a transponder for communicating with an interrogator has a high q - factor resonant circuit of frequency f 1 for receiving rf powering signals . the transponder also has a tuning circuit which when in electrical communication with the resonant circuit is operable to form a lower q - factor resonant circuit of frequency f 3 for receiving rf communications from the interrogator unit . the transponder also includes a demodulator which is in electrical communication with said resonant circuit . additionally , the transponder also included a control circuit which receives a demodulated data signal from the demodulator . the control circuit is further connected to the tuning circuit and is operable to connect the tuning circuit to the high q - factor resonant circuit in order to form the lower q - factor resonant circuit . control circuit also converts the rf powering signals to a dc current for storing energy . the energy is stored in an energy storage device such as a storage capacitor . other devices , methods and systems are disclosed .