ECEN5341/4341Bioelectromagnetics
Spring 2013
Frank S. Barnes
Contact Info:
(303)492

8225
frank.barnes@colorado.edu
ECOT 250
http://ecee.colorado.edu/~ecen4341/index
.html
INTRODUCTION
OBJECTIVES:
•
To explore the field of
bioelectromagnetics
and maybe to push the frontier a little
bit.
•
To have you become acquainted with the complexity of going from the physics
through the chemistry to the biology and possible health effects to public policy
for risk.
•
To have you gain some experience in acquiring information from the literature and
putting it into a useful form.
OUTLINE OF THE COURSE
•
A review of some of the electrical properties of biological materials and the
problems of coupling electric and magnetic fields in to them.
•
A review of the physics of the effects of electric fields on biological systems at low
frequencies.
•
A review of the physics of the effects of magnetic fields on biological systems
•
A discussion of some possible health effects of these fields
INTRODUCTION
•
A review of radio and microwaves
–
The coupling of radio waves into a biological system
–
Some physics of the interactions of RF on biological systems and some effects.
•
A review of lasers and laser safety if time
APPROACH TO THE SUBJECT
•
Start with the physics at the simplest levels and work up through the layers of
biological complexity.
The scope of the problem is from:
10

12
seconds to generations.
•
From electrons and atoms to the whole body.
•
From DC to gamma rays
•
The major part of the problem is our lack of understanding of the biology
INTRODUCTION
COURSE OPERATIONS
:
•
Assigned reading:
"Handbook of Biological Effects of Electromagnetic Fields", 3rd Edition,
Edited by Frank Barnes and Ben
Greenebaum
... and other literature much of which will be handed out.
Requirements.
Work through a large part of
the material in the Handbook Biological effects of
Electromagnetic fields.
•
Bring at least two new reprints on the subject of the class discussion to class each
week and be prepared to present it to the class. For example the first assignment
will be to read the preface in the hand book for Wednesday. The second will be to
find papers on the measurement of the electrical properties of biological materials
and related it to the material in the Handbook. As the class is about 30 you will
need to write up each paper you read at the level of about one page per paper. I
want critical comments on the papers like what are the strengths and weakness of
the papers as well as brief review of the important results it contains. Also you
should be prepared to present some of the most interesting result in class.
•
Two term papers. These papers may be presented to the class and discussed. They
may also be handed back for farther development.
•
Two
one hour tests and a final.
The course will be flexible in the choice of material to be covered to match the
interests of the class.
Research topics that we might include:
•
The treatment of electromagnetic fields as a source of biological stress. What do
we mean by stress?
•
What are the effects of small periodic temperature variations on biological
systems? In particular what might they do to the brain and nerve cells?
•
What are the differences between cancer and normal tissues that can be observed
with electromagnetic fields from DC to light? Can we build an optical fiber system
that will detect cancer that will fit in a needle?
•
Can we change growth patterns with magnetic fields?
•
Are there some ways to use electric or magnetic fields in therapy?
•
What are the effects of electric and magnetic fields on the immune system?
•
How are Type

B Cytochromes and Free Radicals effected by electric and magnetic
fields.
•
The effects of DC Magnets on pain
Definitions of Electric and Magnetic
Fields
qE
F
2
0
2
1
4
r
q
q
F
q
F
E
B
x
I
B
x
v
E
q
F
H
B
Define the electric field E by where F is the force and q is the charge on the particle
The force between two charges is given by
Coulomb’s Law
Where
ε
0
is the dielectric constant and r is the separation between charges.
We can define the magnetic flux density B in terms of the time rate of change of
Charge or in terms of the velocity of the charge by the Lorentz force law.
v
q
I
Where
The magnetic field is defined from Maxwell’s equations and is related to the
The magnetic flux density by
sin
qv
F
B
sin
IdlB
df
t
q
~
Magnetic Fields
2
4
sin
r
dl
I
dH
I
dl
H
dt
dI
L
dS
t
B
dl
E
V
s
The magnetic field around a current carrying wire is given by
The induced voltage V is given by
The magnetic field from a short wire is given
By : Ampere’s Law
Radiation .
km
x
f
c
5000
60
10
3
8
The difference between induced fields and radiation depends on the dimensions of
the device and the wave length where the wavelength is given by
The radiation resistance for short linear dipoles of length
l
<<
λ
is given by
The radiated power is given by
3
0
2
2
3
4
2
c
a
q
W
The power radiated from a charged
q
is given by
Where
a
is the acceleration and
c
is the velocity of light
2
2
0
2
2
2
0
40
3
l
I
l
I
W
η
Is the impedance of free
space
Electromagnetic Fields Near a Dipole
2
0
1
4
r
r
jk
e
h
I
H
jkr
sin
2
2
4
3
2
0
r
j
r
e
h
I
E
jkr
r
sin
sin
1
4
3
3
0
r
r
j
r
j
e
h
I
E
jkr
Near E Fields
Near H Field
H is the height of the dipole, k is the propagation constant k=2
π
/
λ
, is the
angular frequency is the wave impedance r is the distance from the radiating
element
Radiated field
Radiated field
Induced E Field
Results for Low Frequencies
1. Almost all the fields are static or induced
2. At 60Hz fields with in a few
km the radiated
fields
are orders of magnitude smaller than
the static or induced fields .
3. Heating from radiated fields is very small at
low frequencies but not at RF.
At DC the Parallel Components
Tangential components
For Air
For tissue
So that for a wave from air to tissue
And
θ
2
is nearly 0 so that E
1
is nearly perpendicular and E
2
is nearly parallel to the
surface.
The perpendicular Components
The penetration of DC Electric
Fields from Air to Tissue
Low Frequency Field Penetration from
Air to Tissue
Boundary conditions for incident wave with the E field
Where is the surface charge density
s
For tissue at very low frequencies
1
6
2
10
m
F
36
10
9
0
At 60Hz this gives
So the induced field inside the body is very small for reasonable external fields!!
Low Frequency Field Penetration from
Air to Tissue
•
For DC
•
For 60 Hz
12
int
10
external
ernal
E
E
8
int
10
4
x
E
E
external
ernal
This says that the high conductivity and dielectric constants
of tissue basically shield the body from external low
frequency electric fields.
However, you need to be more careful if you look at skin
and the sensory nerves near the surface.
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