ECEN5341/4341Bioelectromagnetics

Spring 2015Frank S. Barnes

Contact Info: (303)492-8225

frank.barnes@colorado.eduECOT 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 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• 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 GreenebaumAlso 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: 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

EqF

221

4 r

qqF

q

FE

Define the electric field E by

The force between two point charges is given by Coulomb’s Law

Where F is the force and q is the charge on the particle

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.

Where

Static Case N S N S

BxIEqEqBxvEqF

)(

vqI

sinBldIFd

sinqv

FB

t

q

~

B~

F

Magnetic Field• The magnetic field is defined from Maxwell’s equations and is

related to the magnetic flux density by

• Where µ is the magnetic permeability magnetic Fields

HB

The magnetic field around a current carrying wire is given by

IdlH

The induced voltage V is given by

dt

dILdS

t

BdlEV

s

The magnetic field from a short wire is givenBy : Ampere’s Law

24

sin

r

dlIdH

Radiation .

kmx

f

c5000

60

103 8

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

The radiation resistance for short linear dipoles of length l <<λ is given by

The radiated power is given by

30

22

34

2

c

aqW

The power radiated from a charged q is given by

Where a is the acceleration and c is the velocity of lightFor a short wire power radiated is given by

220

222

0 403

l

IlI

W

η Is the impedance of free space

Electromagnetic Fields Near a Dipole

20 1

4 rr

jkehI

H jkr

cos22

4 320

rjrehI

E jkrr

sin

sin

1

4 230

rrjr

jehI

E jkr

Near E Fields

Near H Field

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

Radiated field

Radiated fieldInduced 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.

1

At DC the Parallel 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.

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 sFor tissue at very low frequencies 1

62 10

mF

36

10 9

0

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

12int 10external

eranal

E

E

8int 104 xE

E

external

eranal

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

17

Endothelial Cell Growth

18

Low level fields45T static field