To detect targets with low dielectric constant, which proximity sensor variant is typically chosen?

• A. Shielded capacitive sensors are used for high dielectric targets
• B. Shielded capacitive sensors are used to detect low dielectric constant targets
• C. Unshielded capacitive sensors are used to detect low dielectric constant targets
• D. Inductive sensors are used for capacitive targets

Answer: (B)

Capacitive proximity sensing relies on how the target’s dielectric constant changes the capacitance between the sensor and its surroundings. When the target has a low dielectric constant, that change in capacitance is small, so detecting it reliably requires concentrating the electric field where the target is and minimizing interference from the environment. A shielded capacitive sensor has a grounded shield around the sensing face that confines the field to the target region and reduces stray coupling to nearby materials. This makes the small capacitance change caused by a low-κ (low dielectric constant) target more noticeable, improving sensitivity and stability. In contrast, unshielded sensors have broader, more environment-influenced fields, which can wash out the small signal from low-dielectric targets. Inductive sensors detect metals, not dielectrics, so they’re not suitable for low-dielectric targets.