In the 8–12 μm band, which pair of materials is a good transmitter?

• A. Geranium and Thin Plastics
• B. Metals and Glass
• C. Water and Concrete
• D. Wood and Stone

Answer: (A)

In the 8–12 μm longwave infrared band, the material’s ability to transmit depends on low absorption in that window. A good transmitter is a material that lets LWIR pass through with minimal loss. Germanium is widely used as an IR window because it transmits well in this range; plastics can also be transparent to LWIR if they’re thin enough, making thin plastics effective transmitters. In contrast, metals reflect infrared rather than transmit it, and common construction materials like water, concrete, wood, and stone absorb or scatter LWIR, hindering transmission. So the pair that provides transmission in this band is germanium and thin plastics.