.  Hill Country Research Innovations in Telecommunication and Automation     Electromagnetic Obstacle Sensor .

This sensor detects metallic objects in the vicinity of its electromagnetic field.  It is driven by a 36 MHz transmitter which feeds the signal to a resonance circuit.  The resonators amplitude, which is  a function of externally induced attenuation, is fed to the receiver and converted to a DC signal, controlling a relay. The complete system is designed to fit inside a 10 mm tube and runs on 24 V.