Size-Controlled LiDAR-Detectable Black Pigments: Comparative Study from the Nano- to the Micron-Scale

Abstract

Light detection and ranging (LiDAR) sensors emit pulsed nearinfrared (NIR) lasers toward targets and detect the reflected signals to measure the distance between LiDAR-equipped autonomous vehicles and surrounding objects. However, LiDAR sensors have difficulty recognizing black and dark objects owing to their intrinsic light absorption characteristics, including NIR light, which limits their practical application in autonomous driving environments. In this study, NIR-reflective silica/black titania core/shell (SBT/CS) pigments of various sizes (140 nm, 1.3 μm, and 6.6 μm) ranging from the nanoto micron-scale are synthesized to evaluate the suitability of LiDAR-detectable paints in car coatings. The silica cores are fabricated using the Stober method by adjusting the quantity of the reagents and then coated with a black titania shell via titanium tetrachloride sol−gel and NaBH 4 reduction methods. In practical LiDAR applications, the SBT/CS pigments with 100 nm cores exhibit the highest NIR reflectance (27.8 R% at 905 nm) owing to their high specific surface area. Conversely, SBT/CS pigments with 6 μm cores demonstrate excellent spreadability and durability owing to their increased contact area and mechanical strength. All of the SBT/CS-painted objects are successfully recognized using commercial LiDAR sensors, thus confirming the advantages of micronscaled SBT/CS-based paints in autonomous driving environments.