Excitation of Surface Electromagnetic Waves on Railroad Rail

Excitation of Surface Electromagnetic Waves on Railroad Rail

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    UMTA's Office of Rail Technology research programs aim to improve urban rail transportation systems safety. This rail-transit research study attempts to develop an onboard, separate and independent obstacle-detection system--Surface Electromagnetic Wave (SEW)--so that rear-end train collisions can be avoided. The use of SEW for communication, control, and obstacle-detection on guided railroad systems is already underway in the United States, United Kingdom, Japan, and Canada. SEW have been sucessfully used on the surface of standard railroad rail and other metallic surfaces. In this report, the preliminary investigation of the propagation properties of SEW on rail surfaces indicates that there exist applications in train-and-obstacle detection. The excitation efficiencies of two types of SEW couplers (prism and grating) are measured as functions of frequency, vertical displacement (h) of the coupler above the rail, horizontal displacement (a) of the coupler from rail center, pitch angle (Phi) of the couler, and yaw angle (Psi) of the coupler. The coupling efficiencies for both prism and grating couplers show a dependence on vertical displacement above the rail; horizontal displacement from rail center, pitch, roll, and yaw angles of the couplers. Measurements of radiation patterns are also made on the two types of SEW couplers in the vicinity of the rail and in isolation at several microwave frequencies. The results of radiation pattern data show that to meet the FCC specification of 500 uV/m at 100 ft from the coupler for 100 mW input, the couplers must be redesigned. The data indicate that both the prism coupler and grating coupler will operate successfully on a moving track-guided vehicle.
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