Technical Brain Wave

We all know that electronics has helped in hundreds of medical applications and been the driving force in the development of some groundbreaking equipment like magnetic resonance imaging and laser surgery. But despite these medical innovations, areas still remain in medical testing and evaluation that can only be described as archaic and uncomfortable for the patient.

One example of where technology continues to stand still involves those patients who require 24-hour monitoring to evaluate heart performance. Patients will tell you how uncomfortable it is to wear a heavy belted monitor around their waist for 24 hours.

So I was very interested when Belgian research centre IMEC sent me some information about its development of a battery-free, wireless two-channel EEG (electroencephalography or brain wave monitoring) system. A smart design aspect of the system is that it’s powered by a hybrid power supply—it uses the patient’s body heat coupled with ambient light.

The hybrid power supply combines a thermoelectric generator with silicon photovoltaic cells. This is integrated into a design that resembles headphones.

Understandably, the thermoelectric generators using body heat will show a drop in generated power when ambient temperatures drop, such as when the patient being goes outside. This is where the hybrid system’s photovoltaic cells come in. They counter this energy drop and ensure continuous power generation.

The thermoelectric generator in the system consists of six thermoelectric units made up from miniature commercial thermopiles. Each of the two radiators, on the left and right sides of the patient’s head, has an external area of 4 × 8cm2 that’s made of high-efficiency Si photovoltaic cells.

Furthermore, thermally conductive comb-type structures (so-called thermal shunts) are used to eliminate the thermal barrier between the skin and the thermopiles that’s caused by the person's hair on the thermoelectric generator.

So, what exactly will the monitoring system be used to check? 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.

A final point is that the EEG system uses IMEC's ultra-low-power biopotential readout ASIC to extract signals with micropower consumption. A low-power digital-signal-processing block encodes the extracted EEG data, which is sent to a PC via a 2.4GHz wireless radio link.

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