Multistate multiresonator spectral signature barcodes implemented by means of S-shaped split ring resonators (S-SRR)

Spectral signature barcodes functional at the S frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide 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 paper 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 with previous approaches based on two logic states per resonator. This multistate 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 triand fourstate multiresonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation are achieved. This multistate strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth are improved as compared with twostate-based barcodes or to multistate barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multiresonator barcodes with eight S-SRRs (providing 48 = 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 and 8.2 cm2, respectively, are designed, fabricated, and characterized

Front-to-back ratio improvement of printed antennas based on electrically small resonators for microwave presence detectors

The improvement of the front-to-back ratio (FBR) in low-profile antennas to be used in presence detection devices is explored. The main idea is to use electrically small resonators as radiating elements. This minimises the electric currents in the boundary of the ground plane at the working frequency, thus reducing the backward radiation. The choice of the resonant particle and its electromagnetic properties, along with the antenna structure, are discussed. The simulated results indicate that there is good impedance matching (-18 dB) at the operating frequency (3 GHz) and an excellent FBR of 24 dB. These characteristics are validated experimentally and the FBR is compared with that of a conventional patch antenna

On the radiation properties of split ring resonators (SRRs) at the second resonance

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 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

Upper bounds on the bandwidth of electrically small single-resonant UHF-RFID tags

In this communication, the upper limits on the bandwidth of single-resonant UHF-radio frequency identification (RFID) tags as a function of the tag size are investigated, with and without forcing perfect matching between the antenna and the application-specific integrated circuit. By means of a circuit network analysis, it is found that bandwidth upper bounds of small tags are significantly higher in comparison with considering conjugate matching. Particularly, it is shown that the half-power bandwidth is √2 times (approximately 41%) higher, requiring a proper relaxation of the matching level at resonance. It is also shown that bandwidth of small real tags with perfect matching, which is typically far from its upper bound, can also be enhanced approximately the same factor at the expense of a small reduction (13.4%) in the peak read range. A practical example is provided, where two small split-ring resonator-based tags of the same size (k 0 a = 0.31) are designed. It demonstrates that such improvement on the tag bandwidth can be approximately obtained by simply changing the chip position, without the need of an external matching network. The improved tag was fabricated and measured, as a proof of concept. The results obtained from the proposed analysis allow RFID designers to determine how well a tag performs, compared to theoretical bandwidth limits

Broadband UHF-RFID passive tag based on split-ring resonator (SRR) and T-match network

A novel broadband design of a planar passive UHF-RFID tag based on a split-ring resonator (SRR) antenna and the T-match network is presented in this work. The radiation properties of the SRR working at its second resonance are exploited to design a radio frequency identification (RFID) tag for the first time. The potential usefulness of the T-match based design methodology to achieve perfect matching between the SRR antenna and any typical RFID chip is demonstrated. A 0.23 λ₀ × 0.23 λ₀ tag has been fabricated. The measured read range is higher than 13 m within the whole UHF-RFID band with a peak value of 16 m at 915 MHz

2-SR-based electrically small antenna for RFID applications

In this work, the 2-turn spiral resonator (2-SR) is proposed as an electrically small antenna for passive radio frequency identification (RFID) tags at the European ultra-high frequency (UHF) band. The radiation properties are studied in order to explore the viability of the 2-SR applied to tag antenna design. Based on analytical calculations, the radiation pattern is found to provide a cancelation of the radiation nulls. This results in a mitigation of the blind spots in the read range, which are present in typical UHF-RFID tags as an undesired feature. As a proof of concept, a passive tag of size 35 mm × 40 mm (λ₀/10 × λ₀/9) based on the 2-SR antenna is designed and fabricated. Good radiation efficiency (75 %) and a quasi-isotropic radiation pattern are obtained. The experimental tag read range for different directions is in good agreement with the simulation results. The measured read range exhibits maximum and minimum values of 6.7 and 3.5 m, respectively

A high-gain passive UHF-RFID tag with increased read range

In this work, a passive ultra-high frequency radio-frequency identification UHF-RFID tag based on a 1.25 wavelengths thin dipole antenna is presented for the first time. The length of the antenna is properly chosen in order to maximize the tag read range, while maintaining a reasonable tag size and radiation pattern. The antenna is matched to the RFID chip by means of a very simple matching network based on a shunt inductance. A tag prototype, based on the Alien Higgs-3 chip, is designed and fabricated. The overall dimensions are 400 mm × 14.6 mm, but the tag width for most of its length is delimited by the wire diameter (0.8 mm). The measured read range exhibits a maximum value of 17.5 m at the 902-928 MHz frequency band. This represents an important improvement over state-of-the-art passive UHF-RFID tags

Antenna design solutions for radio frequency identification (RFID) tags based on metamaterial-inspired resonators and other resonant structures

Premi Extraordinari de Doctorat concedit pels programes de doctorat de la UAB per curs acadèmic 2017-2018Avui dia, la identificació automàtica i unívoca d'objectes s'està imposant com a necessitat creixent a nivell global, degut al ràpid increment de la producció i del comerç mundial. En resposta, la identificació per radiofreqüència (RFID) està emergint com una alternativa viable i més evolucionada al codi de barres, i està sent utilitzada en una multitud d'aplicacions diferents, tal com el seguiment de paquets, els inventaris intel·ligents, el control d'accessos i el pagament sense contacte. Encara que la tecnologia RFID ha aconseguit entrar amb èxit en la nostra vida diària, oferint una solució convenient en moltes aplicacions, existeixen alguns reptes que estan frenant la seva difusió. Per exemple, l'etiquetatge de petits objectes metàl·lics necessita de més recerca, per tal d'obtenir etiquetes RFID més primes i petites, donat que actualment les etiquetes RFID per metall són més gruixudes i més cares que les etiquetes RFID convencionals. El disseny d'etiquetes RFID miniaturitzades amb una resposta independent de l'orientació és també un problema encara pendent. En altres casos, el context d'etiquetatge requereix maximitzar la distancia de lectura, encara que això impliqui augmentar les dimensions de l'etiqueta. Per tant, el disseny d'etiquetes RFID d'alta distancia de lectura és un altre repte interessant en la investigació sobre la tecnologia RFID. L'objectiu principal d'aquesta tesi és la recerca de solucions pràctiques als problemes mencionats, que contribueixin al desenvolupament de la tecnologia RFID, així com a la seva ulterior difusió en les aplicacions de la vida diària. En concret, aquest treball es focalitza en el disseny d'antenes per etiquetes passives de RFID a la banda UHF basades en ressonadors inspirats en el món dels metamaterials (ressonadors d'anells oberts i estructures derivades) com a elements radiants, explorant també solucions alternatives basades en altres estructures ressonants.Nowadays, the automatic and univocal identification of items all around the world is becoming a growing necessity, as a consequence of the rapid increase of the global production and trade. In this regard, radio frequency identification (RFID) technology has been emerging as a suitable and more evolved alternative to barcodes, being already used in a multitude of applications in everyday life, such as items tracking through the supply chain, smart inventory, access control and contactless payment. However, although RFID has achieved entering into the mainstream of technology, already providing a cost-effective solution in many scenarios, several challenges are still waiting response. Among these, the identification of small metallic objects still requires further efforts for obtaining thinner and smaller RFID tags, being the current on-metal tagging solutions thicker and much more expensive than conventional RFID tags. Also, the design of miniaturized RFID tags presenting uniform (or quasi-uniform) reading pattern, which would allow identification of small objects independently from their orientation, is still troublesome. On the other hand, some applications require maximizing the reading distance, even at the expense of the tag dimensions, so that the design of RFID tags with optimized reading distance is another interesting research subject within the frame of RFID technology. The main objective of this thesis is to explore solutions to the aforementioned problems, thus contributing to the advance of RFID technology, and to its further extension to everyday life applications. To this end, this work is focused on the antenna design for passive RFID tags working at the UHF frequency band (passive UHF-RFID tags), exploring the use of metamaterial-inspired resonators (i.e., the split-ring resonator and its derived structures) as radiating elements, and also considering alternative solutions based on other kinds of resonant structures

Recent advances in multiband printed antennas based on metamaterial loading

It is shown that printed antennas loaded with metamaterial resonators can be designed to exhibit multiband functionality. Two different antenna types and metamaterial loading are considered: (i) printed dipoles or monopoles loaded with open complementary split ring resonators (OCSRRs) and (ii) meander line or folded dipole antennas loaded with split ring resonators (SRRs) or spiral resonators (SRs). In the first case, multiband operation is achieved by series connecting one or more OCSRRs within the dipole/monopole. Such resonators force opens at their positions, and by locating them at a quarter wavelength (at the required operating frequencies) from the feeding point, it is possible to achieve multiple radiation bands. In the second case, dual-band functionality is achieved through the perturbation of the antenna characteristics caused by the presence of the metamaterial resonators. This latter strategy is specially suited to achieve conjugate matching between the antenna and the chip in radiofrequency identification (RFID) tags at two of the regulated UHF-RFID bands