- 2075 Chaitra · 4 marks
Short note: EEG recorder
Short answer
An EEG recorder captures brain electrical activity (10-100 µV, 0.5-70 Hz) via 21 Ag/AgCl electrodes placed per the 10-20 system. The signal passes through a differential preamplifier (high gain, CMRR >100 dB), filters (0.5-70 Hz bandpass, 50 Hz notch), main amplifier, and is recorded on paper at 30 mm/s or digitally. Brain waves include delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), and beta (>13 Hz). Used for epilepsy, tumors, sleep disorders, coma, and brain death diagnosis.
Write a short note on EEG Recorder.
An EEG (electroencephalograph) records the electrical activity of the brain from electrodes placed on the scalp. The amplitude is very small, 10 to 100 µV, with a frequency range of 0.5 to 70 Hz.
Block diagram
Scalp electrodes (10-20 system)
|
[Electrode selector / montage switch]
|
[Pre-amplifier (differential)] -- [Calibrator]
|
[Filters: LPF 70 Hz, HPF 0.5 Hz, 50 Hz notch]
|
[Main amplifier / driver] --> [Pen recorder / ADC + display]
Parts
- Electrodes: Ag/AgCl cup or disc electrodes, 21 in number, placed by the international 10–20 system and attached with conductive paste or held in a cap; the ear lobes are used as reference, and there is a ground electrode.
- Electrode selector: chooses a bipolar or referential montage.
- Differential preamplifier: high gain (about 1000), high CMRR (>100 dB), high input impedance (>10 MΩ).
- Filters: remove noise, and a notch filter removes the 50 Hz mains interference.
- Recorder: a pen recorder on paper moving at 30 mm/s, or digital storage with a computer display.
Brain waves
| Wave | Frequency | State |
|---|---|---|
| Delta | 0.5–4 Hz | deep sleep |
| Theta | 4–8 Hz | drowsiness |
| Alpha | 8–13 Hz | relaxed, eyes closed |
| Beta | >13 Hz | alert, mental activity |
Uses: diagnosis of epilepsy, brain tumours, sleep disorders, coma, and brain death.
✓ Answer checked by Claude Opus 5.5 (high effort)