Split-ring Arrays Research Articles

Quasi-bound state in the continuum in a dielectric double-gap split-ring metasurface structure with large split angles

It was reported previously that the quality factor of a symmetry-protected quasi-BIC mode increases as the degree of structure asymmetry is reduced. In this work, we propose and investigate an alternative approach to increase the quality factor of a quasi-BIC mode without reducing the degree of asymmetry. Specifically, we calculate the quality factor of the quasi-BIC mode of a double-gap dielectric split-ring metasurface for different split angles. It is found that the quality factor increases exponentially with the increase of the split angles while the degree of asymmetry of the structure is constant. To explain the phenomena, multipole moment decomposition of the local electromagnetic field is conducted to calculate the change of major multipole moments versus the split angles. It is revealed that the double-gap split-ring array structure stores more energy in the higher order multipoles, and the rate of radiation energy loss stays constant when the two splitting angles increase simultaneously. Additionally, the enhancement of third harmonic generation is investigated in the double-gap split-ring metasurface structure.

Design of Circularly Polarized Microstrip Antenna with slotted Split ring array for Video Surveillance Applications at C-Band

Design of Circularly Polarized Microstrip Antenna with slotted Split ring array for Video Surveillance Applications at C-Band

Split Ring Antennas and Their Application for Antenna Miniaturization

This paper investigates the miniaturization capability of split ring array antennas embedded in a low-permittivity dielectric substrate, in comparison with the same-sized high-permittivity dielectric resonator antennas (DRAs). In order to understand the miniaturization performance, a size-fixed dielectric substrate with different split ring arrays is studied. The simulation results show that the miniaturization capability increases with decreased unit cell resonant frequency and/or increased unit cell induced permeability. Miniaturizations as high as 25.54 times that of a high-permittivity DRA are obtained with split rings, etched on a dielectric substrate having a low permittivity of 2.2. Furthermore, this excessive miniaturization does not come at the expense of excessive deterioration of the antenna impedance bandwidth, gain, and radiation efficiency. Consequently, the miniaturized split ring arrays still provide high gains over wider bandwidths. This inference is further verified by comparing the miniaturization and other antenna performance parameters with three other modified split ring configurations. To experimentally verify this work, a split ring antenna was fabricated and tested, and good agreement between the simulated and measured results was observed. The results of this study indicate that adding resonant metallic inclusions into low- permittivity DRAs significantly increases their miniaturization capability, without overly deteriorating the performance.

Terahertz Resonators Based on YBa2Cu3O7 High-Tc Superconductor

Superconducting split-ring resonator arrays allow to overcome two main limitations affecting metallic metamaterial resonating in the terahertz (THz) range: ohmic losses and tunability of their optical response. In this work, we design and experimentally realize direct and complementary square arrays of superconducting YBa2Cu3O7 (YBCO) split-ring resonators working in the THz spectral range. The main purpose of this paper is to show how the metamaterial resonances can be tuned by temperature (T) when crossing the superconducting transition temperature Tc of YBCO. The tuning property can be quantified by describing the THz transmittance of the patterned YBCO films vs. T through a model of coupled resonators. This model allows us to estimate the THz resonances of split-ring arrays and their interaction, showing how the kinetic inductance Lk in the superconducting state is the main parameter affecting the metamaterial properties.

Multispectral higher-order Fano resonant metasurface based on periodic twisted DNA-like split ring arrays with three modulation methods.

The active modulation of the Fano resonance is rare but desirable. However, recent studies mostly focused on a single modulation method and few reported the use of three photoelectric control methods. A tunable graphene DNA-like metamaterial modulator with multispectral Fano resonance is demonstrated. In experimentally fabricated metamaterials with six photoelectric joint modulation patterns, each joint shows different optoelectrical response characteristics. Ultrahigh modulation depth (MD) up to 982% was achieved at 1.5734 THz with a 1.040 A external laser pump by involving combined optoelectrical methods. These results show that the metasurface modulator is a promising platform for higher-order Fano resonance modulation and communication fields.

Comparison of second harmonic generation from cross-polarized double-resonant metasurfaces on single crystals of Au

Abstract Second harmonic generation (SHG) from metasurfaces consisting of square array of split ring, heptagon and triangle cross-polarized double resonant resonators, is investigated both experimentally and numerically. The structures are fabricated on single crystalline Au plates using Focused Ion Beam technique. Array of the triangular structure exhibits most efficient SHG. Experimental observation is explained reasonably well by theoretical evaluation of SHG using the overlapping integral of nonlinear polarization and the microscopic field distribution on the metal surface at the SHG frequency taking phase relation between the two fields into account.

Quad-band plasmonic perfect absorber using all-metal nanostructure metasurface for refractive index sensing

A quad-band plasmonic perfect absorber (PPA) based on all-metal nanostructure metasurface in infrared regime has been proposed and investigated numerically, which could be applicable for refractive index (RI) sensing. The proposed PPA is made of all-metal nanostructure with an assembly array of vertical split-ring and multiple cylinders. The proposed PPA can achieve the absorbance of 99.34 %, 99.87 %, 99.85 %, and 99.85 % at 86.05 THz, 239.35 THz, 297.45 THz, and 344.35 THz, respectively. In addition, the quality-factor (Q-factor) of the PPA is about 9.6, 23.9, 40.7, and 74.1, respectively. The quad-band perfect absorptions are mainly originated from the hybrid modes between the surface plasmonic resonances (SPRs) and guided modes (GMs). Due to its higher Q-factor, it is believed that the proposed PPA could be served as a RI sensor. As a proof, a designed PPA based sensor has been demonstrated a high sensitivity of about 4367, 2162, 1059, and 908 nm/refractive index unit (RIU), respectively. Relying on its excellent performance, the proposed quad-band PPA could be found potential applications in the sensing, detecting and infrared spectroscopy.

A complementary split‐ring array for compact decoupling 2 × 2 circularly polarized antenna

AbstractIn this letter, a complementary split‐ring array (CSRA) for decoupling compact (edge‐to‐edge spacing of 0.078 λ0) 2 × 2 circularly polarized (CP) microstrip antenna is proposed. The CSRA is the ground plane with the etched split‐ring array (SRA) which is composed of 12 split‐rings. Each element is surrounded by four etched split‐rings, and the two adjacent elements share the same etched split‐ring between them. The decoupling mechanism of the CSRA is to alter the amplitude and phase of the original coupling field and make the polarization of the adjusted coupling field mismatch with the receiving field. To verify the idea, the 2 × 2 CP antennas with and without CSRA are simulated and measured. The experimental results show that the maximum mutual coupling reduction is 29.6 dB for S12, 23.6 dB for S14, and 5.6 dB for S13. Meanwhile, the impedance bandwidth and radiation characteristics remain almost unchanged. The measured results agree well with the simulated results, which showed new light on application of the proposed CSRA for multiple‐input‐multiple‐output systems.

Band-stop filter design based on split ring resonators loaded on the microstrip transmission line for GSM-900 and 2.4 GHz ISM band

Split-ring resonator is a popular research topic in literature. As known, it may be used in the design of electromagnetic metamaterials. Additionally, these structures can be preferred in microwave filter devices. In this study, a band-stop filter was designed for GSM-900 and 2.4 GHz ISM band by using split-ring resonators. Two split-ring arrays (sizes of one of these arrays were larger than the other) were loaded on the transmission line and each array consisted of four identical rings. Thus, a dual-band pass filter was obtained and this filter covered the frequency of 0.91 (GSM) and 2.43 (ISM) GHz. Then, this proposed design was fabricated and measured. According to the measurement results, the fabricated structure operated at 0.93 GHz and 2.47. The experimental results were consistent with the simulation results. As a result, thanks to the proposed structure, two frequencies can be stopped at the same time. There is no need to design a different filter structure for each frequency.

High quality factor fractal inductor with complementary split-ring array inclusion

PurposeThis paper aims to present an efficient method to improve quality factor of printed fractal inductors based on electromagnetic band-gap (EBG) surface.Design/methodology/approachHilbert fractal inductor is designed and simulated using high-frequency structural simulator. To improve the quality factor, an EBG surface underneath the inductor is incorporated without any degradation in inductance value.FindingsThe proposed inductor and Q factor are measured based on well-known three-dimensional simulator, and the results are compared experimentally.Practical implicationsThe proposed method was able to significantly decrease the noise with increase in the speed of radio frequency and sensor-integrated circuit design.Originality/valueFractal inductor is designed and simulated with and without EBG surfaces. The measurement of printed circuit board prototypes demonstrates that the inclusion of split-ring array as EBG surface increases the quality factor by 90 per cent over standard fractal inductor of the same dimensions with a small degradation in inductance value and is capable of operating up to 2.4 GHz frequency range.

Triple-band perfect metamaterial absorber with good operating angle polarization tolerance based on split ring arrays

In this paper, a triple-band perfect metamaterial absorber based on Cu-dielectric-Cu triple-layer nanostructure is reported. The top metal film structure consists of a ring and four pairs of capacitor plates, which has a frequency selection effect, allowing the absorber to resonate in the near infrared range. Theoretical study shows that the absorption of the three absorption peaks (872.54 nm, 1008.69 nm and 1138.62 nm) are 87.1%, 99.9% and 99.6%, respectively. The average absorption is 95.53%, including two perfect absorption peaks. Changing the structural parameters can affect its absorption peaks and resonant wavelengths. At the same time, due to the high symmetry of the absorber, it is not sensitive to the polarization angle and incident angle. Whether in the TE mode or the TM mode, the absorber at a wide incident angle (0-60°) also exhibits good operating angle polarization tolerance. Therefore, the perfect metamaterial absorber we designed can be widely used in sensing.

Tunable circular conversion dichroism and asymmetric transmission of terahertz graphene metasurface composed of split rings

The asymmetric transmission (AT) has attracted wide attention due to its novel applications. In this paper, we propose and investigate a tunable polarization-dependent intrinsically chiral graphene metasurface composed of split ring arrays in terahertz (THz) region. The resonance frequency of the structure is sensitive to the graphene chemical potential. Circular conversion dichroism (CCD) of the proposed structure is tunable and is reached to 0.36. Our work paths a new approach to propose some other compact and on-chip polarization-dependent structures in THz region. Furthermore, our proposed structure could be a useful segment in polarization-dependent systems.

Plasmon excitation of gold split-ring array: spectral studies and numerical simulation

Strongly focused femtosecond laser pulses at a wavelength of 515 nm were used for the single-pulse ablative nano-texturing of a 50 nm thick gold film using a diffractive optical element, which enables the production of nanoelements in the form of a U-split-ring. The optical properties of such U-shaped split-ring arrays and their optimal conditions for the near-field enhancement, depending on the shape and size of the individual element, were investigated using optical microspectroscopy and numerical simulations.

High-sensitivity and label-free identification of a transgenic genome using a terahertz meta-biosensor.

A high-sensitivity and label-free method for identifying a transgenic plant genome is highly desirable in plant biotechnology. Here, we present a terahertz (THz) metamaterial (MM)-based biosensor that comprises a planar array of gold split-ring (SR) resonators capable of sensing a considerable shift in the resonance frequency due to the change of the dielectric environment on the MM chip. The meta-sensor is employed to detect transgenic tomato genome DNAs by THz time-domain spectroscopy. The experimental results were confirmed by finite-element modeling through varying the thickness and dielectric constant of the DNA overlayer. Consequently, high-efficiency and label-free discrimination between the wild-type and transgenic genome DNA was achieved.

Experimental Study of Transmission and Reflection Characteristics of a Gradient Array of Metamaterial Split-Ring Resonators

A study of a nonuniform metamaterial array consisting of six split-ring resonators of varying diameters is conducted experimentally to measure the transmission and reflection characteristics that arise from asymmetry in the longitudinal direction. Such characteristics are examined and compared with their counterpart symmetric scattering coefficients associated with a uniform split-ring array. In the nonuniform array the ring diameters vary in steps of 0.5 mm, which yields a gradient geometry. Inserting the nonuniform array in an X-band waveguide operating below cutoff provides a transmission band wider than that obtained from the uniform array.Â

Lithographically Patterned Nanoscale Electrodeposition of Plasmonic, Bimetallic, Semiconductor, Magnetic, and Polymer Nanoring Arrays.

Large area arrays of magnetic, semiconducting, and insulating nanorings were created by coupling colloidal lithography with nanoscale electrodeposition. This versatile nanoscale fabrication process allows for the independent tuning of the spacing, diameter, and width of the nanorings with typical values of 1.0 μm, 750 nm, and 100 nm, respectively, and was used to form nanorings from a host of materials: Ni, Co, bimetallic Ni/Au, CdSe, and polydopamine. These nanoring arrays have potential applications in memory storage, optical materials, and biosensing. A modified version of this nanoscale electrodeposition process was also used to create arrays of split gold nanorings. The size of the split nanoring opening was controlled by the angle of photoresist exposure during the fabrication process and could be varied from 50% down to 10% of the ring circumference. The large area (cm2 scale) gold split nanoring array surfaces exhibited strong polarization-dependent plasmonic absorption bands for wavelengths from 1 to 5 μm. Plasmonic nanoscale split ring arrays are potentially useful as tunable dichroic materials throughout the infrared and near-infrared spectral regions.

Ubiquity of Optical Activity in Planar Metamaterial Scatterers

Recently it was discovered that periodic lattices of metamaterial scatterers show optical activity, even if the scatterers or lattice show no 2D or 3D chirality, if the illumination breaks symmetry. We demonstrate that such "pseudochirality" is intrinsic to any single planar metamaterial scatterer and in fact has a well-defined value at a universal bound. We argue that in any circuit model, a nonzero electric and magnetic polarizability derived from a single resonance automatically imply strong bi-anisotropy, i.e., magnetoelectric cross polarizability at the universal bound set by energy conservation. We confirm our claim by extracting polarizability tensors and cross sections for handed excitation from transmission measurements on near-infrared split ring arrays, and electrodynamic simulations for diverse metamaterial scatterers.

Fabrication of split-ring resonators by tilted nanoimprint lithography

An efficient fabrication technique for large area periodic metallic split-ring arrays has been demonstrated by the combination of tilted nanoimprint lithography and nanotransfer imprinting. The feature size of the split-rings can be adjusted by varying the key geometry parameters of the original imprinting mold. Due to the flexible nature of PDMS molds, these arrays can be patterned on curved surfaces. The molds for nanoimprint lithography and nanotransfer imprinting can be used multiple times without a loss of fidelity.

Tunable plasmonic properties and giant field enhancement in asymmetric double split ring arrays

Localized surface plasmon resonances (LSPRs) and field enhancement in asymmetric double split rings (ADSRs) are numerically investigated. It is found that either two or three resonances can be excited in the visible and near infrared regions depending on the degree of asymmetry. While the fundamental resonance is from a dipole–dipole bonding mode, the second/third resonances originate from a dipole–dipole/dipole–quadrupole anti-bonding and a dipole–quadrupole/dipole–hexapole bonding at lower and higher degrees of asymmetry, respectively. The different physical origins of these resonances at different asymmetries make them different frequency tunability and field distribution characters. The dipole–multipole bonding resonances in the two arcs are shown to give rise to larger field enhancements and more hotspots than the anti-bonding ones in the gap regions. By exciting the bonding modes at the second or third resonances, intense field with an enhancement factor of more than 10 2–10 3 can be achieved at hotspots, implying a Raman enhancement factor of over 10 8. The results indicate that the array of ADSRs is very promising for applications as highly reproducible surface enhanced Raman scattering substrates.

Fabrication and tuning of nanoscale metallic ring and split-ring arrays

Metallic structures with dimensions smaller than the wavelength of light demonstrate optical properties which depend strongly on the nanoparticle size, shape, and interparticle spacing. The optical properties are caused by the excitation of localized surface plasmon resonances that lead to strong enhancement and confinement of the optical field and can be exploited for many applications including surface-enhanced Raman spectroscopy, near-field scanning optical microscopy, and negative refractive index materials. In order to fully exploit the properties of these structures, both a highly reproducible and flexible fabrication technique and an in-depth understanding of the optical properties are needed. In this article, the authors demonstrate the fabrication of arrays of gold rings and split rings on glass using electron beam lithography. Electron beam lithography allows not only precise control of the size, shape, and spacing of the arrays but also the scope to design novel shapes at will. We characterize these arrays using polarization dependent spectroscopy. The structures can support multiple plasmon resonances, demonstrating that excellent uniformity across the array is achieved. These resonances are further characterized using a finite difference time domain method to model the electric field distribution around the ring structures.