Researchers have used electroencephalography (EEG) as a window into the activities of the
brain. High temporal resolution coupled with relatively low cost compares favourably to
other neuroimaging techniques such as magnetoencephalography (MEG). For many years
silver metal electrodes have been used for non-invasive monitoring electrical activities of
the brain. Although these electrodes provide a reliable method for recording EEG they
suffer from noise, such as offset potentials and drifts, and usability issues, e.g. skin prepa-
ration and short circuiting of adjacent electrodes due to gel running. Low frequency noise
performance is the key indicator in determining the signal to noise ratio of an EEG sensor.
In order to tackle these issues a prototype Electric Potential Sensor (EPS) device based on
an auto-zero operational amplifier has been developed and evaluated. The absence of 1/f
noise in these devices makes them ideal for use with signal frequencies ~10Hz or less. The
EPS is a novel active electrode electric potential sensor with ultrahigh input impedance.
The active electrodes are designed to be physically and electrically robust and chemically
and biochemically inert. They are electrically insulated (anodized) and scalable. These
sensors are designed to be immersed in alcohol for sterilization purposes. A comprehensive
study was undertaken to compare the results of EEG signals recorded by the EPS with
different commercial systems. These studies comprised measurements of both free running
EEG and Event Related Potentials. Strictly comparable signals were observed with cross
correlations of higher than 0.9 between the EPS and other systems.

For exactly 90 years researchers have used electroencephalography (EEG) as a window into the activities of the brain. Even now its high temporal resolution coupled with relatively low cost compares favourably to other neuroimaging techniques such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). For the majority of this time the standard electrodes used for non-invasive monitoring of electrical activities of the brain have been Ag/AgCl metal electrodes. Although these electrodes provide a reliable method for recording EEG they suffer from noise, such as offset potential drift, and usability issues, for example, difficult skin preparation and cross-coupling of adjacent electrodes. In order to tackle these issues a prototype Electric Potential Sensor (EPS) device based on an auto-zero operational amplifier has been developed and evaluated. The absence of 1/f noise in these devices makes them ideal for use with signal frequencies of ~10 Hz or less. The EPS is a novel active ultrahigh impedance capacitively coupled sensor. The active electrodes are designed to be physically and electrically robust and chemically and biochemically inert. They are electrically insulated (anodized) and scalable. A comprehensive study was undertaken to compare the results of neural signals recorded by the EPS with a standard commercial EEG system. These studies comprised measurements of both free running EEG and Event Related Potentials (ERPs). Results demonstrate that the EPS provides a promising alternative, with many added benefits compared to standard EEG sensors, including reduced setup time, elimination of sensor cross-coupling, lack of a ground electrode and distortion of electrical potentials encountered when using standard gel electrodes. Quantitatively, highly similar signals were observed between the EPS and EEG sensors for both free running and evoked brain activity with cross correlations of higher than 0.9 between the EPS and a standard benchmark EEG system. Future developments of EPS-based neuroimaging include the implementation of a whole head ultra-dense EPS array, and the mapping of distributions of scalp recorded electrical potentials remotely.

Low frequency noise performance is the key indicator in determining the signal to noise ratio of a capacitively coupled sensor when used to acquire electroencephalogram signals. For this reason, a prototype Electric Potential Sensor device based on an auto-zero operational amplifier has been developed and evaluated. The absence of 1/f noise in these devices makes them ideal for use with signal frequencies ~10 Hz or less. The active electrodes are designed to be physically and electrically robust and chemically and biochemically inert. They are electrically insulated (anodized) and have diameters of 12 mm or 18 mm. In both cases, the sensors are housed in inert stainless steel machined housings with the electronics fabricated in surface mount components on a printed circuit board compatible with epoxy potting compounds. Potted sensors are designed to be immersed in alcohol for sterilization purposes. A comparative study was conducted with a commercial wet gel electrode system. These studies comprised measurements of both free running electroencephalogram and Event Related Potentials. Quality of the recorded electroencephalogram was assessed using three methods of inspection of raw signal, comparing signal to noise ratios, and Event Related Potentials noise analysis. A strictly comparable signal to noise ratio was observed and the overall conclusion from these comparative studies is that the noise performance of the new sensor is appropriate.