A based microcontroller technique to achieve capacitive multisensing in passive RFID UHF tags

In this work, we propose a multiplexable low power capacitive sensor measurement circuit that can be incorporated in passive RFID UHF tags in order to achieve passive capacitive multisensing. Circuit parameters as excitation frequency, measurement time, sensor selection and sensor data can be controlled by any standard reader that access the tag RFID chip memory. The circuit was tested under the range of 22 to 220 pF with an excitation frequency of 10 kHz and the results demonstrated a 6% maximum deviation from the results obtained by an oscilloscope based measurement. It also was demonstrated that the RF harvested power can be enough to guarantee the permanent power supply stability, which enables continuous measurement operation in fully passive mode.