Imagine a network of sensors embedded in the pulse points of our infrastructure, in the inner workings of engines and in the most hard-to-reach areas. What if these sensors, forever vigilant, never needed battery replacements or wiring? This transformative vision takes a leap forward with a revolutionary development from MIT: a self-powered sensor that autonomously harvests magnetic energy.

Featuring in the January issue of the IEEE Sensors Journal, the sensor, instead of relying on batteries or wiring, taps into the ubiquitous, ambient magnetic field around it to produce power.

The researchers used the technology to create a temperature-monitoring sensor that uses the magnetic field produced around a wire. A miniaturized rectifier coil then efficiently converts the fluctuating magnetic field into usable electrical current.

This harvested energy then powers the sensor's internal circuitry, enabling it to perform its designated function. The sensor then sends the data to a cell phone-like interface using Bluetooth.

The project faced three key obstacles in its creation:

• The system needed to be able to cold start, with no initial voltage. This challenge was overcome using a network of integrated circuits and transistors, which allows the system to store energy once it reaches a certain threshold, and then turn on only when it has enough power to operate.
• The decision not to include a battery was the second obstacle to this sensor’s completion. The system needed to be able to convert and store energy efficiently. The sensor, therefore, has a series of capacitors that store energy in an electric field between two conductive plates.
• Lastly, the sensor must be able to turn on after weeks or months of disuse. Researchers needed to ensure that the capacitors could hold enough energy to do this, even if some energy is lost over time.

This technology is still in its infancy, but its potential is undeniable. “We have provided an example of a battery-less sensor that does something useful, and shown that it is a practically realizable solution. Now others will hopefully use our framework to get the ball rolling to design their own sensors,” said lead author Daniel Monagle, lead author of the project.