Dry electrodes for bioimpedance measurements—design, characterization and comparison

Objective: Bioimpedance measurements are mostly performed utilizing gel electrodes to decrease the occurring electrode-skin impedance. Since in many measurement environments this kind of electrode is not appropriate, the usability of dry electrodes is analysed. Approach: The development of five different kinds of dry electrodes, including gold, stainless steel, carbon rubber and metallized textile as contact materials are proposed. All test electrodes are based on a circular printed circuit board as carrier and have the same contact surface dimensions. To compare the electrodes' characteristics, the occurring electrode-skin impedances are measured under variation of signal frequency, contact duration, contact pressure, placement position and subjects. Additionally, all measurements are performed with silver/silver chloride (Ag/AgCl) hydrogel electrodes for comparison purposes. Main results: The analysed parameters play a significant role regarding the electrode-skin impedance. Choosing a wise setup of these parameters can decrease the electrode-skin impedance of dry electrodes down to ranges of hydrogel electrodes and even below. Significance: The usage of dry electrodes is one of the most difficult challenges when transferring scientific measurement techniques to clinical environments or commercial products but it is indispensable for many applications like body composition measurements or prosthesis control.