Space-Saving Sensors Ease Automotive Design Woes

Self-driving vehicles need enough sensors to guide them safely through all types of traffic situations — and the sensors need enough space to work properly. As more sensors are added to self-driving cars, the design challenges also add up, requiring solutions that are both space-saving and elegant, without compromising function or performance.

Researchers at Fraunhofer-Gesellschaft are developing a way to install multiple automotive sensors in a limited space. The researchers’ solution, which combines optical light, radar, and lidar in the vehicle’s headlights, could be a perfect fit for the systems that guide self-driving vehicles.

LED headlight model with multispectral combiners for coaxially merging optical light, lidar (green), and radar beams (red), with the aim of achieving space-saving sensor integration for next-generation driver assistance systems. Courtesy of Fraunhofer FHR.

“We’re integrating radar and lidar sensors into headlights that are already there anyway — and what’s more, they’re the parts that ensure the best possible transmission for optical sensors and light sources, and are able to keep things clean,” Tim Freialdenhoven, a researcher at Fraunhofer Institute for High Frequency Physics and Radar Techniques, said.

Fraunhofer FHR has joined with other Fraunhofer institutes to launch the Smart Headlight Project, an initiative to develop multisensor-integrated adaptive headlights for driver assistance systems.

“Each individual system has its strengths, but also its weaknesses,” Freialdenhoven said. For example, optical systems demonstrate limited performance when visibility is poor. Radar systems, in contrast, take dense clouds of fog in stride but are not very good at categorization, an area in which lidar systems excel.

The first stage of the project is focused on designing a lidar system that can be integrated into the headlight without blocking the LED light beam, while also leaving room for additional sensors.

To prevent the sensors from interfering with the headlight beam, the research team is positioning the lidar sensors at the top of the headlight casing and the radar sensors at the bottom of the casing. The LEDs that create the headlight beam are located at the back of the headlight.

The beams from the lidar and radar sensor systems need to follow the same path as the LED light, a task made more complicated because each system beams light at a different wavelength. The visible light from the headlight beam measures between 400 and 750 nm and the infrared light from the lidar measures between 860 and 1550 nm. Radar beams have a wavelength of 4 mm.

3D visualization of multispectral headlight optics. Courtesy of Fraunhofer FHR.

“These three wavelengths need to be merged coaxially — that is, along the same axis,” Freialdenhoven said. “This is where what we call a multispectral combiner comes in.”

To combine LED and lidar light, the researchers use a specially coated dichroic mirror to guide the two beam bundles along a single axis by means of wavelength-selective reflection. A second combiner, which is used to combine LED light, lidar light, and radar, has the same effect, although it is more complex to implement due to the broad differences in wavelengths.

The researchers are designing the bi-combiners to be used without the need to modify the existing radar sensors that are widely used by automotive manufacturers.

Guiding the beams coaxially helps prevent parallax errors, which are complicated to untangle. Additionally, by using bi-combiners, the researchers can configure the sensors in a way that takes up significantly less space than if the sensors were arranged next to one another.

A goal of the Smart Headlight Project is to improve how self-driving vehicles use sensors to identify objects on the road, especially other road users such as pedestrians. Lidar sensors, for example, could be used in electronic brake assist or distance control systems.

“We’re also working on merging data from radar and lidar — something which will add huge value, especially when it comes to reliability,” Freialdenhoven said.

The Smart Headlight Project team hopes to create a host of additional options for integrating sensors into driver assistance systems. The team has already submitted a patent application and is working on creating a prototype.

Smaller light modules, more compact lidar sensors, and integrated radar sensors will make it possible to create multisensor designs that are tailored to self-driving vehicle technology, with its exact design requirements and limited installation space. The self-driving systems of the future may not only detect a person, but may also have the ability to analyze their speed, their distance from the vehicle, and their position in relation to the vehicle.

Researchers from Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) are collaborating with colleagues from Fraunhofer Institute for Applied Optics and Precision Engineering IOF and Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology on the project. Fraunhofer FHR is focusing on radar sensing; Fraunhofer IOF is focusing on micro-optic light technology; and Fraunhofer FEP is contributing thin-film technology to the project.