Bendable Folded-Patch Antenna With Resonant Ring Manufactured Based on Foam Support and PET Substrate for On-Metal UHF RFID

A new flexible substrate UHF RFID tag on metal with a resonant ring and surface-etched slots that can be read at a long distance is proposed in this paper. The tag has a compact footprint of 50 mm
$\times50$
mm
$\times1.1$
mm (
$0.152\,\,\lambda \times 0.152\,\,\lambda \,\,\times 0.003\,\,\lambda $
at 915 MHz). It consists of two rectangular patches with a closed resonant ring and 4 surface etching slots, a narrow inductive stub, and a square ground. With the above structure which can make the tag adjusts both the resistance and reactance of the chip. The antenna has 7 adjustable parameters and can also be resonated at different frequencies. In the simulation, the proposed tag reaches a high power transmission coefficient (99.99%), which is an almost perfect conjugate matching, and the tag can reach a long reading distance of about 11 m on the metal containers. Finally, the tag is fabricated on the flexible polyethylene terephthalate substrates and tested. With an EIRP (effective isotropic radiated power) of 4 W, the tag can be read at a long range of 7.29 meters on metal planes and 3.71 meters on curved metal surfaces.