Infrared scanner cell material used in the system is which of the following?

• A. Cadmium sulfide
• B. Germanium
• C. Lead sulfide
• D. Silicon carbide

Answer: (C)

Infrared detection relies on materials whose electronic structure allows absorption of infrared photons and conversion into an electrical signal. Lead sulfide has a narrow bandgap, making it sensitive to infrared wavelengths in the near to mid-IR range. It can operate effectively at or near room temperature, which simplifies the scanner design and keeps costs reasonable. This combination of IR sensitivity and practicality makes lead sulfide a common choice for infrared scanner cells in many gas-detection and scanning systems.

Cadmium sulfide mainly detects visible light, not infrared. Germanium can detect IR but typically requires cooling to achieve good sensitivity and accuracy. Silicon carbide has a wider bandgap and is less responsive in the IR range used by standard scanners. Hence lead sulfide best fits the infrared scanning needs in this system.