Futurists often talk about a world where millions of sensors can gather data and feed them into the Internet.
There's only one problem: who will change the batteries?
Researchers at the CEA in Grenoble (France's atomic energy commission) have published a paper at the International Solid State Circuits Conference that could go a long way to answering that question. The group has come up with a micro charging system that gathers energy from the ambient environment.
The device consists of two power supplies (a radio frequency generator and a thermoelectric generator), power converters for the generators, a power supply manager and a microbattery for storing the harvested energy. The microbattery itself consists of thin films piled on top of a silicon chip.
"Autonomous devices that are self-powered over a full lifetime, by extracting their energy from the environment, are crucial for applications such as ambient intelligent," the group wrote in a summary of the paper.
Charging the battery from thermoelectric energy is preferable, the group stated. It requires no human intervention, and there are no moving mechanical parts. Thermoelectric charging relies on the Seebeck effect, which states that heat can be converted into electrical energy when a temperature differential exists between two pieces of metal in a closed system. The thermoelectric generator in CEA's prototypes have an output of four milliwatts per centimeter square for every (Celsius) degree difference.
The power monitor inside the harvesting system consumes energy, but only a few nanowatts. As a result, 78 percent of the energy absorbed by the device can be stored to the battery.
EnOcean in Germany is similarly working on commercial applications for self-charging sensors.