In this paper a study on the nonlinearities effects on passive UHF RFID tags is established. From experimentation, once the communication is established between reader and tag, the evidence of existence of a 3^rd harmonic carrying information by the backscattered modulation is presented. Contrary to the classic approaches which tend to eliminate the harmonics generated by the rectifier part of the tag, an idea of their exploitation by defining a redundant channel is discussed.