01_Kaniusias

Question 1

Perfectly polarizable Electrodes

Answer 1

• 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

Question 2

Isolation methods patient

Answer 2

• 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

Question 3

Tissue-electrode interface

Answer 3

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

Question 4

Noise sources

Answer 4

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

Question 5

Types of noise

Answer 5

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

Question 6

Passive shielding

Answer 6

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

Question 7

Active shielding

Answer 7

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

Question 8

Electrocardiography (Shielding…)

Answer 8

• 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

Question 9

Noise coupling ar ECG

Answer 9

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

Question 10

Measurement of neural conduction velocity

Answer 10

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

Question 11

Short wave diathermy - Condenser method

Answer 11

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

Question 12

Short wave diathermy - Induction method

Answer 12

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

Question 13

Microwave diathermy

Answer 13

• 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

Question 14

Ultrasonic diathermy

Answer 14

• 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

Question 15

Surgical diathermy

Answer 15

• 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

Question 16

Characteristics ideal operational amplifier

Answer 16

• 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

Question 17

High-pass filter

Answer 17

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

Question 18

Low-pass filter

Answer 18

• 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

Question 19

Brick layer model

Answer 19

• resistance of membrane and cytoplasm almost equal

- capacitance membrane(thin)&raquo_space; capacitance cytoplasm

Question 20

Passive/ Active device

Answer 20

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

Question 21

Conduction band/band gap

Answer 21

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

Question 22

n-doped / p-doped

Answer 22

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

Question 23

What is a resistor and how does he influence signal?

Answer 23

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

Question 24

What is a capacitor?

Answer 24

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

Question 25

What is an inductor?

Answer 25

- inductor in el. circle as "inertia" - inductance resists change of el. current - inductance is caused by magnetic field generated by current

Question 26

Microelectronic fabrication

Answer 26

1. Photolitography 2. Pattern transfer 3. Material deposition 4. Material etching

Question 27

Insulating transformer

Answer 27

- 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

Question 28

What is a diode?

Answer 28

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

Question 29

Operational principle of Biopolar transistor

Answer 29

- 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

Question 30

Permissible current through heart /whole body

Answer 30

``` 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 ```

Question 31

voltage follower

Answer 31

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

Question 32

Harms of ventilation

Answer 32

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

Question 33

Litotriptor

Answer 33

Acoustic shock wave generated by: - high voltage spark - magnetic coil - spherical mounted Piezo elements