Undersökning av vissa beläggningars påverkan på antenners effektivitet i tågmiljö
For several years Uppsala University together with several companies has been involved in a WISENET project aimed at improving railway transport security. By placing a sensor system near the wheels of each wagon, the temperature of the bearings can be measured and transmitted to a collector placed centrally on the wagon. This in turn transmits the collected data to RFID receivers placed intermittently along the railway.As the signals are transmitted wirelessly, problems may occur as the antennas get dirty or coated with ice and snow. To determine the effects of these coatings, several tests were performed examining the reflection coefficient S11, the impedance Z11 and the efficiency eta of an antenna, and how they varied when various coatings were placed over the antenna. Examined coatings were ice, snow and water to determine the effects of weather, and various metal-based coatings: powdered iron both pure and partially oxidized, and iron ore granules. Finally a sample coating taken directly from a car was tested to determine how closely the other coatings resembled what appeared in normal use.Most of the coatings gave similar results; little or no loss of efficiency and a lowering of the resonance frequency by some 75 MHz, with both iron powder samples, the ore granules and the sample coating proved nearly identical in results. Thick layers of snow gave a noticeable drop in efficiency, as did the presence of any amount of water, which also greatly affected the resonance frequency.