Abstract: The invention relates to an inductor, and particularly to an inductor for a transmitter circuit. The invention also concerns a transmitter including said inductor, a proximity detection system employing such a transmitter, and a method of making said inductor. The inductor of the invention includes a core having non-uniform permeability and a conductor winding arranged around the core. When used in a transmitter circuit, this allows an induced electromagnetic field to propagate through the core in a more efficient manner than otherwise possible, so resulting in a higher dynamic field strength for a given resonant circuit drive.