A method and system for communicating state information from a transponder to a reader. The transponder outputs linearly polarized RF signals having either a first polarization, such as horizontal, or a second polarization, such as vertical. The polarization is selected so as to indicate a first state...http://www.google.ca/patents/US7388501?utm_source=gb-gplus-sharePatent US7388501 - Method of enabling two-state operation of electronic toll collection system
