Base acceleration The experimental results for the case where the magnet distances is 27 mm has been illustrated in Fig. 10. When the base excitations are smaller than 3 m.s-2 the beam oscillates about either of the stable equilibriums. The motion is referred to as small amplitude oscillations. For larger base excitations the motion can be chaotic or limit cycle oscillations. The amount of harvested power from limit cycle oscillations is an order of magnitude larger than power from chaotic motion which in turn is an order of magnitude larger than small oscillations’ power. (a) (b) (c) Fig. 10: Relation between the base acceleration and a) power from piezoelectric patched, b) power from electromagnetic coils, c) phase portrait and Poincare map. Excitation frequency 1 2 3 4 5 6 10 -5 10 -4 10 -3 10 -2 base accel. (m.s -2 ) PZT power (Watt) small amplitude Limit Cycle chaos 1 2 3 4 5 6 10 -7 10 -6 10 -5 10 -4 10 -3 base accel. (m.s -2 ) EM power (Watt) small amplitude Limit Cycle chaos -0.04 -0.02 0 0.02 0.04 -1 0 1 1 2 3 4 5 6 base accel. (m.s -2 ) xt (m) vt (m.s -1 ) 473
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