An energy-autonomous battery-less sensor module is presented, entirely powered by a piezoelectric energy converter driven by mechanical vibrations from the environment. The module manages and stores the converted energy, interfaces to one or more passive sensors and periodically sends the corresponding measurement signals over a radio-frequency (RF) link. As an additional variant, the module can send a programmable identification (ID) code on the RF carrier, in order to enable module tagging and tracking by the external receiver unit. The module's general architecture is presented and the strategy used for sensor signal conditioning and transmission is illustrated. The architecture and principle have been experimentally validated on a fabricated prototype including a piezoelectric bimorph converter, two passive sensors made by a resistive-capacitive sensor pair and purposely designed electronic circuitry based on low-power off-the-shelf components. In the tested experimental conditions, the prototype features a typical time interval between measurement-and-transmission events of a few tens of seconds, with event durations of the order of tens of milliseconds, corresponding to an operation duty cycle of the order of 0.1%. Peak power consumption during transmission is of the order of 20 mW and operative range is of the order of meters in a laboratory environment. The obtained results show that the proposed approach has attractive characteristics because of the total absence of batteries and, despite the inherent intermittent operation, provides significant measurement performances in terms of achievable sensitivity and resolution.
