Autonomous vehicles are expected to result in fewer road casualties and more efficient traffic.
But driver assistance systems also protect lives. For a safe function of the optical sensors– the basis of autonomous driving-, the stray light must be certainly suppressed as far as possible.
With a lane departure warning system, it is theoretically possible to practically drive short distances autonomously.
Before true autonomous driving is possible, however, the car must first learn to see and react without errors.
This requires perfectly functioning “eyes” and powerful electronics.
The car sees with optical sensors such as cameras for day and IR, ultrasonic and radar sensors and laser scanners called Lidar (light detection and ranging) and laser systems.
To obtain a perfect 360° image of the surroundings, several sensors are distributed around the vehicle.
For this, the test vehicles are equipped with a good dozen cameras, ultrasonic sensors, several radars, a Lidar sensor, and a powerful onboard computer.
The fact that it took so much time for car manufacturers to develop a driverless car that is ready for serial production, shows that autonomous driving is not easy.
The autonomous car must be able to recognize objects and people beyond doubt, know the traffic rules, and be able to anticipate dangers.
To accomplish this, cameras, radar sensors, and laser scanners must work together.
In other words, what one sensor overlooks is likely to be seen by the other – but only if they work properly.
A big problem here is stray light because it makes the sensors partially blind.
Stray light is caused by the reflected light from lenses and the image sensor, by the diffuse reflection at lens edges, apertures, or other components inside the lens or the camera.
Stray light depends on the lighting conditions, especially if there are bright light sources inside or right outside the image angle.
Bright light sources include sunlight, street lamps, illuminated buildings, illuminated shop windows, etc.
In addition, there is heat radiation corresponding to the temperatures in the vehicle.
Dust particles or other impurities on the lens surfaces also produce stray light.
Optical surfaces can also become dirty by fogging– a milky, cloudy coating of vapors, e.g. from plastic softeners, which condenses on the lenses and scatters the light.
According to the sources, the stray light, therefore, covers a wide spectral range from EUV (extreme UV, from 30 nm) to FIR (Far IR, up to 1000 µm).
Design improvements and matt black absorber coatings provide a remedy.
These coatings tolerate the extreme challenges of optical sensors in vehicles, such as very high-temperature differences, permanent vibrations, etc.
Many of these paint coatings consist of oxides with a carrier material and to apply them, they are sprayed on.
The adhesion of the paint layer to the substrate, however, can be problematic, because the large temperature fluctuations and vibrations that are possible (especially in cars), cause the layer to peel off over time.
In addition, spraying produces a relatively uneven thickness and the carrier material must outgas.
ACKTAR avoids this problem by coating its proprietary Black layers in a vacuum.
This produces optimally uniform, very thin layers with secure adhesion that can even withstand space conditions and absorbs about 99% of EUV-UV, VIS and NIR-FIR.
This allows any opto-mechanical component, whether metal, glass or plastic, to be reliably coated.
Thanks to the coating process, for the Acktar coatings like Magic Black or Fractal Black, there are hardly any restrictions about surface geometry.
Curvature radii up to 3 μm are possible here.
For large partial surfaces, a coating with self-adhesive foils like Metal Velvet or Maxi Black is a good option, which can be easily cut into shape.
In this case, the black coating is vapor-deposited either on an aluminum carrier or on polyamide.
The coating process also holds the secret of outstanding properties.
For example, compared to spray paint, the Acktar Black coating achieves 2000 times the substrate surface in a coating only a few micrometers thick.
The process allows optimal control of the surface morphology, both in terms of shape and structure, and of the physical and optical properties.
The coating can withstand temperatures from -269°C to +450°C, has excellent mechanical strength and abrasion resistance, practically no outgases, is ecologically safe, inorganic, and completely non-toxic (RoHS & REACH compliant) and can be hydrophilic or hydrophobic, depending on the customer request.
Thus, the coatings are stable for UV radiation and maintenance-free.
Furthermore, ACKTAR Black Coatings offers an adjusted, customer-specific, electrical-conductivity property to the coating in order to ensure the proper function of the sensors.
In order to guarantee this, the coatings have been extensively tested, for example VDA 278 or ISO 105-B06, under standardized conditions.
The outgassed and fogged quantities were only in the order of a few micrograms per gram of the coating material.
Thus, the coatings are sure in use with regard to fogging and VOC (volatile organic compounds) in the interior of cars according to DIN 75201.
Thanks to this deepest black, stray-light-reducing coating, the corresponding sensor and camera systems deliver high image quality and allow the use of more cost-effective sensors.
These coatings not only make cars safer but also make the production process of the vehicles safer through their use in image processing systems for quality assurance in the automotive industry.
A safe and fast signal detection guarantees the efficient control of processes.