Potentiometric Sensing by means of Self-tuning RFID ICs

Recently introduced autotuning RFID ICs can provide digital information on the change in the local boundary conditions in the close surrounding of the tag. By exploiting this feature in combination with a varactor diode, a general framework for the controlled sensing of a chemical agent can be achieved. The varactor acts as a transducer converting the potentiometric output of a chemical sensor into a capacitance change that produces in turn a mismatch between the antenna and the IC. Closed-form expressions relate the digital output of the IC to said chemical variation so that it is well mapped within the retuning dynamic range. The method is demonstrated with reference to a pH sensor and looks promising to provide a sensitivity of 18 units per unitary change of the pH and could be read up to 2 m.