  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.
