g.SAHARA: Specs & Features
active dry EEG electrode system
Normally, the electroencephalogram (EEG) is recorded from the surface of the head with gel based electrodes to get a low electrode-skin impedance. If passive electrodes are used, the skin must be abraded beforehand to reduce the impedance. With active electrodes, which contain an amplifier inside, the electrode gel is injected between the electrode material and the skin. This allows the electrode system to be mounted more quickly.
One of the main advantages of gel based active electrodes is their robust signal quality, but the main disadvantages are the long montage time and the need to wash the cap and the user's hair after the recording. g.tec thus developed a dry electrode system that does not require electrode gel, as shown in Figure 1. The patented g.SAHARA electrode system consists of an 8 pin electrode made of a special golden alloy. The pins have sufficient length to reach through the hair to the skin. The golden alloy and the 8 pins reduce the electrode-skin impedance. The electrode itself can be connected with a clip to the active electrode system on top of it.
|Figure 1: g.SAHARA dry active electrode system||Figure 2: 2nd generation of the g.GAMMAcap with highly optimized fit to the head and very narrow joints to maximize possible electrode locations.|
EEG recordings are performed at frontal, central, parietal and occipital regions of the head, and therefore a mechanical system is required that holds the electrode on the skin with a constant pressure at every possible recording location. EEG electrodes are typically positioned according to the international 10/20 system. g.tec hence developed the 2nd generation of the g.GAMMAcap, with a total of 160 positions according to an extended 10/20 system, to allow a very flexible electrode montage, as shown in Figure 2.
- The first and only dry electrode system that works for all frontal, central, occipital, temporal and parietal sites
- The first dry active electrode available on the market
- Patented technology
- The first and only dry system successfully tested with all major BCI approaches in group studies, reported in peer-reviewed papers
- Cost range of an active EEG electrode
- Captures the whole EEG frequency spectrum from 0.1-40 Hz
- Perform EEG recordings without gel
- Mount the cap in under one minute!
- No more need to wash the hair or cap!
- Able to pick up frequency spectra for P300, motor imagery and SSVEP based BCIs
"The g.SAHARA dry EEG electrodes are extremely useful for rapid prototyping and testing of ideas before large scale experiments. The quality of the signal is sufficient for preliminary analysis up to the beta frequency range as well as for educational purposes."
- Lukas Fiederer,
University Hospital of Freiburg, DE
More Product Details
The design of the g.SAHARA electrode system allows users to just plug the electrode and the clip into the cap at the desired location. The clip fits very well in the electrode and provides the electrode a perfect hold inside the cap.
g.SAHARA electrodes are available with different pin lengths. This is very useful for different head shapes and hair thicknesses. For example, users with some hairstyles may prefer to use shorter versions at central regions and longer versions at parietal sites.
BCI and dry electrodes
Brain-computer interfaces (BCI) usually rely on the P300, motor imagery or steady-state visually evoked potentials (SSVEP), measured with the electroencephalogram (EEG), to control external devices. The EEG is measured non-invasively with electrodes mounted on the human scalp using conductive electrode gel for optimal impedance and data quality. But using gel also entails some disadvantages: long montage time, abrasion of the skin and the need to wash the hair and cap after the recording. Using gel also limits the amount of time people can wear a cap each day. Therefore, a dry active electrode system was developed and compared to gel based active electrodes. Numerous subjects performed P300, motor imagery and SSVEP based BCI experiments. Evoked potentials, event-related desynchronization, power spectrum and accuracies were compared for dry and gel based electrodes. The peer-reviewed, published studies showed that the new dry electrodes can pick up the corresponding frequency ranges of the EEG data for all three BCI approaches, and also showed that subjects' accuracy with BCI systems was about the same for gel and dry electrodes. However, the dry electrodes did not require extensive cap mounting time, skin abrasion, or hair washing. Nevertheless, dry electrodes are more sensitive to noise, movements of cables and electrostatic charges. Therefore, carefully mounting the cap and maintaining and a well controlled environment are important.
intendiX and g.SAHARA
The following video shows the montage of the g.SAHARA electrodes for a P300 BCI experiment. The P300 evoked potential depends on EEG activity in a frequency range of 0.1-30 Hz, and is therefore especially challenging for dry electrodes.