Left-handed Passband Research Articles

Implementation of left handed transmission lines based on waveguide TM modes

AbstractIn this article, a novel left‐handed (LH) waveguide transmission line with good filtering performance is proposed and implemented below the TM mode cutoff frequency. TM11 mode is employed and transmitted inside the waveguide. The LH passband is achieved by TM mode cutoff operation and complementary split‐ring resonator (CSRR) loading, which are able to provide negative μ and ε, respectively. It constitutes the main novelty here with the rectangular waveguide TM mode and CSRR to realize the LH characteristics, which has not been done before. Based on this passband, two bandpass filters with high‐selectivity are designed and fabricated. The measured results are in agreement with the simulated data. It shows a good LH passband below the cut‐off frequency and TM11 mode propagation is also detected at higher frequency above the cutoff.

A Numerical and Experimental Study of a Low-Loss Wideband E-Shaped Meta-Atom for LHM Characteristics

A planar left-handed metamaterial (LHM) based on E-shaped resonator (ESR) configuration is demonstrated, which provides a methodology in designing loss wideband negative-refractive-index (NRI) materials. When a plane wave propagates perpendicularly toward the ESR metamaterial (MTM) layer, a left-handed (LH) transmission passband is realised from a frequency band of 4.31 GHz to 5.24 GHz, where both effective permittivity and effective permeability are negative. Numerical and experimental results predict a LH transmission band near 4.16-GHz resonance. The retrieval algorithm and dispersion characteristics confirm the double-negative (DNG) constitutive parameters and NRI passband. Simple expressions for the electric and magnetic resonance frequencies of an ESR MTM structure are also presented. CST Microwave Studio EM simulation was used to obtain the complex values of S-parameters data of the MTM unit cell and to examine E-field distribution. The implemented experimental results reveal that the proposed compact ESR MTM structure provides a wide left-handed transmission passband with small material losses and ease of fabrication, making the suggested ESR LHM a good candidate for radio-frequency (RF) and millimetre applications.

A transmit/reflect switchable frequency selective surface based on all dielectric metamaterials

In this paper, we propose a novel transmit/reflect switchable frequency selective surface (FSS) in millimeter wave band based on the effective medium theory under quasi-static limit, which is designed with square-hole elements cut from continuum dielectric plates. The building elements of the surface are composed of all dielectric metamaterial rather than metal material. With proper structural design and parameters tuning, the resonance frequencies can be tuned appropriately. The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface [Formula: see text], which means under different incident polarizations. The reflective response can be realized due to the effect of electric and magnetic resonances. Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances. And the transmitting response is the left-handed passband, arises from the coupling of the electric and magnetic resonances. In addition, effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses. The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.

Band split in multiband all-dielectric left-handed metamaterials

In this paper, we propose and fabricate multiband all-dielectric left-handed metamaterials (ADMs) in the X-band microwave regime. The ADMs are fabricated by a combination of dielectric resonators in shapes of cubes and rods. The ADMs can exhibit two left-handed pass bands while the rods contact the sidewalls of the waveguide. A band split phenomenon is observed when the boundary conditions of dielectric rods change. The two pass bands can diverge into three left-handed pass bands when the rods do not contact the waveguide. By using field analysis and dielectric resonator theory, we prove that the boundary conditions have a strong influence on the resonant modes of the rod resonator, which plays key roles in left-handedness. The boundary tuned resonant modes can broaden our ways of designing new types of metamaterials.

Dual-Band Ring Coupler Based on the Composite Right/Left-Handed Folded Substrate-Integrated Waveguide

In this letter, a dual-band ring coupler based on the folded substrate-integrated waveguide (FSIW) is proposed. The artificial structure, the composite right/left-handed (CRLH) transmission lines were implemented in the FSIW by loading the interdigital capacitors in the middle metallic layer to generate a left-handed passband region below the cutoff frequency of the ordinary waveguide ${\rm TE}_{10}$ mode for coupler miniaturization. The FSIW is the folded counterpart of the substrate-integrated waveguide (SIW) and thus can prevent the CRLH transmission lines from radiation loss by shielding the interdigital capacitors in the waveguide. Besides, the FSIW-based coupler is able to eliminate the electromagnetic interference (noise) with adjacent objects and lend itself to multilayer circuit integration. A ring coupler that operates at 4.3 and 7.6 GHz was developed and experimentally verified. To the best of the authors' knowledge, it is the first time that a dual-band rat-race was implemented and reported based on the CRLH-FSIW structure.

Multi-band terahertz two-handed metamaterial based on the combined ring and cross pairs

We present the design of a Multiband two-handed metamaterial (MM) with the composite structure combined ring and cross pairs (RP+CP) in the terahertz regime. The dual-band left-handed and single-band right-handed transmission properties of this composite structure were explored by the FDTD method. The MM exhibits left-handed and right-handed transmission pass bands around the frequencies of 0.43THz, 1.32THz and 0.85THz for the terahertz electromagnetic (EM) wave normal incidence, respectively. The surface currents distributions are demonstrated to discuss the physical mechanism of the left-handed properties of the proposed MM. The retrieved equivalent EM parameters and the refraction phenomenon based on a wedge-shaped model verify the left-handed properties. Furthermore, the dual-band left-handed transmission properties of RP+CP structure can be tunable individually by changing the structural parameters. The presented design of terahertz two-handed MM offers a flexibility for investigation of their novel EM properties, and important terahertz device applications.

Broadband and compact double negative composite metamaterials with low losses

In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single sided S-shaped resonators are proposed. One of them is a reduced-size resonator which uses superposition hypothesis to achieve adjacent reso- nances for a much broader negative refraction passband. The other is a modified planar structure with improved electromagnetic coupling and reduced electrical size. Both structures are truly matched to free space in almost whole left-handed frequency band. It will be shown that these metamaterials are robust to the fabrication errors of misalignment printing on both sides of the substrate. The superior performance of these structures are investigated numerically and experimentally and compared with the other split ring resonators. Wedge shape simulation and experimental results confirm the left-handed passband.

S-type metamaterial operating under normal incidence

Abstract In this manuscript, we report an S-type negative index metamaterial composed of via holes and strip wires. Unlike common S-type microstructure working mainly under grazing incident wave, it can operate under normal incidence directly. From the experiment and numerical results, it is shown that such a microstructure exhibits left-handed passband around 8.5 GHz, where the effective index is confirmed to be negative by retrieval effective parameters. In addition, the left-handed passband of S-type metamaterial can be tailored by varying the radius of via hole.

Leaky-Wave Radiation Behavior From a Double Periodic Composite Right/Left-Handed Substrate Integrated Waveguide

A double periodic composite right/left-handed ( DP-CRLH ) substrate integrated waveguide (SIW) is proposed based on the transmission line theory. A new leaky-wave radiation is observed at low frequency below the left-handed passband in addition to the composite right/left-handed property. First, the equivalent circuit of the proposed structure is analyzed, and dispersion characteristics are obtained including the expression for the cutoff frequencies. It is noted that transmission lines double periodically loaded with either alternate capacitances, or alternate inductances will contribute the new leaky-wave behavior. Next, SIW implementation of a DP-CRLH transmission line is designed and illustrated with simulated and experimentally demonstrated results. The electric field distribution plots are extracted from a full-wave simulation tool and exhibit the forward and backward wave propagation in the new leaky-wave region and the typical left-handed region, respectively. Finally, a compact leaky-wave antenna based on the DP-CRLH SIW is designed, and the radiation characteristics are tested and demonstrated to exhibit forward radiation at the new leaky-wave region from 5.2 to 5.8 GHz (covering IEEE 802.11a band) and frequency scanning from backward to forward directions in the left-handed and conventional right-handed region from 12.6 to 17.8 GHz.

Design and analysis of double incidence metamaterials composed of mushroom-shaped structure

An ultra-wide band metamaterial may be achieved via the design of some structures. A metamaterial unit supporting two-dimensional (2D) incident electromagnetic (EM) wave is proposed based on the mushroom type-structures, which has an ultra-wide band with seamlessly combined band of right-handed and left-handed pass-bands. This unit is designed by setting two reverse symmetrical mushroom-shaped strips on each side of the dielectric substrate respectively, and the electric resonance and the magnetic resonance could be excited simultaneously. With CST software, the right-handed and left-handed properties are analyzed and verified by means of spectrum analysis, effective parameters of permittivity, permeability and index of refraction extracted from S parameters, and equivalent magnetic resonance circuits. The results show that the structure can present left-handed properties with 1 GHz left-handed pass-band in X waveband, either EM wave is incident in the direction perpendicular or parallel to the plane of the substrate. When the EM wave is incident in the direction perpendicular to the substrate, the right-handed and the left-handed pass-bands appear at 7.2 GHz9.3 GHz and 9.3 GHz11 GHz respectively; while when the EM wave is incident in the direction parallel to the substrate, the right-handed and the left-handed pass-bands appear at 7.0 GH9.0 GHz and 9.0 GHz10 GHz respectively. It also shows that the zero indexes of refraction occur at 9.3 GHz and 9.0 GHz in the tow instances above. So that a plus-zero-negative metamaterial is constructed and a 2D incident balanced-structure with an ultra-wide band of 3 GHz is achieved.

DOUBLE PERIODIC COMPOSITE RIGHT/LEFT HANDED TRANSMISSION LINE BASED LEAKY WAVE ANTENNA BY SINGULAR PERTURBATION METHOD

The paper proposes a Composite Right/Left Handed double periodic transmission line structure with both inductance and capacitance loaded. The structure exhibits leaky wave radiation and hence can be considered for leaky wave antenna (LWA) applications. We have theoretically obtained dispersion characteristics using Singular perturbation method. Also, the radiation e-ciency has been obtained for difierent modulation indices. A novel leaky wave radiation has been obtained below the left handed passband with narrow bandwidth. The proposed structure has been fabricated on FR4 substrate and measured. The simulated and measured results seem to be in good agreement.

LEFT-HANDED METAMATERIALS MEASUREMENT UTILIZING PARALLEL-PLATE WAVEGUIDE SYSTEM

A novel measurement method of parallel-plate waveguide (PPW) system is introduced to detect the characteristics of left-handed metamaterials (LHMs). A sample of LHM composed of triangular open-loop resonator plus wire structures is proposed and measured by using this PPW system. The measurement results are in good agreement with the simulation results. Furthermore, the parametric retrieval algorithm, the calculated negative phase shift and the simulated subwavelength imaging result are given to validate the authenticity of PPW measurement system, which effectively demonstrates the measured transmission passband is indeed a left-handed passband.

Investigation of negative index properties of planar metamaterials based on split-ring pairs

A low losses broadband planar negative refractive index metamaterial based on split-ring resonator (SRR) pairs is proposed and investigated experimentally and numerically at microwave frequency range. The transmission spectra of the single-layer SRR pairs were measured, and exhibited left-handed (LH) transmission passband clearly. The metal-dielectric-metal structure exhibits strong magnetic and electric responses simultaneously, and leads to negative permeability and negative permittivity. To further verify the LH properties of planer structure metamaterials, effect media parameters were retrieved, a refraction phenomenon based on a wedge-shaped model and negative phase advance between consecutive numbers of layers were also demonstrated.

Zeroth-Order Resonators With Variable Reactance Loads at Both Ends

Effects of the reflection condition at both ends of a zeroth order-resonator are investigated. The proposed resonator is composed of a composite right/left-handed transmission line (CRLHTL) and two reactive elements as reflectors at both ends. The load reactance at one end is chosen as the complex conjugate of the other. The balanced case without bandgaps between right- and left-handed passbands, as well as the unbalanced cases, are discussed for CRLHTLs employed in the resonators. The superposition of stored energies of series resonance in the series branch and parallel resonance in the shunt branch in the ladder network can be continuously and arbitrarily controlled by changing only the load reactance at the terminals. For unbalanced cases, the resonance occurs within the bandgap. Coexistence of the two different resonances is verified by directly observing the near-field distribution of the resonator in the numerical simulation and the measurement.

Electrically controllable fishnet metamaterial based on nematic liquid crystal

A variable index metamaterial is demonstrated by embedding nematic liquid crystal inside fishnet layers' void at microwave frequencies. With an external electric field, the left handed passband can be reversibly shifted from 9.14 to 8.80 GHz, whereas the upper right handed passband is nearly unchanged. It is shown that during LC molecular reorientation, magnetic resonance is shifted to a lower frequency because of the permittivity increase between fishnet layers, leading to an effective index change of 1.1 within negative index regime.

Leaky-wave characteristics from double periodic composite right-/left-handed transmission lines

A double periodically loaded leaky-wave antenna (LWA) based on composite right-/left-handed transmission lines is proposed. Dispersion characteristics and the radiation efficiency are investigated with the help of a singular perturbation procedure, and the radiation efficiency is numerically estimated as a function of the antenna length. In addition to the left-handed (LH) characteristic of the structure, a novel leaky-wave radiation is obtained below the LH passband with narrow bandwidth, and this point is focused on the leaky-wave phenomenon because of space harmonics of the Bragg reflection from double periodically loaded inductances and/or series interdigital capacitances. Compact LWAs are designed using microstrip lines with double/single periodically loaded inductances and/or capacitances. Radiation characteristics are measured for the investigated compact antenna, and the results demonstrate the expected novel leaky-wave behaviour.

Study on double incidence left-handed material composed of double Z-shaped metal strips

A new 2D left-handed material structural unit is proposed by setting two reversely symmetrical Z metal strips on each side of the dielectric substrate respectively. The structure can present left-handed properties in X waveband, with electromagnetic waves incident either perpendicularly or parallel to the plane of the substrate. By means of numerical simulation, extracting the effective permittivity and permeability from S parameters and building the equivalent magnetic resonance circuits of the structure, the left-handed property is further analyzed and verified. And by comparing the double Z-shape unit with the traditional H-shape unit, it is shown that they have similar responses of presenting left-handed pass band when electromagnetic waves are incident perpendicularly to the substrate, but only the double Z-shape unit can achieve left-handed features when electromagnetic waves are incident parallel to the substrate. The results indicate that the double Z-shape left-handed structural unit is superior to the traditional H-shape structure, namely, the double Z-shape can redound to design left-handed structural unit for double dimension incidence of electromagnetic waves.

All-dielectric left-handed metamaterial design basedon dielectric resonator theory

By analyzing dielectric cube with high permittivity based on dielectric resonator theory, a new approach to the analyzing of left-handed metamaterials simultaneously with negative permittivity and negative permeability is proposed. The approach indicates that dipoles with Lorentz-type resonance electromagnetic responses can realize negative effective parameters in their negative resonant region. The dipole originates from standing wave in high permittivity dielectric cube. By combining electric dipole with magnetic dipole together, the interaction between two kinds of dipoles will destroy the standing wave and realize a left-handed passband. Numerical simulations indicate that by combining dielectric cubes with same sizes but different permittivities together, the electric resonant frequency and the magnetic resonant frequency can be coincident. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial constructed by this means.

THz meta-foil – a platform for practical applications of metamaterials

The meta-foil, an all-metal fully self-supported locally stiff and globally flexible metamaterial, is presented. Its architecture is based on an array of parallel S-strings interconnected by transverse metal rods that are periodically repeated along the strings. For the present samples, this period is about once or twice the length of an S, which is 31 µm. The resonance frequency of the left-handed pass-band is 3.2 THz or somewhat higher depending on geometry. The meta-foil is manufactured by UV or X-ray lithography-based microfabrication. In the end, it may be produced cost-effectively by plastic moulding. The physical function is explained by numerical simulation and equivalent circuit theory. The spectra are measured by Fourier transform infrared spectroscopy. Maximum transmission is achieved at normal incidence with a cosine-square-like decrease with incidence angle. A change of geometrical parameters alters the resonance frequency as expected. The spectra are also rather sensitive to surrounding dielectrics, indicating a sensor capability. As the meta-foil can be bent, a cylindrical hyperlens set-up is discussed as a forthcoming application to sub-wavelength resolution imaging.

Characteristics of Left-Handed Materials with Magnetic Resonance and Electric Anti-Resonance Based on Ceramics

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.