Overview
Modern vehicles equipped with Advanced Driver Assistance Systems (ADAS) rely heavily on radar sensors for safe operation in various driving conditions. Radar systems are critical because they perform well in all-weather types—rain, snow, fog—and under both light and dark conditions. However, when radar sensors are housed behind bumpers, any modifications or repairs to the bumper can significantly impact their performance. This bulletin provides a detailed overview of how radar sensors work, the effects of bumper repairs, and best practices for maintaining radar accuracy.
Why is Radar Important in ADAS?
Radar sensors are key components in ADAS, providing essential data that helps the system perform functions such as:
• Adaptive cruise control
• Automatic emergency braking
• Lane-keeping assist
• Blind spot detection
Unlike LIDAR (affected by weather conditions) or cameras (requiring light), radar can operate reliably in various environments. This makes it indispensable in ensuring that ADAS functions properly across a wide range of conditions.
How Bumpers Affect Radar Performance
When a bumper is placed in front of a radar sensor, it affects radar functionality in three main ways:
1. Power Loss: Radar waves have to travel through the bumper, which causes a loss in signal power. Manufacturers typically accept up to a 10% power loss due to the bumper material.
2. Sensitivity Loss: The shape, angles, and material of the bumper can cause radar waves to scatter or reflect incorrectly, resulting in decreased sensitivity.
3. Wave Distortions: If the bumper’s material or structure is changed—through repair or repainting—it can distort radar waves, affecting their ability to detect objects accurately.
Example Illustration: The diagram below shows how the thickness and shape of the bumper can impact radar signal power and accuracy.
OEM Validation: Bumpers and Radar Sensors
Original Equipment Manufacturers (OEMs) design bumpers specifically to work with radar systems. The radar sensors and bumper covers are tested and validated to ensure proper radar coverage, power, and performance.
For example, the Autoliv WU8NB24G1V2 blind spot sensor, used extensively by GM, illustrates how
radar sensors are integrated behind bumpers in a way that maintains accuracy and efficiency.
Why Bumper Repairs Can Compromise Radar Performance
Impact of Bumper Repairs:
• Increased Material Thickness: Adding filler or other materials during repairs increases the thickness of the bumper, which reduces radar transmission efficiency.
• Material Composition Changes: Changes to the material (e.g., plastic repairs) can introduce air gaps, inclusions, or density variations, all of which distort radar waves.
• Shape and Curvature Changes: Even the smallest distortion in the bumper’s shape can alter the radar’s angle, making it miscalculate distances and object positions.
Graphic Illustration: The following diagram from Rhode & Schwarz illustrates how improper repairs
impact radar wave transmission and detection.
Repainting Bumpers with Radar: Special Considerations
Even repainting a bumper can interfere with radar systems. Differences between factory and aftermarket paint application can cause problems:
• Metallic Paints: Aftermarket paint may contain metallic particles that interfere with radar signals. In particular, white paints with titanium dioxide can be problematic.
• Paint Thickness: Excessive layers of paint can block or distort radar signals. OEMs specify paint thickness limits (e.g., GM allows up to 13 mils, Audi 6 mils).
Manufacturer Guidelines:
• Permissive: BMW allows repainting over radar-equipped bumpers within specific thickness guidelines.
• Restrictive: Nissan/Infiniti and Subaru prohibit repainting bumpers that house radar sensors.
Aftermarket Bumper Covers: Not Recommended
OEMs do not recommend the use of aftermarket bumper covers for vehicles equipped with ADAS radar sensors. Aftermarket parts are generally not tested and validated for radar compatibility, and thus they risk compromising ADAS functionality.
Study Findings
Rhode & Schwarz found that improper covers significantly reduce radar performance in power, sensitivity, and accuracy.
Future Trends
As ADAS continues to evolve, radar placement may shift. Some automakers, like Volvo, have moved front radar sensors behind the windshield, reducing the chance of damage in minor collisions. This trend may continue as ADAS technology advances.
For More Information:
Please consult OEM service manuals for detailed specifications on radar-compatible bumpers and recalibration procedures.