Pau Aguila

Analysis of the Split Ring Resonator (SRR) Antenna Applied to Passive UHF-RFID Tag Design

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 radio-frequency identification (RFID) application-specific integrated circuit (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 (λ0/11 × λ0/11) 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.

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.

An impedance matching method for optical disc-based UHF-RFID tags

An impedance matching method applicable to UHF-RFID tags mounted on optical discs, where the main radiating element is the disc metallic layer (from now on optical disc-based tags) is presented in this paper. Such a method provides a very simple analytical approach and allows us to obtain any arbitrary matching level at the desired frequency, by using only one reactive element as a matching network. As a demonstration, the method is applied to the design of a DVD;R based tag, using the Alien Higgs 3 RFID ASIC, and forcing conjugate matching at 915 MHz. The tag design and synthesis process is explained and a bandwidth optimization analysis is also provided. The validity of the method is confirmed by EM simulations and experimental measurements. The measured read range of the fabricated tag reaches 8.3 m at 915 MHz and presents 50 MHz half-power bandwidth.

Passive UHF-RFID tag based on electrically small square-shaped split ring resonator (SRR) antenna

An electrically small passive UHF-RFID tag based on a square-shaped split ring resonator antenna is presented. An analytical formulation of the radiation properties and the chip impedance matching is provided. A tag prototype of size 31 mm × 31 mm (λ0/11 × λ0/11) is designed and fabricated. The simulated and measured results are in good agreement with the theoretical analysis and the measured read range reaches 12 m. The tag also features a significant mitigation of blind spots, providing a minimum measured read range of 5.5 m.

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.

Design of printed antennas based on electrically small resonators for microwave applications

This paper is focused on the design of printed antennas based on electrically small resonators for microwave applications. Nowadays, low cost radiofrequency devices usually incorporate common planar microstrip antennas, consisting of a rectangular metal patch placed on top of a dielectric substrate mounted over a large ground plane. This type of antennas is supposed to provide a radiation diagram located in the half-space due to the presence of the ground plane. Nevertheless, since this kind of antennas can be viewed as an open circuited transmission line, the electric field at the edges of the conductor patch will spread into the surrounding substrate. This results in the extension of currents over a significant area of the ground plane. For this reason, the ground plane should be maintained electrically large, in order to preserve the radiation diagram and hence minimizing the radiation to the back side of the antenna. However, in some applications, the size of the antenna is a critical issue and should be minimized. To overcome this drawback, the use of an electrically small resonator is proposed, which concentrates the currents around its geometry, as a radiator. Considering that the particle is relatively close to the ground plane (and also its image, located on the opposite side of the ground plane), the induced currents in the ground plane are expected to be concentrated in a relative small region around the resonator. This fact leads to a reduction of the currents at the edges of the ground plane, resulting in the optimization of the FBR when its dimensions are decreased.

Passive UHF-RFID tags for Blu-ray discs

Summary form only given. RFID technology allows identification of objects, animals and persons by using electromagnetic waves. In the last years, the use of such technology has experienced a rapid increase, whereas the cost of the tags has dropped down. Nevertheless, a major challenge is tagging metallic objects, since conventional UHF-RFID tags do not work properly over this kind of surface material. Optical discs, which are commonly used nowadays, are among these items due to the presence of a metal film under the disc surface. For this reason, optical discs cannot be tagged efficiently by using conventional UHF-RFID tags, and special solutions need to be developed. a UHF-RFID passive tag for Blu-ray discs (BDs) will be presented in this work.The tag design is based on the approach (proposed by Zuffanelli et al., IEEE Transactions on Antennas and Propagation, 61, 5860, 2013) where the sputtered metallic layer of the optical disc behaves as the main radiator. This strategy allows obtaining read ranges in the order of several meters, while providing worldwide operation. In the abovementioned work, a UHF-RFID tag for DVD discs was proposed as a proof of concept. Based on the NXP UCODE G2XM integrated circuit, a prototype was simulated and fabricated, and a peak read range of 5 m was measured, in very good agreement with simulations. The method can in principle be applied to all kind of optical discs, though some structural differences (e.g. thickness and composition of the metal layer, geometric arrangement of the disc layers) between the disc types could lead to changes in the radiation efficiency of the tag, which is related to its final read range. Moreover, the same differences could cause a variation of the antenna impedance, as seen from the ASIC, thus requiring the study of an impedance matching strategy. In this work, the authors explore the possibility of applying the abovementioned method to the design of UHF-RFID tags for Blu-ray discs. Firstly, in order to study the performance of the tag in terms of read range, the antenna gain of the disc was evaluated by means of EM simulation. Then, following the design process established in the previous work, the tag geometry was adjusted. At this stage, in order to obtain good impedance matching between the antenna and the Alien Higgs3 ASIC, an additional matching element was introduced in this work. To validate the simulated results, a prototype of the tag was fabricated, and the read range was measured.

Planar fan-beam reflective array antenna based on non-bianisotropic complementary split-ring resonators (NB-CSRRs)

A novel fan-beam reflective array antenna is presented in this work. The proposal is made up of a linear planar arrangement of small antennas with a ground plane spaced from the array, acting as a parasitic reflector. The main idea consists in using non-bianisotropic complementary split-ring resonators (NB-CSRR) as radiating elements, which are fed in phase to achieve broadside radiation. This approach allows obtaining a fan-beam antenna with reduced dimensions, compared to conventional designs, which are usually based on half-wave dipoles or patches. As a proof of concept, an 8-elements array antenna prototype working within the C-band frequency band has been designed and fabricated, showing good agreement between simulated and measured results.

Controlling the Electromagnetic Field Confinement with Metamaterials

The definition of a precise illumination region is essential in many applications where the electromagnetic field should be confined in some specific volume. By using conventional structures, it is difficult to achieve an adequate confinement distance (or volume) with negligible levels of radiation leakage beyond it. Although metamaterial structures and metasurfaces are well-known to provide high controllability of their electromagnetic properties, this feature has not yet been applied to solve this problem. We present a method of electromagnetic field confinement based on the generation of evanescent waves by means of metamaterial structures. With this method, the confinement volume can be controlled, namely, it is possible to define a large area with an intense field without radiation leakage. A prototype working in the microwave region has been implemented, and very good agreement between the measurements and the theoretical prediction of field distribution has been obtained.

Quasi-isotropic electrically small antennas for UHF-RFID passive tags based on 2-turns spiral resonators

Most of the current RFID passive tags in the UHF band are based on resonant dipoles, which are usually meandered in order to reduce dimensions. The dipole antennas provide single linear polarization, which involves the existence of blind spots in some regions of the radiation pattern (Brouwer, Proc. of KNAW, 11, 850–858, 1909) (e.g. the dipole antenna has a toroidal radiation pattern with two nulls in the direction of dipole axis). Thus, passive tags are not detected when the reader is placed in the direction of a blind spot. To overcome this drawback, some passive tags use specific ASICs with two fully independent, differential inputs enabling isotropic (or quasi-isotropic) reading patterns. However, two orthogonal antennas are required to avoid blind spots. Consequently, more complex tags with increased dimension are required.