Multistate Chipless RFID Tags for Robust Vibration Sensing

This article introduces multistate (M-S) chipless radio-frequency identification (RFID) tags that can be utilized to enhance the vibration sensing range and reading robustness in real environments. The proposed M-S chipless tag consists of a resonant scatterer trapped between two different dielectric layers, which causes the near-field 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 M-S 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 M-S chipless tag is studied using presented mechanical and electromagnetic models that are verified by simulations. The designed M-S chipless tag is implemented, and the concept is experimentally proven. The differential radar cross section (RCS) of the vibrating M-S 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 M-S chipless RFID tag is utilized to successfully detect a submillimeter vibration through a wall in an indoor environment at low microwave frequencies, while the vibrating tag is located at a 2.5-m distance.