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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 18:17 |
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Conference: Bucharest University Faculty of Physics 2009 Meeting
Section: Biophysics; Medical Physics
Title:
A WIDEBAND AMPLIFIER FOR NEURAL RECORDING APPLICATIONS
Authors:
Cristi DONOS, *Ovidiu PACALA and Liviu GIURGIU
Affiliation:
Faculty of Physics, University of Bucharest, *Yarc-Design S.R.L.
E-mail
cristidonos@yahoo.com , opac@yarc-design.ro , liviu.giurgiu@g.unibuc.ro
Keywords:
EEG, instrumentation amplifier, FFT
Abstract:
Electroencephalography (EEG) consists in the recording of the electrical activity produced by the brain, by electrodes placed on the scalp. The data measured by the scalp EEG are used for clinical and research purposes. The EEGs used for medical purpose are limited up to 40 Hz due to the power supply noise (50 Hz). In our research, we took the measuring process even further, up to 100 kHz. The amplitude of the signal in the 0-40 Hz frequency band is around 100 μV rms. For higher frequencies (100 kHz), the amplitude of the signal drops to a couple of nanovolts. For this reason, we used a very low noise preamplifier and an instrumentation amplifier to amplify the signal. We eliminated the power supply noise by using an instrumentation amplifier and by using a battery powered backup supply instead of the regular power supply, then we eliminated the electromagnetic interference from external sources by using a Faraday cage. Also, we used EEG electrodes attached to short coaxial cables, both cables having the same length and capacity.
We measured the signal from the electrodes for 2000 ms, at first with no stimuli, then with 2 different stimuli: sound (1 kHz sound signal) and an intermittent beam of light.
The stimulus signal was used as a trigger for recording the brain EEG. We recorded the EEGs with and without stimulation in order to make a comparison between the two cases. It turns out that the brain signal with 1 kHz sound stimulus has a bigger amplitude than without it. Also, after a Fourier spectral analysis (FFT), we found a big peak at 1 kHz together with its harmonics at 2, 3 and 4 kHz. For the intermittent light stimulus, we found that the brain signal changes when the light goes on and off. The FFT analysis revealed 2 peaks at 55 and 60 kHz, and a couple of artifacts around 63-72 kHz and 83-92 kHz.
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