Which materials are good transmitters in the 8–12 μm infrared waveband?

• A. Water, Concrete
• B. Glass, Metal
• C. Geranium, Thin Plastics
• D. Wood, Ceramic

Answer: (C)

In the 8–12 μm infrared window, transmission depends on having low absorption in that range. Germanium is a classic IR optical material because it remains relatively transparent from about 8 to 12 μm, making it a reliable transmitter for that band. Thin plastics can also transmit in this window, especially when they’re very thin and made of polymers with weaker absorption in that region, so they can pass long-wave IR signals effectively.

Water and concrete absorb strongly in the LWIR due to moisture and mineral vibrations, so they don’t transmit well. Glass and metal either absorb or reflect in this band, not pass through, and wood and ceramic tend to scatter and absorb, also limiting transmission.