A UHF RFID Tag Embeddable in Small Metal Cavities

A compact in-metal ultrahigh frequency radio frequency identification tag for identification of metal components is described. The radiating element is printed on a <inline-formula> <tex-math notation="LaTeX">$23\times 23 \times 1$ </tex-math></inline-formula> mm³ copper-clad alumina (Al₂O₃) substrate (<inline-formula> <tex-math notation="LaTeX">$\varepsilon _{\mathbf {r}} = 9$ </tex-math></inline-formula>, tan<inline-formula> <tex-math notation="LaTeX">$\delta = 0.0003$ </tex-math></inline-formula>) and consists of two rectangular quarter-mode patch antennas properly arranged to make the tag performance as robust as possible even when the tag is embedded in small cavities carved out of metal objects. The entire structure has been optimized by taking into account the presence of a thin superstrate of commercial epoxy resin used to protect the tag. The effect of the cavity size on the tag performance is numerically analyzed. Measurements on a tag prototype are also described and discussed.