Which statement about capacitive sensors is true?

• A. They can detect only metallic materials
• B. They can detect any type of material
• C. They require direct contact with the target
• D. They are unaffected by humidity

Answer: (B)

Capacitive sensing works by creating an electric field at the sensor’s sensing face and measuring how the field changes when a target enters that field. Any material with a dielectric constant different from air will disturb that field, changing the capacitance the sensor detects. Because most materials have a distinct dielectric constant from air, capacitive sensors can sense a wide range of targets—metals, plastics, liquids, powders, wood, and more. This breadth is why the statement about detecting any type of material is true. They don’t need to touch the target, which makes direct contact unnecessary, so that other idea isn’t correct. Humidity and moisture can affect the sensor’s readings because moisture changes the dielectric properties of materials and air, so the sensor isn’t completely immune to humidity.