# Need refractive index for Radio wave propagation model

1. Jun 23, 2011

### anarachy

I am modelling a radio wave propagation simulator for a Wifi at 2.4 Ghz.
I know that the refracted index of glass for light is around 1.5, how do I translate this to a 2.4 Ghz radio wave.
such as concrete, brick wall etc.

Thanks.

2. Jun 23, 2011

### skeptic2

I haven't heard of a refractive index being applied to radio waves. About the only instance I can think of where it would be relevant would be with regards to the ozone layer. Building materials generally use a penetration loss factor. Generally these are so variable that it is best to measure the penetration loss of a building rather than try to calculate it. In my experience most buildings are assumed to have a penetration loss of 15 dB or less, however many modern buildings exceed that figure, some by more than 10 dB. In many instances, if building penetration loss exceeds 15 dB and there must be coverage inside the building, a bidirectional amplifier is used.

3. Jun 24, 2011

### Skaperen

You aren't, by chance, trying to put the radiating elements inside the glass to try to achieve total internal reflection, are you?

http://en.wikipedia.org/wiki/Total_internal_reflection

4. Jun 25, 2011

### sophiecentaur

A few of examples.
1. They make dielectric lenses for directing microwave beams. They are shaped just like optical glass lenses and can be made of expanded polystyrene - just bigger, because you need a bigger aperture because of the longer wavelength.

2. UHF and VHF radio signals can be bent by air layers of different temperatures which can produce fading. A cold layer between two warm layers can produce the effect of ducting because of total internal reflection of waves at the boundary of a high refractive index and a low refractive index.

3. The refractive index of polythene is about 0.6 and this tells you why signals travel much slower in a coax cable then in space.

btw, I think you may have been referring to the ionosphere - not the ozone layer(?). RF propagation is modified (bent and/or reflected) by the layers of ionised gas, which, again, have lower refractive indices due to the electrons being moved about by the EM fields.

5. Jun 25, 2011

### anarachy

I am modeling an indoor based propagation model. I am simulating a light to show radio wave propagation through ray tracing techniques.As light and radio wave operate at different frequencies , I want to translate properties like refraction index for light to radio wave.

Thanks.

6. Jun 25, 2011

### sophiecentaur

Scaling is difficult, in many respects but you could, I'm sure, show a light based model of ionospheric propagation using layers of liquids of different densities - and get total internal reflection. You could try the effect of a layer of glycerine underneath a layer of water. The difference in refractive index would be enough, I think, to show total internal reflection and you could let the boundary diffuse with time to show a curved path on reflection - just like you get at the boundaries of the ionospheric layers. Actual angles could be all wrong, though, but it could look good I think. A laser beam and slightly milky water. Then you could rock the container - or stir it up - and see the resulting spot of red light move about - just like HF transmissions.

7. Jun 28, 2011

### Skaperen

Scaling between light and radio is also a matter of (extreme) size to account for the diffraction, interference, resonances, etc. Radio in a room would be like light in a super miniature model. It's all about wavelength and propagation.

8. Jun 28, 2011

### sophiecentaur

It is certainly true that you can only do one aspect at a time and with a different 'fudge factor' on each demo.

9. Jul 1, 2011

### anarachy

How much does refraction effect say a 2.4ghz wifi router in an indoor environment through concrete walls?

10. Jul 1, 2011

### sophiecentaur

Look it up. There are tables of almost all physical properties of all materials if you hunt around enough. But the effects of absorption and scattering by steel mesh etc. Would also be relevant. Hard to quantify this sort of thing in many cases. It's often a matter of using lots of measured data and getting the statistics.

11. Jul 1, 2011

### anarachy

Can you recommend a source for this data, I cant seem to find any focused material on the web.

12. Jul 1, 2011

### sophiecentaur

First page of my second search gave me:
http://www.microwaves101.com/encyclopedia/Miscdielectrics.cfm" [Broken]
http://www.antd.nist.gov/wctg/manet/docs/models.pdf#search=%27dielectric%20constant%20building%20walls%20concrete" [Broken]

Any use?

Last edited by a moderator: May 5, 2017
13. Jul 1, 2011

### anarachy

Thanks a lot.

14. Jul 1, 2011