RF transmission through various materials
 

I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

On 14 Jun 2004 09:06:12 -0700, (David Harper)
wrote:
The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Hi Dave,

Such material at that frequency is often used to construct a
di-electric lens. That is, when the di-electric constant (which is
analogous to index of refraction) is taken into account of curvature
which, in turn, is of sufficient size with respect to wavelength; then
you have the means to construct lens of the common shape you encounter
for light lenses. This means both follow the same characteristics
given the same shape. For a slab of Polystyrene, it would be
equivalent to plate glass (no gain/magnification).

As long as your di-electric is free of impurities, then for all
intents and purposes it is as clear to RF as glass is to light. Add
impurities and you stand the chance of making sunglasses for your
antenna (unfortunately the analog of sunlight would be your precious
RF).

Optical lenses are hundreds to thousands to millions of wavelengths
across. On the other hand, RF lenses stand to be much smaller in
relation, and as such there is a minimum size whereby no advantage may
be found (don't expect to build an effective, but sloppy quarterwave
lens).

73's
Richard Clark, KB7QHC

"David Harper" wrote in message
m...
I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

Off the cuff, I'd say it'll have no noticable effect...
Some of this can have additives which may change the equation.

Lenses...Hmmm. Interesting idea.

I can try it and see what effect I can see on the signal strength bars on
the GPS.

I do know that my older GPS (Sequential receiver) doesn't receive in the
house. I suspect it is from the foil backing on the fiber glass insulation
in the ceiling.
Steve N.
--
Steve N, K,9;d, c. i My email has no u's.

"Ability to transmit" is a bit vague. In any material, a wave will
encounter attenuation, an impedance, and a velocity, all of which are
determined by material properties of permeability, permittivity, and
loss tangent. The change in impedance from free air causes reflections,
and the change in velocity causes refraction. If your main concern is
attenuation, it'll be negligible for the styrofoam at that frequency. If
you're interested in calculating precise values or investigating other
materials, a good reference is Kraus's _Electromagnetics_.

Roy Lewallen, W7EL

David Harper wrote:

I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

Transmission loss through materials depends on 2 factors. Loss tangent and
dielectric constant. Loss tangent is often the lesser of the problems, but
is simple exchange of the wave energy for heat caused by several possible
mechanisms. Look up the operating principles of microwave ovens.
Dielectric constant manifests itself as an impedance mismatch at each
surface, which causes reflections. At a specific frequency, this
characteristic can be used to make the material transparent, as in ceramic
radomes for spacecraft.

In your case, the loss tangent of polystyrene for RF is among the best if
there is no moisture trapped in the foam (closed cell type preferably), and
since the dielectric constant approaches that of air, then the loss at the
GPS frequency will be virtually nil.

--
Crazy George
Remove N O and S P A M imbedded in return address
"David Harper" wrote in message
m...
I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

I noticed some electromagnetic waves will travel through distilled water,
and some will not... then when you put mud in it - those that could -
can't - and those that couldn't - can.

light was one


"David Harper" wrote in message
m...
I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave


---
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Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.690 / Virus Database: 451 - Release Date: 5/22/2004

"David Harper" wrote in message
m...
I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

Dave

How much of *what you want to know* could be learned from a test in the
microwave??

As you probably know, it will be very difficult to include enough
Polystyrene around a GPS receiver (and its antenna) to effect the accuracy
of its readings.
I get pretty good accuracy from my DeLorme GPS while it is inside my
house. That is actually a statement about the poor construction of the
house, I suppose.

Jerry

"David Harper" wrote in message
...
(David Harper) wrote in message
om...
I was wondering what the general relationship between frequency and
its ability to transmit through various materials? For instance, 1GHz
and 1MHz obviously transmit differently through materials. I'm
curious as to what material properties are involved (i.e. dielectric
constant, density, etc?)

The main reason for this questions is I'm wondering how well 1+ GHz
(GPS) signals transmit through about 1.5 inches of expanded
polystyrene (styrofoam).

Thanks in advance for any insight!
Dave

Thanks everyone for all the info! That was definately educational and
answered my quesiton.

Dave


It did?



--
Steve N, K,9;d, c. i My email has no u's.

"Steve Nosko" wrote in message ...
"David Harper" wrote in message
...
Thanks everyone for all the info! That was definately educational and
answered my quesiton.

Dave


It did?

Yeah, now I can amaze all my friends and co-workers. All I need to do
now is get some of that "male enhancement" Enzyte and I'll probably be
CEO by next month.

What I was looking for was really this: tangent loss and dielectric
constant are the two main factors that determine RF propogation
properties through a material.