1. Nov 16, 2005

### dervast

Hi i need to read somewhere about polarization. What polariation is.. Why we need it? What types of polarization exist and what are the differences.. and so on

2. Nov 16, 2005

### marlon

Here and here you go...

feel free to ask more clarification, if you need.

marlon

3. Nov 16, 2005

### marlon

using a simple vocabularium, one could define polarization as the "way" a material reacts when you apply an incident electric field onto it.

Reacts means (and this is the clue) the change in charge distribution. Like for example the way the electron cloud will change its structure because of this incident E-field.

this E-field has a frequency and depending on that value, you get different contributions to the polarization. Ie, different mechanism react to the incident E-field like dipoles, ionic contribution, electronic contribution...

Another classical example is this : suppose you have 5 + charges and 5 - charges that are randomly distributed in a medium. the net charge is zero. If you apply a voltage onto this medium, the - charges will go to the positive side (electrode) and the + charges wil go to the negative side. Now you do have a net charge in the medium, you see ?

marlon

4. Nov 16, 2005

### dervast

Thx i ll read your interesting links.. I am asking because we are using polarization in wireless communications.. and he polarization seems to be a factor that alters somehow the attributes of the signals/

5. Nov 16, 2005

### Ouabache

Polarization is important in wireless communications. This technology comes from one that has been developed since 19th century, radio communications. When radio waves are generated, the polarity of the electric field defines the polarity of the antenna. The electric field is perpendicular (orthogonal) to the magnetic field in a linearly polarized antenna.

Here is a http://www.hp.com/rnd/images/pdf_html/antennas_figure7.jpg [Broken] example of horizontal versus vertical linear polarization (They are showing the orientation of the electric field). A recieving antenna ought to be of the same polarity as the transmitting antenna to recieve the maximum signal. That does not mean you cannot use a horizontal antenna to recieve a vertically polarized radio wave or vice versa. I've done it.. However it is not as efficient as the signal is attenuated. Both of these antennas radiate linearly polarized waves.

Other kinds of polarization are circular or more generally elliptical. In circular polarization, the orientation of both the electric field and magnetic field rotate through 360 degrees. Depending on which way the field rotates, a circularly polarized wave may be clockwise or counterclockwise. marlon's second ref is a good technical discussion of what I have given.

[edited by Russ on request]

Last edited by a moderator: May 2, 2017