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A chipless RF identifiction (RFID) sensor system platform consisting of passive chipless RFID sensor tags and specialized reader has been developed for cyber centric monitoring applications. The sensor tags are fabricated on a flexible substrate, and the tag identification (ID) generation circuit consists of microstrip transmission lines. Two tag configurations are presented. The first configuration (conf-I) consists of an antenna and an integrated sensor. The second configuration (conf-II) consists of an antenna, ID generation circuit, and a sensor. The specialized reader system, consisting of an analog reader section and an on-board computer system, communicates with the sensor tags using load modulated backscattered communication techniques, at 915-MHz carrier signal. The reader, receiving the ID code generated by a tag, constructs it into a standardized RFID data frame, suitable for cyberspace information exchange. The developed system has been tested for wireless monitoring of ethylene gas. Using a conf-I tag, demodulated voltage change of 3.05 mV is observed at the reader, when the ethylene gas concentration changes from 0 to 100 ppm. The presented conf-II tag prototype allows generation of eight different ID codes and an average of 26.51deg/pF phase change in the backscattered signal, when the load capacitance (sensor) of the tag changes between 1-5 pF.