Small Split-ring Resonators Research Articles

Polarization multiplexing multichannel high-Q terahertz sensing system

Terahertz functional devices with high-Q factor play an important role in spectral sensing, security imaging, and wireless communication. The reported terahertz devices based on the electromagnetic induction transparency (EIT) effect cannot meet the needs of high-Q in practical applications due to the low-Q factor. Therefore, to increase the Q-factor of resonance, researchers introduced the concept of bound state in the continuum (BIC). In the quasi-BIC state, the metasurface can be excited by the incident wave and provide resonance with a high-Q factor because the condition that the resonant state of the BIC state is orthogonal is not satisfied. The split ring resonator (SRR) is one of the most representative artificial microstructures in the metasurface field, and it shows great potential in BIC. In this paper, based on the classical single-SRR array structure, we combine the large and small SRR and change the resonance mode of the inner and outer SRR by changing the outer radius of the inner SRR. The metasurface based on parameter-tuned BIC verified that the continuous modulation of parameters in a system could make a pair of resonant states strongly coupled, and the coherent cancellation of the resonant states will cause the linewidth of one of the resonant states to disappear, thus forming BIC. Compared with the single-SRR array metasurface based on symmetry-protected BIC, the dual-SRR array metasurface designed in this paper has multiple accidental BICs and realizes multichannel multiplexing of X-polarization and Y-polarization. It provides a brilliant platform for high-sensitivity optical sensor array, low threshold laser and efficient optical harmonic generation.

Two-Channel VO2 Memory Meta-Device for Terahertz Waves.

Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown favorable application prospects in memory-related devices once combined with metamaterials or metasurfaces. However, to date, VO2-based memory meta-devices are usually in a single-channel read/write mode, which limits their storage capacity and speed. In this paper, we propose a reconfigurable meta-memory based on VO2, which favors a two-channel read/write mode. Our design consists of a pair of large and small split-ring resonators, and the corresponding VO2 patterns are embedded in the gap locations. By controlling the external power supply, the two operation bands can be controlled independently to achieve at least four amplitude states, including “00”, “01”, “10”, and “11”, which results in a two-channel storage function. In addition, our research may provide prospective applications in fields such as THz switching, photon storage, and THz communication systems in the future.

Small Split-Ring Resonators as Efficient Antennas for Remote LoRa IOT Systems-A Path to Reduce Physical Interference.

While wireless IOT modules can be made extremely compact, antennas typically protrude from the module, providing the potential to catch near moving/rotating equipment or transfer loads to the PCB through end forces, which can lead to failures. This work explores the use of split-ring resonator (SRR) designs to achieve a planar antenna with a maximum dimension less than a monopole working at the same frequency. The very narrow bandwidth of the SRR required detailed physical models to create printed circuit board (PCB)-based antenna designs that could be used at LoRa frequencies of 433 MHz and 915 MHz. Uncertainty analysis allowed for the impact of geometrical and physical tolerances on the resonant frequency to be evaluated. Nearfield and farfield measurements were performed allowing for the resonant frequency, directionality, and range of the antenna to be evaluated. An unbalanced SMA port was added to the SRR design to allow for the use of a network vector analyser to determine the input impedance of various designs. The optimum design achieved an input resistance of 44 Ω at a resonant frequency of 919 MHz, close to the target values (50 Ω at 915 MHz). Field measurements of the received signal strength from a planar antenna design indicated a gain of 5 dB over a conventional quarter-wave monopole antenna, in a footprint that was 40% smaller than the monopole.

Anapole moment of localized spoof plasmon polaritons based on a hybrid coupling mechanism.

In the past several years, the anapole mode has received increasing interest and has been used in numerous applications. However, little relevant work exists on localized spoof plasmon polaritons (LSSPs), which are limited by the excitation of the electric dipole in a symmetrical structure. The lack of an electric dipole makes the excitation of the anapole moment difficult. In this study, we experimentally demonstrate that compact planar metadisks can exhibit a radiationless anapole mode of LSSPs at microwave frequencies. By integrating large and small split-ring resonators, the strong interaction between conductive and inductive coupling is shown to excite the electric dipole. The necessary condition for excitation of the electric dipole using the hybrid coupling mechanism is derived by analyzing equivalent LCR circuits. The proposed structure exhibits nearly equal magnitudes of the toroidal and electric dipoles. Moreover, analytical and numerical approaches are developed to explain the physics of the hybrid coupling mechanism accurately. Further experimental measurements confirm the theoretical predictions.

Improved Methanol Detection Using Carbon Nanotube-Coated Carbon Fibers Integrated with a Split-Ring Resonator-Based Microwave Sensor

A novel microwave sensor based on the electrically small split ring resonator (SRR) integrated with the hierarchal carbon nanotube coated carbon fiber (CNTCF) for gas-sensing applications is proposed. The CNTCF is synthesized via catalytic chemical vapor deposition process and investigated by scanning electron microscopy and transmission electron microscopy for their structural information. The CNTCF integrated SRR is excited by the electromagnetic field through high impedance microstrip line. The use of highly conductive CNTCF as sensing material facilitated extremely large surface area causing a substantial change in the inherent resonant frequency as a sensor response at room temperature (25 °C) for methanol, nitrogen dioxide (NO2), ethanol, and chloroform gases. This change in resonant frequency facilitates the detection and sensing of the analyte gases under controlled environment and constant relative humidity of 32%. The CNTCF-SRR sensor exhibited high selectivity and sensitivity toward the methano...

Printed multi‐band compound meta‐loop antenna with hybrid‐coupled SRRs

A novel printed loop antenna with hybrid-coupled split ring resonators (SRRs) is proposed to realise multi-band and impedance-enhanced performances. Design guidelines and a step-by-step derivation of the proposed antenna based on SRRs are given in detail. On the basis of a one-wavelength rectangular loop, by splitting the left-/right-hand sides of the loop, the input impedance of the loop antenna is reduced and an additional resonance can be generated. Four identical SRRs are then symmetrically placed inside the loop, which not only introduces a resonance by the electrically small SRRs array, but also forms multiple hybrid resonances at the high frequencies. To improve impedance matching, two parasitic strips are added besides the splits of SRRs. This antenna is numerically and experimentally studied. It is demonstrated that this antenna achieves three operating bands with improved impedance matching (i.e. two narrow-bands at 0.729 and 0.797 GHz and a wide band from 0.935 to 1.1 GHz), a loop-dipole-liked radiation pattern, a maximum realised gain with a value of 4.8 dBi and radiation efficiency above 72.5%.

Electrically small particles combining even- and odd-mode currents for microwave energy harvesting

We present a structure composed of an ensemble of electrically small resonators for harvesting microwave energy. A flower-like structure composed of four electrically small split-ring resonators (SRRs) arranged in a cruciate pattern, each with a maximum dimension of less than λo/10, is shown to achieve more than 43% microwave-to-alternating current conversion efficiency at 5.67 GHz. Even- and odd-mode currents are realized in the proposed harvester to improve the efficiency and concurrently reduce the dielectric loss in the substrate. An experimental validation is conducted to prove the harvesting capability.

From Isolated Metaatoms to Photonic Metamaterials: Evolution of the Plasmonic Near-Field

Metamaterials are artificial media which can provide optical properties not available from natural materials. These properties often result from the resonant excitation of plasmonic modes in the metallic building blocks ("metaatoms") of the metamaterial. Electromagnetic interactions between the metaatoms significantly modify the resonances of the individual metaatoms and influence the optical properties of the whole metamaterial. To better understand these interactions, we study in this Letter the evolution of the plasmonic near-field in the course of the transition from an isolated metaatom, in our case a split-ring resonator (SRR), to a photonic metamaterial via electron energy-loss spectroscopy. For small SRR ensembles, we observe the formation of discrete optical bright and dark modes due to coupling of the metaatoms. Large SRR arrays reveal a quasi-continuum of modes in the interior and distinct edge modes at the boundaries of the array. Our experimental results are in excellent agreement with numerical calculations.

Electrically small tunable antennas using split ring resonators

Presented are tunable electrically small antennas composed of split ring resonators (SRRs), which are used to reduce antenna size. To control the resonance frequency, a lumped inductor is inserted between the SRRs and the ground. The proposed antenna operates within Korean personal communication services (PCS) frequency bands of 1750–1870 MHz, and the size of the antenna is 1/33λ0×1/33λ0 with an operating frequency of 1800 MHz. In spite of its small size, the radiation efficiency and −10 dB bandwidth were measured as 82% and 2.4%, respectively. Good agreement between the predicted and measured results ensures the validity of the design method to provide a frequency adjustment using lumped inductors in small SRR antennas.

Electrically small split ring resonator antennas

We studied electrically small resonant antennas composed of split ring resonators (SRR) and monopoles. The antennas considered have the same ring radius, but slightly different geometry. The resonance frequency depends on the geometry of the SRRs. Two SRR antennas are designed. The first one, which operates at 3.62 GHz, is demonstrated theoretically and experimentally. The size of this antenna is 0.095λ0×0.100λ0 and is low profile at the other dimension. The gain and directivity of the antenna was 2.38 and 5.46, respectively. The corresponding efficiency was 43.6%. The estimated radiation Q (rad Q=23.03) was much larger than the minimum radiation Q (min Q=1.78). The second one is a rather small SRR antenna in which the capacitance between the rings is increased. The size is reduced to 0.074λ0×0.079λ0. This structure is called serrated SRR (SSRR). Both antennas have similar far-field patterns but the efficiency of the SSRR antenna is less.