A lightweight battery-free headset can continuously monitor human brainwaves, and is powered by body heat and sunlight.

The portable electroencephalogram (EEG) device resembles a set of headphones. It could provide wireless monitoring of patients at risk of seizures, have cars or other machinery respond to stressed users, or provide new ways to interact with computer games.

Researchers at the Interuniversity Microelectronics Centre (IMEC), in Belgium, created the headset.

Brainwave

It generates some power using thermoelectric materials which turn heat gradients into electrical energy, using the difference between a warm human head and the cooler surrounding air.

"If there is a lot of sun, it is quite hot, the temperature difference between the body and the environment is small," says Guy Beaucarne of IMEC. That means thermoelectric materials can harvest less power.