Smart glass as Faraday shielding

[hilbert2]

TL;DR Summary

Using tunable mirrors as Faraday shielding

Some companies seem to be selling "smart glass" products that can be electrically tuned at will to be either mirroring or transparent, at least in visible wavelengths.

Suppose someone were to Faraday shield a room to prevent van Eck phreaking or whatever kind of eavesdropping from outside, using that type of surfaces as part of the shielding, and make their conductivity/reflectivity change randomly at a very high frequency. Then I guess any signals leaking out would have an additional random high-frequency modulation in them, making them impossible to interpret? That would seem to be even better than normal EM shielding, but a problem is that mobile network signals from phones or computers would become unwanted radio noise when mangled in that way, and possibly disturb everyone else's communications.

This is just a theoretical idea, as the current tunable smart mirrors only seem to reflect EM radiation on a limited range of wavelengths.

 

[tech99]

I think it is just a liquid crystal device which operates slowly to give a frosted appearance, so cannot respond to high frequencies. I imagine the surface will still reflect light in the usual way so might be subject to eavesdropping.

 

[hilbert2]

Some of them actually become mirroring and not just opaque, but there doesn't seem to be much data about the transmittance on a large wavelength range that includes radio and microwave frequencies.

 

[Baluncore]

The refractive index of materials, is usually different between optical and radio frequencies.

The thin transparent electrodes (indium) printed on glass have a high resistance. That slows the switching response to applied voltages to microseconds. The high resistance electrodes are very poor at reflecting RF.

Your enemy could radiate your smart glass, with sufficient RF power to lock it in a transparent optical mode, or destroy the conductive film on the glass.

If you want EM privacy, you need to build a double wall screened room without windows, and with a conductively-fitting door. Ventilation will need to be through metal screens. Power supplies must be decoupled.

You could increase security by transmitting one watt of random spread spectrum signal on the outside of the box, to mask the greatly attenuated internal signals that might escape.