Lecture 15 Flashcards
What is the equation for the differential form of Gauss’ law?
E = electric field
ρ = charge density
ε = permittivity of free space
What is the equation for the differential form of Gauss’ law for magnetism?
B = magnetic field
What is the Maxwell-Faraday equation for the differential form of Faraday’s law of induction?
E = electric field
B = magnetic field
t = time
What is the equation for the differential form of Ampere’s circuital law?
B = magnetic field
µ = permeability
ε = permittivity of free space
E = electric field
t = time
What is the equation for current density?
J = current density
σ = conductivity
E = electric field
What is the wave equation in a conductive medium?
What is the equation for specific absorption rate (SAR)?
SAR = specific absorption rate
σ = conductivity
E = electric field
ρ = charge density
What is the equation for radiation penetration depth (sometimes called skin depth)?
δ = penetration depth
σ = conductivity
µ = permeability
f = frequency
What are the biological uses of radio frequencies?
- Radio-frequency heating
- Bacteria (in vitro) experiments
- Psychology and cognitive experiments
What are the safe and maximum allowed degrees of heating of tissue?
Safe: 0.1ºC
Maximum: 1ºC
What is the equation for the specific absorption rate (SAR) using experimental measurements?
SAR = specific absorption rate
c = specific heat capacity
T = temperature rise
∆t = time for increase
Give 2 ways of measuring specific absorption rate (SAR)
- Numerically using finite element calculations
- Experimentally in anthropomorphic phantoms
What is the SAR limit in the EU?
2 W/kg averaged over 10g of tissue
What is the SAR limit in the US?
1.6 W/kg averaged over 1g of tissue
How are SAR limits determined?
Using the metabolic rate of tissue (1.6 W/kg) and completing experiments using phantoms that don’t allow for a temperature rise exceeding 0.1ºC.
