Fwd: [BioExplorer] QDS amplifier review

[Guest guest]

Listmates,

On the BioExplorer list, the question has come up about using ActivEEG electrodes with the QDS amplifiers as I mentioned in my review. Since I really didn't know how the Activ's do what they do, and whether their approach would be inconsistent with the QDS system's commitment to staying away from high input impedances, I asked the Brainquiry guys to clarify. This response is from Martijn Arns:

the active electrodes really don't do any magic. The principle quite straight forward!

Usually when EEG is recorded it is from a high impedant source (skin), and the signal intrensity is very low in the order of 20 uV. Therefore, the wire which transmits the signal starts acting as an antenna picking up all kinds of artefacts e.g. 50-60 Hz noise, movement. Reducing the impedances below 5 kOhm will mostly eliminate these, sometimes not completely.

The active electrodes contain a buffer amplifier, hence they do NOT amplify the signal, but buffer the signal. This means that they basically reduce the impedance at the site of recording whereby a 'low impedant' signal is transferred across the wire, hence preventing the wire to act as an antenna, and delivering a noise free input to the amplifier.

This technique is quite old and well know already in research settings (e.g. animal EEG research) where this is traditionally being used to get noise free signals and prevent movement artefacts. Surpsingly we were the first party to make this technique generally available based on snap-on electrodes inside the electrode, requiring micro-electronics.

Pete