Screw Relaxing Detection With UHF RFID Tag

This paper presents a simple and low cost solution for the implementation of a screw relaxing sensor based on ultra-high frequency (UHF) radio frequency identification (RFID) passive tags. The proposed method opportunistically uses the natural capability of a metallic screw (or a metallic part fixed on a plastic screw) to realize an electrical continuity between two electrical lines, which is exploited to realize an open/closed switch mechanism associated to the tightened/relaxed screw status. Several switch-like possible realizations are described according to different working environments and situations, as well as tag-sensor implementation schemes. Three tag-sensors are designed and manufactured to comply with metallic or non-metallic application surfaces and to work within the UHF RFID Chinese band 920.5 - 924.5 MHz, showing a reliable discrimination capability between well-tightened and relaxed screw states. Finally, parameters such as maximum detection surface and minimum detection time are evaluated for completing the analysis of the presented detection system.