What are proximity sensors? A proximity sensor is a sensor able to detect the

presence of nearby objects without any physical contact.

Most likely a plate of glass or plastic separates the two. Although you are likely to touch the separating element, there is no physical contact with the sensor.

Proximity sensing technology enables adaptive controls, alleviates isolation issues, improves overall application robustness, generates almost unlimited design flexibility and fosters new functionalities.

TYPES OF PROXIMITY SENSORS

Capacitive

Capacitive displacement sensor

Doppler effect (sensor based on effect)

Eddy-current

Inductive

Laser range finder

Magnetic, including Magnetic proximity fuse

Passive optical (such as charge-coupled devices)

Passive thermal infrared

Photocell (reflective)

Radar

Reflection of ionising radiation

Sonar (typically active or passive)

Ultrasonic sensor(sonar which runs in air)

LASER RANGE FINDER A laser rangefinder is a rangefinder which uses

a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender.

Working A proximity sensor often emits an electromagnetic field

or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target.

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.

Working

PROXIMITY SENSING TECHNOLOGIES

Common Sensing Technologies

Technology Detection Mode Advantages Disadvantages

Inductive Metal

Induced

electromagnetic

currents

Operates in harsh

conditions

Rapid response

time

Short range

Detects only

movement

Difficult array

setups

Ultrasonic Virtually all objects Sound wave echo Long range

Measure distance

Cost

Dead zone

No idea of

size/shape

Photoelectric Solid objects

Reflection or

absorption of light

different to

background

Medium range

Possibility of

interference

Cost

Pb in

fog/smoke/nontransp

arent materials

Objects capable ofPermitivity variation

Simple array

construction Short range

Applications Parking sensors, systems mounted on car bumpers that sense distance to

nearby cars for parking Ground proximity warning system for aviation safety Vibration measurements of rotating shafts in machinery Top dead centre (TDC)/camshaft sensor in reciprocating engines Sheet break sensing in paper machine. Anti-aircraft warfare Roller coasters Conveyor systems Beverage and food can making lines Mobile devices

Touch screens that come in close proximity to the face Attenuating radio power in close proximity to the body, in order to

reduce radiation exposure

Proximity Sensors in smartphonesThe proximity sensor is common on most smart-

phones, the ones that have a touch screen. This is

because the primary function of a proximity sensor is to

disable accidental touch events. The most common

scenario being- The ear coming in contact with the

screen and generating touch events, while on a call.

If a proximity sensor close to the speaker,

then it will detect any object in the vicinity of

the speaker. If any object is present (ex.

user's ear), then the touch events can be

assumed to be accidental & ignored.

Parking sensors Parking sensors are proximity sensors for road vehicles designed to

alert the driver to obstacles while parking. These systems feature ultrasonic proximity detectors to measure

the distances to nearby objects via sensors located in the front and/or rear bumper fascias or visually minimized within adjacent grills or recesses.

The sensors emit acoustic pulses, with a control unit measuring the return interval of each reflected signal and calculating object distances. The system in turns warns the driver with acoustic tones, the frequency indicating object distance, with faster tones indicating closer proximity and a continuous tone indicating a minimal pre-defined distance. Systems may also include visual aids, such as LED or LCD readouts to indicate object distance. A vehicle may include a vehicle pictogram on the car's infotainment screen, with a representation of the nearby objects as coloured blocks.

Automatic Door Openers One of the most common applications for presence detection is the automatic

door. Typically, as you approach a door you are detected by an optical sensor, or your weight closes a contact in the floor.

The electric field sensor can be integrated into the floor and can detect the presence of a person through different substances (wood, tile, carpet, etc.). There are no moving parts and the sensor is impervious to rust and virtually indestructible, making it a suitable replacement technology for the mechanical pressure sensor. The physical nature of the electrode ensures a well defined and limited sensing area, unlike that of an optical solution where you need to define a volume and sensitivity threshold.

Alternatively, proximity sensors can be embedded in the wall or other object to be activated only by voluntary movement. This also allows the door to be opened without any physical contact.

Optimizing access control can also lead to benefits in energy consumption. Minimizing the time a doorway remains open ensures the shortest possible exchange between hot or cold outside air with the conditioned air in the building.