Magnetic Field sensors

[Builder1]

Hello Everyone,
I would like your opinions on an idea that I have, please tell me whether its something that is feasible or not. I thought about using an inductive proximity sensor to keep my robot from straying outside of a target area, but I didn't like the fact that it requires cables which have to be hooked up to a power source, to be used as targets. My idea is instead of using cables, I would use magnets. I would embed small pieces of magnet into the ground at regular intervals which will serve as navigation markers. Then use magnetic field sensors to pickup the magnetic fields of each piece of magnet. I would program the robot to count each magnet piece as it is encountered. The robot will start off from a reference point where everything else is based off of. Each time a piece of magnet is encountered I will tell the robot to do something based on whether it is the first, second, third, etc. magnet to be detected. For example if I put the first piece of magnet on the foot of a round object, when the robot detects this magnet it will be told to circle around this object then keep on going until it picks up a new magnetic field. Then a new set of instructions will be given. If I couple this type of sensor with range finders, I think  navigation should be pretty straight forward. Please leave your comments or concerns on this approach to navigation, thanks in advance for your time.

[HDL_CinC_Dragon]

You can use Hall Effect Sensors to pick up the MF
Or you can try top rig something up that basically works like a relay which uses an electromagnetic field to pull(or push?) a contact onto another contact point to make the connection and just use that so that when its over a magnetic field, the field pulls a contact onto another contact.

[ArcMan]

I have also thought about a similar thing for navigation.  But instead of magnets, use RFID tags.  The robot then carries an RFID tag reader.  Since RFID tags can be encoded with unique IDs, there is no need to count magnets and thereby risk losing count.  It's absolute positioning.  I read about this in an article about a year ago - I forget which mag.  I thought it might be a good way to correct IMU drift errors.

[Builder1]

Thank you all for your response,
I am currently looking into using both magnets and RFID tags as possible navigation markers. RFID tags are interesting, do they require an energy source at all to operate? I have been searching online for waterproof RFID tags and have found some on EBAY, the problem is the seller did not answer my inquiry into the energy source and range of operation of these tags. The RFID tags of interest are the 5PCS 125Khz waterproof cylindrical RFID tags, they are small and encased in a cylindrical casing which are perfect for my intended purpose. If you have any ideas on what energy source they operate on, please let me know.

[madchimp]

http://electronics.howstuffworks.com/rfid.htm