An embedded UHF RFID label antenna for tagging metallic objects

The drill strings used in oil drilling have a limited life in that a section may be used 400 times or until the diameter reduces 20 mm from wear against the surrounding rock. RFID labelling the pieces of the drill string allows the recording of usage and location data at a particular depth of the drill head, aiding in the planning of a rotation scheme, so that any one particular section is not constantly at a position of high stress. Such RFID tags embedded in metal may be used for other metal asset tracking applications. Previous work (Pope, G. et al., Proc. 1st Ann. Wireless and Portable Design Conf., p.240, 1997; Cole, P.H. and Hall, D.M., "Metal Screened Electronic Labelling System", PCTWO0005675, PCT/AU99/00587) has been performed at HF frequencies but there is increasing interest in UHF frequencies as the frequency of choice for object tracking (Cole and Hall). We show that suitable antennas can be made from capacitor structures sensitive to electric fields perpendicular to the metal surface. An HFSS simulation environment for antenna applications was used to relate simulated results to known empirical results from both publications and their own experiments. Both the simulations and the measurements indicate that the antenna concept is suited to the application.