ITO/AR
Coated v ITO Coated
Shielding
(dB) v Freq for 9 & 125 W / square
&
Transmission v W / square
Calcualted
reflection v l
|
ITO (Indium Tin Oxide - a transparent semiconductor) is often used
to coat glass to provide surface electrical conductivity, whilst still
maintaining good transparency. This is necessary for example to
prevent electrostatic charge build up, and more importantly to provide EMC
screening, for example for visual displays in electrically noisy
environments.
Clarity is an important consideration for such display filters, but
choosing an EMC-shielded filter often involves a trade-off between clarity
and shielding effectiveness. Conventional meshed windows offer good
shielding (up to 80dB), but have poor light transmission (~60-70%), and
can produce very undesirable optical distortions as a result of aliasing
and Moiré etc.
Thin metallic coatings are also sometimes used, which avoid the
distortions but offer worse transmission, and shielding effectiveness.
ITO is usually the best compromise. At Torr Scientific we can
provide ITO coated glass with surface resistivities as low 10 W
/ square giving good EMC attenuation ~ 40dB @100MHz (depending on
geometry), and good transmission ~ 80%.
All windows and viewports, however suffer Fresnel reflectivity losses
R = [(n-1)/(n+1)]2 per face
It
is for this reasons that Torr Scientific have developed a proprietary,
cost effective AR (Anti-Reflection) coating for ITO glass, which means
that you can have simultaneously good conductivity <10 W
/ square, and good transmission >90% - something that would not be
possible with a mesh.
How
does this translate into reality …. See for yourself !
- the top fig shows
2 sheets of 10 W/square
glass, photographed against a dark background showing a reflection of the
ceiling – one is untreated and the other has a central windowed area
coated with TSL’s proprietary AR coating, the difference is
striking. Imagine the improvement in your application.
The
bottom figure compares the spectral response of regular 10 W
/ square glass versus the new AR version. |
