In 2019, the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) published a draft pedestrian automatic emergency braking (PAEB) test procedure. When, the results of testing conducted in 2022 on 12 light vehicles were published in 2023 (2022 Light Vehicle Pedestrian Automatic Emergency Braking Test Summary, March 2023), one conclusion was:
- No vehicles demonstrated crash avoidance for S1d daylight and darkness lower beams at 60 km/h and darkness lower beams at 50 km/h.
The 12 vehicles were equipped with camera, camera+radar, and vision sensing systems. The test procedures were developed to evaluate the two most frequent U.S. crash scenarios involving pedestrians. In scenario S1, the pedestrian crosses the road in front of the vehicle. In scenario S4, the pedestrian walks along the road in the path of the vehicle.
While NHSTA proposed Automatic Emergency Braking standards (May 31, 2023) that would include PAEB, they also noted that full implementation of desired PAEB functionality depends on the availability of suitable technologies. One technology, currently being reviewed and tested by leading car makers, can see and identify warm objects in total darkness, up to 200 yards ahead. Long wave infrared (LWIR) or far IR (FIR) can “see” in bright and blinding light to complete darkness (zero lux illumination). In addition, visibility is not affected by snow, rain, or fog. Unlike LiDAR or cameras imaging in the visible or shortwave infrared (SWIR) bands, it operates at 8- 14 µm spectral range, detecting thermal energy. Table 1 shows the difference between different IR bands.
The LWIR is actually a microbolometer image sensor that consists of an array of microelectromechanical systems (MEMS) detector elements. Constructed from an absorber, each element is supported by a mechanical suspension platform on legs that conduct electricity as shown in Figure 1.
With a thermal radiation signal continuously arriving at the microbridge’s surface, the temperature of the element tracks the thermal emission of the object it is viewing. The operation of each detector element is controlled by a readout integrated circuit (ROIC) located below the element array. To assure that the thermal data received by the ROIC from every element is accurately preserved, each pixel element has its own analog-to-digital converter (ADC) and the suspended structure is sealed in a vacuum. A 1280×800 high density (HD) passive array that requires no active illumination has been qualified to meet Automotive Electronics Council’s AEC Q100 standards.
Since 2009, a 51% increase in pedestrian fatalities in the U.S resulted in 6,205 pedestrians losing their lives in 2019. These deaths are 17% of all traffic fatalities. Other parts of the world report similar and alarming numbers. For example, Japan’s Transport Ministry reports that 70% of pedestrian fatalities occur at night. Also, the European Traffic Safety Council (ETSC) has recognized that AEB systems need to work better in wet, fog, and low-light situations. A sensor that works in all lighting situations and is not affected by snow, rain, or fog should be quite interesting for PAEB systems.
Filed Under: Sensor Tips