Array Of Split-ring Resonators Research Articles

Radiation Characteristics of Artificial Magneto-Dielectric Antenna Loaded with Split-Ring Resonator Array

This study proposes a simple artificial magneto-dielectric (MD) antenna with a split-ring resonator (SRR) loaded in an array configuration. This SRR element is used to realize the MD characteristic that is beneficial for antenna miniaturization. The simulation of material permittivity and permeability is conducted to ensure that the proposed SRR-array configuration has the expected MD characteristic. Configurations of SRR in arrays of 3×3, 5×5, 7×7, and 9 × 9 are realized to obtain its radiation characteristics when embedded in the antenna ground plane. A rectangular patch antenna is used in this study. Based on the simulation, the proposed antenna with an SRR array of 5×5 achieves excellent MD characteristics with high permittivity and permeability of 32.44 and 51.39, respectively. Furthermore, a microstrip antenna loaded with the SRR 5×5 arrays are fabricated on RT/duroid 5880 substrate. It has a dimension of 0.31λ0 × 0.26λ0. The simulation and measurement results of the proposed antenna show a fractional bandwidth of 4.79% and 5.2% at 1.5 GHz; and a maximum gain of 5.20 dB and 4.95 dB, respectively. Good agreement between the simulated and the measured results was achieved.

Magnetic metamaterials with correlated disorder

We examine the transport of magnetic energy in a simplified model of a magnetic metamaterial, consisting of a one-dimensional array of split-ring resonators (SRR), in the presence of correlated disorder in the resonant frequencies. The computation of the average participation ratio (PR) reveals that on average, the modes for the correlated disorder system are less localized than in the uncorrelated case. The numerical computation of the mean square displacement of an initially localized magnetic excitation shows an asymptotic behavior 〈n2〉∼tα, where α∼0 for uncorrelated disorder, and α>0 for the correlated case, spanning a whole range of behavior ranging from localization to super-diffusive behavior at finite system sizes. The transmission coefficient of a plane wave across a single magnetic dimer reveals the existence of well-defined regions in disorder strength-magnetic coupling space, where unit transmission for some wavevector(s) is possible. This explains the finite degree of mobility for magnetic excitations in the presence of correlated disorder, in the spirit of the random dimer model (Dunlap et al., 1990 [14]). Finally, the transmission of plane waves across an array with correlated disorder shows a power-law decrease with system size, in contrast to the exponential decrease found in the standard Anderson model.

Wideband Absorption at Low Microwave Frequencies Assisted by Magnetic Squeezing in Metamaterials

In this paper, the magnetic squeezing effect in metamaterials is explored and applied to achieve wideband absorption in low-frequency microwave bands. To this end, a metamaterial absorber (MA) is proposed, which consists of a square lattice of a split ring resonator (SRR) placed on top of a magnetic absorbing material (MAM) layer backed by a conducting ground. In the positive resonance region of SRRs, a strong magnetic squeezing effect occurs and more concentrated magnetic field lines are confined within SRRs. This results in significant magnetic field enhancement within the MAM layer, which provides a prerequisite for high-efficiency absorption enhancement at low frequencies. To verify this method, we fabricated a prototype using a 3.0 mm thick silicone MAM sheet. Both the simulation and experiment results show that with the assistance of magnetic squeezing in the SRR array, the absorption at lower frequencies is significantly enhanced and is above 90% in 1.25–2.31 GHz under normal incidence. Furthermore, the MA exhibits satisfactory stability for different polarization states and incident angles due to the square lattice of the SRR array. This design method may find potential applications in fields such as electromagnetic compatibility, wireless communication, and others.

Fractional dynamics in nonlinear magnetic metamaterials

We examine the existence of nonlinear modes and their temporal dynamics, in arrays of split-ring resonators, using a fractional extension of the Laplacian in the evolution equation. We find a closed-form expression for the dispersion relation as a function of the fractional exponent as well as an exact expression for the critical coupling between rings, beyond which no fractional magnetoinductive waves can exist. We also find the low-lying families of bulk and surface nonlinear modes and their bifurcation diagrams. Here the phenomenology is similar for all exponents and resembles what has been observed in other discrete evolution equations, such as the DNLS equation. The propagation of an initially localized magnetic excitation is always ballistic, with a ‘speed’ that is computed in exact form as a function of the fractional exponent. For a given exponent, it increases with an increase in coupling up to a critical coupling value, beyond which the ballistic speed could diverge inside the fractional interval [0,1]. Examination of the modulational instability shows that it tends to increase with an increase in the fractional exponent, where the decay proceeds via the formation of filamentary structures that merge eventually and form pure radiation. The dynamical selftrapping around an initially localized excitation increases with the fractional exponent, but it also shows a degree of trapping in the linear limit. This trapping increases with a decrease in the exponent and can be explained by near-degeneracy arguments.

Mitigation of mutual coupling in 2 X 2 dual slant polarized MIMO antennas using periodic array of SRRs loaded with transmission line for LTE band 40

2 X 2 dual slant polarized multiple input multiple output (MIMO) antennas with reduced mutual coupling is presented for polarization and spatial diversity. The design of printed periodic array of split ring resonators (SRRs) loaded with horizontal strip transmission line is proposed to mitigate the mutual coupling among the MIMO antenna elements. An equivalent circuit model, characterizes the effect of coupling between the array of SRRs and the loaded transmission line, which together reduces the near field coupling between the adjacent antenna elements. The additional horizontal strip at the bottom is utilized to seek the return current path to the ground plane. Polarization and spatial diversity is achieved by utilizing dual slant 450 polarized antenna elements with eight independent channels. All four dual polarized antenna elements are designed to operate with a VSWR of <2 for (2.3-2.4 GHz) Band 40. Dual slant 450 polarization is achieved by utilizing two printed planar bow-tie antennas in orthogonal orientation. Measured and simulated results shows by incorporating periodic array of SRRs loaded with transmission line a considerable mutual coupling reduction of 25 to 50 dB is achieved in E-plane, H-plane, and D-plane over the required band 40. An isolation of 30 dB and an average gain of 7.5 dB is measured for dual slant 450 polarized antenna elements. MIMO performance metrics in terms of envelope correlation coefficient and diversity gain are also investigated.

A Split Ring Resonator-Based Metamaterial for Microwave Impedance Matching with Biological Tissue

A metamaterial lens based on a split ring resonator (SRR) array has been designed and optimized to improve the focusing and the penetration depth in human biological tissue of a microwave beam irradiated by a substrate integrated waveguide (SIW) cavity backed patch antenna. The impedance matching of the antenna loaded with human tissue is strongly improved. The simulations have been performed by using CST Microwave Studio®. A prototype of the device has been fabricated with the printed board circuits (PCB) process and has been characterized using a Network Analyzer and an antenna measurement system in anechoic chamber. A novel microwave applicator for hyperthermia therapy of skin cancer could be developed. The performances of the proposed applicator have been evaluated in terms of measured S11 scattering parameter modulus and simulated power loss density. The obtained results indicate that an SRR-based metamaterial is a promising solution for external microwave applicators to employ in dermatology.

Kirigami-Enabled Microwave Resonator Arrays for Wireless, Flexible, Passive Strain Sensing.

Wireless and highly sensitive flexible strain sensors would have widespread application across a number of different fields. Here, the novel combination of two different metamaterials, one mechanical and one electronic, is demonstrated for its potential as such a sensor. An array of split-ring resonators (SRRs) were mounted on a bespoke kirigami sheet. The hybrid kirigami structure was designed specifically for the resonator array, in terms of both its physical dimensions and elastic response. Mechanical tests in concert with finite element modeling confirmed that the hybrid kirigami structure, containing two disparate kirigami motifs, exhibited a high range of strain and out-of-plane rotation without plastic deformation. The microwave sensing was designed to monitor variations in the S11 response of the resonators as a function of out-of-plane kirigami hinge rotation. The mounted array of SRRs on the hybrid kirigami sheet could wirelessly detect changes in strain with high sensitivity (>30 MHz shift in resonant frequency; >30 dB shift in resonant amplitude) over a large range of strain, from 0.6 to 21.3%.

Optically Reconfigurable Graphene/Metal Metasurface on Fe:LiNbO3 for Adaptive THz Optics

We demonstrate, experimentally, nonvolatile optical control of terahertz metasurfaces composed of a metallic split-ring resonator array sandwiched between monolayer graphene and a photoconductive F...

Exploring performance of THz metamaterial biosensor based on flexible thin-film.

To extend the application of flexible metamaterial in the biosensor field, a metamaterial biosensor, which consisted of metal elliptical split-ring resonator array with a subwavelength structure based on flexible thin-film (parylene-c), was presented. The structure parameters (ring width, period ratio of structure, gap width, axial ratio) of the elliptical split-ring resonator and polarization direction of incident light were investigated as to how to affect the performances of the flexible metamaterial biosensor. Meanwhile, the permittivity (ε) of the tested sample on the surface of metamaterials biosensor also affected the shift of transmission spectra. The results showed that the sensitivity, quality (Q) factor, and figure of merit (FOM) of the flexible metamaterial biosensor could reach 243 GHz/RIU, 14.2, and 3.3, respectively. Moreover, the full-width-half-maximum (FWHM) was only 82 GHz. Therefore, these results provided an improved direction to design metamaterial biosensors with high Q-factor, low FOM, and high sensitivity, which could meet the need for sample detection in the terahertz regime.

Probing Composite Vibrational Fingerprints in the Terahertz Range With Graphene Split Ring Resonator

Sensors with single resonant mode often produce false positive when detecting the composite vibrational fingerprints of molecules in the terahertz (THz) range. In this study, a multi-resonant plasmonic structure, consisting of periodic graphene split ring resonator (SRR) arrays, is proposed for THz sensing. The effective detection of ultrathin (0.1 μm) lactose layer is given as an example to demonstrate the detection sensitivity. The vibrational fingerprints of lactose at 0.53 THz and 1.37 THz are enhanced in transmission spectra. Besides, resonant frequencies could be actively adjusted with the gate voltage applied on the SRR array. The physical mechanism of multi-resonance can be explained by a combination of LC resonance and dipole resonance of the structure, which can be observed in the electric field distributions. Moreover, the sensing performance can be further optimized by varying geometric parameters. Furthermore, the refractive index sensing performance of the sensor is also investigated by altering the surrounding medium on the surface. The designed sensor can work under an oblique incidence, which provides potential applications in biological analysis and medical diagnostics.

The Complex Permeability of Split-Ring Resonator Arrays Measured at Microwave Frequencies

We have measured the relative permeability of split-ring resonator (SRR) arrays used in metamaterials designed to have $\mu^\prime< 0$ over a narrow range of microwave frequencies. The SRR arrays were loaded into the bore of a loop-gap resonator (LGR) and reflection coefficient measurements were used to determine both the real and imaginary parts of the array's effective permeability. Data were collected as a function of array size and SRR spacing. The results were compared to those obtained from continuous extended split-ring resonators (ESRRs). The arrays of planar SRRs exhibited enhanced damping and a narrower range of frequencies with $\mu^\prime<0$ when compared to the ESRRs. The observed differences in damping, however, were diminished considerably when the array size was expanded from a one-dimensional array of $N$ SRRs to a $2\times 2\times N$ array. Our method can also be used to experimentally determine the effective permeability of other metamaterial designs.

Reconfigurable Terahertz Metamaterial Using Split-Ring Meta-Atoms with Multifunctional Electromagnetic Characteristics

We propose a reconfigurable terahertz (THz) metamaterial (RTM) to investigate its multifunctional electromagnetic characteristics by moving the meta-atoms of split-ring resonator (SRR) array. It shows the preferable and capable adjustability in the THz frequency range. The electromagnetic characteristics of the proposed RTM device are compared and analyzed by moving the meta-atoms in different polarized transverse magnetic (TM) and transverse electric (TE) modes. The symmetrical meta-atoms of RTM device exhibit a resonant tuning range of several tens of GHz and the asymmetrical meta-atoms of RTM device exhibit the better tunability. Therefore, an RTM device with reconfigurable meta-atoms possesses the resonance shifting, polarization switching, electromagnetically induced transparency (EIT) switching and multiband to single-band switching characteristics. This proposed RTM device provides the potential possibilities for the use of THz-wave optoelectronics with tunable resonance, EIT analog and tunable multiresonance characteristics.

Dual Band Octagonal Microstrip Patch Antenna Loaded with Array of Split Ring Resonators

This article presents a proposal about an octagonal microstrip patch antenna (MPA) loaded with Split Ring Resonators (SRR) the antenna’s ground part. The antenna size reduction using multiband radiators will suits for miniaturization of day-to-day handheld devices. The dual band behaviour of the antenna will integrate more communication standard in one system which saves the installation space in the device. In this context, an octagonal antenna structure is conceived for a dual operational frequency of 5.63 GHz and 5.97 GHz. Hereby, a Co-planar Waveguide (CPW) structure is adapted to the octagonal patch and the structure has been observed by simulation analysis under HFSS platform. The overall geometry of the antenna is 30 x 26 x 1.6 mm3. The antenna feed using a microstrip for earning a better impedance matching between the antenna and transmission line. The antenna design provides a wider bandwidth of 580MHz and average gain of 3.25 dBm. The attainment of dual band operational frequencies is due to the CPW and SRR structure in the antenna design.

4D Optically Reconfigurable Volumetric Metamaterials

Metamaterials are artificially created media, which allow introducing additional degrees of freedom into electromagnetic design by controlling constitutive material parameters. Reconfigurable time‐dependent metamaterials can further enlarge those capabilities by introducing a temporal variable as an additional controllable parameter. Herein, a first‐of‐its‐kind reconfigurable volumetric metamaterial‐based scatterer is demonstrated, wherein the electromagnetic properties are controlled dynamically with light. In particular, hybridized resonances in arrays of split ring resonators give rise to a collective mode that presents properties of artificial high‐frequency magnetism for centimeter waves. Resonant behavior of each individual ring is controlled with a photocurrent, which allows the fast tuning of macroscopic effective permeability. Thus, the artificial gigahertz magnon resonant excitation within a subwavelength spherical scatterer is governed by light intensity. 4D control over electromagnetic scattering in both space and time opens new avenues for modern applications, including wireless communications and automotive radars to name just a few.

Poynting Localized Energy: Method and Applications to Gain Enhancement in Coupled Antenna Systems

We present a general and comprehensive approach to evaluate spatio-temporal localized energy around radiating structures of arbitrary shapes and excitation signals. The method utilizes the finite-difference time-domain (FDTD) algorithm to calculate the Poynting localized energy for any antenna by working directly with computed fields, rather than source currents. It is established that this localized energy is fundamentally different from the classical antenna reactive energy associated with frequency-domain Q-factors of electrically small antennas. The proposed localized energy theory leads to the formulation of new performance evaluation measures, effectively going beyond traditional S-parameters and far-field patterns, which are then applied in several design examples involving strongly coupled arrays and weakly coupled antenna systems. It was found that gain enhancement caused by strong mutual coupling in the near zone (directors in Yagi-Uda systems or split-ring resonator arrays) is closely correlated with localized energy enhancement (but such correlation does not hold in weak mutual coupling scenarios). The new performance metrics are also used to generate spatial distributions for energy localization in MIMO printed dipoles. We propose that this proposed localized energy concept and the apparatus developed to investigate its relevant new data can assist in implementation of ultrahigh gain closely spaced antenna elements needed for the upcoming sub-6 GHz/mmWave 5G MIMO systems.

High-sensitivity biosensor for identification of protein based on terahertz Fano resonance metasurfaces

Terahertz metasurface biosensors have gained significant attention in biological field due to its label-free, real-time and in-situ detection properties. In this paper, a planar array of Fano asymmetric split ring resonators (ASRs) fabricated on 25μm flexible polyimide substrate was proposed for new terahertz metasurface biosensors. It is shown that 160 GHz/RIU and 240 GHz/RIU refractive index sensitivity can be severally obtained near 0.81 and 1.13 THz transmission dips of the proposed system. Correspondingly, for biosensor samples that protein A/G, A/G + IgG were spotted on ASRs surface in our experiment, shifts of 8.9 GHz and 11.7 GHz, 17.6 GHz and 52.9 GHz toward low frequency were observed, respectively. These results illustrate high-sensitivity and label-free detection of proteins, implying a new feasible way of sensing in terahertz domain.

Plasmonic Metasurfaces Situated on Ultrathin Carbon Nanomembranes

During the past decade, optical metasurfaces consisting of designed nanoresonators arranged in a planar fashion were successfully demonstrated to allow for the realization of a large variety of flat optical components. However, in common implementations of metasurfaces and metasurface-based devices, their flat nature is thwarted by the presence of a substrate of macroscopic thickness, which is needed to mechanically support the individual nanoresonators. Here, we demonstrate that carbon nanomembranes (CNMs) having nanoscale thicknesses can be used as a basis for arranging an array of plasmonic nanoresonators into a metamembrane, allowing for the realization of genuinely flat optical devices. CNMs belong to the family of two-dimensional materials, and their thicknesses and mechanical, chemical, and electrical properties can be tailored by the choice of the molecular precursors used for their fabrication. We experimentally fabricate gold split-ring-resonator (SRR) metasurfaces on top of a free-standing CNM, which has a thickness of only about 1 nm and shows a negligible interaction with the incident light field. For optical characterization of the fabricated SRR CNM metasurfaces, we perform linear-optical transmittance spectroscopy, revealing the typical resonance structure of an SRR metasurface. Furthermore, numerical calculations assuming free-standing SRR arrays are in good overall agreement with corresponding experimental transmittance spectra. We believe that our scheme offers a versatile solution for the realization of ultrathin, ultra lightweight metadevices, and may initiate various future research directions and applications including complex sensor technologies, conformal coating of complex topographies with functional metasurfaces, fast prototyping of multilayer metasurfaces, and studying the optical properties of effectively free-standing nanoparticles without the need for levitation schemes.

Microfabrication of monolithic wafer-level miniaturized millimeter-wave air-filled half-mode waveguide filter based on the inward curving split ring resonator array

In this paper, we propose a miniaturized monolithic bandpass filter utilizing an air-filled half-mode waveguide and an inward curving split ring resonator array in the millimeter-wave band. The waveguide blocks the wave below cutoff frequency and the uniplanar array forms a rejection band above the transmission band. The microfabrication process of the filter adopts photoimageable technology and the combination of films with different thicknesses to build a 3D structure. The measured prototype has a center frequency at 65.5 GHz with a 3 dB fractional bandwidth of 30.7%. The minimum insertion loss is 2.1 dB. The proposed component offers excellent performance including a wide transmission band, a low pass-band insertion loss, an excellent isolation in the stop-band, and a steep roll-off at the upper cutoff frequency. Besides, due to the scalability of the waveguide and periodic array, this filter can be adapted for other frequency ranges.

A tunable double negative device consisting of a plasma array and a negative-permeability metamaterial

Extraordinary wave transmission is demonstrated through a double-negative composite comprised of a negative-permeability array of double split ring resonators and a negative-permittivity array of plasma discharge tubes at microwave frequencies. A transmission peak emerges in a double-negative band and controlling the electron density inside the plasma tubes dynamically regulates the transmission properties. By performing experiments and theoretical calculations, we verify that the composite permits wave propagation with negative permeability and controllable permittivity, which indicates that a tunable negative-refractive-index device is achieved.

Rotated fourfold U-shape metasurface for polarization-insensitive strong enhancement of mid-infrared photodetection.

Metasurface with thin planar resonant elements offers great capability in manipulating electromagnetic waves and their interaction with semiconductors. Split-ring resonator (SRR), as the basic building block, has been extensively investigated for myriad applications owing to its multiple electric and magnetic resonant modes. In this work, we report a rotated fourfold U-shape SRR metasurface for polarization-insensitive strong enhancement of mid-infrared photodetection. The integrated photodetector consists of a rotated fourfold SRR array and an InAsSb based heterojunction photodiode. A photosensitivity enhancement factor as high as 11 has been achieved by adoption of superimposed high order magnetic and electric resonant modes in the SRR metasurface. This work provides a promising pathway for exploring high performance polarization-insensitive photodetection in different electromagnetic wave ranges.