Abstract-An electrically small planar passive UHF-RFID tag based on an edge-coupled split ring resonator (EC-SRR) antenna is presented in this work. In order to explore the potentiality and limitations of the SRR antenna and to aid the tag design, an analytical study of the SRR radiation properties at its fundamental resonance is presented for the first time. Radiation resistance, efficiency, polarization, bandwidth and impedance matching with the RFID ASIC are treated in the study. Based on such analysis, the tag design process is presented, and a tag prototype of size 30 mm × 30 mm (λ 0 /11 × λ 0 /11) is designed to operate in the North-American UHF-RFID band (902−928 MHz) and manufactured. The measured read range is in good agreement with the simulation, and reaches 9.3 m at 911 MHz. The tag also features a mitigation of the blind spots, providing a minimum measured read range of 4.2 m.Index Terms -Split ring resonators (SRRs), electrically small antennas (ESAs), radio frequency identification (RFID).
Abstract-Spectral signature barcodes functional at the S frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide (CPW) transmission line by means of multiple S-shaped split ring resonators (S-SRRs), each one tuned to a different frequency. The main particularity of this work is the fact that more than two logic states (i.e., three or four, depending on the implementation) are assigned to each resonant element. By this means, the total number of bits of the barcode (for a given number of resonators) is increased, as compared to previous approaches based on two logic states per resonator. This multi-state functionality is achieved by rotating the S-SRRs. Such rotation modulates the line-to-resonator coupling intensity, and consequently the notch depth at the S-SRR fundamental resonance. Therefore, by considering three or four fixed rotation angles (or orientations) between the line axis and the S-SRR (for the tri-and four-state multi-resonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation, are achieved. This multi-state strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth is improved as compared to two-state based barcodes or to multi-state barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multi-resonator barcodes with eight S-SRRs (providing 4 8 = 65.536 different codes, or 16 bits) and with nine S-SRRs (equivalent to 18 bits), occupying a spectral bandwidth of 1 GHz and less than 6.75 cm 2 and 8.2 cm 2 , respectively, are designed, fabricated and characterized.Index Terms-S-shaped split ring resonators (S-SRRs), coplanar waveguide (CPW) technology, spectral signature barcodes.
Abstract-The radiation properties of split ring resonators (SRRs) at their second resonance frequency are studied for the first time in this work. In particular, the electric and magnetic dipole moments of the edge-coupled SRR (EC-SRR) are calculated analytically under the assumption of strong coupling between the internal and external rings. Based on these results, the radiation resistance and the radiation efficiency are obtained theoretically. Electromagnetic simulations of the structure reveal that there is very good agreement with the theoretical predictions, pointing out the validity of the proposed analysis. As a proof of concept, an SRR antenna prototype is designed and fabricated. Experimental data are in good agreement with the theoretical and simulated results, and demonstrate the validity of the SRR working at its second resonance frequency as a radiating element.Index Terms-Split ring resonators (SRRs), planar antennas, radiation efficiency, metamaterials.
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