Radar Transparency and Paint Compatibility - A Study of Automobile Bumper and Bumper-Skin Complex Permittivities for 77GHz Microwaves

Examensarbete för masterexamen
Master Thesis
Engineering Physics (300 hp)
Emilsson, Erik
This study aims to identify the key factors, regarding bumper and bumper coatings, that affect radar transparency for radar at 77GHz. Dielectric spectroscopy in the 60-90GHz microwave region was performed using the free- space method was performed on 21 flat plastic substrates with various combinations of primers, basecoats and topcoats. 4 additional plates were repainted to simulate aftermarket paint. The substrates were PP-blends and some of the basecoats had effect pigments such as aluminum metal flakes, mica and Xiralic. The samples were received from a Volvo Cars supplier, so there is limited information of the composition of plastic substrates and coatings available. The free space method was done using a two-port network analyzer. Time-domain clipping and normalization was done on the S-parameters. Complex permittivities for each plastic substrate and coating were calculated from the curve fitting values of a multi-layer dielectric model. Both the obtained radar measurements and thickness measurements were required for the calculation of the permittivities. Thickness measurements were done on the cross-sections of all cut samples using an optical microscope. Effect pigments were observed in both optical microscope and SEM. FT-IR spectroscopy was done on the plastic substrates to obtain information on the compositions. TGA was done on the plastic substrates to measure polymer matrix and filler concentrations. DCS was done on the plastic substrates percent crystallinity was calculated using a reference value for the enthalpy of 100% crystallinity for Polypropylene, after deducting the fillers. The results from the materials analyses were compared to the calculated permittivities. Reflection losses, were modeled with MATLAB to show the approximate permittivities of the aftermarket basecoats that were difficult to perform curve fittings on. Metal flake content correlated to a greater real permittivity of the basecoats. A non- metallic effect pigment in similar concentrations as the metal flakes also increased real and imaginary permittivity in a basecoat. Talc, and likely carbon black, also increased real permittivity. MATLAB was also used to show that plastic substrate thickness is to minimize unwanted reflections in radar, as well as a low permittivity for the basecoat.
Materialvetenskap , Fysik , Textil-, gummi- och polymermaterial , Materials Science , Physical Sciences , Textile, Rubber and Polymeric Materials
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