MF Info and Bioelectromagnetics Background

Question 1

parameters for ELF, MF and HF magnetic fields

Answer 1

extremely low frequency (ELF, <300 Hz) low to medium frequency (300 Hz – 3 MHz) high frequency (3 MHz – 300 GHz)

Question 2

what are the units for the intensity of a MF and how is it commonly expressed?

Answer 2

intensity (H) in amperes per meter (A/m) commonly expressed in Tesla (T)

Question 3

how are MF intensity and flux density related?

Answer 3

B = μ*H μ is a permeability constant (in free space, μ = 1.256×10^-6)

Question 4

describe the relationship between MF flux density and the distance from the source

Answer 4

B = (μ*I)/(2*π*r) I is current intensity, r is radius, μ is permeability constant

Question 5

how are E-fields and induced current density (by an AC source) related?

Answer 5

E=J/s s is conductivity J is current density E is electric field

Question 6

what is the unit for E-fields?

Answer 6

N/C (Newtons per coulomb) or V/m (Volts per meter) SI units: (kg*m)/(s*A)

Question 7

what are induced current density values dependant on?

Answer 7

J = s*π*r*f*B conductivity of the material (s), the distance from the MF source (r), the MF value (B), and the MF frequency (f)

Question 8

describe the right hand rule

Answer 8

Question 9

what is the value of earth’s geomagnetic field?

Answer 9

35- 70 μT

Question 10

what is current and its units

Answer 10

Current (i) = the flow of electric charge across a surface

unit: Ampere (1 Coulomb per second)
- note a coulomb is the charge of roughly 6.24x10^18 electrons

Question 11

what are average residental power-frequency MF levels?

Answer 11

0. 07 μT in Europe (50 Hz)
1. 11 μT in North America (60 Hz)

When considering average exposure levels for the general public including both residential and rural areas, the value is 0.1 μT

Question 12

describe MF levels inside the house or office

Answer 12

0.05 – 0.15 μT

These values can rise however when near a switchboard (1.0 – 3.0 μT, measured at a 300 mm distance from the source)

Question 13

what are values of MF when standing directly under power lines?

Answer 13

20 μT for 225 kV power lines and 30 μT for 400 kV power lines

Question 14

describe MF values for common household appliances

Answer 14

microwave ovens (> 0.6 μT), coffee grinders (> 0.6 μT ), electric shavers (0.3 μT), and electric hair dryers (0.3 μT) - measured wearing a portable device

up to 2 mT when using hair dryers, electric hair clippers, electric shavers and electric drills - measured more directly at 3 cm from the source

Question 15

describe MF values for workers

Answer 15

power line workers, industrial welders, and electricians can experience average exposure levels during the work day greater than 3 μT

exposure levels of above 1 mT for power line operators can be reached

up to 10 mT for those working closely with high current conductors, such as live-line electric utility workers

Question 16

when were mangetophosphenes first reported?

Answer 16

in 1896 by d’Arsonval

Question 17

describe the study of magnetophosphene perception thresholds

Answer 17

reference study in the domain is from 1980 and it reports a lowest threshold for magnetophosphene perception at 8.1 mT in the dark for a MF stimulus delivered at 20 Hz (Lovsund, Oberg, Nilsson, & Reuter, 1980)

Increasing the frequency of the signal increases the required flux density to reach the perception threshold (Souques et al., 2014)

Question 18

what is the potential reasoning behind magnetophosphene perception?

Answer 18

It is suggested that this perception is due to the modulation of rod cells in the retina, due to their specific properties including a sensitivity to weak membrane depolarization, on the order of 0.6 to 200 μV (Attwell, 2003)

Question 19

describe the difference btw graded potential cells and action potentials

Answer 19

Question 20

what is a derivative?

Answer 20

It describes how fast a quntity is varying (ie divide by time and thats the derivative)

*note if a quantity is constant for some time, then that derivative will be 0

Question 21

what is the derivative of a sinusoid function?

Answer 21

• another sinusoid

Question 22

what is magnetic flux density and units? compared to other measures of a MF?

Answer 22

Magnetic Flux Density (B) is measured in Tesla (relating to the amplitude of the wave)

dB/dT is a measure of change in magnetic field over time (measured in T/s)

Question 23

what is the root mean square and peak to peak?

Answer 23

RMS = Peak / Square root of 2

*note peak!! not peak to peak

• the root mean square (abbreviated RMS or rms) is defined as the square root of mean square (the arithmetic mean of the squares of a set of numbers)

Question 24

what is the formula for a sinusoidal MF?

Answer 24

Question 25

how to convert db/dt to flux density

Answer 25

dB/dT = 2(pi)fB

Question 26

why are charged particles important for bioelectromagnetics?

Answer 26

- because electric and magnetic fields interact with charges

Question 27

what is the formula for the force between two electric charges?

Answer 27

charge (q) is in coulombs

Question 28

what is an electric potential? - formula

Answer 28

Question 29

why is electric potential important for bioelectromangetics? - formula and units!

Answer 29

Question 30

formula for E-fields exerting a force on a charged particle

Answer 30

Question 31

define electric current and formula

Answer 31

- measured in amps!

Question 32

define current density (and formula!)

Answer 32

Question 33

link current density to electric field in a formula

Answer 33

Question 34

what is the relation of electric fields and dB/dT? - link MFs to elextric field induciton

Answer 34

- A constant MF B does NOT induce currents (E=R/2.dB/dt=0). - A time-varying MF DOES induce currents at the same frequency: E =R/2. dB/dt =R/2. B0.2π.f.cos(2πft)

Question 35

relate electric fields and current density

Answer 35

J=σ.E σ is electrical conductivity

Question 36

describe the Lorentz force

Answer 36

Question 37

what is the visual relationship between an elextric an dmagnetic field?

Answer 37

Question 38

what does the strength of the Mf produced by a solenoid depend on?

Answer 38

B = unI u = permeability (magnetic iron is aorund 200) n = turn density (number of turns/length) I = current

Question 39

calculate the induced E-field in the brain for example

Answer 39

Question 40

What type of GVS exposure did we use?

Answer 40

a bilateral, bipolar GVS signal (stimulation anode and return cathode)

Question 41

what happens to each side of the vestibular system with the GVS exposure we use?

Answer 41

bilateral, bipolar GVS induces current - causes perceived acceleration away from stimulation anode, correction by tilting towards anode. - cathode (-) will depolarize the stimulated region (excitation), but the anode (+) will hyperpolarize the region (suppression) - as stated by Fitzpatrick and day 2004

Question 42

What is Faraday's law?

Answer 42

Faraday's law of induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF) - (denoted E, measured in volts = the voltage developed by any source of electrical energy)

Question 43

What is the Maxwell-Faraday Equation?

Answer 43