It is a pair of dry electrodes wired to a 3.5mm jack. Each electrode consists of a small printed circuit board (PCB) wrapped into conductive soft silicone. The silicone component has spikes to go thru hair when attached to head.
The main circuit of the active electrode is a unity gain amplifier to buffer very low level EEG signals. This model has advantages comparing to passive electrodes:
- The electrode doesn’t require skin preparation and special paste (to lower impedance between electrodes and skin) improving user comfort. Thanks to amplifier’s very high input impedance, which allows using of dry electrode without affecting signal quality.
- Low output impedance of the amplifier almost completely eliminates cable motion artifacts.
- Because path to the first amplifier stage is very short, the electrode has minimal stray-capacitance.
- Low output impedance of the amplifier allows you not to use low noise heavy coaxial cables and plugs.
- Safety. Since the dry skin impedance is very high, then the isolation barrier is much higher and chance for an electrocution is much smaller comparing to passive electrodes.
When connected to a single ended input of the main unit the electrode at short wire corresponds to the lower channel number and at long wire – to the higher channel number. E.g., if a pair of electrodes attached to socket “1 & 2”, then electrode at short wire is channel 1 and electrode at long wire – channel 2.
When connected to a differential input of the main unit the electrode at short wire corresponds to negative line and at long wire – to positive line of the input channel.
There is a special pair of electrodes with a clip at long wire and normal soft silicone electrode at short wire. It must be connected to “REF / BIAS” socket of the main unit. The electrode at short wire is a reference (see 3.1.Analog Biopotential Inputs) and at lone wire with a clip – bias (see 3.2.Device Analog Outputs).
There are 2 types of active electrodes: Dry Active EEG (black color) and Dry Active EEG+ (orange color) Electrodes. They come with EEG Only Dev Kit and EEG+ Dev Kit respectively. The difference that Dry Active EEG+ electrode has an extra circuit to disconnect electrode’s input. It is necessary when tES enabled and EEG electrodes left on head. So, EEG electrodes don’t create wrong paths for tES current.
If electrode is used with a third party EEG system, please, follow this specification:
- Tip: Short end electrode
- Ring: Long end electrode
- Ring: Power (+)
- Sleeve: Power (-)