Planar Split Ring Resonators Research Articles

A split-ring resonator full/sparse planar array based on Chebyshev polynomial

A planar split-ring resonator (SRR) antenna full/sparse array, fed by a Chebyshev distribution, is proposed in this paper. Following the Yagi principle, the antenna element consists of SRRs and an I-shaped resonator. The inclusion of the I-shaped resonator enhances coupling, resulting in high gain. Additionally, a 14 × 13 Chebyshev planar antenna array, based on corporate feed, allows for a non-uniform amplitude distribution to suppress side lobes. The proposed Chebyshev planar array exhibits high gain characteristics and low side lobe levels (SLL) in both the E- and H-planes. For sidelobes suppression further, by utilizing a genetic algorithm, a planar sparse array is constructed based on the proposed Chebyshev array. The measured gain of the array at 10.1 GHz is 22.4 dBi, with SLL values of −20.4 dB and −17.5 dB in the E- and H-planes, respectively. These results meet the requirements for wireless communication.

A Microwave Voyage into Swelling Phenomenon: Investigation of Polydimethylsiloxane and VOCs Interaction.

When exposed to specific gases, polymers undergo swelling, leading to physiochemical changes that can significantly affect their performance. Monitoring this swelling phenomenon requires innovative approaches. This study focuses on investigating the real-time resonant microwave behavior of two polydimethylsiloxane (PDMS) structures (solid and porous) in interaction with tetrahydrofuran (THF) and acetone, which are primary swelling agents. A microwave measurement method is proposed using an 8.63 GHz planar split ring resonator (SRR). The device's resonant frequency downshifts to 7.75 and 8.42 GHz when solid and porous PDMS blocks are placed on the split ring gap. Interaction of the solid PDMS and porous PDMS with target gases caused a change in PDMS structure resulting in alterations in the dielectric properties of the PDMS/gas system, as evidenced by the resonator's transmission amplitude and resonant frequency shifts. The magnitude of these shifts depends on the type and concentration of the solvent gas. The PDMS-integrated SRR exhibits a sensitivity of 25.3 MHz/1 ppt THF and 7 MHz/1 ppt acetone. Additionally, the solid block demonstrates response times of 6800 and 4200 s for swelling and deswelling, respectively, when in exposure to 25 ppt concentrations of THF and acetone. Overall, this study underscores the substantial potential of microwave resonators as versatile tools for investigating the physical changes in polymers during their interaction with gases, contributing to the understanding of polymer-gas interactions and opening avenues for further research and diverse applications.

Enhancement of the microwave photon-magnon coupling strength for a planar fabricated resonator

Planar resonators have a wide usage in modern microwave technologies and perspectives in novel quantum technologies development. As was demonstrated earlier, their utilization allows to achieve high values of microwave photon-magnon coupling strength—an important parameter in technologies of information coherent transfer from electromagnetic GHz range to the optical range. In the present work, the achievement of the high value of the microwave photon-magnon coupling strength by exploiting the increase of the spatial concentration of the magnetic component of the planar resonator electromagnetic field is reported. Starting from the conventional planar split-ring resonator design we increased the coupling strength up to 40% by modifying the resonator shape. The numerical simulation and experimental verification showed a predicted increase in the spatial concentration of the microwave magnetic component and showed the increased value of the microwave photon-magnon coupling strength as a sequence.

Miniaturization and performance enhancement of super wide band four element MIMO antenna using DNG metamaterial for THz applications

A compact semi-hexagonal-shaped MIMO antenna loaded with a planar SRR (split-ring resonator) structure is presented for Terahertz applications. The single radiating element consists of a semi-hexagonal shape metallic patch loaded with SRR-CC (Split ring Resonator-Connected C shape) metamaterial unit cell to enhance the impedance bandwidth as well as gain of the proposed antenna. The proposed antenna element can be easily extended into two-port and four-port MIMO antenna configurations. Four radiating elements of the proposed antenna are printed on 122.4*122.4 μm2 quartz substrate having a thickness of 10 μm. The radiating elements are placed orthogonally to achieve high isolation and miniaturization in the MIMO system. The proposed antenna exhibits super-wide impedance bandwidth (S11 ≤ − 10 dB) in the range of 0.9–10.1 THz (with fractional bandwidth of 168% at f0 = 5.5 THz) while isolation of antenna is more than 20 dB in the whole operating band. The peak gain of the antenna is 7.51 dBi with more than 95% radiation efficiency in the entire band. The stable radiation pattern, high gain, high radiation efficiency, and good diversity performance of the proposed antenna make it suitable for many THz applications such as breast cancer detection, sugar measurement, drug detection.

Magnetic excitation of high-Q resonance with split-ring resonators

Planar split-ring resonators (SRRs) with broken symmetry, excited by the electric field of incident wave, have been widely used to realize the high-Q resonance. In this paper, we report by theory and experiment an alternative scheme to induce the SRR-based high-Q resonance. The proposed scheme utilizes a two-dimensional array of vertical SRRs with vertical air gaps, which enables the excitation of narrow resonance with magnetic field and strong enhancement of local electromagnetic fields. The working mechanism correlates with the strong directional dependence of the dipole radiation (i.e., the elimination of electric-dipole radiation of the SRRs in the propagation direction), rather than the destructive interference due to the structural symmetry breaking. The dependence of Q factor on the structural parameters has also been studied theoretically, suggesting that a Q factor more than 2000 can be achieved. The results may be useful for designing narrow-band filters and sensors in the microwave or THz regime.

3-Dimensional Anisotropic Split Resonant Cavity

An innovative 3-Dimensional split resonant cavity (SRC) is introduced here as an enhancement of planar split-ring resonators (SRRs), which could overcome the strong dependence of SRRs on polarization. Numerical simulations demonstrate that multiple resonances, including electric dipole mode, magnetic dipole mode and interaction of both modes, can be excited by three different polarized incident electromagnetic (EM) waves. Fano resonance characterized by asymmetric transmission line shape due to interference of multiple modes is observed in the simulation.

Three-Dimensional Split-Ring Resonators-Based Sensors for Fluid Detection

This paper presents a sensitive microwave near-field sensor based on utilizing a three-dimensional capacitor within a planar split-ring resonator. The planar resonator is etched in the ground plane of a microstrip line, where the resonator's length is relatively smaller than the guided wavelength. The sensor was fabricated utilizing PCB technology and used to detect the presence of dielectric fluids. The numerical analysis shows that the three-dimensional capacitor significantly enhances the electric field in the sensing area (free space) leading to an increase in the sensitivity. The electric field enhancement was quantitatively investigated using numerical analysis. The analysis shows that a loaded-quality factor of 1556 can be achieved using a three-dimensional capacitor with a length of 29 mm, which is significantly higher than what can be achieved by using planar resonators working in the same range of frequency. In addition, the utilization of the high-dielectric substrate can enhance coupling to the resonator. The proposed sensor was experimentally tested on two fluids, chloroform and dichloromethane with the relative permittivity of 4.81 and 8.93, respectively. The proposed sensor shows higher sensitivity of 700% and 374.5% in detecting the presence of chloroform and dichloromethane, respectively. Furthermore, the proposed sensor was utilized to detect the changes in fluid levels.

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.

Ultrafast polarization-dependent all-optical switching of germanium-based metaphotonic devices

Metamaterials play an important role in the modulation of amplitude and group delay in the terahertz (THz) regime on account of their optical properties, which are rare in natural materials. Here an ultrafast anisotropic switch of the plasmon-induced transparency (PIT) effect is experimentally and numerically demonstrated by metamaterial devices composed of two pairs of planar split-ring resonators and a pair of closed-ring resonators. By integration with a germanium (Ge) film, a recovery time of 3 ps and a decay constant of 785 fs are realized in the metadevice. Stimulated by the exterior optical pump, the PIT windows at different frequencies are switched off with an excellent property of slow light for vertical and horizontal THz polarizations, realizing an astonishing modulation depth as high as 99.06%. This work provides a new platform for ultrafast anisotropic metadevices tunable for amplitude and group delay.

A Label-Free, Non-Intrusive, and Rapid Monitoring of Bacterial Growth on Solid Medium Using Microwave Biosensor.

Microwave resonator sensors are attractive for their contactless and label-free capability of monitoring bacterial growth in liquid media. This paper outlines a new label-free microwave biosensor based on a pair of planar split ring resonators for non-invasive monitoring of bacterial growth on a solid agar media. The sensor is comprised of two split ring resonators with slightly different resonant frequencies for differential operation. The transmission coefficient (S21) of the sensor is considered as the sensor's response with a designed and measured quality factor above 200 to ensure a high-resolution operation of the biosensor. Two resonant frequencies of 1.95 and 2.11 GHz represent the sensing signal and the reference signal, respectively. The developed sensor demonstrates high performance in monitoring the growth dynamics of Escherichia coli (E. coli) on Luria-Bertani (LB) agar with 4 mm thickness. The sensor's resonant amplitude response demonstrated 0.5 dB variation corresponding to the bacterial growth over 48 hours when bacteria were spread on LB agar starting with initial OD600 = 1.5. Moreover, 0.6 dB change in the sensor's response was observed over 96 hours of bacterial growth starting with an initial OD600 = 1.17 spotted on LB agar. The measured results fit well to the curves created using Richards' bacterial growth model, showing the strength of the sensor as a potential candidate for use in predictive food microbiology systems.

Ultra-thin subwavelength film sensing through the excitation of dark modes in THz metasurfaces

We demonstrate ultra-subwavelength thin film sensing through experimental and numerical studies of the transmission characteristics of several symmetric and asymmetric planar split ring resonator (SRR) based terahertz metasurfaces coated with thin film of analyte layer(s). A sharp narrow-band dark mode resonance excited in the asymmetric metasurfaces is seen to be particularly very interesting to be exploited in thin film sensing, which is otherwise absent in the symmetric case. For this mode, our experiments clearly have demonstrated sensing of extreme subwavelength (close to thousandth part of the wavelength) thickness film. With the increasing thickness of the analyte layer a gradual red-shift of the resonance mode is observed. The sensitivities and figure of merit (FoM) of all the metasurfaces are derived and compared. The resonant dark modes in asymmetric metasurfaces are found to display substantially better FoM as compared to the typical dipolar modes.

Enhancing Absorption Bandwidth through Vertically Oriented Metamaterials

Metamaterials research has developed perfect absorbers from microwave to optical frequencies, mainly featuring planar metamaterials, also referred to as metasurfaces. In this study, we investigated vertically oriented metamaterials, which make use of the entire three-dimensional space, as a new avenue to widen the spectral absorption band in the infrared regime between 20 and 40 THz. Vertically oriented metamaterials, such as those simulated in this work, can be experimentally realized through membrane projection lithography, which allows a single unit cell to be decorated with multiple resonators by exploiting the vertical dimension. In particular, we analyzed the cases of a unit cell containing a single vertical split-ring resonator (VSRR), a single planar split-ring resonator (PSRR), and both a VSRR and PSRR to explore intra-cell coupling between resonators. We show that the additional degrees of freedom enabled by placing multiple resonators in a unit cell lead to novel ways of achieving omnidirectional super absorption. Our results provide an innovative approach for controlling and designing engineered nanostructures.

Second Harmonic Light Manipulation with Vertical Split Ring Resonators.

The second harmonic generation (SHG) of vertical and planar split-ring resonators (SRRs) that are broken centro-symmetry configurations at the interface of metal surface and air is investigated. Strong interactions, better electromagnetic field confinements, and less leakage into the substrate for vertical SRRs are found. Experimental results show a 2.6-fold enhancement of SHG nonlinearity, which is in good agreement with simulations and calculations. Demonstrations of 3D metastructures and vertical SRRs with strong SHG nonlinearity majorly result from magnetic dipole and electric quadrupole clearly provides potential applications for photonics and sensing.

Dual Active Resonator for Dispersion Coefficient Measurement of Asphaltene Nano-Particles

Dispersion and diffusion of Asphaltene particles in n-Heptane is measured to investigate the solution characteristics of different concentrations in wide range of 0.000625-0.625 (%wt). Planar split ring resonator (SRR) is armed with active circuitry (active resonator) to enhance the quality factor over 3 K to achieve ultra-high resolution sensing and track minute variations in microfluidic tube. Parallel SRRs as dual active resonator are performing independently, both in sensing and resolution, at 1.03 GHz (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ) and 1.149 GHz (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ) as the sensing tool in non-contact mode to monitor the spread of model oil (short pulse) in n-Heptane (continuous flow). With the frequency shifts (Δf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , Δf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ), average flow rate, and the inner diameter of the tube, the molecular diffusion coefficient, and then the dispersion coefficient can be rapidly derived according to two-window solution of Taylor-Aris dispersion analysis. Samples with higher concentration of Asphaltene are shown to have faster spread and larger dispersion in the flow. Dispersion coefficients of the samples cover the range of 5.2-7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /s in great agreement with conventional methods.

Enhancement of higher-order plasmonic modes in a dense array of split-ring resonators.

It is demonstrated that higher-order plasmonic modes in the split-ring resonators (SRRs) are strongly enhanced when SRRs are arranged in a densely spaced two-dimensional array. The mode enhancement results from the near-field electrical coupling between the adjacent resonators. The effect is most pronounced in narrow gap SRRs which allows to observe experimentally plasmon modes up to the seventh order. In the array of narrow gap SRRs, the fifth-order resonance demonstrates high Q-factor, high resonance strength and wide tunability which opens up attractive features for practical applications of planar SRR structures.

Coupled Split-Ring Resonator Circular Polarization Selective Surface

A novel class of circular polarization selective surfaces (CPSSs) consisting of a pair of planar split-ring resonator arrays is proposed. A significant advantage of the proposed structure over existing designs is its manufacturing simplicity compatible with standard printed technology processes. Its operating principle is reviewed alongside that of the Pierrot cell and in light of the linear polarization reflection and transmission characteristics of CPSSs. Guidelines for the initial design of the proposed CPSS concept are thus derived. Further design considerations and tradeoffs are also discussed. The validity of the concept is confirmed by means of a design example entailing a right-hand CPSS at 20 GHz. Full-wave simulation results and experimental testing on a fabricated prototype are presented and agree well with the theoretical predictions.

Vertical Split Ring Resonator Using Vias With Wide Bandwidth and Small Electrical Size

In this letter, we propose a vertically inserted split ring resonator (SRR) in microstrip lines. Since the top and bottom layers of the resonator are electrically connected by using via holes and it has a 3-D shape, it occupies a small electrical size. Through numerical simulations and measurement, it is shown that it can provide a wider range variation of bandwidth than conventional planar SRRs and the resonant frequency and the bandwidth can be adjusted by its length and width, respectively.

Vertical split-ring resonator based nanoplasmonic sensor

Split-ring resonators (SRRs) have been the subject of investigation as plasmonic sensors that operate by sensing plasmon resonance shift δλ when exposed to a medium with a refractive index change δn. However, conventional planar SRRs have their plasmon fields spread into the substrates, reducing accessible sensing volume and its sensing performance. Such a limitation can be eradicated with vertical SRRs in which the plasmon fields localized in SRR gaps are lifted off from the substrate, allowing for greatly enhanced sensitivity. Here, we demonstrate the highest sensitivity among reported SRR-based sensors in optical frequencies.

Effects of oblique incidence on terahertz responses of planar split-ring resonators

Effects of oblique incidence of terahertz waves on the response of planar split-ring resonators are investigated, both experimentally and by simulation. It is found that the incident angle dependent phase delay and coupling conditions of neighboring split-ring resonator (SRR) units play important roles and greatly change both the transmission and reflection spectra for the resonant feature of linear charge oscillations. Our results show that the SRR structure-supported magnetoelectric couplings at oblique excitation are trivial and can be ignored. A highly symmetric response is found in the cross-polarization effects, which may manifest the bianisotropic properties of the SRR system but this needs further study.

THz near-field Faraday imaging in hybrid metamaterials

We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal. Normally incident terahertz radiation couples to the resonator inducing a magnetic dipole oscillating perpendicular to the crystal surface. Faraday rotation of the polarisation of a near-infrared probe beam directly measures the magnetic near-field with 100 femtosecond temporal resolution and (λ/200) spatial resolution. Numerical simulations suggest that the magnetic field can be enhanced in the plane of the resonator by as much as a factor of 200 compared to the incident field strength. Our results provide a route towards hybrid devices for dynamic magneto-active control of light such as isolators, and highlight the utility of split ring resonators as compact probes of magnetic phenomena in condensed matter.