Yoshihito Hirai

An Improvement of Communication Environment for ETC System by Using Transparent EM Wave Absorber

When a large-size car exists on the ETC lane (Electronic Toll Collection System), there is the possibility that the interference on the adjacent lane occurs by the scattering waves from one. In this paper, we propose a new improvement method which the transparent EM wave absorber is placed between the ETC lane and the adjacent one in order to suppress the scattering waves from a large-size car. Therefore, we design the transparent EM wave absorber which consists of the transparent resistive and conductive films. Then, this absorber is produced, and its reflection and transmission coefficients are evaluated. In addition, its transmittance in optics is evaluated. As the results, the reflectivity of this absorber is obtained lower than -20dB in the oblique incident angle from 0° to 30 at 5.8 GHz circular polarized wave, abbreviated as CP wave, and also the transmittivity is obtain lower than -27 dB in the oblique incident angle from 0° to 70°, respectively. On the other hand, the transmittance in optics is obtained higher than 60%. Moreover, we study experimentally on the ETC system with placing this absorber between the ETC lane and the adjacent one. We measured the distribution of receiving power on the adjacent lane, when a water sprinkler existed on the ETC lane. As a result, it is confirmed that the receiving power on the adjacent lane could be realized lower than -70.5 dBm, and then a new improvement method has proven to be very useful in the ETC system.

Investigation on convenient measuring method of oblique incident characteristics for absorbing panel in low frequency range (lower than 1 GHz)

The ferrite absorbing panel used for suppressing TV ghost images caused by TV wave reflection from tall buildings and the RF absorber used for an anechoic chamber have been realized for many years. The convenient and accurate measuring method of the reflectivity characteristics of RF absorbers against the oblique incidence in the low frequency range (lower than 1 GHz) is investigated by using a new time domain reflectometer method. The direct wave vector from the transmitting antenna to the receiving antenna and the undesired reflection vector can be eliminated by means of a mathematical treatment or by subtraction of the receiving signal without the target from that signal with the target in advance of time gating in the desired response. By using these new methods, a convenient and efficient evaluation method for an RF absorbing panel and absorber could be realized.