Single Split Ring Resonator Research Articles

Mechanism insights for impedance matching in split-ring resonator topologies under bio-medical scenarios

The utilization of microwave radiation has gained increasing importance in various biological applications. However, a significant challenge remains in the interaction between the microwaves and the human skin, primarily due to the impedance mismatch. Recently, the employment of split-ring resonator (SRR) topologies has become increasingly prevalent for addressing such a problem. Despite this, most existing literatures lack a comprehensive understanding of the underlying mechanisms. In this study, we follow Babinet’s principle and numerically study the dispersion relations of a single-split-ring resonator (S-SRR) and its complementary topology, single-complementary-split-ring resonator (S-CSRR). We focus on conducting the impedance analysis, along with far-field and near-field excitation characterizations. The results indicate that S-CSRR ensures an improved impedance matching, thereby significantly enhancing microwave power flow within the bio-tissue. A 2 × 2 array of S-CSRR is experimentally examined for validation. We demonstrate that the S-CSRR array enhances the total specific absorption rate (SAR) of a deeply-implanted-tumor-phantom by a factor of 1.95. Our work may provide a broader understanding towards impedance matching, which may facilitate the design of more efficient diagnostic tools in bio-medical field.

A polarization conversion metasurface for broadband and high-efficiency bidirectional filtering

Here, we demonstrate a polarization conversion metasurface which is composed of a single layer square split-ring resonator and bi-layered slotted perfect electrical conductor (PEC) to realize broadband and high-efficiency bidirectional filtering. The numerical results indicate that y-polarized waves can be converted to x-polarized transmission waves in the frequency range of 6.6 GHz to 13.9 GHz, while prevent this polarized waves with frequency beyond this band, and purity x-polarized waves can be obtained as electromagnetic (EM) waves are incident along negative z-axis, meanwhile, x-polarized waves can be converted to y-polarized transmission waves and only y-polarized waves available when EM waves are incident along positive z-axis. This designed polarization conversion metasurface has the function of bidirectional filtering in a wideband frequency range. Furthermore, the broadband property can be maintained as the incident angle up to 30°. The Fabry–Pérot-like cavity model is established to clarify the interference and enhancement effect of polarization conversion, and the electrical field and surface current distributions are used to elucidate the physical mechanism of polarization conversion and filtering. The experimental results are coincident with the numerical simulations. This metasurface can be employed in controlling the filtering signal of the polarized devices and can be functional as a bandpass filter in communication systems.

Manipulation on radiation angles via spatially organized multipoles with vertical split-ring resonators

Abstract Herein, the radiation patterns of single-split ring resonators (SSRRs) and double-split ring resonators (DSRRs) in the vertical direction are tailored by reconfiguring the resonator geometries. To design unequal arm lengths for controlling the floating split angle of the resonators and changing their electromagnetic multipole compositions, vertical metamaterials were fabricated using the metal-stress-driven self-folding method. The simulation results well agree with the experimental transmittance and reflectance results and demonstrate the geometry-dependent angle variation of the far-field radiation. Symmetric SSRRs and DSRRs radiate in the vertical and horizontal directions, respectively. With increasing pad shift, the radiation angle of the asymmetric SSRR completely rotates toward the horizontal direction along the ring plane, but the DSRRs can rotate only from 0° to 45° to the horizontal plane. Furthermore, by decomposing the multipoles into their constituents, we show that the directional scattering performance can be verified by manipulating the horizontal and vertical components of the electric dipoles. This novel combination of SSRRs and DSRRs can effectively and efficiently reconfigure the radiation direction in the infrared (IR) region, paving the way for color routers, metasurfaces, and directive IR emitters in compact optical metadevices.

Nonlinear dynamics of a single-gap terahertz split-ring resonator under electromagnetic radiation.

Research into metasurfaces is developing rapidly and is topical due to their importance and applications in various fields such as communications, cryptography, and sensing, to name a few. These materials are artificially engineered to manipulate/control electromagnetic (EM) waves, in order to present a particular functionality. In this regard, nonlinear metasurfaces may present particular functionalities that remain to be discovered. In this paper, we numerically investigate the dynamic behaviors caused by the motion of charge carriers under the intense EM field at the gap of a single nonlinear split-ring resonator (NSRR) in the terahertz (THz) frequency range. We derive the mathematical model that is used to examine the excitation properties of the NSRR and then demonstrate various tuning regions. Analysis of the two-dimensional parameter space reveals that the NSRR exhibits periodic, chaotic patterns as the amplitude of the excitation field and the loss parameter vary. However, this chaotic behavior disappears when the loss parameter is very large. The period doubling that confirms the transition between the periodic and chaotic modes is explored using the bifurcation diagram. The sensitivity of the initial conditions is examined on three dynamic region plots. Our results correctly demonstrate that the NSRR exhibits the attractive phenomenon of multistability. The coexistence of two stable states is studied and confirmed on the basin of attractions for a fixed set of amplitude or loss parameters. The energy balance of the proposed model is well analyzed on the dynamic states and parameters to characterize the different oscillation regimes. The study of the multistability in the work represents an important first step toward the development of photonic memory devices in the THz frequency range.

Multimode hybridizations in surface plasmon resonances excited in terahertz dipole cavities

Inventive design variations in subwavelength plasmonic structures can excite unconventional surface plasmon resonances (SPRs) that can enormously contribute to developing futuristic terahertz (THz) devices and components. Therefore, in this work, we demonstrate multimode resonance features in SPR characteristics through the introduction of split-ring resonators (SRRs) in plasmonic dipole cavities operating in the THz domain. Here, we propose a hybrid plasmonic system, where a single SRR is placed in the middle of a dipole cavity sustaining SPRs in the THz domain. Further, the SRR is displaced in orthogonal directions (horizontally as well as vertically) from the center of the cavity introducing asymmetry in the hybrid SRR–dipole cavity system. In such a way, introduced asymmetry resulted in diverse transmission responses with the realization of multiple SPR peaks. Such multi-SPR features are explicated using two-state and three-state mode hybridization schemes, which arise due to the near-field electric coupling between the SRR and the dipole cavity. Our findings based on multimode SPR characteristics excited in planar dipole cavities can contribute to realizing compact biosensor, absorber, and nonlinear THz devices operating simultaneously in multiple frequency bands.

Graphene-Based Metasurface Refractive Index Biosensor for Hemoglobin Detection: Machine Learning Assisted Optimization.

Machine learning is the latest approach to optimize the performance of absorbers, sensors, etc. A sensor with behavior prediction using polynomial regression is presented. Three different variations of metasurfaces namely double split-ring resonator, single split ring resonator, split ring resonator with thin wire are analyzed. The proposed design aims to achieve the highest sensitivity by observing different designs and different parameter variation. The highest sensitivity is achieved for double split-ring resonator and single split ring resonator designs. The change in thickness of different parameter affect the absorption and the highest sensitivity is calculated based on these variations. The polynomial regression (PR) model is employed to predict the absorption values for assorted combinations of intermediate wavelength values with angle variation, substrate thickness, substrate length, substrate width, graphene potential, and resonator thickness values. Test Cases R-30 and R-50 are evaluated using R2 score metric to assess the effectiveness of PR model for predicting the values of absorption. R2 score close to 1.0 is achieved for all the experiments at a higher (more than 5) polynomial degree, which proves the prediction efficiency of a regression model. The proposed biosensor designed with a PR model can be applied in biomedical applications for hemoglobin detection.

Terahertz high-Q magnetic dipole resonance induced by coherent Fano interactions

High Q-factor resonance holds great promise for bio-chemical sensing and enhanced light–matter interaction. However, terahertz (THz) magnetic resonances usually demonstrate low Q-factors, resulting in huge energy radiation loss particularly in high frequency bands. Here, we show that high Q-factor magnetic dipole resonance at THz frequencies can be achieved by exploiting the coherent Fano interactions with strong field enhancements in an array composed of single metallic split-ring resonators, working at Wood–Rayleigh anomalies. It can give rise to ultrahigh Q-factor beyond 104 in the THz regime. Experimentally, the measured Q-factor of dominant magnetic dipole resonance can achieve no less than a level of ∼261 by Lorentzian fitting to the experimental data. In addition, a high Q-factor of the fundamental-order magnetic dipole resonance is demonstrated beyond 30. High-Q magnetic dipole resonance is closely associated with ultralow-damping and negative permeability in the THz band. The measurements of magnetic dipole resonances are in good agreement with the theoretical analyses. Our scheme suggests a feasible route to suppress radiative loss for enhanced THz field-matter interaction.

Improved circuit model for plasmonic resonance of single split-ring resonators

In this work, an improved circuit model is presented for the single split ring resonator (SRR), taking into account non-uniform distribution of conduction current and surface charges. To determine the circuit elements of the SRR, the electron kinetic, electric, and magnetic energy have been derived theoretically. Moreover, in addition to gap and surface capacitances, coupling capacitance is introduced to characterize the electric coupling effect between them. A formula for the fundamental resonance wavelength has been obtained, which shows good agreement with numerical simulations in both optical and microwave frequency ranges. The model will be instructive for engineering resonant properties of the SRRs and provide valuable insight into other complex plasmonic structures.

Design of triple-/six-spectral perfect absorber using multiple resonance responses of metallic split-ring resonator

Multiple-spectral absorber is a kind of functional device with important applications in optoelectronic technology areas. However, the implementation of multiple-spectral absorber usually requires many metallic elements relying on design methods of stacking or coplanar, leading to complex structure design, time-consuming and laborious fabrication procedures. Simplified design of multiple-spectral absorber is given and suggested in this paper. It is revealed that the triple-spectral absorption is realized by merely using single metallic split-ring resonator (SRR). Combined effect of fundamental mode LC resonance, quadrupole resonance and high-order response of SRR gives rise to the triple-spectral absorption. What is more important is that six-spectral absorption can be achieved via embedding one more SRR on the basis of original SRR. Under the aid of the near-field maps, the formation mechanism of six-spectral absorption is discussed. Compared with previous metamaterial absorbers, the suggested devices have the obvious advantages of simple structure design, low construction cost, and thus can have large potential for applications.

Gain Enhancement of Patch Antenna Using High Refractive Index Metamaterial-based Bi-convex Lens for Base Station Applications

ABSTRACT In this paper, a high refractive index-based metamaterial Bi-convex lens superstrate for the gain enhancement of broadside radiating antennas like microstrip antennas is presented. Fundamentally, an effective HRI medium is created by the Single Ring Split Ring Resonator unit cells printed on an FR-4. By stacking the multiple layers of the superstrate, a virtual HRI-based equivalent Bi-convex lens is constructed to focus the incoming diverged beam from a patch antenna. A gain enhancement of 4.42 dB is achieved with the help of a 3-layer HRI-based Lens superstrate. The simulation and measurement results are also almost agreed on the same.

A square ring and single split resonator based wearable antenna for Microwave energy harvesting for IoT nodes

A wearable antenna utilising metamaterial radiating elements, which operates at two frequency bands, are presented in this paper. A closed-ring resonator and a single split-ring resonator of square shape have been used to provide dual resonance. The work develops a compact microstrip patch antenna having radiating patch dimensions of 24.8 × 24.8 mm2, that generates electromagnetic energy exhibiting dual band from 2.3 to 2.5 Giga Hertz (WiMAX, ISM) and 3.4 to 3.6 Giga Hertz (WiMAX band). This work provides relevant parametric analyses, such as free space, on-body, and antenna bending effects. Microstrip antenna is designed to be built on flexible dielectric substrate named Rogers RT-5880 Material with dielectric constant 2.2 and thickness of 0.787 mm. The design is validated by a comparison of numerical and actual antenna measurements. Between simulated and measured findings, good equivalence has been discovered. The fabricated antenna provides an impedance bandwidth of 1036 Mega Hertz in lower and 352 Mega Hertz in upper-frequency range, a gain of 2.7 dB,2.35 dB, the directivity of 3 dB, 2.9 dB, the radiation efficiency of 93.32%,88.21 % at 2.4 and 3.6 Giga Hertz respectively in free space condition. The results highlight the applicability of an energy efficient dual-band proposed antenna in wearable applications and microwave energy harvesting for IoT nodes within the ISM and WiMAX bands.

Lagrangian formulation to investigate the effect of coupling on resonant microstrip transmission line

AbstractAn analytical and a numerical study on coupling in microstrip transmission line (MTL) are reported for different split-gap orientations of a single gap square-shaped split-ring resonator (SRR). Taking both magnetic and electric couplings and adopting Lagrangian formulation for this coupled system, mathematical relations are found for each orientation of SRR to determine the connection between coupling co-efficient and resonant mode frequency. It is shown that coupling results in higher resonance frequency when the SRR, with parallel split-gap, has the gap far from the MTL. But, a lower resonance frequency is obtained when the SRR is placed at shorter distances with parallel split-gap near to the MTL. Again, for perpendicular split-gap orientation of SRR, the resonant frequency is found in terms of an effective coupling co-efficient; at shorter distances it is found to be lower than the fundamental resonance frequency of uncoupled SRR and an opposite effect is obtained at longer distances. Using CST Microwave Studio, the resonance frequency for each split-gap orientation of SRR is also studied as a function of separation between MTL and SRR. It is observed that this phenomenon strongly depends on SRR side-length, substrate height, and separation between MTL and SRR.

Terahertz 3D bulk metamaterials with randomly dispersed split-ring resonators

Abstract While optical systems using terahertz wave are expected to achieve beneficial applications, at present, the materials of the optical elements that compose them must be selected from limited choices. In this study, we propose a three-dimensional bulk metamaterial in which metal microstructures are dispersed in the bulk resin randomly. A bulk metamaterial was designed and fabricated, in which split-ring resonators known as typical metamaterials were dispersed in cyclo-olefin polymer. In the fabrication method, a resin sheet containing split-ring resonators was first prepared and then diced into resin grains containing a single split-ring resonator. Finally, they were filled in a mold and solidified with a resin solution to obtain the target bulk metamaterial. The optical properties of the fabricated bulk metamaterial were measured by terahertz time-domain spectroscopy. The measurement results confirmed that the refractive index deviated from the original refractive index of the cyclo-olefin polymer due to the resonance of split-ring resonators, suggesting that the proposed bulk metamaterials could be used as a new optical material in the terahertz band.

Compact microwave sensor for monitoring aging of oil and fuel adulteration

Adulteration detection of liquids is an emerging field in the present scenario. Purity detection of engine oils and fuels is essential for the smooth functioning of automobiles. An asymmetric coplanar strip fed stepped impedance resonator (SIR) coupled single split ring resonator (SSRR) sensor is used for purity and adulteration detection of engine oil and fuels in automobiles. The sensor operating at 5.95 GHz in free space on a low-cost substrate with a compact size of 10 × 11.5 × 1.6 mm3 is demonstrated in this article. The impedance contrast between the two lines of SIR and the coupled SSRR improves the electric field distribution and thus the sensitivity. The resonant frequency of the proposed sensor changes with the aging of the oil or the adulteration level. The sensor performance is analyzed with simulations and validated with measurements.

Comparison of single and concentric split-ring resonator generated microplasmas

Microplasmas generated by a single split-ring resonator and a dual concentric split-ring resonator operating at the same frequency are compared. Argon is used as the working gas and held at a pressure of 0.5 Torr. The surface electric fields in the resonators were simulated to gain insight into the behavior of the fields in each device. Double Langmuir probes were used to measure the plasma density and electron temperature in a 2D plane 2 mm above the surface of the resonators. The single and the concentric ring resonators both had a maximum electron temperature in the discharge gap of 2.5 eV. The single and concentric split-ring resonators had the same maximum measured plasma density of 1.19 × 1017 m−3. Plots of the measured properties and comparisons with electric field simulations show the field coupling to the concentric ring and ignition produced in the secondary discharge gap. The concentric ring resonator has more spatially uniform temperature and density distributions relative to the single split-ring resonator.

A CPW-Fed Circular SRR-Inspired Flexible Antenna Using Polydimethylsiloxane (PDMS) Substrate for WLAN and WBAN Applications

This article presents a <inline-formula> <tex-math notation="LaTeX">$50\times40$ </tex-math></inline-formula> mm² coplanar waveguide (CPW)-fed triple-band flexible antenna operating at 5, 5.8, and 6.6 GHz for wireless local area network (WLAN) and wireless body area network (WBAN) applications. In the proposed design, polydimethylsiloxane (PDMS) is used as a substrate with a dielectric constant <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> of 2.65 and a loss tangent tan<inline-formula> <tex-math notation="LaTeX">$\delta _{\varepsilon r}$ </tex-math></inline-formula> of 0.02. In addition to the rectangular slot on the ground, the presented antenna has a single circular split-ring resonator (SRR) structure on the same side of the patch. This provides the required frequency notched characteristics for the targeted frequency bands, compactness, minimize losses, and backward radiation when used in close proximity to the human body. The proposed flexible antenna provides stable results in terms of performance parameters and specific absorption rate (SAR). We have also investigated the antenna under different operating conditions of moisture and bending. There exists a strong correlation between the simulation and measured findings.

Bandwidth Enhancement of Circular Ring Patch by Loading Single Split Complementary Split Ring Resonator

Metamaterials have gained a lot of interest in modern wireless devices due to their electromagnetic characteristics and it is employed to improve antenna parameters such as bandwidth, gain and efficiency. The study presents a novel strategy of single split non-uniform width Complementary Split Ring Resonator (CSRR) equipped Circular ring Microstrip Antenna (CRMA). The radiating element dimensions are seen to be 20 mm x 20 mm at the initial working frequency wherein the CSRR is incorporated on the ground plane of CRMA. The single split non-uniform width metamaterial (CSRR) structure displays -10 dB impedance bandwidth at 11.1 and 13.56 GHz which is beneficial for applications pertaining to X and Ku band. The total bandwidth of the said metamaterial antenna is 4 GHz (10.73-14.75). Optimization is undertaken with the help of commercially assessable simulation software tool Ansys HFSS 2019 version and practically measured using network analyzer. It is quite obvious from the experimentation that the results calculated get along well with the assumed outcomes.

Patterned PEDOT:PSS-enabled organic planar microwave resonator sensors

The demand for low-cost and environmentally friendly electronics has required novel materials that have high electrical performance while being mechanically stable and sustainable. Capitalizing on the water-dispersibility and high electrical conductivity of intrinsically conductive polymers, we first devise an all organic, environmentally friendly, and reformable microwave split-ring resonator (SRR) using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and second optimize its performance in solid and gas sensing applications. The conducting polymer layer is obtained by the solution-processing of PEDOT:PSS with dimethyl sulfoxide (DMSO) and is subsequently able to substitute metal traces used in conventional SRR structures. The performance of the fabricated organic microwave resonators (OMRs) in various sizes demonstrates the scalability of these resonators to be calibrated in a wide range of operational resonant frequencies, similar to their metal-based counterparts while being low-cost, environmentally friendly, and compatible with industrial-scale production. Moreover, by coupling two identical D-PEDOT:PSS resonators, an enhanced notch profile with an amplitude of −48.47 dB at the resonant frequency of 4.76 GHz is achieved, which is four times more sensitive than a single polymeric SRR at the same resonant frequency. The sensing capability of the polymeric microwave resonators is investigated by using solid standard materials, wherein the change in resonant frequency and resonant amplitude is observed in accordance with the permittivity of the test samples. Furthermore, the D-PEDOT:PSS OMRs developed in this study shows great potential when subjected to relative humidity sensing applications as a proof of concept. The performance of the OMRs is investigated for a wide relative humidity range of 3 % to 90 %, which demonstrates a sensitivity of 28 mdB and 300 kHz per unit relative humidity change on the resonant amplitude and the resonant frequency, respectively. The presented D-PEDOT:PSS split ring resonator paves the way for a novel generation of OMRs to be further developed in flexible and wearable microwave sensor applications in a wide variety of scenarios.

The Study of the Altering Substrate Refractive Index on Single Symmetry Split-Ring Resonator Unit Cell Metamaterial

This study employed single symmetry split-ring resonator (SRR) to implement biosensor applications. The behavior of the applied mechanism was observed comprehensively by altering the substrate refractive index. Also, numerical functions were evaluated using CST microwave studio, while the Maxwell’s equation was resolved by finite integration technique (FIT). Furthermore, impedance of SRR metamaterial tends to reduce by increasing the refractive index for both the substrate and initial substance. These conditions consequently influenced the permittivity and the permeability. However, permittivity was presented with a significant modification for separate refractive index values, but was not the case for permeability. Meanwhile, both properties obtained varying amplitudes under distinct refracted conditions.

Graphene-Based Plasmonic Absorber for Biosensing Applications Using Gold Split Ring Resonator Metasurfaces

We propose a novel graphene-based metasurface plasmonic biosensor. The gold split-ring resonator is used as a metasurface element in the biosensor. Split Ring Resonator structures are used to localize and increase electromagnetic field incidents. Two types of split-ring resonator based metasurface (Single split-ring resonator and Double split-ring resonator) designs are analyzed to observe its effect on biosensing. The proposed biosensor is used to sense hemoglobin and urine biomolecules for their different concentrations. The design results in the form of absorption, electric field, and magnetic field are presented. The sensitivity for hemoglobin biomolecules and urine biomolecules are calculated from their absorption peak difference and refractive index difference. The sensitivity results are compared with previously published designs. The proposed single split ring resonator metasurface design has the highest sensitivity for hemoglobin-urine concentrations. The proposed biosensor can become a building block for future medical biosensing devices.