77 GHz Metamaterial Absorbers Composed of Crossed Dipoles on Grounded Dielectric Substrate for Automotive Application

In addressing the needs of automotive radar designers, this study investigates the 77 GHz radar absorbing materials (RAMS) suitable for the automotive environment. A metamaterial structure is composed of metallic conductors of cross pattern on a grounded dielectric substrate (FR4). Computational tools (ANSYS HISS 13.0) were used to model the interaction between electromagnetic waves and the metamaterial structures. The simulation output included the reflection coefficient. Another parameter of interest was the surface currents and electric fields, which were used to depict the resonating behavior of the metallic portions of the metamaterials. Magnetic resonance resulting from antiparallel currents between the strip conductors on front surface and ground bottom plane was observed at the frequency of minimum reflection loss (-23 dB at 77 GHz) with a small substrate thickness as low as 0.2 mm. The simulated resonance frequency and reflection loss can be explained well on the basis of the circuit theory of an LC resonator.