Wireless EEG system is powered by body heat and light

In cooperation with the Holst Centre (Eindhoven, The Netherlands), IMEC has developed a wireless 2-channel EEG system with a hybrid power source driven by body heat and ambient light. It combines a thermoelectric generator that uses heat from the subject’s temples and silicon solar cells. The entire system is wearable and resembles a set of headphones. It can supply more than 1 mW on average indoors, which is more than enough for the target application.

Thermoelectric generators using body heat typically show a drop in generated power when the ambient temperature is close to the body temperature. Especially outdoors, the photovoltaic cells counter this energy drop and ensure continuous power generation. They also act as radiators for the thermoelectric generator, which are necessary for high efficiency.

Compared with previous devices, the new EEG unit increases the patient’s autonomy and quality of life. Potential applications include detection of imbalance between the two halves of the brain, detection of certain kinds of brain trauma, and monitoring of brain activity.

The thermoelectric generator consists of six miniature commercial thermopiles. The two radiators (one on each side of the subject’s head), which are made from high-efficiency silicon solar cells, have a combined area of 9.6 cm². Thermally conductive comb-type structures are used to eliminate the thermal barrier between the skin and the thermopiles due to the subject’s hair.

The EEG system uses IMEC’s proprietary ultra-low-power ASIC for biopotential readout applications to extract high-quality EEG signals. A low-power DSP encodes the extracted EEG data, which are sent to a PC via a 2.4-GHz wireless link. The entire system consumes only 0.8 mW, well below inherent capacity of the power source.