A proximity sensor is a device used to determine the relative distance of another object. There are many different types of these sensors, and they can be used for many purposes. Long range sensors are commonly used in navigation to determine whether there are any other vessels or obstructions nearby. Short range sensors may be used to warn that an object is too close to the sensor. Versions of these sensors are also used in various types of electronic equipment and security systems.
There are a number of different ways that a proximity sensor can determine where an object is relative to the sensor's location. One way is by emitting sound and detecting the time it takes for sound to bounce off of another object and return. Sound navigation and ranging (SONAR) is one example of this type of proximity sensor and is frequently used to determine how close aquatic vessels are to one another. Electromagnetic radiation, such as radio detection and ranging (RADAR) can also be used to determine how near an object is to the sensor based on how long it takes to hit the object and then return to the source.
A change in the sensor's electric or magnetic field can also be used to determine proximity. A proximity sensor that is sensitive to this type of change, such as an eddy current sensor, is frequently used in touch screens. It can determine that a person's finger or that a stylus made from a conductive material has touched the screen because it conducts a small amount of electricity onto the screen. Photo sensors, which detect changes in the light that reaches the proximity sensor, are also frequently used to determine short range proximity.
There are many applications for technologies that use proximity sensors. The first use for these types of technologies was tracking the movements of large objects, such as boats or aircraft. In 2011, many private vehicles are equipped with proximity sensors, especially at the rear of the vehicle, in order to alert the driver that the vehicle is approaching another object. Homes and certain appliances also make use of proximity sensors that determine whether doors and windows are closed. Electronics have proximity sensors on touch screens or, in the case of many cellular phones, to determine when the screen is near a person's face.