Edge-coupled Split-ring Resonators Research Articles

Dispersion diagram reconstruction of effectively bianisotropic composite periodic media

A dispersion diagram reconstruction technique is proposed for arbitrarily bianisotropic composite periodic media, which utilizes a previously introduced parameter retrieval technique based on eigenvalue analysis and field averaging. We initially retrieve the effective electromagnetic parameters of a composite periodic medium consisting of Edge-Coupled Split-Ring Resonators (EC-SRRs) via this homogenization technique using alternative integration approaches for the averaging of the field components. Subsequently, we derive the analytical framework for the wave propagation in a homogeneous medium of arbitrary bianisotropy and extract the appropriate equations which solve for the complex propagation constants. We then involve the retrieved effective parameters in these equations and reconstruct the dispersion diagrams for all three orthogonal directions, thereby spanning the whole irreducible Brillouin zone. An excellent agreement is found between the original dispersion diagrams and the reconstructed ones; a result which further validates the utilized parameter retrieval technique. The reconstruction technique moreover allows one to interpret the slope differences observed in the dispersion diagrams for in-plane and normal incidence modes of the examined composite medium. It may also be used as a tool for the confirmation of the accuracy of other formerly proposed homogenization techniques existing in the literature.

Enhanced WPT structures via EC-SRR-based metasurfaces

PurposeThe purpose of this paper is to present a family of robust metasurface-oriented wireless power transfer systems with improved efficiency and size compactness. The effect of geometric and structural features on the overall efficiency and miniaturisation is elaborately studied, while the presence of substrate losses is, also, considered. Moreover, to further enhance the performance, possible means for reducing the operating frequency, without comprising the unit-cell size, are proposed.Design/methodology/approachThe key element of the design technique is the edge-coupled split-ring resonators patterned in various metasurface configurations and optimally placed to increase the total efficiency. To this goal, a rigorous three-dimensional algorithm, launching a new high-order prism macroelement, is developed in this paper for the fast evaluation of the required quantities. The featured scheme can host diverse approximation orders, while it is drastically more economical than existing methods. Hence, the demanding wireless power transfer systems are precisely modelled via reduced degrees of freedom, without the need to conduct large-scale simulations.FindingsNumerical results, compared with measured data from fabricated prototypes, validate the design methodology and prove its competence to provide enhanced metasurface wireless power transfer systems. An assortment of optimized 3 x 3 and 5 x 5 metamaterial setups is investigated, and interesting deductions, regarding the impact of the inter-element gaps, the distance between the transmitting and receiving components and the substrate losses, are derived. Also, the proposed vector macroelement technique overwhelms typical implementations in terms of computational burden, particularly when combined with the relevant commercial software packages.Originality/valueSystematic design of advanced real-world wireless power transfer structures through optimally selected metasurfaces with fully controllable electromagnetic properties is presented. The analysis is performed by means of a rapid prism macroelement methodology, which leads to very confined meshes, accurate results and significantly reduced overhead. The selected metamaterial resonators are found to be very flexible and reconfigurable, even in the case of large substrate conductivity losses, whereas their contribution to the system’s total efficiency is decisive.

Metamaterial inspired fidget spinner-shaped antenna based on parasitic split ring resonator for multi-standard wireless applications

This paper presents the design of fidget spinner-shaped antenna (FSSA) loaded with parasitic EC-SRR (edge coupled-split ring resonator) for multi-standard wireless applications. Parasitic EC-SRR element-loaded antenna helps to improve the impedance matching and bandwidth of antenna in comparison to the unloaded FSSA. The 50 Ω microstrip line fed has been applied to the structure of proposed antenna to obtain the distinct performance parameters such as reflection coefficient, gain, radiation pattern and efficiency. Comparison of the proposed antenna with and without SRR is made and found that the later case exhibits better results in terms of reflection coefficient and bandwidth. Bandwidth is increased by 21.61% at first two resonance points, 57.57% at third and 32.76% at fourth resonance point. A prototype of the proposed FSSA has also been fabricated and tested for validation of simulated results with measured results, and found in good agreement with each other. The overall dimensions of the proposed FSSA are 30 mm × 30 mm and can be used for different wireless applications in the frequency range 1.88–7.0 GHz, 7.81–8.85 GHz and 9.6–14.3 GHz.

Multiband low‐cost fractal antenna based on parasitic split ring resonators

This study presents the design of a low-cost fractal antenna loaded with parasitic edge-coupled (EC) split ring resonators (SRR). Parasitic EC SRR elements result in improved impedance matching leading to improved bandwidth. The basic resonant structure is a circular patch antenna designed at 3.2 GHz on low-cost FR4 substrate with relative permittivity 4.4, and 1.6 mm thickness. A single iteration of circular patch and slots is used to make it fractal and in order to achieve multiband performance, the antenna is inset fed by a 50 Ω microstrip line. A prototype of the proposed antenna is fabricated and tested for results, a comparison between fractal antenna with and without SRRs is made and the results confirm that a better impedance matching is achieved in the later case, also a 3% increase in bandwidth is achieved at 8.5 GHz. A good agreement between simulated and measured results is obtained, an estimated gain of 13.3 dB is provided by the proposed antenna. The overall dimensions of the antenna are 45 mm × 45 mm and it may be used for wireless applications at 3, 5, 6.8, 7.5 and 8.5 GHz with an average bandwidth of 200 MHz.

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 $30\;\text{mm}\times30\;\text{mm} (\lambda_{0}/11\times\lambda_{0}/11)$ 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.

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.

Retrieval and validation of the effective constitutive parameters of bianisotropic metamaterials

In this paper we present the exact bianisotropic parameter retrieval procedure for the case of transmission line metamaterials. The procedure assigns two different sets of effective parameters for two directions of propagation, which can be modelled by a bianisotropic medium. The procedure is applied to a microstrip line loaded with asymmetric edge-coupled split-ring resonators with gaps parallel and perpendicular to the line. The standard Nicolson-Ross-Weir procedure based on averaging of the S-parameters is not applicable to this case due to pronounced asymmetry. We also present the reverse procedure, which recovers the original S-parameters using the extracted effective permittivity and permeability, that fully validates the correctness of the proposed retrieval method.

Implementation of a novel broadband microstrip metamaterial power divider

A low-loss, planar, and compact metamaterial broadband power divider is presented in this paper. The power divider uses novel two parallel microstrip transmission-line coupled-line couplers with negative-refractive-index characterization allowing it to be compact in the longitudinal direction. The method of designing two turns spiral resonators (2-SRs) is detailed starting from edge-coupled split-ring resonator (SRR), and full-wave simulations of novel power divider are fulfilled by HFSS. A power divider with 5.40 GHz center frequency is fabricated for demonstration purpose. The measurement results show that a ultra-wide band of 50% is achieved with . While maintaining similar performance, a 50% reduction in impedance transformer is achieved in comparison to a conventional design.

Improved Performance of a Microstrip Phased Array Using Broadband and Ultra-Low-Loss Metamaterial Slabs

A novel broadband and ultra-low-loss electric metamaterial EM isolation slab is proposed to improve the performance of a microstrip array. The metamaterial slab is formed by periodically grounded edge-coupled split-ring resonators (PGE-SRRs). Outstanding improvements - including over -50 dB peak isolation, 15% fractional bandwidth (-10 dB isolation) and almost lossless operation - are obtained. The metamaterial slab is inserted halfway between the adjacent E-coupled elements in the microstrip array to suppress mutual coupling. A strong mutual-coupling suppression of -16.8 dB was exhibited experimentally in a two-element microstrip array with an element spacing of three-quarters of the operating wavelength. Theoretical and numerical studies were done to improve the performance of microstrip phased arrays using the proposed metamaterial slab. The analysis indicated that the scan blindness in an infinite phased array is well eliminated, the wide-angle impedance matching is remarkably improved, and the scanning range is extended from [-13°, 13°] to [-28°, 28°]. A 7×3 microstrip array was simulated to study the influence of the metamaterial slab on the array's performance. The results indicated that the metamaterial slab can also enhance the radiation characteristics, extend the scanning range and suppressing grating lobes in microstrip phased arrays.

Design of novel cross-coupling elliptic function filters with the miniaturized edge-coupled split ring resonators

In this paper, a new class of cross-coupled planar microwave filters using the microstrip edge-coupled split-ring resonator (EC-SRR) is introduced and its simple equivalent circuit is proposed. The utilization of the microstrip split-ring resonators not only makes the filters compact, but also allows either positive or negative cross coupling to be realized. Also, three-pole and four-pole cross-coupled microstrip elliptic function bandpass filters using the EC-SRR are presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 495–499, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20862