Very often a signal is disturbed by artifacts and most of these are so called movement artifacts. Movement artifacts originate from two different phenomena:
- Movement of the cables
- Movement of the electrode
The movement artifacts from the cables can be solved in a very simple way; shielding the cables with the electrode signal itself.
Movement artifacts from the electrode are very often measured. They are caused by the pressure, which is exerted on the gel layer of the electrode. That pressure is modifying the double layer between the tissue and the metal (often with gel in between) of the electrode itself. This double layer is responsible for the offset of the electrode, so the offset of the electrode is modified by any pressure that is exerted on the surface of the interface. The amount of movement artifact can be minimized by using a special type of electrode, the so called micro electrodes. When an electrode is used with very small amount of gel and a very small surface for the measurement, the movement artifact is reduced considerably. The micro electrodes have much higher impedance than the standard ECG electrodes, so using this type of electrode a special amplifier system with a very high input impedance is required.