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Biomedical instrumentation > 01_Kaniusias > Flashcards

01_Kaniusias Flashcards

1
Q

Perfectly polarizable Electrodes

A
  • Polarization by current; overpotential induced
  • no chemical reaction at boundary
  • no net charge over electrode-electrolyte when voltage is applied
  • only displacement current
  • electrode/electrolyte interface as capacitor
  • only AC
  • for stimulation
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2
Q

Isolation methods patient

A
  • current limiting resistor / voltage limiting diode
  • optical isolation (light mediated transmission) short distance
  • wireless isolation, long distance
  • photo-optic isolation (LED + photodetector)
  • transformer isolation
  • capacitive coupling
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3
Q

Tissue-electrode interface

A
  1. Formation of H2O Shell
  2. Adsorption of extracellular matrix proteins
  3. Cell attachment
  4. Migration, differentitation, proliferation
    - -> Hydrophobic regions hinder attachment
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4
Q

Noise sources

A
  • power line interference
  • biosignals (muscle contraction)
  • electrode contact noise
  • motion artifacts
  • data collecting device noise
  • signal processing artifacts
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5
Q

Types of noise

A

Noise states indicate how fast noise lowers over frequency
- white: ß=0
- pink: ß=1
- brown: ß=2
the whiter noise the more significant distortion

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6
Q

Passive shielding

A
  • noise through shield instead of signal conductor
  • conductive layer around wire (grounded)
    effects:
  • reduced measured output
  • introduced time const. through cable capacity
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7
Q

Active shielding

A
  • very reduced leakage current
  • high shunt resistance
  • low shunt capacity
  • low loading error
  • low settling time
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8
Q

Electrocardiography (Shielding…)

A
  • active shielding electrodes: reduction of capacitive coupling
  • active grounding by “right-leg-drive” : reduction of common mode interference
  • “right-leg-drive” increases overall amplifier CMRR
  • buffer: low output impedance; to eliminate need for impedance matching
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9
Q

Noise coupling ar ECG

A
  • capacitive coupling NOT in leg, due to low output impedance –> currents would bypass ground
  • inductive coupling: –> small area between wires
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10
Q

Measurement of neural conduction velocity

A

MOTOR NERVES
- stimulation at two spacial distinct points –> v=D/t
- cardiac conduction disorder can be checked
SENSORY NERVES
- stimulus at finger –> reaction impulse
- the further the less dominant due to varying size of volume conductor

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11
Q

Short wave diathermy - Condenser method

A
  • two metal plates
  • low f (MHz)
  • fat heated better, due to e_F < e_M
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12
Q

Short wave diathermy - Induction method

A
  • wire around leg
  • higher f
  • muscle (conductive tissue) heated more
  • superficial heating
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13
Q

Microwave diathermy

A
  • higher f & shorter wavelength (2,45 GHz, 11cm in air)
  • water molecule vibration and dipole rotation
  • the higher conductivity, the higher current density (heat)
  • the higher water content, the higher absorption, the lower penetration depth
    + easy to use, but little penetration depth
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14
Q

Ultrasonic diathermy

A
  • 1MHz, acoustic waves
  • Mechanic micro massage -> tissue relaxation, break down scar tissue, local blood flow
  • the higher f, the less depth, the less diffuse
  • heat mainly on bone surface due to reflection
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15
Q

Surgical diathermy

A
  • 1-3MHz
  • cutting and coagulation
  • excessive local heating (high local current density)
  • large indifferent reference electrode for low density at reference site
    + instantaneous sealing of capillaries
  • high voltage -> disadvantageous tissue carbonisation
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16
Q

Characteristics ideal operational amplifier

A
  • infinite gain G = V_out / V_in
  • infinite input Impedance 0 output impedance
  • infinite voltage rate available at output
  • infinite CMRR
  • infinite power supply rejection ratio
17
Q

High-pass filter

A
  • capacitor = frequency dependent
  • capacitor passes much current –> shorting between in- and output
  • -> attenuation of low frequencies
18
Q

Low-pass filter

A
  • at low f. capacitor does not pass much current
  • at high f. capacitor passes much current which makes shorting from output to ground
  • -> attenuation of high frequencies
19
Q

Brick layer model

A
  • resistance of membrane and cytoplasm almost equal

- capacitance membrane(thin)&raquo_space; capacitance cytoplasm

20
Q

Passive/ Active device

A 
Passive: (e.g. Resistor, Capacitor...)
- no power gain
- no control action 
Active: (e.g. Transistor, Amplifier...)
- power gain to system
- control voltage /current
21
Q

Conduction band/band gap

A

def: energy range where no electron state can exist
- factor to determine conductivity of material
- Insulators: LARGE band gap
- Semiconductors: doped with impurities, conductivity can be enhanced largely
- Metals: SMALL band gap

22
Q

n-doped / p-doped

A
  • semiconductors at certain T shake out electron –> hole and free electron (carriers)
  • by doping, process increases
  • n-doped: Electron conductivity
  • p-doped: hole conductivity
23
Q

What is a resistor and how does he influence signal?

A
  • resists the flow of electricity
  • can be voltage divider
  • used to: create reference voltage or signal attenuator at low frequencies
24
Q

What is a capacitor?

A
  • 2 conductive parts separated with dielectric
  • stores electrical energy depending on charge Q
  • C = Q/U
  • polarized / non-polarized capacitor
25
Q

What is an inductor?

A
  • inductor in el. circle as “inertia”
  • inductance resists change of el. current
  • inductance is caused by magnetic field generated by current
26
Q

Microelectronic fabrication

A
  1. Photolitography
  2. Pattern transfer
  3. Material deposition
  4. Material etching
27
Q

Insulating transformer

A
  • 1:1 power transformer used as safety precaution

- by using Ins. trafo bonding (neutral wire connected to ground) is eliminated and shock hazard stays in device

28
Q

What is a diode?

A
  • one way valve out of p-type semicond. and n-type semicond.
  • with time depletion region arises
29
Q

Operational principle of Biopolar transistor

A
  • two diodes with shared anode region
  • E-B junction is forward biased
  • B-C junction reverse biased
  • positive voltage to B-E junction –> unbalanced –> thermally generated carriers inject into base region
  • thin base region –> fast diffusion
30
Q

Permissible current through heart /whole body

A 
Whole body: 
- normal 100 muA til 1000 Hz
- abnormal 900muA til 1000 Hz
Heart:
- normal 10 muA til 1000 Hz
- abnormal 80 muA til 1000 Hz
31
Q

voltage follower

A
  • Electrometer amplifier
  • non-inverting, V=1
  • high input resistance and impedance
  • low output resistance and impedance
32
Q

Harms of ventilation

A

Barotrauma:
- too high p –> pneumothorax
Volutrauma:
- too high V –> hyperextension of lung –> edema–> no gas exchange
Low-Total-volume-injury:
- alveoli collapse due to low p –> open again–> shear stress –> rupture
Biotrauma:
- less surfactant due ventilation –> to high surface tension

33
Q

Litotriptor

A

Acoustic shock wave generated by:

  • high voltage spark
  • magnetic coil
  • spherical mounted Piezo elements

Biomedical instrumentation (2 decks)

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