Motion Sensor | Definition | Its 6 Important Types | Applications

MOTION SENSORS

Contents

What is a motion sensor?

A motion sensor is a type of electrical instrument that uses a detector or a sensor for detecting proximal motion. A motion sensor device is integrated with a sensor and a component that alerts the user about the motion. Such types of sensors are incorporated in automatic lighting control devices, security systems, video cameras, gaming devices, and numerous other automated devices.

Motion sensor
a motion detector. image source: CHGMotion detector, marked as public domain, more details on Wikimedia Commons

What are active and passive motion sensors?

Active motion sensors: Active sensors (also called radar-based motion detectors) refer to the type of sensing technologies that detect motion by transmitting and receiving sound or radiation waves. These types of sensors have both transmitter and receiver. When an interruption occurs in the path of the wave, an electric pulse is directed to the embedded microcomputer which then interacts with the mechanical component of the sensor.

Passive motion sensors: Passive sensors work by detecting the constant reflection of radiations from the surrounding. These types of sensors do not use a transmitter. They perceive the change in radiation from the objects and directs an electric pulse to the embedded microcomputer which then interacts with the mechanical component of the sensor.

Motion sensor technology

Motion sensor technology can be of different types:

Passive infrared sensors: Passive infrared sensor or PIR sensors are extremely sensitive to the temperature of a person’s skin. The black body radiation emitted by the person (at mid-infrared  wavelengths) in comparison to the temperature of the background objects are sensed by the detector. The name “passive infrared” comes from the fact that the sensor does not emit any kind of energy. Such devices are specialized in detecting the motion changes in objects, animals birds, and humans with respect to their infrared radiations.

PIR sensor. Image source: DantorPhotospirpCC BY-SA 3.0

Microwave sensors: Microwave sensors use the principle of Doppler radar for detecting motion (similar to radar speed gun) of objects and humans. This instrument works by emitting a continuous wave of microwave radiation. Depending upon the motion of the person or object (away or towards the receiver), the phase of the reflected microwave shifts. This generates a heterodyne signal having a low frequency.

Ultrasonic sensors: Ultrasonic sensors rely on ultrasonic waves i.e. the sound waves that have a frequency higher than the audible frequency range for humans, for detecting the human-motion. These sensors are based on the principle of Doppler radar which demonstrates how the motion of objects or humans is detected by gathering the reflections of ultrasonic waves from objects. Depending upon the motion of the person or object (away or towards the receiver), the phase of the reflected microwave shifts. This generates a heterodyne signal having a low frequency. However, at times ultrasonic sensors can take into consideration, the motion in certain areas where coverage is not required.

Tomographic motion sensor: Tomographic motion sensors work by sensing the radio wave disturbances when they pass through the node to node in a mesh network. Tomographic motion detectors have a wide range as they can sense the motion of objects through walls and other hindrances. RF tomographic motion detectors incorporate the use of wireless devices and hardware.

Gesture detector: Gesture detectors sense the motion of a person with the help of infrared radiations and photodetectors. These types of sensors generally sense the gestures made with hand and leg and then carry out their functions as specified by the machine learning algorithms.

Computer vision software: Computer vision software detects the movement of people by analyzing their field of view with the help of certain algorithms. the video camera software can also record the footage for future analysis. this is generally a passive device as it uses an illuminated scene and does not produce any energy of its own. However, at times this technology is coupled with infrared sensor technology to sense the movement of objects.

What are the applications of motion sensor?

Motion sensor camera: Smart motion-detecting cameras generally use light pulse technology, thermal measurement technology, radio wave technology, etc. The most common technology used by the motion-sensing camera is the passive infrared sensing technology and computer vision software. These two are often used together to produce optimum results. Certain algorithms used in computer vision technologies allow recording the video of the motion and the infrared radiations allow the camera to detect objects even when there is no external light present. Motion-sensing cameras are mostly used for security purposes.

Motion detecting camera. Image source: SanderflightCCTV dome camera subway RotterdamCC BY-SA 4.0

Motion Sensor switch: A motion sensor switch uses a gesture detector (comprising of a photodetector) to sense the motion of a person and then execute its operation according to it. The photodetector is used for converting the wavelengths of light into electrical current signals that trigger a program on the microcomputer chip present inside the detector. To prevent false triggering, the microcomputer ignores slight changes in room temperature that is caused by sunlight. At times this technology is coupled with infrared sensor technology to sense the movement of objects.

Motion Sensor alarms: Motion sensor alarms can incorporate two different sensor modes: active and passive, based on the needs of the surroundings. These sensors are used for detecting the variation or change in the amount of radiation in the objects. The microcomputer present receives a signal depending on the variation amount and directs the device to perform various functions such as turning the alarms on. Motion sensing alarms often come with motion-sensing cameras for better performance. These devices are generally used for security applications.

Motion-sensing alarm Image source: Michelangelo-36, ALARMACC BY-SA 3.0

What are the improvements in modern motion sensing technologies?

Motion sensing technologies have been developed highly over the years. A combination of two or more different types of motion-detecting technologies is used for obtaining optimum results. Passive infrared technologies combined with computer vision software are gaining popularity in the motion-sensing domain significantly. These technologies have less probability of producing error results and also provide the feature of rechecking the motion (recorded by the computer vision camera).

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About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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