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6 Applications and Methods in Biosignal Processing

Normal EEG Waves of an Adult

deep sleep

sleep

awake at rest

mentally

awake

Delta

< 3.5 Hz

Theta

4-7 Hz

Alpha

8-13 Hz

Beta

14-30 Hz

1 s

Fig. 6.2: EEG signal at different mental states. From top to bottom: mentally awake, awake at rest,

sleep and deep sleep.

power density

Fig. 6.3: EEG spectrum with a maximum at 11 Hz. This corresponds to alpha waves in the EEG signal

that occur prominently in the relaxed awake state with eyes closed.

and a reference electrode (ear electrode) or from the voltage difference between a pair

of two measuring electrodes (bipolar measurement). In an EEG measurement, several

measurement curves are usually recorded and displayed simultaneously via different

electrodes.

The dependence of EEG rhythmicity on wakefulness state is exploited for sleep

diagnostics. A number of complaints and chronic diseases are due to sleep disorder.