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Advanced modeling of AlN-based micromachined energy harvesters driven by β-emitting radioisotopes

This work presents mathematical modelling of unimorph and bimorph AlN piezoelectric micromachined harvesters utilizing an energetic electron source - amenable to powering miniaturized devices such as MEMS(micro electro mechanical system) sensors. Tritiated silicon, as the energetic electron source, is appropriately aligned under a cantilever structure such that the emitted electrons are trapped by the collecting surface of the cantilever, thereby rendering it negatively charged while the electron emitting surface becomes positively charged. As a result, the attractive electric force causes the cantilever to bend towards the electron emitting surface until it makes contact and is discharged, and thus the cantilever snaps back. The resulting energy from the piezoelectric capacitor is rectified to provide electrical power to MEMS devices. Detailed electromechanical analysis and modelling of unimorph and series and parallel bimorph architectures are presented. Very good agreement between the results of the analytical model and the available experimental findings is demonstrated, thus providing assurance for the optimization study of tritiated silicon radioisotope excited piezoelectric energy harvesters.