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."

Comments

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: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: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. 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: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. 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.