![]() EEG signals are usually measured in microvolts (μV). The EEG sensor records a “raw” EEG signal, which is the constantly varying difference of potential between the positive and negative electrode, and the software usually processes that signal by applying a variety of digital filters to the recorded signal, in order to extract frequency-domain information. The frequencies most commonly looked at, for EEG, are between 1 and 40 Hz. Similarly to muscle fibers, neurons of different locations can fire at different rates. ![]() It amplifies the small electrical voltages that are generated by brain cells (neurons) when they fire. An added requirement for EOG measurements is very good low frequency, or even dc, response.The EEG sensor is an electroencephalograph sensor, or pre-amplifier, for measuring the brain’s electrical activity from the surface of the scalp. Image courtesy of Vermed, A division of Nissha Medical Technologies.Īll of the biopotential signals have low and even very low amplitude so instrument amplifiers are typically used to obtain a consistent, low noise signal. ![]() Their cost, as opposed to more expensive reusable electrodes, allows them to be disposable. Silver (Ag) – silver chloride (AgCl) is a typical electrode material for ECG and other biopotentials. In fact, measurement of the retina within the eyes produces another type of measurement called an electroretinogram or ERG.Įlectrical performance and biologic response requirements for ECG electrodes are defined in the national standard ANSI/AAMI EC12:2000/(R)2005 Disposable ECG electrodes. ![]() Finally, eye movement is measured by electrodes placed above, below and at the side of each eye. Pairs of electrodes are used on a specific muscle and a separate location is used as a reference for EMG measurements. In contrast, several EEG electrodes are uniformly attached to the forehead with the ears used as a reference for monitoring brain activity. SourceĪn ECG determines heart activity by measuring signals from electrodes placed on the torso, arms and legs. The table shows the values for each biopotential group according to the article “Biopotentials and Electrophysiology Measurements” in The Measurement, Instrumentation, and Sensors Handbook. ![]() However, the amplitude and bandwidth of the measurements vary for each of these. An electrocardiogram (ECG or EKG), electroencephalogram (EEG), electromyogram (EMG) and electrooculogram (EOG) all measure biopotentials, the electrical output of human activity. ![]()
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