Multistate Chipless RFID Tags for Robust Vibration Sensing

Overview & Synopsis

This paper introduces multi-state chipless RFID tags which can be utilized to enhance the vibration sensing range and reading robustness in real environments. The proposed multi-state chipless tag consists of a resonant scatterer trapped between two different dielectric layers, which causes the nearfield boundary of the scatterer to be modulated during vibration and results in the appearance of multiple modulation states. The motion-induced near-field modulation provided by the multi-state chipless tag is much more effective than the natural Doppler modulation caused by vibration, which significantly increases the modulated portion of the backscattered power, and consequently, enlarges the sensing range. The backscattering from the vibrating multi-state chipless tag is studied using presented mechanical and electromagnetic models which are verified by simulations. The designed multi-state chipless tag is implemented and the concept is experimentally proven. The differential RCS of the vibrating multi-state chipless tag is 45 times greater than that of a vibrating classical chipless tag, which translates into an increase of factor 2.5 in the read range. The multi-state chipless RFID tag is utilized to successfully detect a sub-millimeter vibration through a wall in an indoor environment at low microwave frequencies, while the vibrating tag is located at 2.5 m distance.