01_Kaniusias Flashcards
Perfectly polarizable Electrodes
- 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
Isolation methods patient
- 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
Tissue-electrode interface
- Formation of H2O Shell
- Adsorption of extracellular matrix proteins
- Cell attachment
- Migration, differentitation, proliferation
- -> Hydrophobic regions hinder attachment
Noise sources
- power line interference
- biosignals (muscle contraction)
- electrode contact noise
- motion artifacts
- data collecting device noise
- signal processing artifacts
Types of noise
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
Passive shielding
- noise through shield instead of signal conductor
- conductive layer around wire (grounded)
effects: - reduced measured output
- introduced time const. through cable capacity
Active shielding
- very reduced leakage current
- high shunt resistance
- low shunt capacity
- low loading error
- low settling time
Electrocardiography (Shielding…)
- 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
Noise coupling ar ECG
- capacitive coupling NOT in leg, due to low output impedance –> currents would bypass ground
- inductive coupling: –> small area between wires
Measurement of neural conduction velocity
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
Short wave diathermy - Condenser method
- two metal plates
- low f (MHz)
- fat heated better, due to e_F < e_M
Short wave diathermy - Induction method
- wire around leg
- higher f
- muscle (conductive tissue) heated more
- superficial heating
Microwave diathermy
- 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
Ultrasonic diathermy
- 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
Surgical diathermy
- 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
Characteristics ideal operational amplifier
- 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
High-pass filter
- capacitor = frequency dependent
- capacitor passes much current –> shorting between in- and output
- -> attenuation of low frequencies
Low-pass filter
- 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
Brick layer model
- resistance of membrane and cytoplasm almost equal
- capacitance membrane(thin)»_space; capacitance cytoplasm
Passive/ Active device
Passive: (e.g. Resistor, Capacitor...) - no power gain - no control action Active: (e.g. Transistor, Amplifier...) - power gain to system - control voltage /current
Conduction band/band gap
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
n-doped / p-doped
- semiconductors at certain T shake out electron –> hole and free electron (carriers)
- by doping, process increases
- n-doped: Electron conductivity
- p-doped: hole conductivity
What is a resistor and how does he influence signal?
- resists the flow of electricity
- can be voltage divider
- used to: create reference voltage or signal attenuator at low frequencies
What is a capacitor?
- 2 conductive parts separated with dielectric
- stores electrical energy depending on charge Q
- C = Q/U
- polarized / non-polarized capacitor
What is an inductor?
- inductor in el. circle as “inertia”
- inductance resists change of el. current
- inductance is caused by magnetic field generated by current
Microelectronic fabrication
- Photolitography
- Pattern transfer
- Material deposition
- Material etching
Insulating transformer
- 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
What is a diode?
- one way valve out of p-type semicond. and n-type semicond.
- with time depletion region arises
Operational principle of Biopolar transistor
- 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
Permissible current through heart /whole body
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
voltage follower
- Electrometer amplifier
- non-inverting, V=1
- high input resistance and impedance
- low output resistance and impedance
Harms of ventilation
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
Litotriptor
Acoustic shock wave generated by:
- high voltage spark
- magnetic coil
- spherical mounted Piezo elements
