When would you want to use a shielded capacitive sensor as opposed to an unshielded variant?

• A. To detect targets with high dielectric constant
• B. To detect metallic targets
• C. To detect liquids with strong conductivity
• D. To detect triggers with low dielectric constant

Answer: (D)

Shielded capacitive sensors are designed to minimize interference from the surrounding environment by using a driven shield around the sensing surface. This keeps stray field lines from leaking into nearby objects and reduces parasitic capacitance to ground, which makes the sensor more stable and less sensitive to clutter or moisture. Because of that, they are especially helpful when the target causes only a small change in capacitance—that is, when the target has a low dielectric constant. In those cases, the shield concentrates the sensing field and improves detectability of the small capacitance variation. Targets with high dielectric constants tend to produce larger changes and can be detected well by unshielded sensors, while metals or highly conductive liquids introduce other issues that shielded designs don’t specifically address.