It was mentioned earlier that communication between the tags and the reader is by radio waves. These waves have a magnetic and an electric component. Both LF and HF systems use the Magnetic or "H" field to transfer energy to a tag by induction. This creates a homogeneous RF field but the strength of this field falls off sharply. UHF systems use the Electric field to transfer energy to a tag by propagation. The strength of this field doesn't fall off as quickly as the magnetic field, giving UHF tags an extended reading range but reflected signals result in a reading zone that is less well defined.