Active electrode design suitable for simultaneous EIT and EEG

Presented is an active electrode design for electrical impedance tomography spectroscopy (EITS) which contains both current stimulation and sensing pathways, and also enables the simultaneous measurement of bio-potential signals (EEG/ECG). The entire circuit is manufactured on a small circular FR4 PCB with the bottom layer forming the electrode plate. A custom sealed plastic enclosure was designed and forms a classical `cup`-shaped scalp electrode to hold the conductive paste. The proposed design is of low power, drawing 8`mW when powered at 5`V, and provides a large bandwidth (20`MHz). It has a large input impedance (`10¹⁰[Ω] // 5Ω[pF]) and is low noise (Ω300ΩnV_pp in the EEG bandwidth 0.1÷10 [Hz] and of negligible noise figure in the EIT bandwidth ÷10÷kHz). Performance was evaluated using a bench test (EIT image phantom) and in vivo recordings (EEG).