Sensor Technology
Sensors for motion detection - What about radar?
InnoSenT explores the latest developments in radar technology M
otion sensors make our daily life more efficient, comfortable and safe. They help us to save energy, trigger the
alarm, enable the automatic control of our technology or touch-free operation. For motion detection the devices use different measurement methods in order to capture movements of people or objects. Due to their low price, PIR sensors are the most common. However, the technology reaches its limits in certain applications. Thus, many integrators are looking for other options for motion detection. One promising alternative is radar technology.
Functionality of radar vs PIR The two sensor technologies differ significantly in how they work. PIR sensors detect thermal radiation emitted by people or objects. To identify movement, they measure the temperature change over time. As a passive measurement method, the devices do not transmit a signal, but receive the data when a change occurs. Radar, on the other hand, is an active measurement method. Radar sensors send an electromagnetic pulse in the high- frequency range. When this signal bounces on people or objects in its way, it will be reflected to the radar antenna as an echo. With the changes of the received signal, it is possible to locate the object and recognize a movement.
Strengths and weaknesses The functional differences of the measurement methods also have an impact on the capabilities. The functionality determines the advantages and disadvantages of both technologies. How? As we already learned, PIR sensors work depending on heat radiation. In practice, this means thermal energy sources like a heating unit can be a trouble for PIR motion detection. In addition, people wearing heat-insulated clothing will
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possibly be ignored. Some weather conditions such as fog or direct sunlight are also a challenge for PIR sensors. A big advantage of PIR is that the technology is really cheap. So, if the price is the most relevant factor for the application, users accept the weaknesses of PIR. But when it is important that external circumstance will not lead to false alarms, other technologies like radar are considered. Radar waves are detectable regardless of weather or light conditions. They also radiate through a variety of materials - plastic covers or dirt will not interrupt the detection. But radar technology is much more complex. Besides motion detection, radar outputs additional object information which can be used for extended functionality. This is why the technology is more expensive. The named strengths and weaknesses are the reasons why the technology is present in different motion detection applications. PIR is standard for the low-cost sector and simple motion detection applications. For example, it is used for indoor light automation or contactless activation of sanitary devices. In contrast, radar proves its worth for complex detection tasks and outdoor applications. For example, radar motion sensors are used for door opening in outdoor areas or for intruder detection of alarm systems, where false alarms cause unacceptable consequences.
Improvements open up new application possibilities
Recent developments in radar technology now blur the clear classifications of use cases. Research findings for autonomous driving and industrial automation are
Components in Electronics
also having an effect on radar motion detectors in other markets. One result is that radar technology is becoming cheaper. Even 24 GHz sensors are now available at competitive prices. Due to modern manufacturing processes, high-volume production and technical enhancements, they can be offered at a lower cost.
The technology has also evolved, so you will get improved performance and more functionality for less cost. Radar offers extended functionality for motion detection. For example, it is possible to specify the detection range or filter out irrelevant movement detection. The technical features of radar such as speed measurement or determining movement direction will be useful for detection efficiency and will also open up new use cases of motion capturing. Highly integrated sensors including signal processing and intelligent algorithms allow non-radar experts to
handle the integration.
Radar sensors have also become incredibly small. Unlike 10 GHz, the new sensors at higher frequencies are smaller and can now easily be retrofitted into existing product designs of multimedia, kitchen devices or even light switches. Another trend caused by the new possibilities is the sensor fusion, where different technologies are combined to achieve the best performance. For example, a dual-tech motion detector of PIR and radar sensor: If one measuring technology fails, the other takes over in order to prevent malfunctions.
Radar has evolved from a former “too expensive and complex” measurement technology to a serious competitor in motion detection. And due to its features and falling price, it will become more common in consumer products. With radar entering the PIR dominating market, many innovations for motion detection will be waiting for us.
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