Do Carbon Fiber Layers Effect RF Transparency?

[Yukon@K-9 Rocket Tech]

I'm new to RF telemetry, and I bought a 3DR Telemetry module recently. I built some custom carbon fiber tubes which is composed of 1 layer of fiberglass and 1 layer of carbon fiber (I know that's a horrible idea because they have different properties, but I did it because I wanted wiring to be integrated into the tube itself via copper tape in the future and don't want it touching CF). I decided not to add more layers of CF to ensure the 3DR module could still hopefully transmit data though the tube. However this was based on my assumption. I would assume a faraday cage's metal thickness won't matter so long every hole is smaller than the wavelength it's trying to block, so would CF be the same way where tube thickness have no effect in increasing or decreasing radio transparency? Or since CF is conductive, but not as conductive as metal, would thickness of the tube actually effect transparency. Please point it out if my knowledge is incorrect and I'd also be happy to hear from your experience and expertise!

 

[MClark]

Yes, carbon fiber interferes with RF

 

[Yukon@K-9 Rocket Tech]

Yes, carbon fiber interferes with RF

Yes I understand that, but is there more interference per mm thickness of CF the RF has to transmit through?

 

[watheyak]

Any thickness attenuates the signal enough to be considered non-transparent.

 

[Titan II]

Yes I understand that, but is there more interference per mm thickness of CF the RF has to transmit through?

Yes

 

[SDramstad]

Use a fiberglass nosecone and put the transmitter there

 

[thequick]

This paper describes the effects of carbon fiber in nylon. I’d expect this to be pretty similar to cf in epoxy


https://www.ece.mtu.edu/faculty/wfp/articles/shielding1.pdf
sounds like you have all the parts available, you could always do some ground testing.

 

[David_Stack]

In the ceaseless quest for strength and lower wing loading, R/C sailplane fuselages eventually moved to construction primarily of carbon. Pilots who were still using 72Mhz had to resort to running antennas outside of the fuselage, and pilots on the (then) new 2.4Mhz band ended up drilling small holes in their fuselages and routing 'whiskers' out into the airstream in order to ensure signal strength.

 

[Tim Crabtree]

The amount of attenuation is a function of the thickness of the material, the material's attenuation coefficient (more conductive, higher attenuation) and the wavelength of the electromagnetic radiation - lower frequencies are attenuated less, higher frequencies attenuated more. The attenuation is basically linear with thickness and frequency, so twice as thick, twice the attenuation, twice the frequency, twice the attenuation, etc. Our Marco Polo tracking system operates in the 900Mhz band and we don't recommend any conductive material be used for enclosing the antenna. If necessary the antenna can be fed outside the enclosure, as David Stack suggested. Even then, if a conductive material runs along the length of the antenna that can have a large effect on the antenna gain and radiation pattern, conductive material at the base of the antenna (assuming it is a monopole antenna) will have little effect on the gain but can also affect the radiation pattern. At some level "everything matters" and we have never once had anyone complain that their tracking system had too much range!

As an example of poor material selection, we sell a hunting arrow tracking system on an OEM basis and when testing the prototypes we discovered that the logo label over the antenna doors was metalized polyester film. Even though it was very thin and only covered about 30% of the area, it totally destroyed the performance of the system (more than just attenuation of the signal, but that is another story). Not to go down a rathole here but non-conductive materials can also affect antenna performance because their dielectric constant is different from that of the air that is usually assumed to surround the antenna....

 

[Yukon@K-9 Rocket Tech]

The amount of attenuation is a function of the thickness of the material, the material's attenuation coefficient (more conductive, higher attenuation) and the wavelength of the electromagnetic radiation - lower frequencies are attenuated less, higher frequencies attenuated more. The attenuation is basically linear with thickness and frequency, so twice as thick, twice the attenuation, twice the frequency, twice the attenuation, etc. Our Marco Polo tracking system operates in the 900Mhz band and we don't recommend any conductive material be used for enclosing the antenna. If necessary the antenna can be fed outside the enclosure, as David Stack suggested. Even then, if a conductive material runs along the length of the antenna that can have a large effect on the antenna gain and radiation pattern, conductive material at the base of the antenna (assuming it is a monopole antenna) will have little effect on the gain but can also affect the radiation pattern. At some level "everything matters" and we have never once had anyone complain that their tracking system had too much range!

As an example of poor material selection, we sell a hunting arrow tracking system on an OEM basis and when testing the prototypes we discovered that the logo label over the antenna doors was metalized polyester film. Even though it was very thin and only covered about 30% of the area, it totally destroyed the performance of the system (more than just attenuation of the signal, but that is another story). Not to go down a rathole here but non-conductive materials can also affect antenna performance because their dielectric constant is different from that of the air that is usually assumed to surround the antenna....

Thank you! That was the details I was looking for