For a college project i need to build a car which can follow a wire with an current flowing through it. My first thought is a coil of wire to pick up the EMF. Are there any other ways to detect the wire? are there sensors that i can buy that can do this?
I think if you tell us more about the current source being used in the guide wire it would help. Is it DC or AC, if AC what frequency and is it continous wave or pulsed or otherwise modulated?
Lefty
Its ac, 20Hz sine wave. Not sure about the voltage atm.
Thanks
You might also look into Hall-effect sensors, which can detect a magnetic field.
do you really want to sense current and not voltage? Sensing current requires you to put a load on the AC wire while sensing voltage just means the wire has a potential.
Here's an explanation of using capacitive sensing for voltage:
http://www.techni-tool.com/content/resources/articles/Fluke-Understandingcapacitivevoltagesensor.pdf
Depending on how accurate you have to be, there might be a signal put on the wire so you can tell one wire from another and don't jump the track and follow the wrong wire.
I didn't read the entire article or look for capacitive sensors but googling should help you there.
Doug
its not quite a case of voltage or current. Basically ive got to build a line follower that follows a wire rather than a different coloured line! I have to reaserch each option and have to compile and present a report. Im just after "avenues" that i can research and compaire in terms of effictive ness and cost etc!
I hadnt thougth of capacitive sensors, or hall efect. Thanks guys, keep the ideas comming 
its not quite a case of voltage or current. Basically ive got to build a line follower that follows a wire rather than a different coloured line! I have to reaserch each option and have to compile and present a report. Im just after "avenues" that i can research and compaire in terms of effictive ness and cost etc!
then don't leave out fiber optics. It's all about sensing radiation of some sort. A colored line or fiber optic is photonic and the wire is electro-magnetic.
I hope you can post your results or link it here when you're done.
Doug
i've got a year and half to research, design build, programm and build and tinker. mind you thats only 3 hours a week, plus what ever time i can find at home after the rest of my assignments!
Its ac, 20Hz sine wave.
Are you sure, this is very difficult to detect. You would be much better off using 20KHz as you could get some inductive coupling with that but 20Hz is too low to be useful.