By Yuejun Zhao and Songwei Lu, PPG Industries, Inc., and Calvin Stargaard and Muluneh Sime, Nevada Automotive Test Center
The increasing adoption of advanced driver assistance systems (ADAS) and autonomous vehicles (AVs) demands highly reliable sensors that can operate effectively in adverse environmental conditions. Fog, rain, mud, and debris accumulation can compromise sensor performance, posing challenges for safe and efficient operation. To address these issues, UV-durable hydrophobic (UVH) coatings designed to improve sensor reliability have been developed.
The effectiveness of UVH coatings was evaluated under both simulated and realworld conditions. The study assessed vision cameras, IR cameras, LiDAR, and radar sensors exposed to various environmental stressors, including fog, rain, mud, insect splatter, and off-road terrain while operating the vehicle at representative speeds. The results demonstrated that UVH coatings effectively reduced environmental contamination on sensors, enhancing imaging, target recognition, and signal clarity, though the impact on LiDAR was less significant.
These findings suggest that UVH coatings can enhance ADAS and AV sensor reliability by reducing maintenance requirements and improving sensor functionality, particularly in wet and debris-prone environments. This article details the coating formulation, testing methodology, results, and broader implications for ADAS and AV systems, highlighting their potential for both commercial and military applications.
Introduction
Advanced driver assistance systems (ADAS) and autonomous vehicles (AVs) depend on a suite of sensors to interpret and navigate the driving environment. Cameras, LiDAR, radar, and infrared sensors provide critical data for object detection, environmental perception, and decision making. However, environmental contaminants such as rain, fog, mud, and debris on sensor covers can significantly degrade sensor performance, potentially compromising both functionality and safety. As a result, maintaining clean and dry sensor surfaces is essential to ensuring the reliability of ADAS and AV technologies.
To address these challenges, several automatic cleaning systems have been developed. For instance, Valeo1 and Continental2 have introduced fully automatic cleaning systems that employ retractable liquid-jet nozzles to spray cleaning fluid onto sensor lenses, effectively removing debris. Ford’s3 AV development team has designed aerodynamic shields to divert airborne contaminants away from rooftop-mounted LiDAR sensors, reducing the accumulation of dirt and moisture. While these active cleaning solutions enhance sensor reliability, they introduce additional costs related to installation, maintenance, and long-term repairs, making them less desirable for large-scale implementation.
A promising alternative to active cleaning mechanisms is the application of hydrophobic self-cleaning coatings that passively repel water, dirt, and environmental contaminants. Such coatings could significantly reduce the need for frequent cleaning cycles, minimize the consumption of cleaning fluids, and lower overall energy requirements. However, the development of hydrophobic coatings suitable for sensor applications presents several challenges, particularly in achieving high optical transparency while maintaining essential properties such as scratch resistance, UV durability, self-cleaning capabilities, and stain resistance.
Several fabrication methods have been explored to produce transparent nonwettable surfaces, including self-assembly techniques, sol-gel processes, micro-phase separation, templating, and nanoparticle assembly.4, 5 Additionally, mold transfer methods such as nanoimprint lithography have been employed, utilizing hydrophobic transparent elastomer precursors or UV-induced polymerization.6, 7, 8 Some ceramic precursor-based transparent hydrophobic films have also been proposed for applications in windows and solar energy conversion surfaces.9 However, many of these techniques lack the mechanical durability and weatherability necessary for long-term use in automotive sensor applications, as they suffer from poor adhesion to substrates and inadequate scratch resistance, leading to rapid degradation under environmental stressors.
To address these limitations, a fluorinated silane-based coating system was developed as a UV-durable hydrophobic (UVH) coating with enhanced UV stability, optical transmission, and mechanical durability. The coating was designed to maintain high hydrophobicity over extended periods while withstanding environmental exposure and mechanical wear. Initial performance validation was conducted in a stationary testbed under simulated weathering conditions, including fog, rain, mud, and insect splatter, confirming both the coating’s durability and its ability to improve sensor performance.10 To further evaluate real-world effectiveness, PPG Industries, Inc., in collaboration with the Nevada Automotive Test Center (NATC), conducted comprehensive field tests. The results demonstrated that UVH coatings significantly enhanced sensor clarity and functionality, reinforcing their potential as a cost-effective and durable alternative to active sensor cleaning systems.
Experimental Design
UV-Durable Hydrophobic (UVH) Coatings
Hard coat-coated borosilicate glass, as well as hard-coated polycarbonate (PC) and silicon substrates, were pretreated with air plasma for 15 min using an ATTO™ plasma treater (Diener Electronics, Germany). Proprietary UVH coatings, formulated with fluorinated silane from PPG Industries, Inc., were subsequently applied to the pretreated substrates via an ultrasonic spray coating technique. The coatings were deposited using a Prism Ultra-Coat ultrasonic spray system (Ultrasonic Systems, Inc., Haverhill, MA).
The coated samples were cured at 100 °C for a duration of 10 to 15 min. Post-curing, the static water contact angle (sWCA) was measured by placing three 2.0 μL droplets of deionized water onto the surface of each sample using Kruss Drop Shape Analyzer DSA100. The average sWCA was determined using ADVANCE software in conjunction with a Kruss Drop Shape Analyzer DSA100 Instrument. Due to the inherent hydrophobic properties of the UVH coatings, the sWCA was measured to be 115° ± 1°.
Continue reading in the November-December issue of CoatingsTech