This work reports the design and electromagnetic optimization of a MEMS-scale turbo generator for harvesting fluidic energy in human exhalation. The device is composed of a turbine with dual -layer integrated permanent magnets, ball bearings, and stators with micro coils. For an efficient energy conversion, number of magnetic poles should be optimized to obtain maximum flux density in a given device geometry, where magnetic reluctance and leakage act as two competing effects. This optimization has been performed for different commercially available magnet thicknesses with fixed inner and outer radii of 2 mm and 8 mm, respectively. It has been shown that the optimum number of poles for 0.5 mm -thick magnets is 28, while pole numbers as high as 32 lead to higher flux densities for thinner magnets. The results presented here shed light on the efficient design of magnetic micromachines in similar scales. (C) 2014 The Authors. Published by Elsevier Ltd.