# Car Bumper Effects in ADAS Sensors at Automotive Radar Frequencies
## 3 Car Bumpers Characteristics  
Most modern bumpers are produced using polymer materials with different fillers (mainly carbon black and talc). [PERSON] et al. [29] performed thermal analyses on recycled bumper materials to gain insight into the most commonly used polymer materials. Their research found that most car bumpers are made of a blend of polymers consisting of a large amount of polypropylene (PP) and smaller amounts of high-density polyethylene (HDPE) and ethylene propylene diene methylene (EPDM).  
Besides the material that composes the bumper, the covering paint may also play an important role in radar signal propagation. As discussed by [PERSON] [30], most modern car paints contain acrylic and/or alkyne resins and cross-linking agents like amino resins,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Azimuth**} & \multicolumn{2}{c}{**Elevation**} \\
**Type of Radar** & \multicolumn{2}{c}{**3 dB-BW**} & \multicolumn{2}{c}{**3 dB-BW**} \\ \cline{2-5}  & **Tx** & **Rx** & **Tx** & **Rx** \\ \hline Radar A. & & & & \\ Automotive radar. & 5\({}^{\circ}\) & 5\({}^{\circ}\) & 3\({}^{\circ}\) & 3\({}^{\circ}\) \\ Front applications (250 m). & & & & \\ \multicolumn{5}{c}{Radar B.} \\ Automotive high-resolution radar. & 12.5\({}^{\circ}\) & 13.5\({}^{\circ}\) & 5.5\({}^{\circ}\) & 5.5\({}^{\circ}\) \\ Front applications (100 m). & & & & \\ \multicolumn{5}{c}{Radar C.} \\ Automotive high-resolution radar. & 12.5\({}^{\circ}\) & 16\({}^{\circ}\) & 5.5\({}^{\circ}\) & 5.5\({}^{\circ}\) \\ Corner applications (100 m). & & & & \\ \multicolumn{5}{c}{Radar D.} \\ Automotive high-resolution radar. & 16\({}^{\circ}\) & 16\({}^{\circ}\) & 5.5\({}^{\circ}\) & 5.5\({}^{\circ}\) \\ \multicolumn{5}{c}{Radar E.} \\ Automotive high-resolution radar. & & & & \\ \multicolumn{5}{c}{Very short range} \\ \multicolumn{5}{c}{applications (50 m).} \\ \hline \hline \end{tabular}
\end{table}
Table 1: 3 dB-beamwidths for automotive radar antennas.  
urethanes or styrene. Most car paints are applied in multiple layers. Usually, a layer of primer is followed by a few layers of base coat [31]. This is confirmed in the information provided by the company that supplied the bumper test samples we analyzed. Thus, the car bumper has a layered structure, as shown in Figure 1.  
The bumper samples used in this work were kindly provided by an automotive sector company, supplying external components and modules to major car manufacturers. Table 2 provides information on some characteristics of the five samples that were analyzed (labeled as samples A, B, C, D and E). Most of the samples were made of a copolymer of polypropylene (PP) and polyethylene PE, except for sample E, which also contained 10% of talc. Samples C, D and E were painted with a primer layer, a base layer and a layer of colored varnish. Sample A was unpainted, and sample B was painted with a layer of primer, two base layers and a layer of varnish.  
All samples had a thickness of around 4 mm, and the manufacturer provided elements as flat as possible, cut from the most uniform section of the bumper design. They were parts of the current pieces and thus their shapes depend on the car model project. Figure 2 shows some of the samples used.  
Figure 1: Layer distribution schema of car bumpers.  
Figure 2: Front- and backsides of bumper samples D (**down**) and E (**up**).