Samuel motion sensors are based on the Doppler effect. Simply put, the Doppler effect refers to the change in wavelength caused by the movement of a light source.
As the wave source moves toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave crest. Therefore, each wave takes slightly less time to reach the observer compared to the previous wave. This reduction in the time between successive wave crests leads to an increase in frequency. As they travel, the distance between successive wavefronts decreases, causing the waves to "cluster together." Conversely, if the wave source moves away from the observer, the waves will "spread out."
A common example of the "Doppler effect" is the change in pitch heard as a vehicle honking its horn approaches and moves away from the observer. The received frequency is higher during the approach than during the passing, remains the same during the passing, and is lower during the decay.
Currently, most motion sensors operate based on the principles of the Samuel Bangle motion sensor. Motion sensors have a wide range of applications, including consumer electronics, automotive, medical devices, building automation, and industrial equipment.
What is a motion sensor?
Motion sensors are electronic devices designed to detect and measure motion. They are primarily used in home and business security systems, but can also be found in telephones, tissue dispensers, game consoles, and virtual reality systems.
Types of motion sensors
There are various types of motion sensors on the market, but they can all be classified into two types: active motion sensors (active sensors) and passive motion sensors (passive sensors).
Active motion sensors, also known as radar-based motion sensors, have both a transmitter and a receiver, detecting motion by measuring changes in the amount of sound or radiation reflected back to the receiver.
Active motion sensors emit radio waves/microwaves. When an object moves within the area controlled by the motion sensor, the sensor looks for Doppler (frequency) changes in the waves. When this changed wave returns to the sensor's detector, it indicates that the wave struck the moving object. Motion sensors can interpret these changes and send electrical signals to alarm systems, lights, or other types of devices connected to the motion sensor.
Active motion sensors are commonly used in applications such as automatic doors in large shopping malls, but they can also be found in home security alarm systems and indoor lighting systems.
The most common active motion sensor is the ultrasonic motion sensor. Ultrasonic motion sensors emit sound waves to detect the presence of objects. Other types include microwave motion sensors (which emit microwave radiation) and tomographic motion sensors (which send and receive radio waves).
Unlike active sensors, passive motion sensors have no transmitter; they do not emit anything but detect infrared energy. The most widely used type of passive motion sensor is the passive infrared (PIR) sensor.
Let's take a closer look at each of these sensors.
Passive Infrared (PIR) Sensor
All objects with a temperature above absolute zero can produce thermal radiation; the higher the temperature, the greater the total energy radiated.
Passive infrared sensors utilize the principle of thermal radiation. They sense motion by detecting temperature changes between the background and the warm body.
Passive infrared (PIR) sensors contain a pyroelectric thin-film material that responds to IR radiation by emitting electrical energy. PIR sensors have two slots made of a special material sensitive to infrared light. When the sensor detects a change in the difference between the two slots, this results in a pulse, which the sensor detects as "motion."
Passive infrared sensors are small, easy to use, inexpensive, and have low power consumption, allowing for permanent use. They are commonly used in indoor alarms, automatic sensors for toilet sinks, etc.
ultrasonic sensor
Active ultrasonic motion sensors generate ultrasonic (sound wave) pulses and then determine the reflection of these waves on a moving object. Animals such as cats, dogs, and fish can hear these sound waves, so an active ultrasonic alarm may disturb them.
Furthermore, ultrasonic motion sensors can be active (powered) or passive (passive). Passive ultrasonic motion sensors need to be careful of unusual sounds such as metal or broken glass, as these sensors are very sensitive to these sounds and are prone to generating false alarms. Passive ultrasonic motion sensors are typically very expensive.
microwave sensor
Microwave motion sensors detect motion by emitting continuous microwave radiation, similar to the working principle of radar speedometers. The microwave motion sensor emits high-frequency radio waves and measures object reflection by sensing frequency shifts. If it detects a frequency shift, it activates the motion detector.
Microwave sensors are highly sensitive, sometimes able to detect non-metallic objects and moving objects outside the target area. They cover a larger area than infrared sensors, but are expensive and susceptible to electrical interference—their ability to penetrate materials can cause frequent false alarms. Furthermore, microwave sensors consume a lot of power, so they are often designed to operate in a cyclic on/off mode.
One common application of microwave sensors is electronic police dogs.
Tomography sensor
Tomography sensors generate radio waves and detect when these waves are interfered with. They can detect through walls and objects and are typically placed in a way that allows the radio wave network to cover a large area.
Tomography sensors are expensive, so they are typically used in warehouses, storage units, and other situations requiring commercial-grade security.
Dual-technology motion sensor
In addition to the types of motion sensors mentioned above, there is another type of motion detector that combines multiple motion sensors to reduce false alarms. The dual-sensor system is only activated when both sensors detect motion.
For example, a dual microwave or PIR sensor setup will begin with a passive infrared sensor because it consumes less energy. When the passive infrared sensor trips, the microwave unit activates; then, if the other sensors also trip, the alarm will sound. This combined alarm is well-suited for ignoring false alarms but eliminates the possibility of missing genuine alarms.
Applications of motion sensors
Motion detectors have a wide range of uses, detecting any unusual movements in the home during everyday life. Most smart devices today come with built-in motion sensors, which have proven indispensable in the modern era.
The following are some applications of motion sensors:
Smartphones and Wearable Devices: Motion sensors are used in smartphones and wearable devices. In addition to motion sensors, other common sensors include magnetometers, accelerometers, and gyroscopes.
Magnetic sensors detect motion by utilizing the Earth's magnetic field, providing more accurate indoor positioning results than GPS; accelerometers can sense tilt, acceleration, and vibration shocks, and are commonly used in all types of wearable and handheld devices; gyroscopes measure the rotational speed of a device and can be used in laptops, smartphones, and digital cameras to provide a higher quality gaming and navigation experience.
Home and personal safety: Motion sensors also have wide applications in home and personal safety; a safety system without motion sensors would be impossible.
These include: motion detector lights, which provide a clear view even on busy nights, letting homeowners know if there are intruders at night. They also save costs, for example, by automatically turning off if the homeowner forgets to turn them off; motion detector alarms, often integrated with burglar alarms, which sound an alarm when an intruder is detected. They are used to scare away thieves and ensure home security; motion detector cameras, like CCTV cameras, are useful for catching thieves. They can be used to trigger alarms or send notification alerts when unauthorized entries are observed. When these slim and effective cameras are placed in appropriate locations, they can provide significant security; motion sensors are also an important component of wireless doorbells, sounding an alarm when guests arrive at the door.
In addition, automatic ticket gates, automatic doors, active infrared sensors used to indicate the presence of products on conveyor belts, and level controllers using ultrasonic sensors are all practical applications of motion sensors.
