Fabio Carati – Surface Solutions
Merck’s Surface Solutions division owns many years of experience in the Automotive sector regarding the chemistry of special effect pigments applied to coating finishes for the various substrates of which vehicles are made. This article is inspired by a technical speech held at the last Paint & Coatings Italy, in which the Surface Solutions team showed the peculiarities of metallic effect pigments, applied to radar technology.
The Iriodin® 9627 SW RDR Silver pigment, for this particular application in the Automotive sector, combines exceptional hiding power with high radar transparency and a luminous and bright metallic flop. Automotive radar beams travel through the pigment without changing direction or intensity.
TECHNOLOGY
The radar (radio detection and ranging) technology exploits the properties of electromagnetic (EM) waves to acquire information about nearby objects. It does this by emitting EM waves at a given frequency, detecting secondary signals. Modern cars are equipped with different types of radar-based assistance systems, from adaptive cruise control (ACC) technology to blind spot detection (BSD) and pre-collision warning (PCW). These systems combine data generated by radar devices with information provided by sensors (such as ESPs).
Modern automotive radars operate at frequencies between 76 GHz and 81 GHz. Compared to optical sensor technology (e.g. cameras and lidar), the advantage of radar is that it is much less sensitive to adverse weather conditions such as fog, snow or rain. Another advantage of radar systems, which should not be underestimated, is that radar sensors can be hidden. In many cases, they can be installed without affecting or changing the design of the vehicle. Short-range radar (SRR) is usually mounted behind the corners of car bumpers, while sensors used for long-range radar (LRR) are mounted frontally behind logos, badges or plastic trim. Such protective covers are known as radomes.
The goal in automotive design is to integrate radars without changing the design of the car itself, making them ‘invisible’ by positioning them behind coated plastic parts. However, to do this it is necessary that all components of the radome, including the coating, are as transparent to radar as possible. Furthermore, post-repair requirements must be considered when formulating new OEM coatings: components must remain transparent to radar even with much thicker coatings. Since most radomes are made of painted plastic, their dielectric properties play a crucial role in automotive radar systems.
The relative electrical permittivity (or the relative dielectric constant εr) describes the behavior of a material in the presence of an electric field, compared to a vacuum. Plastics and coatings typically have a higher permittivity than air. When radar signals are transmitted through dielectric materials, the signals are partially transmitted, reflected and absorbed. It is therefore critical to design radar coverings to achieve sufficiently high transmission levels, not only to meet sensor range requirements, but also to minimize reflection so that signals do not disturb receiving antennas. If the thickness and permittivity of the individual layers are known, the transmission properties of the radomes can be calculated.
SIMULATED BIDIRECTIONAL TRANSMISSION OF AN EM WAVE ON UNPAINTED PP/E TD30 AS A FUNCTION OF LAYER THICKNESS AT 76.5 GHZ AT VERTICAL INCIDENCE
Figure 1 shows the calculated transmission coefficient of uncoated PP/E TD30 as a function of material thickness. If you choose the correct thickness, 98.5% of the signal is transmitted, while in the worst case 61.9% is transmitted.
Modern short-range radar (SRR) sensors require bidirectional transmission levels of at least 25% and long-range radar (LRR) sensors at least 50%, which in this case would be achieved regardless of thickness.
SIMULATED BIDIRECTIONAL TRANSMISSION OF AN EM WAVE ON COATED PP/E TD30 AS A FUNCTION OF SUBSTRATE LAYER THICKNESS AT 76.5 GHZ AND VERTICAL INCIDENCE
Figure 2 shows the result of a calculation for a coated material composed of three layers:
– Conductive primer (10 μm).
– Variable base coat (20 μm).
– Clear coat (30 μm).
For the model, four different base coats have been hypothesized with calculated permittivity εr of 3, 7, 20 and 50. The simulation shows that bases with a permittivity of εr=20 have a non-negligible influence on the radar properties. With an even higher permittivity value of εr=50, the current limit values for SRR can only be achieved by adjusting the bumper thickness accordingly.
RADAR PERMITTIVITY IN SILVER COLORS
Metallic coatings interfere with radar signals. This is because they use metallic pigments, which on the one hand have a pronounced light/dark flop and a strong opacity, necessary to obtain the metallic effect especially in light silver shades, on the other hand they have a strong reflectivity. Unfortunately, aluminum-based pigments also reflect electromagnetic waves from sensors, which can result in permittivities of εr=50 or more, if they are used to coat radomes. In such configurations, the operation of radar systems cannot be guaranteed.
Traditional pearlescent pigments, on the other hand, are almost completely transparent to radar signals and can be used to provide metallic sheen. However, they are also semi-transparent to visible light and pose a challenge to achieve optimal brightness, metallic flop and, most importantly, a right covering.
A NEW GENERATION OF SILVER PIGMENTS
Surface Solutions has developed a technological range of pearlescent metallic effect pigments with:
– Greater transparency to radar than metallic pigments.
– Improved hiding power compared to traditional pearlescent pigments.
– A finer particle size to allow for smoother, satin textures.
– A blue-silver color for high-class styling of neutral-bluish silver.
– Greater sustainability: natural mica-based pigments result in lower water consumption and CO2e emissions compared to synthetic mica-based pigments (-20% CO2e / -25% aBWC/ -60% Aware vs syn.mica).
RADAR PERMITTIVITY OF THE NEW IRIODIN® 9627 SW RDR SILVER
Thanks to their extraordinary visual and technical characteristics, Iriodin® pigments have been used for decades in a wide range of coating applications especially in the automotive, architectural and other industrial sectors. These pigments are also offered with an additional coating, especially for external applications. They are weatherproof and comply with the highest requirements for reproducibility and long-lasting color uniformity.
Among the new pigments from Surface Solutions produced specifically for radar applications in the Automotive sector Iriodin® 9627 SW RDR Silver, is a brilliant pigment to obtain a metallic effect. The high permittivity of the pigment allows for optimal radar transmission values, not achievable with metallic pigments, and is able to guarantee a combination of exceptional covering power and high brightness.
Iriodin® 9627 SW RDR Silver is an ideal pigment for producing satin and shiny-silver gray finishes, combining the typical metallic gray effect with high transparency to radar waves, to meet the latest needs of the Automotive sector.
