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