In this paper, a flexible and wearable fabric-based and highly conductive wrist band with portable electrocardiogram (ECG) equipment is presented for the long-term monitoring of ECG signals. The impedance properties, skin irritation, and sensitivity are then investigated using the proposed wrist band. The wrist band was constructed using conductive fabric, a Velcro strap, a metal snap, and a nickel connector. The entire polyester fabric surface was coated with nickel, copper, and gold. The sheet resistance of the conductive fabric is 0.06 Ω/sq. It is appropriate to use a dry fabric electrode for long-term monitoring purposes, rather than a gel-based Ag/AgCl electrode. The proposed system does not require additional active electrodes, and a single-layer standard printed circuit board (PCB) was developed to allow for portable ECG signal acquisition. We measured the impedance as per the frequency change and compared the outcomes with those of Ag/AgCl electrodes. Subsequently, we measured the ECG signal and investigated the possible artifacts caused by motion. The skin-electrode impedance of the wrist band was measured and compared to the Ag/AgCl electrodes, where we found a lower impedance for the wrist band electrodes. In addition, the power spectrum of the biopotential signals obtained from the wrist band electrodes are evaluated and compared to those obtained with Ag/AgCl electrodes for estimating signal quality. The experimental results show that the proposed electrode can successfully acquire an ECG signal from the wrist when the subject is resting and fewer motion artifacts are shown when the subject moves, rendering the proposed electrode comparable with the traditional disposable and gelled Ag/AgCl electrodes.
A wearable system for real-time outpatient ECG monitoring