Working principle Fig. 1 shows all the components of the device [3]. The scavenger is composed by a floating magnet running into a guide around which are wound in opposite direction two series connected coils so that their electromotive force is summed when the floating permanent magnet is moving. A preload magnet, inserted in the lower lid, push the floating magnet toward the upper lid. Two rubber bumpers prevent excessively rough shocks between floating magnet and lid. When the floating magnet moves along the guide the variation of the magnetic flux linked to the coils produce an electromotive force that can be used as power supply for an electrical load. Fig. 1 Energy scavenger device components When revolving around its axis, the external surface of the tire is subjected to high deformation gradients when contacting ground. This deformations lead to large variation on the radial acceleration acting on the device. Fig. 2 (a) shows a typical acceleration profile for a point on the tire inner-liner during a wheel round: acceleration is about constant (v2/R) during the larger part of the round and has a peak entering and exiting the contact zone. In the contact zone the radial acceleration is close to zero because the point is actually translating and not rotating. Fig. 2 Typical radial acceleration profile (a) and energy scavenger behavior during wheel rotation (b) 340
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