An important limitation in the classical energy harvesters based on cantilever beam structure is its monodirectional
sensibility. The external excitation must generate an orthogonal acceleration from the beam plane to induced flexural
deformation. If the direction of the excitation deviates from this privileged direction, the harvester output power is drastically
reduced. This point is obviously very restrictive in the case of an arbitrary excitation direction induced for example by human
body movements or vehicles vibrations.
In order to overcome this issue of the conventional resonant cantilever configuration with seismic mass, a multidirectional
harvester is introduced here by the authors. The multidirectional ability relies on the exploitation of 3 degenerate structural
vibration modes where each of them is induced by the corresponding component of the acceleration vector. This specific
structure has been already used for 3 axis accelerometers but the approach is here totally revisited because the final
functional goal is different. This paper presents the principle and the design considerations of such multidirectional
piezoelectric energy harvester.
A finite element model has been used for the harvester optimisation. It has been shown that the seismic mass is a relevant
parameter for the modes tuning because the resonant frequency of the 1st exploited flexural mode directly depends on the
mass whereas the resonance frequency of the 2nd flexural mode depends on its moment of inertia.
A simplified centimetric prototype limited to a two orthogonal direction sensibility has permitted to valid the theoretical
approach.
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