A Closed-Loop Ear Wearable EEG Measurement Device with Realtime Electrode Skin Impedance Measurement

Electroencephalogram (EEG) play a vital role in the prediction of neurological disorders including epilepsy, narcolepsy, migraine, etc. The impedance between the electrodes and the skin interface should be within specific range in order to acquire good quality EEG signals. This work focuses on an intelligent, wearable device capable of measuring electrode-skin interface impedance (ESI) in parallel to the EEG acquisition in non-invasive manner. The proposed device includes an analog front end (AFE), back-end micro-controller (BEM), and ESI measuring unit. A novel technique is used for measurement of ESI by connecting known value resistances in parallel at the input terminals of the low noise amplifier (LNA) of AFE and measuring the change in the output signal. This unique technique is suitable in wearable medical devices as it is safe to use, results in high-quality EEG signals, and consumes negligible power. A PCB prototype is developed using the available commercial components. The designed prototype has a small form factor (52mm x 53mm), is lightweight, and easily behind the ear wearable.