15:00 18 April 2008
NewScientist.com news service
Phil McKenna
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.
A previous prototype relied on that alone, but was sometimes short of power.
"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.
Adding two solar panels to the device can address that. "Typically in such conditions you have more sunlight, so the solar generator compensates for the low thermoelectric power." The solar panels also have heat sinks that cool the device to preserve the thermal gradient needed by the thermoelectrics.
The new headset is also more comfortable. The original had to cover the skin of the forehead to harvest heat. The new version uses comb-like structures to collect body heat through hair, and is worn like a pair of headphones.
Power supplied
The new headset can generate at least 1 milliWatt of power in most circumstances. That is more than the 0.8mW needed to detect electrical activity observed in the brain, and transmit it over wifi to a computer.
"Using both power sources, you get twice as much power, so it's roughly half the size," say Chris van Hoof, also of IMEC, comparing the new headset to the previous device.
Van Hoof says small, preclinical trials show the headset collects data identical to those of EEGs used in hospitals. The portable headset should provide a look at the brain in environments it has not been studied in before.
Bedtime brains
The low weight and mobility of the latest device would make it ideal for providing biofeedback on soldiers, says Van Hoof.
Cars able to track the brainwaves of drivers can reduce people's mental workload at times of stress by responding to brain states. A portable headset could make that possible on the battlefield or in other areas.
It could also be used to monitor patients at risk of seizure or as an interface for computer games.
Van Hoof says one immediate application is to allow studies of sleep in people's own homes, instead of in hospital wards where sleep patterns can be disturbed. "The more portable and unobtrusive the system, the more true to life the data will be," he says.
Bright future
Arthur DiMartino, of medical technology company TechEn in Milford, US, says perfecting such small autonomous power sources could open up a host of new applications.
"This shows the evolution of what is coming," DiMartino says. His company has developed a bedside device to monitor brain activity by using near-infrared spectroscopy to image blood flow within the brain.
"If your body can provide the basic power, then there are a myriad number of devices, ranging from brain stimulation to glucose monitoring systems, that become much more practical for long term, continuous use," DiMartino says.
The Human Brain - With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
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