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/ External Optical Filter Defogging and Deicing Solution

External Optical Filter Defogging and Deicing Solution

A leading defense customer requested enhancements for external windows to improve defogging and deicing capabilities. This request was identified as a VIS-NIR application and resulted in the custom design of antireflective, transparent conductive coatings to meet their request. Additionally, these exterior windows were a non-standard shape and size.
Despite the complex design, Dontech was able to engineer varying multi-layer thin-film coatings with separate, distinct resistivity requirements, creating an innovative compensation system to ensure uniform heating power density of 4.0 ± 0.6 W/in2 for each window. Reflectance and transmittance measurements were conducted in house with the use of a spectrophotometer at customer-specified angles of incidence.
Coating integrity and durability were verified through thermal cycling, humidity, abrasion, salt fog, and adhesion testing. An infrared camera was used to measure temperature uniformity during heating. Interferometer measurements ensured no significant transmitted wave front errors when the powered heaters were dormant and activated. Wire leads were then attached to the bus bars using Dontech’s proprietary soldering process to prevent degradation to the optics.
After the windows were bonded into the housing, the wire leads were routed and staked, then soldered to a harness that was terminated with a connector that was compatible with the customer’s connector on the targeting system. Dontech performed dielectric strength testing (“Hipot”) to verify electrical isolation between the wire leads, bus bars and transparent heater and the housing. Dontech successfully delivered a completed assembly that not only passed qualification but was unique and highly specialized per customer requests.