The Japanese have discovered a WiFi security paint.

So how does this new blocking paint actually work? Well, electromagnetic (EM) waves can only be blocked when a material's magnetic field resonates at the same frequency as the wave. The New Scientist says that wave absorbers are usually made from iron-rich oxides, but higher-frequency transmissions outstrip the power of iron to absorb electromagnetic waves. This is because the standard oxide coating has a maximum resonance frequency that is outstripped at 48GHz.
But Shin-ichi Ohkoshi's team at the University of Tokyo in Japan has now identified a new aluminium-iron oxide able to block waves with a frequency almost four times higher. They used a sensitive magnetometer (a scientific instrument used to measure the strength and/or direction of a magnetic field) to confirm that a powder of the new oxide can absorb EM waves of up to 182GHz at room temperature.

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http://www.itworldcanada.com//Pages/...A-B2C4D89EE233