| 1888 Articles Home | Study Articles | Science Articles | Science RSS |  |
||
Salisbury screen |
||||
|
The Salisbury screen is a type of Radar Absorbent Material that consists of three layers (the ground plane - a dielectric of a specific thickness - and a lossy thin surface) the specific thickness of the dielectric is a quarter of the wavelenght that will be absorbed by the material. |
||||||||||||
| Author: Dragan Valeriu |
|
|||||||||||
The Salisbury screen is maybe the first ever anti-radar (or to be more precise anti-reflective) concept; the so called RAM (radar absorbent material).
It was first described in 1952 and was applied in ship RCS (radar cross section) reduction.
There have been many design refinements over the years, especially because of the increasing interest for stealth planes, but the principles remain the same.
The easiest to understand salisbury screen design consists of a so-called ‘ground plane’ which is the metallic surface that needs to be concealed , a lossless dielectric of a given thickness (a quarter of the wavelength that will be absorbed) and a thin lossy screen.
The principle is this:
1.The incident wave (which we will consider to be made up by parallel beams), is split into two (equal in intensity) waves that have the same wavelength (λ)
2.The first wave is reflected by the exterior surface (the thin lossy screen) while the second beam travels through the dielectric, and it is reflected by the ground plane (which is the most inner layer of the salisbury screen)
3.The reflected waves interfere and cancel each other’s electric fields (radar is an electromagnetic beam-microwave and IR)
To explain the phenomenon, we need to look at the interference theory: two waves that are coherent interact: the two combine to form a single output wave and if their picks coincide the output intensity is the sum of the two intensities. However if the two waves are completely out of phase the two intensities cancel each other out (that only happens when the two waves are offset by λ/2).
The second wave (in step 2.) travels twice (once from and once to the exterior thin lossy screen) the distance equal to λ/4, the distance is therefore 2* λ/4= λ/2 Thus the two waves cancel each other.
Because of the incidence angle,the waves that are canceled do not come from the same exact incident wave, however they are all similar thus they are coherent and interfere.
There are a few disadvantages inherent to this model (some of which have been solved). One would be the fact that salisbury screens work well only for a very narrow portion of the radar spectrum thus making it very vulnerable to multiple radar protected arias. Another problem is the thickness of the screen itself, the radar wavelengths are between 10cm(ten centimeters) and 1mm(one millimeter), thus for a longer wavelength , the thickness gets up to 2,5 centimeters which is quite difficult to cope with (in the aerospace applications), researches are being made for ultra thin salisbury screens involving Sievenpiper HIGP which shows remarkable improvements to the thickness of the screen.
About Author
Aerospace student at Universitatea Politehnica Bucuresti (Bucharest-Romania)
4 Kyu Ju-Jutsu (Romanian Martial Arts Federation)
Article Source:
http://www.1888articles.com/author-dragan-valeriu-15.html
Other Related Articles Want to freelance as a Programmer, Copywriter, or Web Designer? by Guest Tractrix by Dragan Valeriu Salisbury screen by Dragan Valeriu Iron ball paint by Dragan Valeriu Stockholm syndrome by Dragan Valeriu |
