structure based simulations performed in Abaqus.