A woven electrode with convex structure for electrical impedance tomography

Abstract

We developed a silver/silver chloride (Ag/AgCl) woven electrode, which was woven in a convex high-density structure. The convex structure can decrease the motion artifacts caused by the slippage between human skin and the electrode. The high density can reduce the noise caused by the change of contact resistance. The model of the electrode–skin interface was proposed, and its equivalent circuit model was built, which can present an intuitive understanding of electrode design principles. Furthermore, AgCl particles were electrochemically deposited on the Ag electrode in terms of 23 schemes to optimize the deposition uniformity. The effects of deposition time, electrolyte concentration, and current/voltage magnitude were investigated. According to the result, the best combination is a constant current method, with the current at 0.01 A, the deposition time set to 300 s, and the electrolyte concentration as 0.05 M. The resistances of the deposited electrodes are qualified for impedance monitoring due to their small resistance. A bioimpedance system was assembled followed by the electrical impedance tomography mechanism. The frequency response and bioimpedance–time relationship were measured and analyzed in our bioimpedance system. The result reveals that the frequency response from ${10}^2$ to ${10}^{3.8}$ Hz presents a stable state for the convex woven electrode. The woven electrode system has a wider stable frequency band than the wet electrode. The bioimpedance of wet electrodes is stable in the initial time, whereas that of woven electrodes decreases with time. However, the wet electrode bioimpedance increases with time after 3 h, and the woven electrode bioimpedance is stable after 3 h. Both the interface capacitance and resistance have very important roles in the bioimpedance system. The woven electrode is better in long-term monitoring than the wet electrode. In addition, convex electrode bioimpedance presents less noise than the plain electrode. Therefore, the convex electrode is the best choice for the bioimpedance monitoring system.