How does capasitive sensor work? How does it sense bodies?

Question

I need to know the working mechanism of this sensor & understand how could it sense bodies.
Hint: it's sorted under the proximity sensors types

Answer 1

The sensor is a capacitor constructed in such a way that the electric field from the sensor extends into the space in front of the sensor. The capacitance of the sensor will change if an object is placed close enough to the sensor that the electric field from the sensor passes into the object assuming the object has a dielectric constant different from air.

The circuit used with the sensor is essentially a capacitance meter.

Some uses are sensing a stud behind a drywall wall or detecting liquid in a plastic bottle.

Answer 2

A capacitive sensor uses an internal oscillator with a frequency that depends on the capacitance near the sensing head. If an object is brought close enough to that head the initial capacitance of the sensor is added to by the capacitance of the object that is near the head. New capacitance means new oscillation frequency. The internal circuitry of the sensor recognizes the oscillation at a new frequency by the change in current draw and triggers a comparator to change states. That change is what gives the yes-no signal telling that an object has been detected.

It is equivalent to a metal detecting sensor except that one uses a change in inductance (not capacitance) to change the oscillation frequency.