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2011 ELEC 4810 midterm solution
1. (5points)

i. (1 point)

Ag/AgCl electrode is non-polarizable, while stainless electrode is polarizable.

ii. (2 points)

Ehc-half-cell potential
Rd-leakage resistance
Cd-electrode capacitance
Rs-series electrolyte and skin resistance
iii. (2points)

2. (10 points)

i. (2points)


Biomedical signal decreases exponentially with respect to the distance between sensor and source. When one electrode is inserted into an esophageal sensor, this distance is reduced, making potential amplitude larger. So that this method can improve ECG signal.
ii. (2points)

ECG is caused when the heart muscle depolarizes periodically during each heartbeat. On the other hand, EMG signal is generated from muscle cells membrane potential, and it is not periodic, but stochastic.
iii. (2points)

Please refer to Lab 1 menu.
Attention: Some important parameters (e.g. gain-1000, cutoff frequency-0.5Hz~25Hz) must be specified.
iv. (2points)

Prevent dangerous currents from passing patients.
By using capacitive isolator or inductive isolator. In the following diagram, two sides are separated through capacitor and inductor. In addition, optic isolator can also be used.

v. (2points)

At least, patient leads, differential amplifier, signal isolator, filter, and driven-right-leg circuit must be drawn.

The common-mode voltage on the body is sensed by the two averaging resistors, inverted, amplified, and fed back to the right leg. This negative feedback drives the common-mode voltage to a low value.

3. (5points)

i. (1 point)

EEG signals recorded the summation of the potential of millions of neurons arising from synaptic activity in the brain synchronously.
ii. (1 point)

EEG signals are replaced by asynchronous waves of higher frequency but lower amplitude, when the awake subjects attention is directed to some specific type of mental activity.
iii. (1 point)

Alpha wave: 8~13Hz
Beta wave: 14~30Hz
Theta wave: 4~7Hz
Delta wave: <3.5Hz
iv. (2 points)

At least three conclusions are acquired.
. The EEG signal is small in amplitude, so we see that the EEG signal was extracted from large noise background by averaging over a time interval.

. The delta wave or the low frequency components was recorded throughout the whole measurement.

. Alpha and Theta wave with the maximum power components in the frequency range of 6~10 Hz started from the beginning until at a time of about 8. It probably showed that the human subject was in a light sleep.

. Beta wave with maximum frequency component at 24Hz increased in amplitude from about 10 and significantly reduced at around 18. This Beta rhythm (>13Hz) showed alert wake with eye open.

. After the decay of Beta wave at around 18, Delta wave became the majority frequency components f