2 Jul 2020
Rethinking ADAS materials
New specialized thermoplastics offer greater design freedom to improve sensor performance and packaging, at reduced cost.
Advanced driver assistance system (ADAS) technologies – including automatic emergency braking, collision avoidance, adaptive cruise control and parking assist – are quickly going mainstream. OEMs, regulators and consumers recognize their value in improving driving and preventing accidents. As a global market, ADAS is expected to grow at a CAGR of 19.0% through 2025, according to Grand View Research.
The current ADAS sensor suite also is evolving rapidly to respond to market demand for improved performance, more efficient packaging, and lower costs. For example, engineers are exploring the integration of different sensors into a single unit, as well as “fusing” the radar and camera data into a single output to overcome limitations of the individual technologies and provide safety redundancy. Miniaturization of sensor hardware is aimed at reducing its “footprint” at the expense of potentially generating more heat.
And lidar technology, currently focused on autonomous-driving (SAE Levels 3-5) systems more than on ADAS applications, is transitioning to solid state, from today’s electro-mechanical units.
Specialized thermoplastics are being developed to offer greater design freedom than traditional metal, glass, and lower-performing plastics currently used in sensor systems. They’re key to creating the next generation of ADAS technologies that are more compact and cost-effective. The new materials aim to help engineers consolidate parts, minimize secondary operations, and help improve performance and cost-effectiveness. Key values include EMI/RFI shielding; radar absorption; and heat dissipation.
The new materials also can provide excellent impact and chemical resistance, UV protection; reduction of moisture uptake; and warpage prevention. They also help enable lower total system costs through high-volume, high-speed injection molding processes.
PEI and PPE advantages
Radar sensors for ADAS are typically manufactured from a combination of materials with a plastic housing enclosing a die-cast metal plate. The metal plate acts as a heat sink and shields against interference from other sensor signals. Designers and manufacturers could benefit from switching to all-thermoplastic housings. Specialty compounds offering thermal management properties, EMI shielding capability and radar absorption can replace metal, which further enables part consolidation, simplifies molding operations and offers potential cost savings by avoiding secondary operations.
Looking ahead, polyetherimide (PEI) resins address the need for higher thermal performance as radar sensor designs become smaller – possibly shrinking to a single microchip.
Camera sensors also must be shielded from competing electronic signals. Their housings, which are typically large and made from aluminum, can be replaced with specialty thermoplastics to streamline manufacturing and increase productivity, and aid in weight reduction. In the “every-gram-counts” mantra of vehicle lightweighting, sensor suites with reduced mass contribute to better fuel economy.
Since camera sensors must have a clear line of sight, they are installed flush with the bumper or mounted on the windshield. Their housings must protect against moisture absorption and exposure to thermal cycling and UV light that can cause warpage. Specialty grades of polyphenylene ether (PPE) and PEI resins provide dimensional stability and support laser welding that helps prevent moisture ingress.
Like cameras, lidar sensors must be completely unobstructed to operate properly. While the mechanical “spinning can” lidars typically are roof mounted, the new generation of solid state lidars will be increasingly embedded into front and rear fascia and are trending into headlight systems. Depending on location, these units are exposed to weathering, road chemicals and debris that can affect their optical transparency and durability.
Many lidar units use glass or standard plastic material for protective lens covers to ensure infrared (IR) transparency, optical performance and weather resistance. Specialized thermoplastics offer advantages over these traditional materials. Compared to glass, specialty thermoplastics (with or without coatings) could provide greater freedom to design complex shapes and superior resistance to impact and abrasion. The new materials also can deliver superior UV-, impact-, and scratch-resistance performance.
For example, SABIC’s new family of Lexan CXT resins deliver a unique balance of high temperature resistance, a refractive index that can exceed 1.6, and high IR transparency. Their high flow properties make these resins well-suited candidates for molding complex or thin-wall parts.
Next-gen “fusion” designs
Another factor spurring the need for innovative materials is the transition from lidar designs with multiple mechanical parts to solid-state technology. One approach uses liquid crystals to steer the laser beam electronically, with no moving parts. The resulting reduction in the size of the lidar sensor unit will require materials with better heat dissipation capabilities. High-heat resins such as PEI and thermoplastic polyimide (TPI) provide excellent thermal performance (glass transition temperatures of 217°C and 267°C, respectively) combined with high light transmittance in the IR spectrum range.
Each of the primary ADAS and AV sensors has strengths and weaknesses. The concept of sensor fusion involves combining inputs from two or more types of sensors to overcome shortcomings, improve sensing capabilities in several different scenarios (bad weather, darkness, far distances) and build in redundancy.
Advanced thermoplastics enable new fusion designs, such as “smart” headlamps with integrated sensors, which may require part consolidation and miniaturization. They also offer potential system cost savings through part consolidation and ease of manufacturing.
Material suppliers with automotive experience, especially in lighting and bumper systems, can assist with next-generation design, prototyping and commercialization of the new components and systems.
John Pedrotti is Marketing Business Manager, Mobility, SABIC