Harmonic chipless sensor exploiting wireless autonomous communication and energy transfer

The feasibility study of a harmonic RFID chipless sensing tag is presented. The tag sensor is composed by an antenna at f₀ = 1.2 GHz, a Schottky diode (HSMS2850), a balanced impedances bridge with a sensing variable element, and a second antenna working at 2f₀ = 2.4 GHz. When interrogated with a signal at f₀ the tag responds with a signal at 2f₀ only when the bridge is unbalanced due to a variation of the sensible impedance value of at least 5 Ω. With this approach the system is energetically autonomous, being activated by the received signal and responds only when there is a change in the sensed quantity. No IC for carrier modulation is required to transfer the information.