Optically Unobtrusive Zeolite-Based Dry Electrodes for Wearable ECG Monitoring

Novel dry electrodes are increasingly evolving for monitoring electrocardiograms compared to the widely used Ag/AgCl (wet) electrodes as there is no skin preparation or wet gel needed. Many fabricated dry electrodes are however opaque, and the problem of skin irritation and rashes continue to pose a concern. In this paper, an optically unobtrusive dry electrode based on the iono-electric properties of zeolite is developed and proposed for continuous electrocardiogram (ECG) monitoring. An easily moldable composite of the sodium form of nano-porous zeolite and polydimethylsiloxane (PDMS) is reported for the first time. The electrical and bio-electrical characterizations are evaluated for 24 pairs of electrodes which were fabricated with two filler materials (Zeolite 4A and 13X), two filler concentrations (4 wt% and 12 wt%), three diameters (30 mm, 20 mm, and 10 mm), and differing thicknesses. High input impedance and high conductivity of the electrodes have proven the suitability for biosignal acquisition. ECG signals are acquired using each pair of electrodes. Results related to impedance, conductivity, and SNR measurements over a frequency range up to 10 kHz are presented. Among the 24 pairs, the results indicate that signal-to-noise ratio (SNR) for Zeolite 13X/PDMS- based filler with a concentration of 4 wt% and diameter of 30 mm has the highest SNR of 42.9 dB and conductivity of $0.58 \mu \text{S}$ /mm. These electrodes are optically unobtrusive and easy to fabricate. Hence this process yields promising results for the next generation of wearable cardiovascular heart monitoring systems.