Human Body–Electrode Interfaces for Wide-Frequency Sensing and Communication: A Review

Abstract

Several on-body sensing and communication applications use electrodes in contact with the human body. Body–electrode interfaces in these cases act as a transducer, converting ionic current in the body to electronic current in the sensing and communication circuits and vice versa. An ideal body–electrode interface should have the characteristics of an electrical short, i.e., the transfer of ionic currents and electronic currents across the interface should happen without any hindrance. However, practical body–electrode interfaces often have definite impedances and potentials that hinder the free flow of currents, affecting the application’s performance. Minimizing the impact of body–electrode interfaces on the application’s performance requires one to understand the physics of such interfaces, how it distorts the signals passing through it, and how the interface-induced signal degradations affect the applications. Our work deals with reviewing these elements in the context of biopotential sensing and human body communication.

Me-Doped Ti–Me Intermetallic Thin Films Used for Dry Biopotential Electrodes: A Comparative Case Study

“…As expected, the impedance of dry electrodes based on Ti-Me thin films was always higher than the hydrogel-based electrodes [1]. The replacement of an ionrich electrolyte (incorporated into the hydrogel Ag/AgCl reference electrodes) by a natural perspiration interface for the Ti-Me dry electrodes increased the interfacial impedance [48].…”

“…Despite the higher contact impedance values, the overall Ti-Me nanoelectrodes' absolute impedances follow the trend exhibited by the Ag/AgCl electrodes. The higher impedance at lower frequencies, related to the capacitive components of the contact decreased at higher frequencies values [48]. Nevertheless, for the dry electrodes prepared in the Ti-and Me-rich zones on PU substrates, a partly less pronounced impedance decrease compared to the hydrogel-based reference electrodes could be observed and might be related to a change in the capacitive interface developed by these thin films [12,37,48].…”

“…The overall duration of each impedance spectroscopy per volunteer was about 5 min. Given the foreseen use of the Ti-Me thin films in the biomedical field as dry biopotential electrodes, the selected frequency values covered the frequency range of the standard biopotential signals of EEG (1-40 Hz [4]), sEMG (6-500 Hz [46]), and ECG (0.05 Hz-150 Hz up to 700 Hz [47]) [48].…”

“…The obtained results, presented in Figure 6, take into consideration the substrates used and the (micro)structural zone of the prepared films. For all tested electrodes, including the conventional hydrogel electrodes of Ag/AgCl recognized as non-polarizable in the biomedical field [37,48], the contact impedance depended on frequency. As expected, the impedance of dry electrodes based on Ti-Me thin films was always higher than the hydrogel-based electrodes [1].…”

Influence of the Electrolyte concentration and amount on the Performance of Textile Electrodes in Electrostimulation: a systematic study

“…[29] Air is an electrical insulator wherefore it cannot support the current ow to the body and the charge transfer resistance was highest for the dry electrodes. Furthermore, a direct electrode skin contact was hindered in some parts of the interface by air trapped inside which was acting as local blocking elements, as suggested by Polachan et al (2021). [44] As a result, the capacitive behavior was highest for the dry electrodes, visible in the Bode plot showing the highest phase angle for the dry electrodes.…”