EVALUATION OF ULTRASONIC ACTUATION/VIBRATION FOR LONG-TERM CONTACT IMPROVEMENT OF DRY EEG
EEG electrodes are dumb. Although being used for decades now, EEG electrodes actually are nothing more than metal contact pins made, for example, from silver/silverchloride. Sometimes, the EEG electrodes are upgraded with active shielding providing the only intelligence they have. In addition, they need to be operated with a moisturizing gel. However, this gel is very inconvenient for use in BCI settings, in which the EEG electrodes are applied to the head of the patient for many hours, because the gel impedance changes as it dries, and because the setup requires frequent hair washing. Consequently, dry electrodes (without gel) can be the solution to long term measurements. Nevertheless, they are prone to high pin-skin impedances and sensitive to movement artifacts, both of which lead to low quality recordings.
To tackle this problem, the exploratory project Shiver with Anticipation proposes a different and risky solution: to test whether an ultrasonic stimulation of the dry EEG electrodes can lead to a better performance, and thus, to improved long-term measurements of electric signals of the brain. To do so, we have integrated 4MHz piezoelectric transducers in self- made dry electrodes, and performed experiments with a salt- loaded Agar that simulated the human skin. However, we could not reach any conclusions from these measurements due to the simplified nature of the Agar compared to the human body.
Consequently, we performed additional experiments with humans, in which we compared the performance of our dry electrodes with and without ultrasound. The preliminary results showed that an ultrasonic excitation of the EEG electrodes did not improve the quality of the measured signal in the short term. Nevertheless, further and more extensive experiments should be made to decisively assess whether ultrasonic excitation could be beneficial for the performance of dry EEG electrodes.