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New Technician's Electroencephalogram Measurement Notes ~Artifact ① Power Supply Noise~
Introduction
What are brain waves? What is EEG? what do you know?
"Newcomer Technician's Electroencephalogram Measurement Notes", where newcomer engineers who started in such a situation post what they felt when they actually touched the EEG.
I'm going to tell you a raw voice that challenges without prior knowledge.
Artifact (1) ~ Power supply noise ~
A typical example of environmental artifacts is power supply noise. As you read it, the power frequency of 50Hz in Kanto and 60Hz in Kansai becomes a phenomenon that gets on the brain wave data. Since 50Hz/60Hz overlaps with the gamma wave band, it is a band that is difficult to select a method to remove with a filter. Let's try to understand the phenomenon correctly and think about how to deal with it. First, let's confirm this phenomenon using EEG.
The experimental method is simple. EEGs are measured with an AC-powered EEG and a battery-powered EEG, respectively.
The measurement results are self-explanatory, but let's check the noise width for each.
An AC-powered EEG has a noise width of about 80uV. (Graph.3)
In battery-powered EEG, the noise width is about 10uV or less. (Graph 4) This noise width includes noise other than power supply noise. Let's use FFT to confirm whether the difference between these two waveforms is really power supply noise.
This time, we will focus on the 50Hz band because the experimental facility is in the Kanto region.
The graph on the left (graph.5) is the EEG connected to the AC power supply, and the graph on the right (graph.6) is the FFT of the measured data of the battery-powered EEG. From this experiment, we were able to confirm that "power supply noise", which is the purpose of this time, is an event that should be considered when performing electroencephalogram measurements.
In addition, even when the EEG is not connected to AC power, the same phenomenon was confirmed when the EEG and PC were connected by wire and the PC was connected to AC power, so it is possible that the EEG is battery-powered. In cases where power supply noise cannot be removed by any means, please check the surrounding power supply area as well.
Countermeasures/Requirement of countermeasures/Difficulty of countermeasures
【measures】
Choose a battery-powered EEG
If the noise still appears, check the entire system and eliminate the factors that cause AC noise to enter.
[Necessity of measures]
Required
[Countermeasure difficulty]
easy
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This page is subject to change without notice.
Brain science is a field in which new research results are being announced every day.
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