In the framework of Holst Centre, IMEC
has developed a battery-free wireless 2-channel EEG* system powered by a hybrid
power supply using body heat and ambient light. The hybrid power supply combines
a thermoelectric generator that uses the heat dissipated from a person's
temples and silicon photovoltaic cells. The entire system is wearable and integrated
into a device resembling headphones. The system can provide more than 1mW on
average indoor, which is more than enough for the targeted application.
Thermoelectric generators using body heat typically show a drop in generated
power when the ambient temperature is in range of the body temperature. Especially
outside, the photovoltaic cells in the hybrid system counter this energy drop
and ensure a continuous power generation. Moreover, they serve as part of the
radiators for the thermoelectric generator, which are required to obtain high
Compared to a previous EEG demonstrator developed within Holst Centre, which
was solely powered by thermoelectric generators positioned on the forehead,
the hybrid system has a reduced size and weight. Combined with full autonomous
operation, no maintenance and an acceptable low heat flow from the head, it
further increases the patient's autonomy and quality of life. Potential
applications are detection of imbalance between the two halves of the brain,
detection of certain kinds of brain trauma and monitoring of brain activity.
The system is a tangible demonstrator of Holst Centre's Human++ program
researching healthcare, lifestyle and sport applications of body area networks.
Future research targets further reduction of the power consumption of the different
system components of the body area network as well as a significant reduction
of the production cost by using micromachining. Interested parties can get more
insight in this research or license the underlying technologies through membership
of the program.
The thermoelectric generator is composed of six thermoelectric units made up
from miniature commercial thermopiles. Each of the two radiators, on left and
right sides of the head, has an external area of 4×8cm² that is made
of high-efficiency Si photovoltaic cells. Further, thermally conductive comb-type
structures (so-called thermal shunts) have been used to eliminate the thermal
barrier between the skin and the thermopiles that is caused by the person's
hair on the thermoelectric generator.
The EEG system uses IMEC's proprietary ultra-low-power biopotential readout
application-specific integrated circuit (ASIC) to extract high-quality EEG signals
with micro-power consumption. A low-power digital-signal processing block encodes
the extracted EEG data, which are sent to a PC via a 2.4GHz wireless radio link.
The whole system consumes only 0.8mW, well below the power produced to provide