Does PLA block wifi signals?

7

I printed a raspberry pi case from PLA. This case.

I fitted it to my raspberry pi and now the wifi keeps dropping out. When I take it out of the case there is no problem.

The filament I am using is Black, 3D Hero 1.75mm.

Has anyone experienced anything like this before, if so how did you work around it? Is it common with PLA is there another material that wouldn't cause an issue?

JackU

Posted 2019-03-27T12:04:42.583

Reputation: 171

What color, some colors may contain conductive pigment. – r_ahlskog – 2019-03-27T12:08:52.997

@r_ahlskog Black, 3D Hero, 1.75mm – JackU – 2019-03-27T12:12:15.387

Black would be a prime suspect, probably contains carbon. Being electrically conductive would make it attenuate the WiFi signal and likely be the cause of your problems, even more if it was grounded. – r_ahlskog – 2019-03-27T12:15:47.843

The issue could also be heat. Do yo have ventilation holes? Is there a fan? – user77232 – 2019-03-27T12:59:51.837

1@user77232 - There's a lot of ventilation holes in the pattern. I would doubt the Pi creates enough heat to cause issues, but you never know. – Pᴀᴜʟsᴛᴇʀ2 – 2019-03-27T13:13:24.150

@user77232 There are vent holes in the pattern. There is no fan but the pi doesn't get get that hot. – JackU – 2019-03-27T14:23:59.027

I think @Pᴀᴜʟsᴛᴇʀ2 may be correct, that was my first thought as well. Check out this project from the Pi foundation, it has instructions for monitoring the boards temps using Python. You can then track the see if the dropouts coincide with temperature spikes.

– Dr. Mantis Tobbogan – 2019-03-27T15:46:08.257

Well, your experiment pretty clearly shows that at least the filament in question is at least attenuating the WiFi frequency in use. Perhaps try switching bands (2 vs 5 GHz)? Next trick - identify the location of the WiFi antenna in the R-pi and put a cutout in your case. – Carl Witthoft – 2019-03-27T18:40:32.873

Try a little closer to the wifi source, may be you are too far away and the normal attenuation of an object affects your design. At home I have some interferences with an antenna of phone company, so I have to test on a shielded room. – Fernando Baltazar – 2019-03-27T19:36:20.817

Thanks for your suggestions guys. I will try to add a cutout for the WIFI antenna. Failing that, I will also try a different filament to see the results. – JackU – 2019-03-28T07:31:13.637

It would be interesting to see if the PLA is conductive. If you have a multimeter, measure the resistance between two points, say 1cm apart. – mbmcavoy – 2019-03-28T19:18:54.643

Answers

3

Typically the black pigments in polymers are mineral based. If you are having true WiFi issues then it sounds like your filiment is using black iron oxide also called magnetite for the black pigment. This is the same material they use in radar absorbing paints which would make sense as to why you are having radio related issues.

The Thrifty Engineer

Posted 2019-03-27T12:04:42.583

Reputation: 131

the other common black pigment is carbon. – Trish – 2019-03-28T07:58:25.983

2

It could be several problems

  • Shielding from the material
  • Heat
  • Mechanical load from the casing
  • A metal screw next to the antenna

To learn more about the problem, comparing different configurations is the only way to got (As you guessed, it might be shielding, so you could see how the same shape works when printed in white PLA). Since comparing wifi signals is very prone to random changes, it is important to get better information than "random drops". Signal strength is a much better indicator.

A wifi signal test is shown here, comparing a bare PI with one in a aluminum case https://www.youtube.com/watch?v=26OxCwEHoTk Indeed the aluminum case reduces the signal strength, as it was to expect.

For a faster comparison you can use the command 'iwconfig'. It usually shows a signal strength (Tx-Power)

> iwconfig
wlp4s0    IEEE 802.11  ESSID:off/any  
      Mode:Managed  Access Point: Not-Associated   Tx-Power=20 dBm   
      Retry short limit:7   RTS thr=2347 B   Fragment thr:off
      Power Management:off

A possible workaround might be to add an external antenna. The raspberry pi actually has solder points to add an antenna connector. https://www.mictronics.de/2017/10/raspberry-pi-3-with-external-antenna/

However it might be simpler to produce several iterations of casings and compare the signal strength, depending on availability to SMD soldering.

Kjell

Posted 2019-03-27T12:04:42.583

Reputation: 51