Figure 1: Million sensors in our surroundings
We have chosen to focus our study on industry, which is one of the most economically attractive areas. In order to reduce machine downtimes, costs of maintenance and costs of broken parts replacements, more and more industrialists are interested in developing (wireless) sensor networks able to collect many information (pressures, vibrations, temperatures) from their equipment to implement predictive maintenance.
Unfortunately, it is difficult to deploy many more sensors with today’s solutions, for two main reasons:
1- Cables are becoming difficult and costly to be drawn (inside walls, on rotating parts)
2- Battery replacements in wireless sensor networks are a burden that may cost a lot in large factories (hundred or thousand sensor nodes).
As a consequence, industrialists, engineers and researchers are looking for developing autonomous wireless sensor networks able to work for years without any human intervention. One way to proceed consists in using a green and theoretically unlimited source: ambient energy.