Aluminum-based effect pigments are widely used in automotive coatings,but it has been found that such coatings frequentiy disturb the transmission of radar signals,if the radar source is hidden behind the coating.To measure this reduction in transmission,tne permittivity dielectric constant(ε)and the loss tangent,tan(δ)(dissipation factor)of radio waves in the desired frequency band are used.Many published results show that the e increases with rising pigment mass concentration,while 5 changes are negligible.Figure 1 shows frequentiy cited data where the relative permittivity of automotive effect coating(including metal-based effect pigments)is analyzed with respect to the metal mass content.According to Pfeiffer,the exemplary limits of radar transmission in terms of relative permittivity of automotive coatings are assumed to be50 as highly critical.
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