Lecture Slides - ECEE

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.