(c) Fig. 7: Relation between the base acceleration and a) tip velocity transfer function, b) piezoelectric power transfer function, c) electromagnetic power transfer function. The piezoelectric load The variations in the piezoelectric shunt resistance results in effects similar to changes in resonant frequency and damping. Fig. 8 illustrates that the optimal resistance for Piezoelectric harvesting is 100 kΩ. The optimal piezoelectric load however results in the minimum tip velocity and correspondingly minimum electromagnetic power generation. (a) (b) (c) Fig. 8: Relation between the piezoelectric load and a) tip velocity transfer function, b) piezoelectric power transfer function, c) electromagnetic power transfer function. 4 5 6 7 8 9 0 0.5 1 1.5 2 2.5 3 3.5 x 10 -5R 1 =100k, R 2 =5, =37(mm), legend: a b Frequency (Hz) E.M. power/ Base accel 2 (Kg.S) 0.15 0.29 0.74 1.47 2.94 3 4 5 6 7 8 9 0 0.05 0.1 0.15 0.2 0.25 a b =1.47, R 2 =5, =37(mm), legend: R 1 (k) Frequency (Hz) Tip vel/ Base accel (1/S) 10 56 100 330 680 1000 3 4 5 6 7 8 9 0 0.2 0.4 0.6 0.8 1 1.2 x 10 -3 a b =1.47, R 2 =5, =37(mm), legend: R 1 (k) Frequency (Hz) PZT power/ Base accel 2 (Kg.S) 10 56 100 330 680 1000 3 4 5 6 7 8 9 0 1 2 3 4 5 x 10 -5 a b =1.47, R 2 =5, =37(mm), legend: R 1 (k) Frequency (Hz) E.M. power/ Base accel 2 (Kg.S) 10 56 100 330 680 1000 471
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