Wearable chemical sensors: characterization of ECG electrodes with electrochemical impedance spectroscopy

Wearable monitoring systems have flooded the health and sports industry in recent years. Heart rate monitors have taken many forms, relying on a wide variety of different measurement techniques to measure the heart rate signal [1-3]. Despite these recent advancements, commercially available systems still require improvements in many aspects, including battery life, wearability and signal acquisition to become reliable monitoring systems that are comparable to current inpatient monitoring techniques [4]. Standard Ag/AgCl disposable monitoring electrodes rely on a reduction-oxidation reaction to produce clear, reliable electrocardiogram (ECG) signal for inpatient monitoring [5], however, these electrodes are not suitable for athletic monitoring in real-time, most notably for the difficulty of use. A series of non-motion electrochemical impedance experiments were conducted in order to determine the charge transfer resistance of various types of heart rate monitoring electrodes with respect to temperature. In these experiments, a textile electrode is compared against a solid-gel Ag/AgCl single use monitoring electrode, which are used as the gold standard for non-motion measurements. The test method created here will serve as a basis to evaluate future heart rate monitoring electrodes in both motion and non-motion applications.