Roadworks can take weeks when crews dig up the wrong pipes and then have to start again. So Tempo Research of California has found a way to easily distinguish between buried power conduits and water or gas pipes (US patent application 2004/0178795).
The idea is to fit each set of buried pipes with radio-frequency ID tags that will respond to a different frequency beamed from above. The tags on a gas pipe, for instance, only respond to a signal on a dedicated “gas frequency”. There is a snag – radio signals induce currents in all the tag coils and…
