I. Introduction
An interesting alternative to batteries for feeding wireless sensor networks relies on energy harvesting systems, which are able to convert the ambient energy into electrical energy. Many types of energy harvesting sources were investigated in literature, but vibrations represent one of the most attractive, because they can be found almost anywhere in the ambient [1]–[4]. Among the different types of energy transducers, here piezoelectric cantilevers are considered, as they are widely available on the market. Thus, Piezoelectric Resonant Vibration Energy Harvesters (PRVEH s) are considered [5].