Novel MEMS in-plane energy harvesting concept

Inhalt:
Conventional silicon-based cantilever harvesters with piezoelectric energy conversion provide small energy conversion bandwidth and might show mechanical failure due to mechanical shocks. To overcome those limitations, a new in-plane concept is proposed. A seismic mass is supported by springs on either side, which allow for in-plane displacement and out-of-plane rotational motion. Multiple cantilever connect the mass to the surrounding frame. In-plane shocks or vibrations cause a torsion of the mass and deformation in the cantilever, which generate a voltage in the piezoelectric layer deposited on top of it. Introducing nonlinear behaviour makes the concept ideal for low power consumer applications that operate in the low acceleration range. Simultaneously, the concept provides resilience against accidental drops or potential damages during shipping. Cantilever harvesters are supposed to operate in the linear regime of the employed materials. Furthermore, modelling techniques most often assume small displacements and thus benefit from linear device behaviour. To ensure stability of the harvester with respect to excessive excitation amplitudes, one commonly introduces displacement limitations which compromise the power output. This can be overcome by suspending both the mass and the opposite end of the cantilever by torsional springs. This drastically increases the device’s stiffness in the out-of-plane direction and improves overload stability. The asymmetric mass distribution now renders the device sensitive to energy harvesting from in-plane excitation. The induced tilt of the mass causes the cantilever to bend, which introduces stress in the piezoelectric material. The double-clamped suspension is optimized to create a homogeneous stress distribution to achieve maximum output voltage.