Development of electromagnetic wave absorbers to improve ETC communication environment

In this paper, we investigated EM wave absorber for a ceiling of a tollgate in ETC system. The EM wave absorber samples were made of CPE and Flake Sendust powders, which can be manufactured with mechanical forging of spherical Sendust powders using attrition mill to get high value of magnetic permeability and dielectric permittivity in high frequency range. The absorption ability of the samples were measured by vector network analyzer. We compared the absorption abilities of the samples. These material constants were calculated from the S-parameter. EM wave absorber is designed by using material property and variation of thickness at 5.8 GHz. The optimized composition ratio of absorbing materials was Flake Sendust powders: CPE = 62.5 : 37.5 wt.%, and absorption ability of the EM wave absorber with thickness of 2.85 mm showed more than 20 dB at 5.8 GHz. Therefore, it is expected that the newly developed absorber can be used for countermeasure against EMI from a ceiling of a tollgate in ETC system.