Using Aluminum Oxide Paint To Secure Wi-Fi

eldavojohn writes "The BBC reports on people using aluminum oxide in their paint to block Wi-Fi signals from leaving their home or business. Aluminum oxide resonates at the same frequency as Wi-Fi signals and other radio waves, blocking data from going outside a building. It's not a flawless solution, as it may also block AM/FM signals. You or your neighbors may be unwittingly using this already, as most pre-finished wood flooring uses aluminum oxide as a protective coating."

Note: AlFeO *not* Al2O3

[Anonymous Coward]

Note, the material concerned is Aluminium IRON oxide. Big difference. Aluminium oxide is a good dielectric and would be bugger all use for RF shielding. Oh and the article is a wierd too: it talks about 100GHz shielding where WiFi bands are ~ 2.5GHz.

Re:Cellphone reception?

[RobVB]

Wifi works at around 2.4 Ghz, GSM frequencies [wikipedia.org] are between 380 Mhz and 2 Ghz, with the most frequently used frequencies being GSM900 (890-960 Mhz) and GSM1800 (1710-1880 Mhz).

From the article:

The paint contains an aluminium-iron oxide which resonates at the same frequency as wi-fi - or other radio waves - meaning the airborne data is absorbed and blocked.

I assume this means the aluminium-iron oxide resonates at around 2400 Mhz, which shouldn't interfere with normal cell phones.

Re:Resonance at other frequencies?

[John Hasler]

> What frequencies are not resonant in Aouminum Oxide paint?

The reporter is just yammering. He hasn't the foggiest idea what the word "resonant" means and knows less than nothing about radio. All we can glean from this is that someone has put out a press release about rf absorbant paint, something that has been around for decades.

Re:Cellphone reception?

[morgan_greywolf]

Try reading more carefully:

FTFA:

While paints blocking lower frequencies have been available for some time, Mr Ohkoshi's technology is the first to absorb frequencies transmitting at 100GHz (gigahertz). Signals carrying a larger amount of data - such as wireless internet - travel at a higher frequency than, for example, FM radio.

...

"Our current mobile phones work at much lower frequencies, around 1.5 gigahertz. But, our material can also absorb frequencies that low, so you could block phone signals from outside and stop people's phones ringing during the movie," he said.

From the sounds of it, just about anything below 100 GHz gets blocked. That means cellphones, too.

Re:Note: AlFeO *not* Al2O3

[fuzzyfuzzyfungus]

Unless this stuff is very much unlike a certain other [wikipedia.org] aluminum iron oxide composition, there might be a certain other big difference...

Re:Cellphone reception?

[elashish14]

A conductive metal has free electrons which will block and reflect any waves below its plasma frequency. However, an ionic solid does not have free electrons - instead, it has just a few resonant other mechanisms with limited range so it will block a more specific part of the electromagnetic spectrum than a metal would. The frequency of wifi signals happens to be in the range of one of these mechanisms for the paint used.

Re:Resonance at other frequencies?

[Anonymous Coward]

All we can glean from this is that someone has put out a press release about rf absorbant paint, something that has been around for decades.

Using information in the article I was able to find the actual science paper [acs.org]. It turns out they are able to tune the resonate frequency of this paint. Very cool. However, the it doesn't go all the way down to 2.4 GHz. That's a pretty long wavelength for this process.

Re:Hey, it's good enough for the office...

[Anonymous Monkey]

Looking like a cyborg is good, because the other cyborgs won't try to assimilate you. However, it is important to have a radio transmitter with you everyplace so that you are broadcasting some sort of radio signal at all times. Now, at home, it is still better to line your walls with aluminum foil, but you need to do so INSIDE the walls, behind the drywall, because you don't want the government drones seeing it. You should line your attic as well, but not your basement, because The Worms are attracted to foil. In your basement you should use lots and lots of crushed cans. Sprite cans works best.

Re:Does not resonate with me

[elashish14]

Ionic materials can be polarized to interact with electromagnetic waves to block signal transmission. They have a number of absorptive mechanisms. The highest frequency absorption mechanism is where electrons around the nucleus resonate, roughly at 10^17 Hz. Then there's atomic vibrations where the nuclei themselves vibrate (10^14 Hz I think). Not sure what they are for the material used in particular though, but ionic materials can resonate. It doesn't seem that they're in the range used for this application

Re:Cellphone reception?

[Geoffrey.landis]

Water molecules are famously resonant at 2.45 GHz, that's where microwave ovens operate,

No, they're not. That's a myth [vias.org]. There's no water resonance at or near 2.45 GHz. Water absorbs at pretty much any microwave frequency, with stronger absorption the higher the frequency.

If anything, you'd want to tune a microwave oven away from strong water resonances, because you want the radiation to penetrate (so as to heat the object evenly) and not be shallowly absorbed, which would result in uneven heating. (Note that a microwave oven is a cavity, so you don't need to absorb energy in a single pass-- it will resonate around until it does get absorbed.).

Re:Cellphone reception?

[sunderland56]

The reason is that it can interfere with emergency calls even outside the building.

Actually the primary reason that jammers are illegal is that they are unlicensed. All unlicensed transmitters are illegal in the USA.

There is also a section of the FCC rules that prohibits interference in most cases, and absolutely prohibits willful interference.

Re:Cellphone reception?

[BitterOak]

Was this in the USA? The reason is that doing this, while so very nice to prevent the idiots who don't know how to put their phones on vibrate from bothering everyone else, is also highly illegal.

I think you are confusing active vs. passive blocking. Active blocking is illegal as it involves transmitting signals on the same frequencies as are used by cellphones, and this is regulated spectrum. Passive blocking, by using special paints or metal screens is perfectly legal.

Re:"By coating an entire room..."

[rdnetto]

Actually, no. Transparent aluminium [wikipedia.org] is different, but given the amount of power it would take to maintain it in that state, hiring a dedicated team of ninjas to kill anyone using a wireless device would be cheaper.