Ultrasonic Sensors May Give Way to Near-Field Lidar

Take a look at most vehicles built in the past 10-15 years and you’ll probably notice what look like little round buttons arrayed across the front and rear bumpers. These are the ultrasonic sensors that have become ubiquitous as part of parking assistance systems on most vehicles. Emitting sound waves in the 40 kHz-50 kHz range, they are used as proximity sensors when maneuvering the vehicle in tight spaces. They are cheap and useful but have low resolution, and we may see them supplanted by near-field lidar in the coming decade. 

When most people consider lidar—if they are aware of what it is at all—they probably think of the sensors that look like spinning buckets on the roofs of automated vehicles. Those original rooftop lidar sensors made by Velodyne that debuted during the DARPA Grand Challenge from 2004 to 2007 cost about $80,000 and just went out of production. 

Now, dozens of companies are making lidar sensors using a variety of designs, but they mostly function on the same basic principle: time of flight. A beam of light shoots out, and the time it takes to reflect back is measured to calculate the distance between the sensor and the detected object. These sensors generally use some sort of mechanism to steer the beam and scan an area. Many are available for well under $1,000 when produced in volume. While these sensors are starting to come to market from a variety of automakers, they are still too expensive to replace a $1-$2 ultrasonic sensor. Additionally, they focus on long-range detection. 

Seeing Up Close

This is where the new near-field lidar sensors shown at CES 2022 start to show potential. Both PreAct Technologies and Valeo showed new flash near-field lidar sensors this year. Flash lidar is a technique that works like a camera flash in most cases, pulsing near-infrared light through a diffuser to illuminate an area and using a photodetector to capture all of the returned photons at once rather than scanning the field of view.

Both near-field lidar sensors have a resolution of 320 x 240 pixels, which is plenty at a range of 10-20 meters. The Valeo sensor pulses its laser at a rate of 125 frames per second and achieves an angular resolution of 0.35 degrees. At that range, it is enough to accurately detect and classify pedestrians, cyclists, animals, and other vehicles. Valeo has not revealed a cost for its sensor, but it is targeting 2024-2025 production programs for safe autonomous restart from standstill, parking assist, and automatic emergency braking, among other applications. 

The PreAct sensor uses a continuously illuminated 940 nm LED and can capture 200 frames per second at a range of 20 meters. PreAct is targeting similar applications to Valeo as well as imminent collisions and other use cases. At that high frequency, it could be used to trigger seat belt pretensioning or even airbag deployment. PreAct is targeting a high volume price of about $25 per sensor. 

Short-Range, Low Cost Solutions

While PreAct's price is significantly higher than the cost of ultrasonic sensors, a set of four near-field lidar sensors from either vendor could provide surround protection with much more resolution than is possible with current sensors at a price that is still modest relative to the entire vehicle cost. This is especially important in urban and suburban areas where pedestrians and cyclists are the fastest growing groups for traffic fatalities, especially in low light conditions where visible light cameras often struggle or with larger SUVs and trucks that have limited sightlines for the driver. Near-field lidar may turn out to be the next wave of automotive sensing.