I want to use a length of steel pipe as a communication medium. The pipe is about 20 feet long and the idea is to send some sort of signal along it that can be detected at the far end. I've had various ideas including using acoustic signals, or using the steel as an electrical conductor but I don't think I'll be able to ground the pipe at either end to complete the circuit. I therefore had the idea of using the pipe as a type of transformer core, with the primary and secondary windings rapped around either ends of the pipe. This would be an extremely inefficient transformer of course, I'm not even sure it would work, but I'm hoping just enough magnetic flux might pass through the pipe that it might be detected at the far end. I would like to know if anyone had any thoughts on the idea, is it a viable concept? I haven't tested it yet but some concerns I have are that there is no return path for the flux except through air, the relative permeability of steel is nowhere near that of soft iron and there will probably be large eddy currents. Any replies will be much appreciated.