Wave Absorber for Improving EM-Wave Environment between ETC Lanes and Its Practical Application

近年来，以5.8GHz无线通信作为智能交通系统（ITS）中心服务的不间断自动收费系统被称为电子收费（ETC），在日本得到广泛推广，2008年的普及率已达到75%。当ETC开始运行时，由于来自墙壁、ETC门或其他可能的附近物体的不期望的电磁波（EM），在ETC环境中造成通信错误。波吸收器的最佳使用是缓解这一问题的一种可能方法，各种各样的吸收器被用于不同的地方，例如用于收费站天花板的板型，用于路面的路面型。在这样的背景下，还需要安装在ETC车道之间的吸波器，因为当拥有两个或更多ETC车道时，收费站的数量可能会随着扩散速率的增加而增加。这种吸收器的某些性能是必要的，例如吸收不需要的电磁波，屏蔽到达相邻车道的电磁波，通风以避免风的冲击，以及对相邻车道的可视性。本研究提出在金属网后放置一些吸波器作为背金属，以改善ETC环境，如周期性点阵的含玻璃纤维的增强塑料、周期性布置磁损罩的圆柱棒、圆形点阵的磁性橡胶片等。对各种特性进行了分析和实验评价。结果表明，ETC系统对圆极化波具有良好的反射损耗特性和屏蔽效果。因此，可以定量地确定所提出的吸波器的可行性。

In recent years, the non stop automatic charge payment system using wireless communication at 5.8GHz as central service of intelligent transport systems (ITS), which is called electronic toll collection (ETC), is spread widely and diffusion rate has reached to 75% in Japan at 2008. When the operation of ETC was started, communication errors were caused in ETC environment due to undesired electromagnetic(EM)waves from walls, ETC gates or other possible nearby objects. The optimal use of wave absorber is a possible way to mitigate this problem, and a variety of absorbers are used in various places, such as a board type used for the ceiling of tollgate, a pavement type used for the road surface. In such a background, the wave absorber for installing between ETC lanes is also required because the number of tollgate, where two or more ETC lanes are possessed, may increase with diffusion rate rise. Certain performance is necessary for this absorber, such as absorption of undesired EM waves, shielding effect of EM wave reaching adjacent lanes, ventilation to avoid the shock of the wind, and visibility to adjacent lanes.In this research, some wave absorbers placed behind the metal mesh as back metal for improving ETC environment is proposed such as the type of reinforced plastic including glass fiber with periodic lattice, cylindrical bars with magnetic loss covers arranged periodically, and magnetic rubber sheet with circular lattice. Various characteristics are evaluated analytically and experimentally. As a result, good characteristics of reflection loss and shielding effect are obtained for circularly polarized wave using ETC system. Therefore, feasibility of proposed wave absorbers can be confirmed quantitatively.