Transcript ECEN5341/4341Bioelectromagnetics Spring 2015 Frank S. Barnes Contact Info: (303)492-8225 [email protected] ECOT 250 http://ecee.colorado.edu/~ecen4341/5341 index.html INTRODUCTION • • • • • • • • • OBJECTIVES: To explore the field of bioelectromagnetics and maybe to push the frontier a little bit. To.

ECEN5341/4341Bioelectromagnetics
Spring 2015
Frank S. Barnes
Contact Info:
(303)492-8225
[email protected]
ECOT 250
http://ecee.colorado.edu/~ecen4341/5341
index.html
INTRODUCTION
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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 into 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
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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
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INTRODUCTION
COURSE OPERATIONS:
Assigned reading: "Handbook of Biological Effects of Electromagnetic Fields", 3rd
Edition, Edited by Frank Barnes and Ben Greenebaum
Also of interest will be
“The Physiology of Bioelectricity in Development, Tissue Regeneration, and Cancer Edited”
Christine Pullar and other literature depending on your interests.
Requirements.
Work through a large part of the material in the Handbook Biological Effects of
Electromagnetic Fields.
Review at least two new papers a week and bring in at least a one or two page
review of them to class. Also be prepared to present your review to the class.
For example 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 15 people, 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. It is likely that with 15 students you will
be asked to make presentation every week.
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:
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Can we treat 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.
What are the effects of DC Magnets on pain?
How do we calculate the EMFs at the location of interest in the interior of the body?
How do electric forces on molecules compare with mechanical stresses at membranes in different
directions?
Definitions of Electric Fields
Define the electric field E by


F
E 
q


F  qE
Where F is the force and q is the charge on the particle
The force between two point charges is given by
Coulomb’s Law

q1q2
F
4r 2
Where ε is the dielectric constant and r is
the separation between charges.
Magnetic Flux Density
• 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.

  

  
F  q( E  vxB)  qE  qE  I xB
Where 
  

I  qv
dF  I dl B sin 
F
q
B
~
t
qv sin 
Static Case N
S
N
S


F ~ B
Magnetic Field
• The magnetic field is defined from Maxwell’s equations and is
related to the magnetic flux
 density
 by
B  H
• Where µ is the magnetic permeability magnetic Fields
The magnetic field around a current carrying wire is given by
 H  dl  I
The induced voltage V is given by
B
dI
V    E  dl   
 dS   L
s t
dt
The magnetic field from a short wire is given
By : Ampere’s Law
I sin dl
dH 
4r 2
Radiation .
The power radiated from a charged q is given by
2q 2 a 2
W
4 0 3c 3
Where a is the acceleration and c is the velocity of light
For a short wire power radiated is given by
I  l 
2 2 l 
W
   40 I 0  
3 

2
0
2
2
η Is the impedance of free space
The difference between induced fields and radiation depends on the dimensions of
the device and the wave length.
At 60Hz the wavelength is given by
8
c 3x10
 
 5000km
f
60
The radiation resistance for short linear dipoles of length l <<λ is given by
The radiated power is given by
Electromagnetic Fields Near a Dipole
H
I 0 h  jkr  jk
1 

e
 2  sin 

4
r 
 r
Radiated field
Near H Field
I 0h  jkr  2
2 
Er 
e


 cos
2
3 

4
jr 
r
Induced E Field
Radiated field
Near E Fields
I 0h  jkr  j
1
 
E 
e

 2
sin 

3


4
jr
r 
 r
h is the height of the dipole, k is the propagation constant k=2π/λ,  is the
angular frequency  is the wave impedance r is the distance from the radiating
element
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.
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The penetration of DC Electric Fields from Air to Tissue
At DC the Parallel Components
The perpendicular Components
Tangential components
For Air
For tissue
So that for a wave from air to tissue
And θ2 is nearly 0 so that E1 is nearly perpendicular and E2 is nearly parallel to the
surface.
Low Frequency Field Penetration from
Air to Tissue
Boundary conditions for incident wave with the E field 
Where
s
is the surface charge density
For tissue at very low frequencies
 2  10 1
6
109 F
0 
36 m
At 60Hz this gives
So the E field inside the body is very small for reasonable external E fields!!
Low Frequency Field Penetration from
Air to Tissue
• For DC
• For 60 Hz
Eint eranal
 1012
Eexternal
Eint eranal
 4 x108
Eexternal
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.
EM Waves at a Plane Boundary
Electric Fields and Dielectric Sphere
A Membrane and Cell Model
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Endothelial Cell Growth
45T static field
Low level fields
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