A proximity sensor is a sensor which detects the presence of an object/person. A sensor that can be used for detecting the presence of objects surrounding it without having any physical contact is termed as a proximity sensor. This can be done using the electromagnetic field or electromagnetic radiation beam in which the field or return signal changes in the event of the presence of any object in its surrounding.
The object being sensed is often referred to as the proximity sensor’s target. Different proximity sensor targets demand different sensors.
The maximum distance that this sensor can detect is defined nominal range. Some sensors have adjustments of the nominal range or means to report a graduated detection distance.Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.
The proximity sensor on most smart-phones with touchscreen exists to disable accidental touch events. The most common scenario is the ear coming in contact with the screen and generating touch events, while on a call. The simplest proximity sensors do not measure distance. A bumper can be passive, simply making the robot bounce away from things it hits. More often, a bumper has a switch that closes when it makes contact, sending a signal to the controller causing the robot to back away. When whiskers hit something, they vibrate. This can be detected, and a signal sent to the robot controller.