Miniaturized tuneable passive microwave devices based on transmission line metamaterials

AbsIracf - Two-dimensional backward-wave meta-material based on evanescent parallel-plate waveguide filled with uniaxial magnetic tilling with negative transversal permeability is investigated experimentally. The prototype comprised a two-dimensional array of the double ring resonators sandwiched between two metallic plates and it was operating in 8 GHz frequency hand. The backward-wave propagation was verified by the measurement of negative lateral displacement of the beam impinging the meta-material slab at several different angles of incidence I. INTRODUCTION A material which supports propagation of the backward waves ('left-handed material' or 'backward-wave material') was predicted theoretically in sixties by Veselago (I) and realized experimentally for the first time by Smith at al. (2) in 2000. The rather simple type of one-dimensional backward-wave meta-material based on an evanescent waveguide loaded with the split ring resonators was presented in (3). Such a waveguide was interpreted as one-dimensional material with both negative permeability and negative permittivity (3). In (4,5), it was shown that the propagation below the cut-off frequency actually occurs due to uniaxial anisotropy of negative permeability of the meta-material based on the split ring resonators. The extension of this basic principle to two dimensions, similarly to the idea introduced in (6), is investigated experimentally in this paper. 11. THEORETICAL RESULTS Let us analyze the structure that comprises a slab of anisotropic uniaxial magnetic materials sandwiched within the two infinite parallel PEC plates (Fig.1). If the optical axis of the uniaxial material is perpendicular to the plates (the transversal direction), it is obvious that this structure is essentially isotropic in two dimensions. Thus, the electromagnetic energy will propagate in any direction parallel to the plates (the longitudinal direction) in the exactly the same way (the propagation for two perpendicular longitudinal directions is sketched in Fig. 5). For any particular longitudinal direction, one may think of this structure as a parallel plate waveguide. In the lossles case, the longitudinal propagation factor of such a waveguide is given by the simple set of equations (4,51: Here, k, stands for longitudinal propagation factor, ko is a free space propagation factor, g is relative permittivity and p,, and pi, stand for relative permeability in transversal and longitudinal directions of the waveguide, respectively. The symbol f stands for a frequency of the signal, whereas Lo and L are the cut-off frequency of an empty parallel-plate waveguide and the parallel-plate waveguide filled with a material, respectively. If the transversal permeability is negative &<0 ) and the longitudinal permeability is positive (ppO), one must choose the negative sign in front of the square root in (I) for frequencies below the cut-off. This yields the peculiar phenomenon of the backward-wave propagation. Hence, the structure actually behaves as two-dimensional backward-wave meta-material provided that the vector of the magnetic field is perpendicular to the walls (TE 01 mode). If one stacks more parallel plate waveguides in the transversal direction, it is possible to manufacture the two-dimensional 'backward-wave' material of arbitrary thickness, as proposed in (6). The backward-wave propagation below the cut-off frequency can he simply explained by two-dimensional transmission line equivalent circuit of the structure (Fig.2). The distributed series impedance (212) is associated with the transversal permeability. The distributed shunt admittance associated with the relative permittivity (Y,) and the admittance associated with the longitudinal permeability (Y,) form the tank circuit. In the case of the uniaxial material with positive permeability, the series admittance will he also positive. Below the cut-off, the tank circuit behaves as an inductance and, for any direction parallel to the plates, the whole structure behaves as a transmission line with the distributed series inductance and the distributed parallel inductance (L-L transmission line), This kind of transmission line does not support the propagating waves. If the transversal

In this paper, the bandwidth-enhanced quadrature power splitter (QPS) and balun using metamaterial (MM) transmission lines (TLs) are presented. They consist of a Wilkinson power divider, a conventional TL, and a well-synthesized MM TL. Since the phase response of the MM TL can be arbitrarily synthesized, the slope of the phase-response curve of the MM TL can be achieved as the same as that of the conventional TL with a specified phase difference, such as 90° or 180°, over a wide frequency range. Two components are designed and implemented at 2 GHz and experimentally demonstrated. The QPS has an output amplitude imbalance of less than 0.9 dB and a phase error of less than ±5° from 1.1-3.5 GHz (104% relative bandwidth), while over the frequency range of 1.24-3.58 GHz (97% relative bandwidth), the balun has an output amplitude imbalance of less than 0.7 dB and a phase error of less than ±10°.

ABSTRACTThe control of microwave (MW) radiation transmission through the polarization state of the incident beam is the basis for many applications in sensors and optics. Altering the polarization state of electromagnetic radiation by transmission through a metamaterial (MTM) lens could lead to novel devices and sensors. The polarization properties of 1D split ring resonator and rod type MTM structures were investigated and compared to a previously reported corresponding 2D MTM lens. Unlike the 2D lens, the 1D MTM did not contribute to a change in polarization state of transmitted MWs. The transmission response, however, was found to be determined by the coupling mechanisms between the MTMs constituent elements and orientation of the incident MW polarization. For the 1D lens, changing incident polarization from alignment parallel to the MTMs rod elements to alignment perpendicular to the rods, at resonance frequency, changes the effective index of refraction from net negative to positive. For a MTM structure, facing perpendicular to the incident radiation, the effective electromagnetic properties change from negative permittivity and positive permeability (for polarization parallel to the rod elements) to positive permittivity and negative permeability (for polarization perpendicular to the rod elements). © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1218–1222, 2014

We propose a meander-line resonator, which could provide negative permittivity as a promoted structure from wire lattice. Such a resonator works at relatively low frequencies, and hence has a small unit-to-wavelength ratio. Negative index materials (NIM) is realized by particles composed of meanders lines and split-ring resonators (SRRs), which has simultaneously negative permittivity and permeability in a specified passband with relatively low loss. Simulation results verify the above conclusions.

Periodic arrays of gold wires and split ring resonators (SRR) with a minimum feature size of 50 nm are fabricated on low-doped silicon. To our knowledge, the periodic arrangement of SRRs and wires considered in this work has not been studied in the near-infrared domain yet. For normal-incidence conditions, this metamaterial structure exhibits resonances at 70 and 170 THz (i.e., at λ ≈ 4.3 and 1.75 μm), which are identified as LC- and Mie resonances, respectively. These resonances are also observed for the SRRs alone, but the amplitude of the Mie resonance is reinforced due to the coupling between the SRRs and wires. The structure is simulated using finite-element software, while transmission and reflection measurements are performed with a Fourier transform infrared spectrometer. Numerical simulations are found to be in very good agreement with experimental characterizations, thereby showing that the Drude model used in calculations is well suited to simulate gold structures at near-infrared frequencies. Theoretical calculations predict that the metamaterial has a negative permittivity and a negative permeability near each resonance.

Metamaterial structure based on cascaded split ring resonators (CSRR) is proposed in order to produce a negative refractive index in terahertz regime at near-infrared range. We have incident light horizontally instead of incidenting it perpendicular. We have measured the negative refractive index, permeability and permittivity by using the S-parameter analysis. Furthermore, it is found out that negative refractive index, permeability and permittivity are dependent upon the width of the wire and the gap between resonators at near-infrared range. This work will be helpful for the fabrication and design of double negative metamaterials structure having negative permeability, permittivity and negative refractive index for in plane applications.

Electromagnetic metamaterials (MMs) consisting of highly conducting sub-wavelength metallic resonators enable many unusual electromagnetic properties at user defined frequencies which are not permissible with the naturally occurring materials [1, 2]. Generally the electromagnetic properties of metamaterials are controlled by the design variation of the MM unit cell, often termed as meta-molecule, consisting of single or multiple metallic split ring resonators (SRRs). These metallic resonators are quite often termed as meta-atoms too. The near field electromagnetic coupling between these meta-atoms exhibits an important role in modulating the fundamental resonances of the metamaterials [3-5].

We demonstrate a metamaterial (MM) design capable of showing linear broadband polarization conversion over the terahertz (THz) frequency range. The building block of the proposed MM structure is composed of a strip and four split ring resonators (SRRs), which are coupled through their near fields. To examine co- and cross-polarization transmission amplitudes, we gradually increase the distance between the strip and SRRs. When the SRRs are near (S = 2 μm) the strip, maximum cross-polarization conversion is attained with a resonance mode hybridization effect in the co-polarization transmission due to strong near-field coupling between the strip and SRRs. When the SRRs moved away from the strip (S = 22 μm), minimum cross-polarization conversion is attained due to weak coupling between the strip and SRRs. This MM system exhibits a transition from a strongly coupled state to a weakly coupled state with the rise in displacement between the strip and SRRs. The ability to tune the linear polarization conversion can be useful in the improvement of efficient THz polarization rotation devices. The proposed MM structure can be used in other frequency domains, like the microwave and visible range, by scaling up/down the structure.

Metamaterials have attracted considerable interests (Shelby, 2001, Yen, 2004, Smith, 2004, Linden, 2004, Zhang, 2004) because of their unusual electromagnetic properties (Veselago, 1968) and because of their potential applications such as invisibility cloaks (Leonhardt, 2006, Pendry, 2006, Schurig, 2006, Cai, 2007, Gaillot, 2008, Kante, 2008), the so-called perfect lenses (Pendry, 2000) and gradient index (GRIN) lenses. For example, perfect lenses require the use of Left-Handed (LH) metamaterials (Smith, 2000) having a negative refractive index, which can be produced by a simultaneously negative electric permittivity e and magnetic permeability μ. Invisibility cloaks require adjustable positive permeability and permittivity from near zero values to several tenths. Traditionally, these properties are achieved by the use of a combination of split-ring resonators (Pendry, 1999) and metallic wires (Pendry, 1996), with periods much smaller than the wavelength of the electromagnetic wave, such that the medium can be considered homogeneous. Lately, pairs of finite-length wires (cut wires pairs) (Shalaev, 2005) have been proposed not only to replace the conventional splitring resonators (SRRs) to produce a negative magnetic permeability under normal to plane incidence, but also lead to a negative refractive index n in the optical regime. However in a recent review paper (Shalaev, 2007), Shalaev stated that it is very difficult to achieve a negative refractive index with exclusively wire pairs and that the negative index value observed in the ref. (Shalaev, 2005), was accomplished in part because of the significant contribution from the imaginary part of the permeability. Nevertheless, the negative index from only cut wire and plate pairs has never been verified elsewhere (Dolling, 2005). Instead, continuous wires have been combined to the cut wire pairs to produce simultaneously a negative permittivity to lead to a negative index in the microwave domain (Zhou, 2006a). Zhou et al. also theoretically proposed a left-handed material using only cut wire pairs by increasing the equivalent capacitance between two consecutive short wire pairs so as to adjust the electric resonance frequency (Zhou, 2006b) This increase of capacitance can only be obtained by strongly reducing the spacing between two consecutive wires, which is quite difficult to achieve at high frequencies. These cited results concern mainly the microwave domain. In the optical regime, infrared and visible domains, the main problem concern the design and the characterization of metamaterials made of unit cells

Composite structures based on metal open rings and thin wires are well established, for obtaining efficient negative index materials (NIM), acting as metamaterials in the long wavelength regime. The main losses are due both to metal absorption and to the inner electric resistance of metals; to overcome this latter loss we propose a new metal-semiconductor structure dimensioned by direct synthesis method, which offers an almost perfect Drude-like effective magnetic permeability. The choice of particular semiconductor components allows to get a negative resistance for the current induced by the electromagnetic field, which cancels that of the metal but puts a limit to the spectral response of the metamaterial. We consider some parasite effects, such as bianisotropy and incorrect values of structural parameters, to see limitations and features of this new NIM technology.

This paper presents a new type of thin absorber exhibiting double negative metamaterial (MTM) characteristics. A MTM unit cell was constructed by a multiple split ring resonator (MSRR) and a meander-line arrangement. A MSRR structure exhibits negative permeability and a meander-line structure exhibits negative permittivity. Each unit cell is printed on the two side of a FR-4 substrate (relative dielectric constant = 4.4, thickness = 0.8 mm). The proposed one-layer absorber based on double negative MTM was shown to reach thickness of the order of λ 0 /250 at the aimed frequency of 1.55 GHz. In order to maximize the absorption per unit volume, ten unit cells disposed in an array configuration were considered. Simulated results show a high maximum absorption of 95% at 1.52 GHz. In the design of the double negative MTM unit cell, the complex permittivity and permeability of the cell were retrieved from scattering parameters.

In this paper, the utilization of common fabrics for the manufacturing of e-textile metamaterial transmission lines is investigated. In order to filter and control the signal propagation in the ultra-high frequency (UHF) range along the e-textile, a conventional metamaterial transmission line was compared with embroidered metamaterial particles. The proposed design was based on a transmission line loaded with one or several split-ring resonators (SRR) on a felt substrate. To explore the relations between physical parameters and filter performance characteristics, theoretical models based on transmission matrices’ description of the filter constituent components were proposed. Excellent agreement between theoretical prediction, electromagnetic simulations, and measurement were found. Experimental results showed stop-band levels higher than −30 dB for compact embroidered metamaterial e-textiles. The validated results confirmed embroidery as a useful technique to obtain customized electromagnetic properties, such as filtering, on wearable applications.

Based on ceramics S-shaped left-handed materials with magnetic resonance and electric anti-resonance were prepared by screen printing. The microwave transmittance properties of these samples in a rectangular waveguide were experimentally investigated. It is found that the two frequency bands of negative effective permittivity and negative effective permeability overlap from 8.5 to 9.46 GHz, which is left-handed materials pass-band and the bandwidth is about 1 GHz. Magnetic resonance is due to magnetic coupling between magnetic field component of external fields and the samples, in which the effective permeability could be negative. And electrical anti-resonance originated from electric coupling may contribute to negative effective permittivity. This based on ceramics substrate S-shaped construct possess both remarkable electric and magnetic resonances, which provides a flexible element for constructing planar left-handed materials.

Metamaterials (MMs) are engineered material with electromagnetic properties not commonly seen by natural materials such as negative refraction and near-zero permittivity. These materials have interesting applications ranging from perfect lens and electromagnetic cloaks to leaky-wave antennas and shifters. For such applications, electromagnetic properties of MMs are needed to be known. In this study, we propose a waveguide method for accurate electromagnetic parameter retrieval of weakly-coupled MM slabs (the wavevector is normal to the plane of the metallic inclusions). To achieve our goal, new expressions for effective permittivity and permeability as well as the magneto-electric coupling coefficient are derived. For validation of our waveguide method, we used the simulated scattering parameters of a MM slab composed of split-ring-resonator unit cells by using a commercial 3D electromagnetic simulation program.

Metamaterials are artificially designed materials having electromagnetic properties which are not generally found in nature. Various resonators exhibiting metamaterial characteristics are split ring resonator (SRR), spiral resonator (SR), omega and fractal resonator. This paper presents a new type of resonator called as an open split ring resonator (OSRR) exhibiting negative permeability. OSRR is modified structure of split ring resonator (SRR). A metamaterial cell is constructed by the OSRR and wire arrangement. The complex permittivity and permeability of the cell is retrieved from the scattering parameters. As compared to the split ring resonator, open split ring resonator is smaller in size for the same resonance frequency and hence this leads to a size miniaturization in various metamaterial applications.