Ultrasonic sensor system for detecting falling objects on railways

The current rail security rules require, more and more, the automatic detection of possible obstacles on tracks, above all in areas where a large probability of alive beings intrusion or falling objects exists. In this paper an ultrasonic sensor system is proposed for this aim, paying special attention to the signal coding and processing. This signal coding, based on the use of complementary sequences, makes the system robust against atmospheric turbulence, the phenomenon which turns out to be the most problematic when transmitting ultrasonic waves outdoors.