Abstract
Radio frequency identification (RFID) is a technology permeating both everyday life and scientific applications alike. The most prolific passive tag-based system uses inductively-powered tags with no internal power source [V. Chawla and D. S. Ha, “An overview of passive RFID,” IEEE Commun. Mag. 45(9), 11–17 (2007)]. Here we demonstrate an inductive magnetic field mapping platform on the example of passive near-field RFID tags (ID-1), operating at 13.56 MHz (HF) [Identification cards - Contactless integrated circuit(s) cards - Proximity cards - Part 1: Physical characteristics, ISO/IEC 14443-1, 2000; Part 2: Radio frequency power and signal interface, ISO/IEC 14443-2, 2010; Part 3: Initialization and anticollision, ISO/IEC 14443-3, 2011; Part 4: Transmission protocol, ISO/IEC 14443-4, 2008]. With smaller modules currently being integrated in wrist-bands, watches and items of jewelry, a possible counter-measure to the reduced size is the use of flux-concentrating magnetic material - low-permeability insulating ferrites or high-permeability metallic μ-particle systems such as sendust. Sendust is a magnetically soft iron-rich alloy of Fe, Al and Si - a higher permeability cheaper alternative to permalloy. The integration of sendust components in RFID tags creates a non-trivial multiple-parameter optimization problem, which requires a quantitative RF field imaging system to be used. The RF susceptibility mapping system is comprised of a stepper-motor-driven 4-axial table, which holds the device under test (DUT) or the RFID tag assembly, a source coil (2 turns of 0.5 mm diameter wire, of overall diameter of 21 cm), a 4-micro-coil assembly, allowing for the measurement of Hx, Hy, Hz and dHz/dz, and a 4-channel Vector Network Analyzer (VNA). Four complex transmission spectra are obtained for each spatial point of a rectangular (x, y) grid, and then repeated for a different z-cut. 4D Complex Vector field maps are thus obtained. Simultaneous fitting of the real and imaginary parts of the frequency spectra is possible, at essentially any point of space, to a model comprised of two damped harmonic oscillators. This type of 3D-spatial, full-vector, complex magnetic susceptibility imaging opens ways to the integration of magnetic materials in near-field systems, and is not limited to RFID.
Highlights
The RF susceptibility mapping system is comprised of a stepper-motor-driven 4-axial table, which holds the device under test (DUT) or the Radio frequency identification (RFID) tag assembly, a source coil (2 turns of 0.5 mm diameter wire, of overall diameter of 21 cm), a 4-micro-coil assembly, allowing for the measurement of Hx, Hy, Hz and dHz/dz, and a 4-channel Vector Network Analyzer (VNA)
RADIO frequency identification (RFID) and the corresponding transponders and tags have become ubiquitous in both everyday life and specific scientific applications involving the location and identification of multiple objects over a short range (0 – 10 m)
We describe an apparatus for the characterization of the magnetic field distributions created by passive near-field RFID tags for financial payment and national identity smartcards, operating at 13.56 MHz (HF) as defined by the ISO/IEC 14443 standard for proximity/contactless integrated circuit cards
Summary
RADIO frequency identification (RFID) and the corresponding transponders and tags have become ubiquitous in both everyday life and specific scientific applications involving the location and identification of multiple objects over a short range (0 – 10 m). We describe an apparatus for the characterization of the magnetic field distributions created by passive near-field RFID tags for financial payment and national identity smartcards, operating at 13.56 MHz (HF) as defined by the ISO/IEC 14443 standard for proximity/contactless integrated circuit cards.. The main idea is in the use of calibrated, inductive, complex (amplitude and phase), vector (three vector components), frequency dispersive, threedimensional mapping for the detailed characterization and the direct scitation.org/journal/adv comparison between tags, which do or do not incorporate soft magnetic flux-concentrating materials, such as sendust or ferrites. The integration of sendust components in RFID tags is subject to a number of constraints and poses a non-trivial multiple-parameter optimization problem, which requires the detailed and quantitative understanding of the near field RF distributions created
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