Flexible epidermal device for the RFID-based potentiometric sensing of skin parameters

Non-invasive monitoring of biological parameters can benefit from Radio frequency Identification (RFID) devices attached over the skin. In this paper, a new lightweight, compact, and fully passive epidermal electronic device is proposed, capable of measuring surface pH. By integrating a self-tuning IC and a varactor diode as transducer, the mapping from the chemical agent to the output of the IC itself is achieved. To fully control the sensitivity, a closed-form formulation of the sensing mechanism is derived. The device is applicable over multiple body areas and readable up to 70 cm, with an average realized gain of −12dB at 868 MHz.