When we think about radar, we picture rotating dishes scanning the skies from atop air-traffic control buildings, radomes peering across the sea from coastal hilltops, and roadside police checking the speed of passing motorists. These familiar implementations of RAdio Detection And Ranging (RADAR) are now being joined by a new breed of applications enabled by the development of high-performance solid-state radar sensors.
Data from these radar chips, alone or combined with sophisticated algorithms using the output from other types of sensors, will enable more intuitive user interfaces that make our lives simpler, safer, and more convenient. The lines between the real world and the digital world will blur, context will play a bigger role in shaping the way that user interfaces work, and devices will anticipate our needs almost before we recognize them ourselves.
These opportunities are being enabled by constant improvement of chip manufacturing processes, from BiCMOS on SiGe substrates to deep sub-micron CMOS processes on silicon. These processes allow us to build transistors that can sustain very high operating frequencies necessary for solid-state radar chips that emit and sense radar signals at 60 GHz and above. At these frequencies, a suitably-equipped radar system will be able to sense how far away a person is with a resolution of around 2 cm, over distances of up to 10 m indoors.
Figure 1 A comparison of 24 GHz and 60 GHz radars highlights their respective design parameters. Source: Infineon
Radar sensors working at 24 GHz, on the other hand, will be able to sense the distance to a person with a resolution of about 60 cm over distances of up to 50 m, indoors or outdoors. It’s a powerful new sensing paradigm whose full utility will only be revealed as developers get hold of the parts and put them to work in their designs. But here are some ways we think this technology can be applied now.
New radar sensor applications
One obvious use case, especially in these post-pandemic times, is to make touchless user interfaces more widely available, especially in public places such as office buildings and cafes. We’ve all learnt how to press buttons with our elbows over the past year, but how much more convenient would it be if we could just wave a hand at a panel when we wanted to summon the elevator?
A similar logic applies to other self-service machines, such as the sophisticated coffee machines often found in hotel cafes. These have touchscreen interfaces, allowing guests to order up exactly the coffee they want, but during the pandemic an employee has had to be on hand to sanitize the screen after every use. Rethinking the user interface to incorporate short-range radar sensing could make the whole transaction more hygienic.
Radar sensors can also be put to work to keep track of people in buildings, substituting for the passive infrared (PIR) sensors currently used to control room lighting based on occupancy. PIR sensors have a disadvantage in this application because they tend not to ‘see’ people who remain still at their desks for too long, and eventually plunge them into darkness. Radar, on the other hand, can sense their smallest movements, such as the rise and fall of a person’s chest as they breathe, avoiding false negatives and sudden darknesses.
Such radar sensors can be mounted behind drywall to make them more discreet than PIR options. They can also be mounted in arrays behind ceiling panels, so that lighting controllers in very large rooms can limit the areas they illuminate to where people are present. Street lighting could be made more eco-friendly by using radar sensors in each streetlamp to transform it into an ‘on-demand’ service in which drivers travel in a pool of light on otherwise unlit roads.
Radar sensors, already used in the cruise-control systems of some high-end vehicles, keep a fixed distance between one vehicle and the vehicle in front. But greater use of radar sensors is enabling more sophisticated vehicle autonomy features in addition to collision avoidance. Eventually, through vehicle-to-vehicle and vehicle-to-infrastructure communication strategies, we could see more coordination of traffic flows and hence greater traffic throughput as well as enhanced passenger safety, thanks to the data streams created by multiple low-cost radar sensors.
Figure 2 Radar sensors are a becoming a key ingredient in today’s smart home. Source: Infineon
Collision avoidance schemes, borrowed from the automotive industry and enabled by radar sensing, could make operations such as warehousing and material handling in ports safer. Similar technology could also be applied to industrial robots to make it safe for people and robots to work together in factories, and to drones for inflight collision avoidance.
Radar sensors can also be used to enhance security equipment such as cameras, alarms, and access controls. Radar can sense the presence and direction of motion of an intruder in situations in which a camera’s field of view (FoV) is obscured. Unlike PIR sensors, radar can’t be fooled by intruders wearing heavy clothing to suppress their heat signature. Radar-based presence sensors can also be mounted more discreetly than optical cameras, making the system more effective and less visually intrusive.
Moreover, the sensors can be used to help extend the battery life of remote optical cameras by allowing them to enter a sleep mode until they are awoken by a presence-detection signal triggered by the radar sensor. This last application is just one example of the power of multi-sensor setups, which combine the input from many sensors to give fewer false positives than single-sensor systems could achieve.
Radar sensor selection
Which type of sensor should you use? Parts operating at 24 GHz are more suitable for use in outdoors than those operating at 60 GHz, whose radiated energy can be absorbed by atmospheric moisture, rain, snow, and dirt. As previously discussed, there’s a trade-off between the operating frequency chosen for an application, the operating bandwidth available in the ISM bands defined at that frequency, and the range resolution that radar sensors operating at those frequencies can achieve. The 24 GHz parts also have a longer operating range than those working at 60 GHz.
The distance to a sensed object can be calculated from how long it takes for a modulated radar signal to be reflected off it, and the speed of a moving object can be derived from the Doppler shift of that signal. Direction and angle of motion can be calculated using at least two radar receivers, a known distance apart, to enable triangulation, and the resolution of the angle calculation can be improved by using more transmitter and receiver paths.
As shown in Figure 1, 60 GHz systems can be much smaller than 24 GHz systems, and benefit from the fact that it’s possible, at these high frequencies, to integrate antennas into the parts, saving space and reducing system-level design complexity. Power consumption for radar sensor systems operating at either frequency can be below 1 mW, making them suitable for use in battery-powered devices and even in mobile phones.
Figure 3 The sensor fusion of a radar IC with MEMS microphone along with audio processor enables several voice recognition applications. Source: Infineon
We are already seeing this happening. For instance, Google has added a radar sensor to the Pixel 4 handset to enable gesture-based control of the user interface. The phone can cancel an alarm with a swipe and skip a playlist track with a wave of hand. And Google’s radar sensor technology does more than this, making the phone more intuitive to use, for example, by waking it up when it is being picked up and putting it back to sleep when you put it down.
Large-scale radar was invented for a very specific purpose and has since been pressed into use in a wide range of other applications. The arrival of small-scale radar promises to enable a whole range of new applications, some expected and some unexpected. The question is what will you do with it?
Kim Lee is senior director for system applications engineering at Infineon Technologies’ Sensor Solution & IoT Products Group.
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