Researchers at Noise in Physical System (NiPS) Laboratory of the University of Perugia and INFN Perugia, Italy have developed an extreme low power energy rectification, storage and management circuitry that is used to power a small digital wireless sensor with a piezoelectric non-linear bi-stable vibration energy harvester for automotive application. They designed all the system with off-the-shelf components that sends data in the 2.4 GHz band.
In an article published at the Journal of Wireless Sensor Network (JWSN), Francesco Orfei, Igor Neri, Helios Vocca and Luca Gammaitoni presented a comparison between linear and a non-linear energy harvester, and also presented in simplicity the advantages of using a nonlinear energy harvester with a small microcontroller and a radio frequency transceiver in the 2.4 GHz band. All together they compose a complete energetically autonomous wireless sensor. According to Francesco ‘This wireless sensor can be used in all the situations where extreme low power consumption is mandatory. In particular, we have proposed an autonomous wireless sensor powered only by the vibrations generated by different vehicles on different roads with no requirement of batteries on board.” The block diagram of their system is shown in Figure 1
The bottom side of the proposed sensor is depicted in Figure 2. On the lower left corner four diodes make the rectifier bridge. On the lower side, from left to right, take place the voltage regulator, the voltage supervisor and the FET switch. The capacitances of the capacitors in the center of the picture are, from left to right, is 100 µF, 100 µF and 1000 µF.
The proposed device circuitry has been realized and tested with different vibration time series. The global quiescent current requirement at variable input voltages is a peak in the current required when the voltage is below the nominal 3.3 V of the voltage regulator output. According to the researcher, ‘this is due mainly to a not perfectly predictable behavior of the electronic components, especially the voltage regulator and will be the subject object of future researches.
This device is an evolution of the Hybrid Autonomous Transceiver – HAT, a wireless sensor node composed by a microcontroller and a radio frequency transceiver in the 2.4 GHz band powered with a nonlinear bi-stable vibration energy harvester and solar cells. When vibrations are not strong enough, the solar cells can help powering the circuitry. This can happen, for example, when a car is stopped at traffic light or the engine is turned off. The full article can be read in the open source Journal of Wireless Sensor Network with contacts of the researchers for possible collaboration.