Thin and flexible printed antenna designed for curved metal surfaces

This paper presents a flexible low-profile antenna suitable for tagging onto metal curved surfaces. The novelty of the proposed antenna lies in the design of an extended ground plane and folding it to realize the bottom layer to shield against metal surfaces. This method reduces the manufacturing complexity as no vias are required in the fabrication process. In addition, the antenna impedance for metal and non-metal surfaces could be obtained through a slight tuning of the slot length. The antenna was realized using a novel low-cost thermal ink transfer process and integrated with a radiofrequency identification chip to successfully demonstrate passive wireless communication at 915 MHz. From the wireless results, a maximum read distance of 1.86 m was obtained for the proposed antenna on metal, compared to a distance of 0.31 m for a reference dipole antenna on metal. Furthermore, the return signal strength indicator pattern obtained show a good correlation to the radiation pattern. The effect of different metal sizes and different metal curvatures were investigated, and results suggest that the effect of these parameters on the impedance mismatch and corresponding power transfer coefficient is not significant. The results are promising for the use of antennas in tagging metal surfaces in the airplane, automotive and unmanned aerial vehicle industries.