RF blocking phone case, doesn't impede reception - Page 1
Forum section: electronics / general

author: pjhenley
author_rank: Contributor
timestamp: February 05, 2020, 02:09:58 pm
content: This Kickstarter showed up in my feed today. It's for a "RF radiation blocking smartphone case" that "does not affect phone signal, WiFi or bluetooth reception." One wonders how effective it could be.https://www.kickstarter.com/projects/x-blue/x-blue-rf-radiation-blocking-smartphone-case?ref=Fundedtoday&utm_medium=referral&utm_source=12dsa.fnd.to

author: borjam
author_rank: Unknown
timestamp: February 05, 2020, 04:16:49 pm
content: That reminds me of a claim by a marketingguru: Neoprene cases block cell phone location systems.

author: grifftech
author_rank: Frequent Contributor
timestamp: March 11, 2020, 09:16:32 pm
content: it does look ince tho

author: thm_w
author_rank: Super Contributor
timestamp: March 11, 2020, 10:59:46 pm
content: Quote from: borjam on February 05, 2020, 04:16:49 pmAre you sure about that?How will anyone know where your phone is when it looks like this

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2020, 05:48:06 am
content: Related story:A coworker wanted to test a Bluetooth device with poor reception. They started by putting the device in a foil pouch, but that didn't seem to be doing very much, so asked me about it. I said they're on the right track, it just needs to be deeper inside, and better sealed.The "pouch" in question was a square of kitchen tinfoil, rolled up a few times into a flattened cylinder about the width of your hand, and folded over on one end. The device slides inside, and the open end is just kind of sitting there, hopefully shorting closed but it didn't seem to be doing a good job of it.After some fiddling around, I got the device deeper into the pouch, and crimped the end tighter. Before, the device was still a bit visible from the opening; now it was a good wavelength from the opening. But the pouch itself acts as something of a waveguide, at lucky frequencies, and it's probably just about the right width for Bluetooth to get through, actually. I took the open end and pinched it in the middle, effectively doubling its cutoff frequency -- still not dropping. To my surprise, I had to pinch in three places across the opening to get it to drop. Several paperclips did the job hands-free.It's conceivable that a phone case might reduce near field strengths towards some direction (the front screen, I suppose), without impairing overall response (the radiation pattern will likely be narrower, though). The limiting factor is diffraction, which because a phone is about a wavelength wide, isn't really going to help you out that much.And you're quite limited on what kind of shielding you can place over the display. ITO glass isn't the cheapest thing, nor terribly robust or transparent; and mesh screens are worse, plus you'll inevitably get Moire patterns against screen pixels.I didn't look at the links, don't really care to; so I don't know if they've shown due diligence in this regard. It's interesting that their target market probably isn't expecting them to, so the healthy skepticism is, needless to say... well deserved.Tim

author: Bud
author_rank: Super Contributor
timestamp: March 12, 2020, 06:09:30 am
content: I learned from working with UHF stuff that shielding cans must be soldered throughout the perimeter. Any opening no matter how small caused RF leaks strong enough to produce interferrence.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 12, 2020, 05:37:32 pm
content: Quote from: Bud on March 12, 2020, 06:09:30 amYes, and the cases of RF gear have tons of screws holding them shut, just to make a good seal.