Want to improve the power saving level of smart home? Try millimeter wave radar sensor

Currently, the number of smart homes worldwide is estimated to be over 200 million, and forecasts predict that this number will exceed 500 million within the next few years.

Figure 1: Number of smart homes worldwide in the future.

Only through increasingly digital and sophisticated devices can a house become smart. However, smart devices require energy even when they are "off", because even in standby mode, the device needs to react immediately to user input (e.g. via voice control) or provide the latest information from the smart home or the network. At the same time, in many cases, it is completely unnecessary for the device to run in standby mode and thus consume energy when people are not present - mainly when no one is present.

To address this issue and meet the requirements of digitalization and energy efficiency, Infineon has made use of some interesting semiconductor solutions, one of which is the XENSIV 60GHz millimeter wave radar sensor, which can be applied to almost all smart home devices. The radar sensor is very sensitive and can detect whether a person is present and whether the device needs to be ready - a bit like a screen saver that deactivates the PC display after a period of time without mouse or keyboard input and reactivates immediately upon new input. With this reliable presence and absence detection, Infineon's 60GHz radar sensor can achieve real energy saving in smart devices.

Presence trigger and status monitoring such as continuous or standby

According to a 2021 Statista survey of 3,000 respondents aged 18 to 64 in Germany, almost three-quarters own at least one smart home device. In the United States, the figures are similar, while in China, the user rate of smart home devices is as high as 90%. These devices are as diverse as their applications: they include lighting; security; consumer electronics - such as TVs, laptops and speakers; kitchen appliances, as well as air conditioners. But all these devices increase the demand for energy, especially when energy costs are rising, and customers are more concerned about energy-saving, sustainable and environmentally friendly devices. In addition, the pressure on the power grid infrastructure can also be reduced.

Figure 2: According to Statista, the number of smart devices in U.S. homes is growing rapidly.

Rather than putting devices like thermostats, smart speakers, and digital assistants in normal standby mode, a better way to reduce energy consumption is to put them into “deep sleep mode” when no one is around. For some devices, this can save a few watts or a small fraction of that. But there are some special applications where this can exceed 100W, such as TVs, laptops, sound systems, and air conditioners. By using radar sensors, such devices will be able to sense the presence or movement of people; if no one is around, the smart device can automatically switch to sleep mode. Depending on the sensor and implementation, the radar module itself consumes only a few milliwatts of power, with a maximum power consumption of 0.1 W, which is significantly lower than the energy requirements of many electronic devices in “on” or standard standby mode (Figure 3).

Figure 3: Potential energy savings from radar-powered smart devices

How to use radar sensors to improve energy efficiency

To save energy, devices have to reinvent the power-hungry standby mode. Keep devices active or in standby only when they are really needed. This is what we do in our "non-smart" homes today, turning on the lights when we enter a room or manually starting the air conditioner only when it's too hot inside. Despite this, in many devices, power-saving features are often not implemented or disabled by users because activating wake-up is too cumbersome or too lengthy.

But a new smart approach may be the answer to many problems: Motion detection using radar sensors can wake up devices and run when needed, instead of automatically shutting down when needed. For example, the security system will only be turned on when there is someone, and the display will always be on. The smart thermostat can be turned off by default and only the radar detection module is activated. Once the radar detects movement in the room, the thermostat will be activated and update the data status of the house and display weather data. This concept of presence detection can be deployed in many other smart home devices.

Furthermore, the reverse principle of vacancy detection can also be applied, which offers even greater energy saving potential. In this case, devices such as TVs, speakers, smart lights and air conditioners can be switched off if no movement is detected in the room for a certain period of time. This significantly reduces power consumption. Since vacancy detection does not activate the devices immediately, but rather specifically deactivates them when no one is present for a certain period of time, the sensor module itself can remain deactivated and a check can be performed every few seconds or minutes.

Such a sensor module can therefore save a lot of energy for the entire system while consuming less itself.

Buildings with HVAC systems can benefit from this principle because much of the energy is wasted on heating and cooling even when no one is present.1 Worse, in many cases these devices are left running frequently and for long periods of time.2 The real intelligence would be to deactivate these systems once the area has been vacant for a period of time. This feature is becoming common in lighting systems, but not yet in air conditioners and other devices such as monitors, kitchen appliances, computers, speakers, and sound systems.

Users can also benefit from vacancy detection in other applications, such as TVs. For example, Infineon’s BGT60LTR11AIP radar sensor has been implemented in Samsung’s Frame TV 2021 (Figure 5). When no one is nearby for a user-specified time, the radar sensor switches the TV to sleep mode. This not only saves energy but also extends the life of the display.

Figure 4: Infineon’s XENSIV™ 60-GHz radar sensor enables even better energy savings

Figure 5: The Samsung Frame TV 2021 can switch to sleep mode when no one is detected for a user-specified period of time.

Radar sensors are the best choice for low-power smart homes

Of all the available motion detection solutions, radar sensors have the highest sensitivity for even the smallest movements, some of which are not even visible to the human eye. PIR sensors cannot compete in terms of sensitivity. In addition, radar does not rely on body heat like PIR sensors do, as it is an active sensing technology. This ensures that a person can be detected even if they are barely moving.

But one of the biggest advantages of mmWave radar is that it can detect through non-conductive materials. Infrared, ultrasonic, camera and other image-based sensors must have openings in the housing, but radar sensors can be completely hidden inside the device. As a result, you don’t have to make any compromises in product design and can avoid additional manufacturing steps and the cost of corresponding housing modifications.

Another possibility is camera-based motion detection - for example, for cameras, TVs, laptops and other devices that already have image sensors. Image systems have very high power consumption, and they also require good ambient light, and image processing is needed to detect motion in the video, which further increases power consumption. Privacy is also a big consideration.

In addition, the falling prices of consumer electronics products have increased the cost pressure of components. Therefore, 3DToF and camera sensors are usually too expensive to achieve presence detection. Mature PIR solutions not only affect the design of the product housing, but also require additional lenses, amplifiers, controllers, etc., which will also increase the bill of materials cost. In contrast, Infineon's BGT60LTR11AIP radar sensor requires only minimal supporting components, especially when operating autonomously, so it has minimal impact on system cost.

Due to their small size, radar sensors can be easily integrated into small and thin electronic devices.

Additionally, radar sensors are extremely reliable in dusty, smoky, or humid environments, where the detection performance of some laser-based ToF sensors or other image-based sensors may be significantly degraded.

Radar sensors enable other smart functions

Improper handling of the device can also lead to unnecessary power consumption, which the user will not be aware of, and some users will not accurately set the low power mode. With the help of radar sensors, automatically adjusting the energy saving level can ensure low power consumption of the device.

In addition to being used as presence detectors, radar sensors can also add other functions to smart devices - for example, in air conditioning systems. In such applications, radar sensors are most effective when used in combination with temperature, humidity and CO2 sensors, so that the system is activated as needed, for example, when someone is in the room, the CO2 level is too high or the temperature exceeds a predefined limit. While other sensing technologies usually only provide information about presence or absence, radar sensors can also easily check the number of people in the room and adjust the level accordingly, or even check the position and distance of people to control airflow.

There are many other possible use cases – for example, sound systems that track the listener’s position and continuously optimize volume and sound parameters accordingly; TVs with childcare functions that measure the viewer’s distance and warn if a child’s eyes get too close to the screen; or devices for the elderly or people who need care, such as alarm systems in the event of a fall. Radar sensors can thus very easily enable energy savings and contribute not only to comfort but also to personal well-being and safety in smart environments.