As a part of a school project I am required to build an electromagnetic tether robot. The robot needs to stay a constant distance from an electromagnetic beacon. As well as keeping a constant distance the transmitter can change the desired distance. (eg. move closer/move farther commands). The robot must be able to come as close as 20cm and as far as about 10m or more. After hours of research and internet searching I'm at a loss on how to implement the magnetic transmitter/receiver. I'm thinking the transmitter will give off electromagnetic waves at some frequency and then the receiver will have some sort of LC circuit that has the same resonant frequency as the transmitted signal. Our project description says that the robot should read the signal using a couple of inductive sensors and then use a micro-controller to determine the distance. What I am unsure of is how exactly I can make this transmitter/receiver and how I can get a distance measurement on the receiving end as well as the move closer and farther commands. I was thinking I can use the fact that magnetic field decays at a rate of 1/r^3 but there also needs to be some sort of serial communication in order to command the robot to move farther away or closer. Any tips or resources to help me with this would be awesome.