Can I replace the wet electrodes in EEG Electrode Cap by dry electrodes?
I will need the EEG Electrode Cap in order to record EEG of hockey players while they are on the field (it can sit underneath the helmet). The OpenBCI cap (as shown on website) already has wet electrodes in it. May I buy it with the wet electrodes replaced by dry ones or may I change the electrodes by myself after buying the cap? If I can change the electrodes by myself, what is the dimension of the holes so that I will design the electrodes with that specific size?
Thanks a lot.
Comments
I agree 100% w/ @wjcroft.
Are they really going to play a hockey game? I am going to guess you are not part of a university b/c no human use IRB would allow this. There are major safety concerns. Any conventional electrodes placed under the helmet would get jammed into the head in the event of a crash. And lets face it, crashes are a key part of hockey!
The problem is that all conventional COTS dry electrodes are hard - based on either metal, or flexible plastic. These are already uncomfortable - but pose a serious safety hazard if jammed into the head.
Also - you can expect hat the data will be terrible. Motion artifacts galore. I hope you have a good analysis plan for dealing with the noise.
Now... if you are adventurous... there may be a solution. How much hair do your subjects have?
If you have access to a basic lab, you could design and mold your own carbon nanofiber silicone polymer electrodes, so that they are soft and squishy. We have published the formula here:
https://ieeexplore.ieee.org/abstract/document/8513428
Note, importantly, they will require adding (painting?) a layer of AgCl onto them to stabilize the electrical connection to the scalp. We have previously molded them into a cylinder, kind of like a pencil eraser, so that they fit he pods made for gel, and just carefully moved aside the hair to make a connection.
Our experience is that anything over ~5-6% filler is pretty stable. If you haven't seen it already, there is more information on the formulation process and mechanical properties here:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0189415
re: filler concentration, it's really a matter of how you want to trade off the mechanical stiffness/pliability for conductive stability. 8% filler for example is pretty firm - more like a pencil eraser - and pushing the boundaries to get the material into a mold for curing. But it is the most stable.
If you want to make geometries with "fingers" for penetrating hair.... good luck. This is not an easy task. The problem is that you need pretty substantial stiffness in order to push hair out of the way and make good contact, but the workability of the material at that level of stiffness is challenging. And you then are into the domain of not bein gas comfortable due to lack of pliability. In our experience you can easily make electrodes that are soft and comfortable, but do not get through hair well, or make them so they get through hair, but comfort goes way down. The sweet spot between these two is a magical unicorn.
Regarding how we mounted hem - we designed a little cylinder "cup" device that had a small hole in the top, then fit a standard 2-part snap connector to it going through either side of the hole, and crimped it together. Then painted it in silver paint. With this we could then slip either our CNF-PDMS electrode in cylinder form into the cup, or use a HydroDot in the cup.
I have uploaded a copy of a poster from SfN last year here
https://www.researchgate.net/publication/333631171_Quantifying_performance_of_pliable_dry_polymer_electrodes
There are some images there that might help a little bit with the visualization. Wit hall of the interest in the polymer formulation, we will probably set up a page on Open Science Framework detailing our work and papers so others can duplicate it. Heck, maybe I should write an article for here....