Abstract
Radio frequency identification (RFID) is a mature technology that allows contactless data readout via a wireless communication link. While numerous passive RFID tags are available on the market, accurate alignment between tags and readers is required in a vast majority of cases to mitigate polarization mismatches. We show that enhancing electromagnetic designs with additional mechanical degrees of freedom allows bypassing fundamental limitations and approach ideal performances. Here, we demonstrate a new miniature tag, accessible from any direction and immune to rotations in space. Our tag is made of a high permittivity ceramic resonator, inductively coupled to a metal ring, which contains an RFID chip. The structure is placed inside a spherical plastic holder. In this architecture, the ceramic resonator serves several functions. First, it allows reducing the device footprint without significant bandwidth degradation. Second, it acts as a bob, aligning the electromagnetic structure parallel to the ground, regardless of its initial orientation in space. The bob is designed to slide inside the plastic holder. This roly-poly effect relaxes the constraint on a mutual tag-reader orientation, including the polarization mismatch, and provides next to perfect long-range operation. Being only 55 mm in diameter, our device can be interrogated from a 12 m distance, regardless of the tag’s orientation in space. Introducing mechanical degrees of freedom into electromagnetic designs allows obtaining new functionalities, contributing to applications where a mutual orientation between transvers is required.
Highlights
Radio frequency identification (RFID) is a mature technology that allows contactless data readout via a wireless communication link
Owing to its high efficiency and low cost, RFID is employed in a broad range of practical applications, including warehouses and logistics, billing systems, biometric identifiers, healthcare monitoring, and many other areas
One among prospective future applications of RFID is the Internet of Things (IoT)
Summary
A footprint of RFID tag is governed by its antenna. The miniaturization of the structure can be performed by utilizing dielectric resonators since the wavelength within a material scale with the refractive index. Such parameters allow operation at 865–868 MHz which is Europe EPCGEN2 UHF RFID frequency standard. The step is the resonator’s miniaturization and the related performance assessment For this purpose, the permittivity of the resonator was gradually increased, and the resonant shift was compensated by tuning the cylinder’s height (h) and radius (r). The parameters of the resonator were chosen to be r = 7.25 mm, h = 11 mm, εr = 506 with tanδ = 4 × 10−4 (the permittivity was retrieved at 1 GHz by our vendor) Such parameters allow manufacturing a compact RFID tag with a reading range over 15 m (see Table 1). A slight adjustment of the ring’s position regarding the ceramic resonator can be made to compensate for the spectral shift produced by the surrounding plastic materials
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