Proximity sensors are modules used to detect the presence of nearby objects without requiring physical contact. They are used in many applications such as conveyor systems, touch screens, parking sensors, warning systems and mobile devices. Proximity sensors utilize a number of physical detection methods including capacitive coupling, inductive pickup, infrared, ambient light photo-detection, ultrasonic and Hall effect.
Capacitive sensors detect the presence of a conductive area that disturbs an existing electrical field. Addition of charge coupling or change to the effective dielectric of the existing capacitance creates a change that can be detected. This technique is used to detect human body capacitance as an input (and example being the transparent indium tin oxide transparent capacitor sensors used in many touchscreens). They can also be used for humidity and fluid level sensing.
Inductive proximity sensors detect changes in magnetic resistance (reluctance). An induction loop senses changes in the composition of the material the magnetic flux travels through that creates the reluctance. These are extremely robust sensors used in industrial applications, rotation sensors, metal detectors and traffic lights control. Hall effect sensors operate in a similar manner to inductive sensing, but utilize electron deflection caused by the Lorentz forces created by a magnetic field.
Infrared proximity detectors are a combination of an emitting LED, directional lens, receiving lens and a photodetector array. The sensing range is typically detected by the incident beam angle irrespective of reflected light intensity. They usually have an adjustable range setting and are used in applications like manufacturing assembly lines. Ambient light photo detectors are of similar construction but can lack the range finding capability.
Ultrasonic proximity sensors are used in industrial and medical applications requiring high accuracy. They transmit and receive acoustic waveforms with an ultrasonic transducer with a similar mechanism to that used in sonar and radar systems. Wave energy reflected from objects is detected and analyzed to ascertain distance. They have the advantage of being able to be used in applications where photo detection cannot – for example clear object detection. They can also be used to detect fluid boundaries or in applications like ultrasonic pregnancy scanning. Read more Read less