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Specialist Studies 2 > Electrodes and Filters > Flashcards

Electrodes and Filters Flashcards

1
Q

What is the primary function of electrodes in neurophysiology?

A

Convert ionic changes at the body surface into an electrical current

Electrodes transduce the movement of biochemical ions into a conventional electron current.

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2
Q

What materials are commonly used for electrode design?

A
  • Silver
  • Stainless steel
  • Gold
  • Platinum

These materials are chosen based on their conductivity, non-toxicity, and robustness.

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3
Q

What is the charge carrier in tissue for electrodes?

A

Sodium chloride

Ionic changes are detected at the surface but are attenuated due to tissue resistance.

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4
Q

What creates the electrical double layer at the electrode interface?

A

The potential difference at equilibrium between the electrode and tissue

This results from the movement of ions within the electrolyte and electrons in the electrode.

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5
Q

What is the significance of electrode potential?

A

It generates a potential difference that adds a fixed value to the recorded signal

Electrode potential is typically in the order of millivolts (mV).

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6
Q

True or False: The electrode potential is always lower than the physiological signal potential.

A

False

The electrode potential is greater than the physiological signal potential.

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7
Q

What is the impact of unequal contact impedances on the physiological signal?

A

It attenuates the signal by reducing the common mode rejection ratio

Unequal impedances can create large total contact impedance.

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8
Q

What is the purpose of a high pass filter in electrode applications?

A

To remove low frequency AC components and prevent amplifier saturation

It filters out the DC component of the electrode potential.

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9
Q

Fill in the blank: The degree of filtering depends upon the degree of _______ forming the electrical double layer.

A

polarisation

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10
Q

What are two methods for chloriding silver electrodes?

A
  • Electrochemical method
  • Bleach method

Chloriding reduces electrode potential and double layer effects.

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11
Q

What is the characteristic of a low pass filter?

A

It allows low frequency components to pass while attenuating high frequencies

The output is across the capacitor in an R-C circuit.

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12
Q

What does the common mode rejection ratio (CMRR) measure?

A

The ability to reject common mode signals relative to differential signals

CMRR = Differential gain / Common mode gain.

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13
Q

What is the preferred electrode material to minimize filtering and impedance changes?

A

Silver-Silver chloride

This material is ideal for routine EEG recordings.

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14
Q

What do passive filters manipulate?

A

Biological signals and separate one signal from another

Changes to the signal by passive filters are permanent.

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15
Q

What does an RC circuit consist of?

A

Resistors and capacitors arranged in series or parallel

This configuration acts as a voltage divider.

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16
Q

What is the function of a band stop filter?

A

It removes a specific band of frequencies

Example: Notch filter removes 50 Hz or 60 Hz signals.

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17
Q

What happens in the transition region of a filter?

A

The gain of the filter in this region is 70.7% of the pass band region

Corner frequency = -3dB.

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18
Q

What are the three main regions of a filter?

A

Pass band, Transition region, Active region

19
Q

What occurs in the pass band region of a filter?

A

Frequencies pass with no attenuation

20
Q

What is the gain of the filter in the transition region compared to the pass band region?

A

70.7%

21
Q

What does the corner frequency of a filter represent?

A

-3dB

22
Q

What is the formula for corner frequency (Fc) in terms of R and C?

A

Fc = 1 / (2πRC)

23
Q

What characterizes the active region of a filter?

A

Attenuation of signal, behaving as a filter

24
Q

What is the slope or gain roll off in the active region of an RC circuit?

A

-6dB/octave

25
Q

What does the Q-factor describe?

A

The sharpness of the active region

26
Q

How is the Q-factor calculated?

A

Q-factor = F0 / ΔF (-3dB)

27
Q

What is the time constant in the context of filters?

A

Time taken for the amplitude to fall 30% of the original value in seconds

28
Q

In a high pass filter, what frequencies does it allow to pass?

A

Frequencies above a certain cutoff frequency

29
Q

What is the time constant for a high pass filter setting of 0.5 Hz?

A

0.3 s

30
Q

What does phase shift refer to in filtering?

A

Time delay imposed on a signal due to passive filter characteristics

31
Q

What are active filters built with?

A

Operational amplifiers

32
Q

Name two types of digital filters.

A
  • Finite Impulse Response filter (FIR)
  • Infinite Impulse Response filter (IIR)
33
Q

What is a key difference between FIR and IIR filters?

A

FIR filters do not use feedback, while IIR filters do

34
Q

What technique do digital filters use to convert signals from time domain to frequency domain?

A

Fast Fourier Transformation

35
Q

How can any passive filter be modeled?

A

Using Pole Zero placement

36
Q

What is the advantage of digital filtering?

A

Filtering effects are not permanent as data is manipulated and not lost

37
Q

What is a disadvantage of digital filtering?

A

Misinterpretation of data

38
Q

What does artefact rejection do?

A

Automatically removes muscle and eye movement without filtering

39
Q

What is the frequency response range for EEG?

A

0.5 Hz – 70 Hz

40
Q

What is the frequency range for VEP?

A

0.2 Hz – 100 Hz

41
Q

What is the frequency range for EMG?

A

20 Hz – 10 KHz

42
Q

Fill in the blank: The output of an FIR filter depends upon previous inputs with no _______.

A

feedback

43
Q

True or False: Digital filters are more stable than passive filters.

A

True

Specialist Studies 2 (10 decks)

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