Design and Performance of a Flexible Metal Mountable UHF RFID

The large number of requirements and opportunities for automatic identification in manufacturing domains such as automotive and electronics has accelerated the demand for item-level tracking using radio frequency identification technology. End-users are interested in solutions that enable a range of objects to be identified without changing the structure of the objects. Passive UHF RFID systems have drawn considerable attention due to their long read range, high data rates and small antenna sizes. However, it is difficult to tag metallic objects using a passive UHF RFID tag due, for example, to the impact of reflected signals from the conducting material on the tag antenna performance. The overall reliability of an RFID system depends significantly on the tag antenna performance, which is responsible for receiving and transmitting the RF power to and from the RFID reader. Designing an RFID tag, which can be mounted successfully on metallic objects and meet the end-user requirement is a major research challenge. The aim of the research outlined in this paper is to determine the effects of the harsh manufacturing environments in which RFID tags are used and compare the performance of a range of RFID tag substrates that can be used to isolate the RFID tag antenna from metallic objects. The goal is to determine which substrates allow RFID tags to operate efficiently when attached to metallic, lossy or dielectric objects whilst being low cost, high performance, flexible and in some cases reusable solutions. The main focus is to design a flexible, metal mountable RFID tag by optimising design parameters such as complex impedance, bandwidth and size. An investigation and analysis of the effects of metallic surfaces on the performance of the tag antennas is presented in this paper. Parameters that are investigated are the distance between the metal surface and the tag, the thickness of the metallic plate and the type and thickness of the antenna substrate. It has been observed that the return loss of the tag antenna is significantly increased (D = -n dB) and the resonance frequency shifted (Df = m Hz) from the expected operating frequency as the tag antenna is located closer (Dm range from x –y cm) to the metal. When a substrate with a high dielectric coefficient is sandwiched between the tag and the metallic surface, the orientation of the induced current is influenced by the thickness of the material with the result that the reflected radiation can be strengthened. A flexible RFID tag with a substrate consisting of an elastomer / polymer has been investigated. The tag has been designed, modelled and simulated using the CST electromagnetic field modelling software and the performance is evaluated in terms of the shift in resonance frequency, return loss and bandwidth. Paper, PET and FR-4 substrates integrated with a number of different conductive inks and inkjet/screen printing techniques, have also been investigated as potential optimal solutions for the high volume manufacture of UHF RFID tag suitable for metal objects. The research details the design, engineering and performance of a number of RFID tags when applied to various automotive assets / components such as stillages, crankshafts and fuel injectors used in engine assembly plants, and through the supply chain.