Imec, Holst Centre and Panasonic have developed a new prototype of a wireless EEG (electroencephalogram) headset. The system combines ease-of-use with ultra-low power electronics. Continuous impedance monitoring and the use of active electrodes increases the quality of EEG signal recording compared to former versions of the system. The data are transmitted in real-time to a receiver located up to 10m from the system. The realization of this prototype is a next step towards reliable high-quality wearable EEG monitoring systems.
The system integrates circuit level components including imec’s active electrodes and EEG amplifier together with a microcontroller and a low power radio. It is capable of continuously recording 8 channel EEG signals while concurrently recording electrode-tissue contact impedance (ETI). This simultaneous ETI recording enables continuous, remote assessment of electrode contact status during EEG recording. The active electrodes reduce the susceptibility of the system to power-line interference and cable motion artifacts, thus improving signal quality. The system can be configured at run-time to change the settings of the recordings such as the number of channels, or enabling/disabling the impedance recording. The autonomy of the system ranges from 22 hours (8 channels of EEG with ETI) to 70 hours (1 channel of EEG only).
The system has a high common-mode rejection ratio (>92 dB), low noise (<6 µVpp, 0.5-100Hz), DC offset tolerance of +/- 900mV and is AC coupled with configurable cut-off frequency. Sensitivity and dynamic range are configurable through a programmable gain stage (default 1.5mVpp and 366nV, respectively).The system (with dry electrodes and no skin preparation) is validated against a commercially available wired reference system (with wet electrodes and skin preparation), comparing the spectra between 1 and 30Hz. The high correlation coefficients (ranging from 0.81to 0.98 in four 1-minute recordings with eyes open) indicate that both systems have similar performance.
The heart of the system is the low-power (750µW) 8-channel EEG monitoring chipset. Each EEG channel consists of two active electrodes and a low-power analog signal processor. The EEG channels are designed to extract high-quality EEG signals under a large amount of common-mode interference. The active electrode chips have buffer functionality with high input impedance (1.4GΩ at 10Hz), enabling recordings from dry electrodes, and low output impedance reducing the power-line interference without using shielded wires
The system is integrated into imec’s EEG headset with dry electrodes, which enables EEG recordings with minimal set-up time. The small size of the electronics system, measuring only 35mm x 30mm x 5mm (excl battery), allows easy integration in any other product.