Concentric Split Ring Resonators Research Articles

Novel Complementary Multiple Concentric Split Ring Resonator for Reliable Characterization of Dielectric Substrates With High Sensitivity

Novel Complementary Multiple Concentric Split Ring Resonator for Reliable Characterization of Dielectric Substrates With High Sensitivity

Optically control tissue-independent reconfigurable antenna for body-centric communications at 2.4 GHz ISM band

The objective of this article is to design a tissue-independent reconfigurable antenna that operates at the Industrial, Scientific, and Medical band (ISM band: 2.4 − 2.485 GHz) for body-centric wireless communications. The primary radiator of the proposed antenna consists of three concentric split-ring resonators (SRRs) and a photodiode appropriately placed between the rings. In addition, a hook-shaped slot in the ground plane, and a shorting pin between the radiator and the ground plane are employed to improve the impedance matching and adjust the resonance frequency, respectively. The optically controlled implantable antenna (OCIA) with the novel configuration operates in the respective frequency band in the skin and muscle tissue in the OFF state and the fat tissue in the ON state of the diode. The numerical design and analysis of the OCIA were carried out using CST Microwave Studio and the obtained results were verified by the in-vivo, ex-vivo, and in-vitro measurements of the fabricated antenna. To the best of the authors' knowledge, this is the first optically reconfigurable antenna capable of covering the 2.4 GHz ISM band within three different body tissues.

Compact Quadband Bandstop Filter Based on Concentric Split Ring Resonators with Perturbation for Multifunctional Wireless Systems

Bandstop filters play an essential role in many radio frequency (RF) and microwave communication systems to block undesired signals or reject spurious harmonics. This paper presents the design and experiment of a compact quadband bandstop filter centered at 1.2/1.97/2.96/4.78 GHz with a passband insertion loss ranging from 1.07 to 2.9 dB. The overall volumetric size of the proposed filter is 0.197 λ g × 0.197 λ g × 0.01 λ g , where λ g is the guided wavelength at 1.2 GHz. The desired performance is achieved by introducing two diamond-shaped concentric split ring resonators (DSCSRRs) intercoupled and defected ground structure. The metamaterial properties of the DSCSRR have been verified by extracting and analyzing its effective permittivity and permeability. This research shows that DSCSRRs can generate multiband characteristics and yield high selectivity with good band-to-band isolation by generating transmission zeros between passbands. The filter is designed, optimized, and analyzed using High-Frequency Structural Simulator (HFSS). A good agreement is observed between simulated and experimental results. The measured results demonstrate that the proposed quadband banstop filter exhibits a minimum stopband rejection of 11.22 dB and fractional bandwidth greater than 4.51%, which makes it suitable for front-end transceiver components or multifunctional wireless systems to suppress unwanted signals at four separate frequency bands.

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.

Design of Tunable Terahertz Metamaterial Sensor with Single- and Dual-Resonance Characteristic.

We present two types of refractive index sensors by using tunable terahertz (THz) metamaterial (TTM) based on two concentric split-ring resonators (SRRs) with different splits. By modifying the distance between SRRs and substrate, TTM shows tunable single- and dual-resonance characteristic. The maximum tuning range of resonance is 0.432 THz from 0.958 THz to 1.390 THz. To demonstrate a great flexibility of TTM in real application, TTM device is exposed on the surrounding ambient with different refractive index (n). The sensitivity of TTM can be enhanced by increasing SRR height, which is increased from 0.18 THz/RIU to 1.12 THz/RIU under the condition of n = 1.1. These results provide a strategy to improve the sensing performance of the metamaterial-based sensing device by properly arranging the geometric position of meta-atoms. The proposed TTM device can be used for tunable filters, frequency-selective detectors, and tunable high-efficiency sensors in the THz frequency range.

A mutual coupled concentric crossed-Line split ring resonator (CCSRR) based epsilon negative (ENG) metamaterial for Tri-band microwave applications

A metamaterial design and its analysis based on an epsilon negative concentric crossed-line split ring resonator (CCSRR) have been presented in this paper. The CCSRR unit cell structure is the amendment of the typical concentric split ring resonator (CSRR). The inserted crossed line increases the electrical length of the presented CCSRR unit cell. The dimension of the proposed CCSRR unit cell is 10 × 10 × 1.575 mm3 and it is printed on the Rogers RT 5880 substrate material. The transmission frequency ranges from 6.33 GHz to 6.65 GHz, 10.42 GHz to 10.73 GHz, and 13.21 GHz to 13.42 GHz which covers the frequency bands of C, X, and Ku-band of microwave applications. A complete analysis of scattering parameters, effective medium parameters, mutual coupling effect as well as the unit cell characteristics with electromagnetic analysis have been performed in this study. The proposed CCSRR unit cell structure exhibits epsilon negative characteristics in the frequency ranges of 6.53 GHz to 6.96 GHz, 10.63 GHz to 10.91 GHz, and 13.37 GHz to 13.40 GHz. Experimental validation has also been performed by measuring the scattering parameters of the proposed CCSRR unit cell and its array structure. Furthermore, the capacitive coupling among the concentric split ring resonators within the 1 × 2 and 2 × 2 array structures have been studied which is based on the near field split gaps that lead to the fundamental inductive-capacitive resonances. Besides, the effective medium ratio 4.5 implies the effectiveness and compactness of the proposed CCSRR unit cell structure. The compactness, effective medium parameters, and effective medium ratio make the proposed CCSRR metamaterial appropriate for the microwave applications.

Quad-band linear terahertz frequency conversion in time-varying metasurfaces

In this Letter, a quad-band linear frequency conversion prototype is proposed and investigated in terahertz region based on a time-varying metasurface. The unit cell of the metasurface consists of four pairs of concentric split-ring resonators loaded with photoactive silicon. By changing the conductivity of photoactive silicon via optical pump, both static and time-varying metasurfaces are achieved and investigated. Numerical results show that the transmission spectrum of the static metasurface has four merged resonant frequencies at 0.49THz, 0.58THz, 0.71THz, 0.81THz respectively, and linear frequency conversion appears at these four frequencies under the modulation of time-varying metasurface. The conversion linearity is also verified by applying dual-band bandpass filters with different center frequency. The coefficients of determination are 0.98, 0.94, 0.87, 0.96 correspondingly. This prototype provides a new approach for realizing quad-band frequency conversion for ambient terahertz wave and has wide applications in terahertz imaging and communication systems.

Concentric Split-Ring Resonator Microwave Microplasma Generation at Off-Resonant Frequencies

The driving frequency of a microstrip concentric split-ring resonator (CSRR) was varied to determine how the generated microplasma changes as a function of frequency, specifically at off-resonant frequencies. The microplasmas were generated in argon at 1 torr, using a forward microwave power level of approximately 10 W. The resonant frequency was experimentally found to be 796 MHz, and measurements were obtained at this frequency and ±10 MHz from resonance. Double Langmuir probe measurements were performed on a 2-D grid, parallel to the surface of the device, to obtain plasma density and electron temperature maps. The results show multiple peaks in plasma properties due to electromagnetic coupling with the nested ring. The electron temperature above the primary discharge gap is 8.5 eV at 786 MHz, 9.5 eV at 796 MHz, and 7.6 eV at 806 MHz. A secondary discharge is also observed above the secondary nested ring gap, and the plasma in this region is generally of lower temperature. The off-resonant operation resulted in lower temperatures and densities, with larger decreases in the 806 MHz case. The electromagnetic response of the device was modeled to understand the electric field in the discharge gap. The modeling revealed that the electric field vectors at the bounds of the discharge gap point in the opposite directions for the 786 and 796 MHz cases, increasing the electric field in the gap, but these vectors point in the same direction for the 806 MHz case, decreasing the electric field.

Metamaterial nonlinear and polarization-dependent bi-frequency THz switch

In this work, we propose a novel metamaterial structure with two concentric split-ring resonators. The splits are filled by photoconductive Si. Illuminating the structure using an oblique optical pump with a wavelength of 800 nm, in addition to the normal THz signal wave, excites the structure by varying the Si conductivity. Also, by changing the direction of the incident TE wave by 90°, the transmission frequency is changed. Therefore, the structure operates as a switch at two different windows using two different methods. The response time of the photoconductive switch is less than 3 ps. The substrate was replaced by a more cost-effective and flexible material, polyimide, to achieve even more exciting results in broadening the switching windows. Also, the response time of this switch is less than 1 ps. Finally, for verification of the simulation results, a circuit model of the photoconductive switch is proposed, and the results comply very well with the simulation results. The proposed switch can be used in fast optical systems and networks.

Multi-band planar miniaturised negative-index metamaterials

In this paper, a miniaturised negative-index metamaterial (NIM) based on planar concentric split ring resonators was designed, simulated, fabricated and tested that can maintain NIM properties. The offered metamaterial structure showed miniaturisation factor compared with traditional metamaterial unit cells and conformed better effective medium ratio (EMR). Finite-difference time-domain method-based computer simulation technology for the numerical analyses and a vector network analyser (N5227A) was used for the measurements. The proposed metamaterial exhibited multi-band response in conjunction with the NIM property over the certain frequency bands in the microwave spectra and the EMR considerably improved compared to previously reported metamaterials. The measured results revealed good agreement with the simulated results. The distribution of surface current, electric field and equivalent circuit model were verified for the proposed structure. The size, scattering parameters and EMR parameters of the proposed miniaturised NIM is appropriate for multi-band applications.

Multiple band notch and Dual-Band filter using concentric and contiguous split ring resonators (CCSRR)

A novel, compact, multiple band notch filter and dual-band filters are presented. Contiguous and concentric split ring resonators (SRRs) and Ring resonator are used to achieve desired multiple narrow band notches. These band notches have been designed to avoid the undesired interference between co-existing wireless channels. The dual-band filter consists of a dual SRR having splits on the opposite sides with Inductive Short Stub Split Ring Resonator. Even- and odd-mode analyses have been performed to calculate the resonance frequencies. Three transmission zeros are achieved between the two passbands by both dominant electric or dominant magnetic coupling and also cancellation effect of electric and magnetic coupling. This results in high passband selectivity and improved band-to-band isolation. The proposed dual-band pass filter has the advantages of being compact with more degree of freedom to achieve desired passbands by controlling the electric and magnetic coupling independently. Proposed filter is implemented on RT/Duroid 5880 (εr = 2.2) substrate of thickness 0.785 mm and surface area of 0.27λg × 0.27λg. Insertion loss of the proposed filter at notch bands is high (>13 dB) and low (<0.8 dB) in pass band. Measured results correlate with the simulated results and thus ensure that the proposed filter is a suitable candidate to mitigate interference caused by the co-existing and emerging wireless technologies.

Tunable THz wave absorption by graphene-assisted plasmonic metasurfaces based on metallic split ring resonators

Graphene plasmonics has been introduced as a novel platform to design various nano- and microstructures to function in a wide range of spectrum from optical to THz frequencies. Herein, we propose a tunable plasmonic metamaterial in the THz regime by using metallic (silver) concentric microscale split ring resonator arrays on a multilayer metasurface composed of silica and silicon layers. We obtained an absorption percentage of 47.9% including two strong Fano resonant dips in THz regime for the purely plasmonic metamaterial without graphene layer. Considering the data of an atomic graphene sheet (with the thickness of ~0.35 nm) in both analytical and experimental regimes obtained by prior works, we employed a graphene layer under concentric split ring resonator arrays and above the multilayer metasurface to enhance the absorption ratio in THz bandwidth. Our numerical and analytical results proved that the presence of a thin graphene layer enhances the absorption coefficient of MM to 64.35%, at the highest peak in absorption profile that corresponds to the Fano dip position. We also have shown that changing the intrinsic characteristics of graphene sheet leads to shifts in the position of Fano dips and variations in the absorption efficiency. The maximum percentage of absorption (~67%) was obtained for graphene-based MM with graphene layer with dissipative loss factor of 1477 Ω. Employing the antisymmetric feature of the split ring resonators, the proposed graphene-based metamaterial with strong polarization dependency is highly sensitive to the polarization angle of the incident THz beam.

Spectroscopic Characteristics of Three Dimensional Split-Ring Resonator Arrays at Terahertz Frequencies.

In this work, three-dimensional, stacked arrays of subwavelength, square, dual, concentric split ring resonators exhibiting characteristics at the Terahertz frequencies have been designed, simulated, and fabricated through a photolithographic lift-off process and electron beam evaporation metal deposition. Characterization of the split-ring resonator arrays was performed by transmission mode Terahertz time domain spectroscopy. The effects of the split-ring resonator unit cell spatial dimensions on resonant absorption frequencies and relative absorption strength are investigated as well as effects from the addition of a dielectric spacing layer and additional split-ring resonator layer. The split-ring resonator arrays were seen to develop two distinct and switchable LC resonances as well as a dipole resonance by measuring the arrays at 0° and 90° in-plane rotations about the terahertz propagation vector. The dielectric spacing layer served to effectively lower the resonant frequencies of the split-ring resonantors while the dual split-ring resonator array was seen to have a slight modulating effect on the absorption strength at the resonant frequencies compared to that of the passivated array without the second layer.

Orthogonally twisted planar concentric split ring resonators towards strong near field coupled terahertz metamaterials

We present strongly coupled planar terahertz metamaterials in which the metamolecule design comprised two concentric split ring resonators (SRRs) with their capacitive gaps oriented orthogonally in order to establish strong near field coupling. Experimental results clearly demonstrate huge splitting in the fundamental inductive-capacitive resonance when the incident terahertz polarization couples to the metamolecule system through the outer SRR. However, the strengths of split resonances are too weak to detect experimentally when the meta-molecule system is excited through the inner SRR. Such strongly coupled metamolecules can enable additional dispersion tuning and polarization control in metamaterials.

Electrostatically Tunable Meta-Atoms Integrated With In Situ Fabricated MEMS Cantilever Beam Arrays

Two concentric split ring resonators (SRRs) or meta-atoms designed to have a resonant frequency of 14 GHz are integrated with microelectromechanical systems cantilever arrays to enable electrostatic tuning of the resonant frequency. The entire structure was fabricated monolithically to improve scalability and minimize losses from externally wire-bonded components. A cantilever array was fabricated in the gap of both the inner and outer SRRs and consisted of five evenly spaced beams with lengths ranging from 300 to 400 μm. The cantilevers pulled in between 15 and 24 V depending on the beam geometry. Each pulled-in beam increased the SRR gap capacitance resulting in an overall 1-GHz shift of the measured meta-atom resonant frequency.

SRRs Embedded with MEMS Cantilevers to Enable Electrostatic Tuning of the Resonant Frequency

A microelectromechanical systems (MEMS) cantilever array was monolithically fabricated in the gap region of a split ring resonator (SRR) to enable electrostatic tuning of the resonant frequency. The design consisted of two concentric SRRs each with a set of cantilevers extending across the split region. The cantilever array consisted of five beams that varied in length from 300 to 400 μm, with each beam adding about 2 pF to the capacitance as it actuated. The entire structure was fabricated monolithically to reduce its size and minimize losses from externally wire bonded components. The beams actuate one at a time, longest to shortest with an applied voltage ranging from 30–60 V. The MEMS embedded SRRs displayed dual resonant frequencies at 7.3 and 14.2 GHz or 8.4 and 13.5 GHz depending on the design details. As the beams on the inner SRR actuated the 14.2 GHz resonance displayed tuning, while the cantilevers on the outer SRR tuned the 8.4 GHz resonance. The 14.2 GHz resonant frequency shifts 1.6 GHz to 12.6 GHz as all the cantilevers pulled-in. Only the first two beams on the outer cantilever array pulled-in, tuning the resonant frequency 0.4 GHz from 8.4 to 8.0 GHz.

A Dual-Band Printed Electrically Small Antenna Covered by Two Capacitive Split-Ring Resonators

In this letter, we present a dual-band electrically small antenna (ESA) operating at 934 MHz and 1.55 GHz. The miniaturized radiation structure consists of a small ring and two concentric split-ring resonators on an FR-4 substrate. The resonant response of the proposed radiation structure is characterized by the coupling among two split-ring resonators and the small ring. A weak electric field interaction between two split-ring resonators is observed. This interaction provides an additional capacitance to further reduce the total dimension of the resonant electrical length. The calculated return loss of the proposed structure agrees well with the measured data. Measured radiation patterns are presented. The planar structure is promising for compact wireless devices and may find applications in wireless electrocardiograph sensors, multiband portable MIMO wireless systems, and RF energy-harvesting systems.

Properties of left-handed metamaterials: transmission, backward phase, negative refraction, and focusing

Four properties related to left-handed metamaterials are studied numerically: transmission within a stop-band, backward phase, negative refraction, and partial focusing. The unit cell of the metamaterial under study is composed of a rod and a ring originally proposed at infrared frequencies and redesigned here at microwave frequencies. We show that this ring, because of its symmetry, exhibits a better transmission in a parallel-plate waveguide than the original concentric split-ring resonator. Negative refraction is studied from a prism-shaped metamaterial, while all of the other properties are studied from a slab-shaped metamaterial. In particular, transmission and backward phase are studied on a slab where rings naturally couple with the incident wave, while partial focusing is studied on a slab of rings perpendicular to the direction of propagation. The numerical simulations are based on a two-dimensional periodic method of moments, whose Green's function is computed via Ewald's method, and a three-dimensional finite-difference time-domain technique.