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

近年来，作为智能交通系统（ITS）的中心服务的、使用5.8GHz无线通信的不停车自动收费支付系统（称为电子收费系统（ETC））在日本得到了广泛的普及，2008年普及率已达到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（EM）波，在ETC环境中引起通信错误。最佳地使用波吸收器是缓解该问题的可能方式，并且在各种地方使用各种吸收器，例如用于收费站的天花板的板类型，用于路面的路面类型。在这样的背景下，也需要用于安装在ETC车道之间的吸波器，因为在具有两个或更多个ETC车道的情况下，收费站的数量可能随着扩散速率的增加而增加。这种吸波器必须具有一定的性能，例如吸收不需要的电磁波，屏蔽电磁波到达相邻车道，通风以避免风的冲击，以及相邻车道的可见性。在本研究中，提出了一些放置在金属网后面作为背金属的吸波器，以改善ETC环境，例如包含周期网格玻璃纤维的增强塑料类型，磁损罩周期性排列的圆柱形棒和具有圆形网格的磁性橡胶片。各种特性进行了评估分析和实验。结果表明，ETC系统对圆偏振波具有良好的反射损耗特性和屏蔽效果。因此，可以定量地证实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.