Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only ~10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes.

Today conventional gel electrodes are widely used for biopotential measurements (EEG, ECG,..) despite their important drawbacks, such as signal degradation due to gel drying, skin irritation and the time-consuming set-up. Dry electrodes overcome most of these problems, however, the rigidity of the existing metal and Ag/AgCl dry electrodes causes discomfort and pain. In this paper, flexible polymer-based dry electrodes with high user comfort are presented. They are fabricated from EPDM rubber with various additives for optimization of conductivity, flexibility and fabrication yield. The impedance of these electrodes is measured for various signal frequencies on phantoms to test reproducibility, and on human skin to evaluate the electrode-skin impedance variation between subjects. All the subjects reported that our polymer electrodes were not causing discomfort. The polymer electrodes with optimum composition show ~10 times larger normalized impedance than gel electrodes. Tests showed that skin-electrode impedance reduced significantly by skin hydration, but this effect is only temporally. The 10-fold higher impedance of our polymer electrodes allows for an easy recording of strong biopotential signals such as ECG. For weaker signals, like EEG, the electrodes need to be coupled with an active circuit to compensate for their higher impedance. EEG recordings using active dry electrodes combined with a clinical EEG recording system are promising: visual interpretation of the signals revealed clear alpha-waves when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Based on the obtained results, the polymer-based dry electrodes are promising alternatives for the rigid dry electrodes in development and the conventional gel electrodes.