Infrared Smokes
The proliferation of thermal imaging FLIR systems on the battlefields necessitates the use of obscurant smokes that are effectively opaque in the infrared part of electromagnetic spectrum. To achieve this, the particle size and composition of the smokes has to be adjusted. One of the approaches is using an aerosol of burning red phosphorus particles and aluminium coated glass fibers; the infrared emissions of such smoke curtains hides the weaker emissions of colder objects behind it, but the effect is only short-lived. Carbon (most often graphite) particles present in the smokes can also serve to absorb the beams of laser designators. Yet another possibility is a water fog sprayed around the vehicle; the presence of large droplets absorbs in infrared band and additionally serves as a countermeasure against radars in 94 GHz band. Other materials used as visible/infrared obscurants are micropulverized flakes of brass or graphite, particles of titanium dioxide, or terephthalic acid.
Older systems for production of infrared smoke work as generators of aerosol of dust with controlled particle size. Most contemporary vehicle-mounted systems use this approach. However the aerosol stays airborne only for a short time.
The brass particles used in some infrared smoke grenades are typically composed of 70% copper and 30% zinc. They are shaped as irregular flakes with a diameter of about 1.7 µm and thickness of 80-320 nm.
A dry powder fire extinguisher is said to be a good improvised system for production of aerosol effective even in far infrared.
Some experimental obscurants work in both infrared and millimeter wave region. They include carbon fibers, metal coated fibers or glass particles, metal microwires, particles of iron and of suitable polymers.
Read more about this topic: Smoke Screen