Simulation of the analog part.

Well, it’s first post in this blog. I’ll start from my current project – mobile EEG brain activity classifier, based on neural network. I made some calcutations of analog parts. Below you can see a circuit diagram.

Special attention should be given to the equivalent circuit of contact between the electrodes and the head. I used the basic circuit [1]. My signal propagation model of brain (Fig. left) doesn’t take into account the reactive components.

The electrode attachment points are shown in Fig. rihgt. Electrodes 1,2 (brass, area ~ 1.5 cm2) are fixed on the forehead at a distance of 2-3 cm. The reference electrode is fixed as close to the occipital part of the skull as possible (the proposed site of installation). To calculate the resistances, 2 measurements were taken (Fig. below).

                                                                  Assuming the resistance of the contacts to be equal (by cleaning the skin with alcohol), and solving a trivial equations system, it is easy to find the corresponding resistances.

Below are the frequency response and the FFT of 10 Hz sinusoidal signal at various points in the circuit. As can be seen from the FFT, the signal-to-noise ratio in the main working frequency band (1-100 Hz) at the input (~ 80 dB) and the output (~ 70 dB) is not too different.

Please, if you have any comments about the material, please contact me via the “Contact” section.

Reference:

  1. Jiawei Xu, Low-power active electrode for Wearable EEG, Page 5.
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2 thoughts on “Simulation of the analog part.”

  1. Hello! I have a work question: the EEG procedure is used to detect the smallest electromagnetic bursts in the brain, so doctors use a “cap” with a lot of holes for some numbers of electrodes. Your device uses 2 electrodes for the frontal lobe and the n-th number for the parietal lobe. Do not you think that it will not be enough for a complete and more accurate assessment of the brain’s activity? Thank’s for the answer!

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    1. Hello Anna!
      Thanks for asking. Indeed, in medicine and brain research, electroencephalographs are used that can record hundreds of channels (each channel contains 2 electrodes). The accuracy of brain activity mapping depends on the number of channels. But even using one channel, one can register epileptiform activity of the brain.
      Since my development belongs to the class of portable devices, the increase in the number of channels inevitably leads to an increase in the dimensions, weight of the device and its cost. Therefore, the number of channels is limited. The key task facing my research is the search for an optimal method of processing information in real time, which is incredibly complicated in portable devices, due to limitations in power consumption and size.
      I must apologize for the error in this post – in my EEG contains 2 channels (4 electrodes) (which are designated as “electrodes” in the figure).

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