What materials are transparent to radar? Weatherproofing a radar gun

In summary, the project is trying to produce a roadside speed camera which displays vehicle speed to drivers to improve speed awareness. There is a weather tight plastic box (opaque, at least to visible light) to put this in, also have some transparent 10mm acrylic. The problem is the author has not been able to find information on whether or not the acrylic is transparent to the radar frequency being used and is experimenting with different materials to find a solution. If you have any knowledge in this area please let the author know.
  • #1
Jack_O
65
0
I’m currently working a project to produce a roadside speed camera which displays vehicle speed to drivers to improve speed awareness.

A Doppler radar gun operating at 24.1GHz (1.24cm) is being used as the source and detector. There is a weather tight plastic box (opaque, at least to visible light) to put this in, also have some transparent 10mm acrylic. The idea is to cut a hole in the box and use the acrylic as a window. The problem is I have no idea if the acrylic is transparent to the radar frequency being used and I haven’t been able to find any information online.

If you have any knowledge in this area please let me know!
 
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  • #3
Thanks, think I will experiment with the materials and see if the signal still gets through. There's a limited budget so it would be better not to have to order in specialist materials.

I'll update the thread with my findings.
 
  • #4
I wish you won't succeed. We don't need more speeding tickets... we can get one already :P
lol kidding mate ;)
 
  • #5
I suspect that you should use either a very thin window or a quarter wave window at 24.1GHz, about 3mm. The quarter wave transformer should eliminate the partial reflections at the air-window interfaces.
 
  • #6
Baluncore said:
I suspect that you should use either a very thin window or a quarter wave window at 24.1GHz, about 3mm. The quarter wave transformer should eliminate the partial reflections at the air-window interfaces.

Could you explain the reasoning behind the quarter wave window?

I've been read the article about EM penetration depth on wikipedia, but this has led to more questions than answers really (e.g. how well does acrylic reflect radar and what is the complex refractive index of acrylic at 24GHz?). I suppose the problem is the equations are very general and the specific values for the available materials don't appear to be readily available. Not had a chance to test yet due to the weather conditions here in the uk.

Aero_UoP said:
I wish you won't succeed. We don't need more speeding tickets... we can get one already :P
lol kidding mate ;)

The point of the camera is raise speed awareness and improve safety culture, it won't take pictures or have any way of issuing tickets. Of course there is a simple way to avoid speeding tickets ;)
 
  • #7
Jack_O said:
Could you explain the reasoning behind the quarter wave window?
My idea was like the quarter wave coating on optical surfaces, where the coating has a refractive index close to the geometric mean of the optical material and the environment. If the reflection from the entry interface cancels the reflection from the exit interface then the reflections would disappear.
However, in this case since it is air on both sides without a centre layer maybe it should be a half a wavelength thickness adjusted for the velocity in the window material. I have not thought about it.
 
  • #8
http://www.ece.umd.edu/class/enee381-1.F2004/lectures/lecture16.htm

"the thickness of the dielectric layer be a multiple of a half-wavelength in the dielectric at the operating frequency.
Such a dielectric layer is referred to as a half-wave dielectric window."
 
  • #9
Definitely some good thoughts, I may include in a technical write up.

Had a chance to test the materials this morning, to my surprise the detector continued working with all of them. The first test piece was 10mm 'armoured' clear acrylic normally used in the windows on yachts. The second was 6mm clear 'cast acrylic sheet' made by Altuglas and the final piece was 1mm Clear HIPS (high impact polystyrene). I don't have anyway of measuring the exact drop in signal but as long as it works all is good.

The source and detector is an MPH industries DS4, with a maximum output of 20mW, in case anyone is curious.
 

1. What materials are transparent to radar?

The most common materials that are transparent to radar are glass, plastic, and certain types of composites. These materials do not significantly reflect or absorb radar waves, allowing them to pass through without interference.

2. Is metal transparent to radar?

No, metal is not transparent to radar. Metal reflects and absorbs radar waves, making it difficult for radar signals to pass through. This is why radar detectors are often made with metal casings to block incoming radar signals.

3. Can weather conditions affect radar transparency?

Yes, weather conditions such as rain, fog, and snow can impact radar transparency. These conditions can cause interference and absorption of radar waves, making it more difficult for radar signals to pass through and affecting the accuracy of radar readings.

4. How can you weatherproof a radar gun?

To weatherproof a radar gun, a protective cover or casing can be used to shield the gun from environmental elements such as rain and snow. Additionally, using waterproof materials for the radar gun's components and regularly maintaining and calibrating the gun can also help to weatherproof it.

5. Are there any materials that can enhance radar transparency?

There are certain materials, such as radar-absorbent materials (RAMs) and radar-transparent coatings, that can enhance radar transparency. These materials are designed to reduce or eliminate radar reflections and can be used on surfaces such as aircrafts or buildings to make them more difficult to detect by radar.

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