C-shaped Split Ring Resonator Research Articles

Recent Advances in Terahertz Manipulations Using C‐Shape‐Split‐Ring‐Resonator Metasurfaces (Review)

AbstractMetasurfaces have garnered significant interest owing to their inherent advantages over traditional optical components in manipulating electromagnetic waves unconventionally. Among the fundamental building blocks of metasurfaces, C‐shaped‐split‐ring resonators (CSRRs) have emerged as a highly promising option, enabling strong resonances and precise control over various characteristics of electromagnetic waves, such as phase, amplitude, and polarization. This review aims to showcase recent advancements in CSRR metasurfaces for manipulating THz waves, particularly focusing on both passive and active methods employed for controlling THz waves using single‐layer and multi‐layer CSRR metasurfaces. Moreover, this review will provide valuable insights into potential research directions in this rapidly evolving field.

A conformal beam splitter with polarization transformation operation

A multifunctional beam splitting frequency selective surface (FSS) is modeled, analyzed, and tested in transmission and reflection modes. The proposed FSS comprises a C-shaped split-ring resonator designed and fabricated on an ultrathin, flexible polyimide material. When a linearly polarized incident wave interacts with the unit cell of the proposed FSS, half of the wave is reflected, and the other half is transmitted at two frequency bands from 5.8–6.2 GHz and 18.5–22 GHz. Moreover, the proposed FSS is angularly stable upto 40° and also performs simultaneous beam splitting and quarter-wave operation within one of its two bands of operation i.e., from 16.5–18.2 GHz. Such flexible beam splitting FSSs with polarization transformation operation and having angular stability, size miniaturization and multi-band operation is a specialized component having potential to be used for electromagnetic wave manipulation in antenna systems, radar technology, stealth technology, wireless communication, satellite communication, medical imaging, security and surveillance, aerospace and defense, and automotive radar.

A Metasurface-Based LTC Polarization Converter with S-Shaped Split Ring Resonator Structure for Flexible Applications.

This paper presents a metasurface-based linear-to-circular polarization converter with a flexible structure for conformal and wearable applications. The converter consists of nested S- and C-shaped split ring resonators in the unit cell and can convert linearly polarized incident waves into left-handed circularly polarized ones at 12.4 GHz. Simulation results show that the proposed design has a high polarization conversion rate and efficiency at the operating frequency. Conformal tests are also conducted to evaluate the performance under curvature circumstances. A minor shift in the operating frequency is observed when the converter is applied on a sinusoidal wavy surface.

Methodology and Implementation of Beam Steering Using C-Shaped Split Rings for Fabry–Perot Antennas

The design process of beam-steering partially reflective surface (PRS) made up of C-shaped split-ring resonators (CSRRs) is presented in this article. Through analyzing the transmission characteristics of CSRRs with variable opening angles and orientations, spatially abrupt phase and magnitude are introduced over PRS to reshape the wavefronts of linear polarization waves. Based on the designed two distributions and the two control methods, four arrangements of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times $ </tex-math></inline-formula> 5 CSRRs are fabricated to validate the design methodology of beam steering. Furthermore, two reconfigurable Fabry–Perot (FP) antennas are proposed based on liquid-metal and mechanically rotating reconfiguration. An agreement between simulated and measured results shows higher aperture efficiency and desirable radiation patterns while demonstrating excellent reconfiguration reliability. Besides, an eight-element phased array combined with liquid-metal PRS is fabricated and shows improved scanning performance and stable gain fluctuation.

Simple terahertz metasurface with broadband and efficient functionality.

Pancharatnam-Berry (PB) metasurfaces have demonstrated mighty capability to manipulate electromagnetic (EM) waves, and exhibited potential applications for devices with broadband and efficient functionality. However, it remains a challenge to simultaneously achieve broadband and efficient wavefront manipulation for terahertz (THz) components with simple profiles. Herein, we introduce a simple ultra-thin PB metasurface with superior properties in the THz region. The structure is composed of a simple metallic C-Shaped Split Ring Resonator (CSRR) patterned on a flexible polyimide support layer. It is verified that the circular transmission efficiency is close to the theoretical limit of the single-layer metasurface in the range of 0.6 - 1.2 THz. Furthermore, we design metasurfaces based on the PB meta-atoms with spatially rotated orientation to achieve beam steering and superposition of vortex waves. The results are basically in line with expectations, validating the good performances of our proposal. This simple and easily deployable metasurface will give rise to more possibilities for the design of THz functional devices.

Dynamic Tunable Meta-Lens Based on a Single-Layer Metal Microstructure

Ultra-thin focusing meta-lenses based on the metasurface structure with adjustable focal length show important applicant value in compact systems, especially in on-chip terahertz spectroscopy, imaging systems, and communication systems. A stretchable substrate, dynamic focusing meta-lens based on the cross-polarized metal C-shaped split ring resonators (SRRs) is designed and investigated. At the operation frequency of 0.1 THz, the operation characteristics of the unit cell structure and the formed meta-lens are investigated. The phase of the unit cell structures can be modulated by changing the rotation angle, width, and symmetry axis of the C-shaped metal SRRs. When the terahertz wave is incident vertically, the focusing performance can be achieved based on the specific arrangement of the metasurface unit cells. By stretching the flexible substrate of the meta-lens, the dynamic focusing effect can be realized. When the substrate stretches from 100% to 120%, the focal length changes from 59.8 mm to 125.2 mm, the dynamic focusing range is 109.4% of the minimum focal length, and the focusing efficiency changes between 5.5% and 10.5%.

A Band-Notched Antenna With Two Radiation Zeros Using Grounded Coplanar Waveguide Filter for 2.4/5 GHz WLAN Applications

In this article, a band-notched dual-polarized crossed dipole antenna is proposed for 2.4/5 GHz WLAN applications. The proposed antenna works on the WLAN 2.4-GHz (2.4–2.48 GHz) and 5-GHz (5.15–5.85 GHz) bands for a VSWR &amp;lt;2 with two radiation zeros within 3.4–3.6 GHz. First, an ultra-wideband crossed dipole antenna with an operating frequency of 2.4–5.8 GHz is designed using the grounded coplanar waveguide (GCPW) feeding structure. Second, a miniaturized defected microstrip structure (DMS) is embedded in the GCPW feeding strip to form a stopband behavior with a radiation zero. Finally, combining with the design of a C-shaped split ring resonator (SRR) on the arms of the dipole antenna, a band notch (3.4–3.6 GHz) with two radiation zeros can be realized. These two radiation zeros can be adjusted independently to achieve a wide stopband performance. As a result, compared with the original ultra-wideband dipole antenna, the realized gains of the proposed antenna in the 3.4–3.6 GHz range are all suppressed from 8 dBi to less than −8 dBi. The proposed antenna can realize the stable unidirectional radiation pattern and a high gain of around 7 dBi in the lower band and 8.5 dBi in the higher band of WLAN. As a demonstration, the proposed antenna is fabricated and measured, and the measurement results are in good agreement with the simulation results.

Reflection-less frequency-selective microwave metamaterial absorber

We present a subwavelength-thick reflection-less metamaterial absorber that shows frequency-selective narrow-band near-perfect absorption at 2.4 GHz. The absorber does not have a ground plane and is constructed with a square array of pairs of C-shaped split-ring resonators (SRRs) orthogonally arranged in such a way that induced electric and magnetic dipoles destructively interfere and no reradiation of electromagnetic (EM) waves is observed. The SRRs are made of nichrome with high ohmic loss so that EM energy dissipates as heat. We numerically determined the optimum geometrical parameters of SRRs, and absorption of 97% is achieved at 2.4 GHz. We also fabricated a device using nichrome wire and obtained a huge decrease in transmission at a resonance of –6 dB with no reflection over the entire frequency range of interest. Our basic concept can be extended to higher frequency ranges and may be utilized for next-generation wireless communications, the Internet of Things (IoT), and so forth.

High focusing efficiency terahertz lens based on Huygens metasurface

We propose an ultra-thin Huygens lens with high focusing efficiency and robustness that is composed of a unit cell with a pair of C-shaped split-ring resonators (CSRRs). Compared with the single-layer CSRR lens, the focusing efficiency of the Huygens metasurface lens improves 90% at the best focal lengths and three times at the central frequency. Our device has robustness against geometrical parameters, such as the difference of the opening angle, the mismatch of the opening angle, and the mismatch of the radius, which reduces the manufacturing difficulty. The Huygens lens has unprecedented potential for real-time, quick, electromagnetic wave processing such as holography, beam steering/splitter, imaging, and launcher control.

C-shaped split ring resonator type metamaterial antenna design using neural network

A C-shaped split ring resonator-based metamaterial (MTM) structure placed on a patch antenna is proposed. An artificial neural network (ANN) is applied to design and determine dimensions of an MTM structure that is similar to those used in wireless communication systems, such as Wi-Fi and WiMax, as well as in military vehicles and space stations. The proposed microstrip antenna interacts with the MTM-based structures to improve the reflection coefficient (S11) and quality factor. The design of the proposed structure is optimized for this purpose in accordance with the ANN studies in the related literature. Both simulation and experimental studies show that ANN calculated MTM antennas improved the quality factor, which is calculated as 230 at 5.18 GHz. The simulated S11 is verified by experiment to show the integrity of the proposed work.

Metal-graphene hybrid active chiral metasurfaces for dynamic terahertz wavefront modulation and near field imaging

Chiral metasurfaces can achieve giant chiral optical responses and have been expanded from the optical band to other electromagnetic bands. Here, we propose a new method for dynamic terahertz circular dichroism (CD) manipulation in metasurfaces. By introducing a patterned and electrically doped graphene into the metamirror consists of double layer C-shaped split ring resonators (SRRs), efficient terahertz CD modulation is observed. Since the electrical doping of graphene changes the absorption loss of the metasuface cavity, the structure shows switching between a chiral metasurface and an ordinary metal mirror, which can be seen as "on" and "off" states. The calculation results show an efficient modulation of the terahertz CD in a large dynamic range. In addition, we also use the new method to design two metasurfaces for dynamic terahertz wavefront modulation and near-field digital imaging, both of which show a high-performance electrical switching. This method provides a new way for the design of active terahertz devices based on metasurfaces, and also promotes the applications of terahertz chiral metasurfaces in high-speed wireless communication and dynamic imaging.

C-shaped split ring resonator terahertz toroidal dipole metasurfaces

We designed and fabricated terahertz toroidal dipole metasurfaces based on a C-shaped split ring resonator metallic pattern fabricated on a flexible dielectric material (mylar). The toroidal dipole moment (Ty) was demonstrated as the dominant contribution to two different resonances at low frequency (ω1) and at high frequency (ω2). Simulation and LC circuit model analysis offered a quantitative explanation to the blue shift of the resonant frequencies at ω1 and ω2 as the increase of the opening angle(θ). The resonant frequencies showed a red shift at ω1 and ω2 as the increase of the outer ring radius (QR). Furthermore, the enhancement of the Q factor was attributed to the increase of Ty and the decrease of radiative loss. It was further proven that the model provided a new scheme for designing the toroidal dipole metasurfaces under a terahertz band, which was expected to be used as terahertz functional devices.

Dual-Polarized Band-Notched Antenna Without Extra Circuit for 2.4/5 GHz WLAN Applications

In this paper, a dual-band dual-polarized crossed dipole antenna with good anti-interference capability is proposed for 2.4-/5-GHz WLAN applications. The proposed antenna covers the WLAN 2.4-GHz band (2.4–2.48 GHz) and 5-GHz bands (5.15–5.85 GHz) with isolation >27 dB for VSWR < 2. Without extra filtering circuit, a band-notch (3.4–3.6 GHz) is achieved by introducing the C-shaped split ring resonator (SRR) into the wideband dipole antenna. Compared with the original wideband dipole antenna, the minimum gain in the notched band is suppressed from 8 to −9 dBi and the gain in the higher band is improved from 6 to 9.7 dBi. The proposed antenna can realize a high gain of 7.85 dBi for the lower band and 9.7 dBi for the higher band. As demonstrations, two reference antennas and the proposed antennas are fabricated and measured, and the measured results agree well with the simulated ones.

Improvement of the Frequency Characteristics for RFID Patch Antenna based on C-Shaped Split Ring Resonator

In this paper, we present a new technique for improving frequency characteristics and miniaturizing the geometric dimension of the RFID patch antenna that operates in the SHF band. This technique consists in implementing a periodic network based on a new model of a split C-ring resonator on the square slots of radiating rectangular patch antenna. The results of the simulation have proved that the proposed technique has an excellent radiation efficiency and size reduction compared to the reference patch antenna.

A novel thermo-tunable band-stop filter employing a conductive rubber split-ring resonator

This paper presents the design and related applications of a thermally tunable band-stop filter employing conductive rubber that incorporates electrically conductive particles. The relationship between the environmental temperature and the volume resistivity of conductive rubber materials was experimentally established. The experimental results demonstrated that the conductive rubber has a temperature-sensitive resistance property. The conductive rubber material was employed in the design of a C-shaped split-ring resonator (SRR) structure. The influence of environmental temperature on the electromagnetic properties of the SRR structure was analysed using a numerical simulation and experimental testing. The results demonstrated that the design of thermally tunable metamaterials was possible. As such, an H-shaped conductive rubber SRR was employed in the design of a novel thermally tunable band-stop filter. The results of a numerical simulation and experimental testing verified its band-stop characteristic, and demonstrated that the filtering performance of the H-shaped conductive rubber SRR can be controlled by the environmental temperature. Lastly, by comparison of the effective dielectric properties of the two types of SRRs, it demonstrates the effectiveness of conductive rubber and their temperature-controllable band-stop characteristics.

COMPACT TRIPLE BAND-NOTCHED UWB MIMO ANTENNA WITH SIMPLE STEPPED STUB TO ENHANCE WIDEBAND ISOLATION

In this paper, a very compact ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna, with a high isolation and triple notched bands, is proposed. Its size is dramatically decreased to 30× 26× 0.8mm3 on a cost-effective FR4 substrate. It consists of two rectangular printed monopole (PM) elements and a simple stepped ground stub to enhance wideband isolation. For two different rejected bands of the wireless local area network (WLANs) covering 5.15–5.35 and 5.725– 5.825GHz, four parasitic C-shaped split-ring resonators (PCSRR) are placed on either side of the feed line. By etching two inverted U-shaped slots on the center of the patch, the notched frequency at 4GHz C-band (3.7–4.2 GHz) of satellite communication systems is obtained. The results of simulation and measurement prove a bandwidth of S11 < −10 dB and S12 < −21 dB over the whole band (3.1– 11.2GHz) excluding the three independently adjustable rejection bands. Hence, the proposed UWB MIMO antenna has a very small size, simple structure, higher isolation and three narrower notched bands which effectively save more useful frequencies. Moreover, it is a good candidate for wireless portable UWB MIMO applications.