Circular Ring Research Articles

Metasurface absorber for millimeter waves: a deep learning-optimized approach for enhancing the isolation of wideband dual-port MIMO antennas

In this communication, the concept of metasurface absorber is utilized to enhance the isolation in the dual port multiple-input multiple-output (MIMO) antenna specially designed for a wideband millimeter wave operation. The frequency of operation of the designed module is 32.5–42.5 GHz with sufficient gain attributes. The designed metasurface array consists of two circular rings on two different layers. The concept of deep learning is utilized to optimize the dimensional configuration of the metasurface to achieve the maximum absorption of electromagnetic waves in the band of interest. The suppression of mutual coupling by double-ring metasurface is analyzed with the help of the wave theory concept. In contrast to previous decoupling methods using metasurfaces, the suggested metasurface is intended to be in the same plane as the array. The findings demonstrate the capability of effectively separating antenna elements in wideband MIMO antenna without compromising the geometrical complexity. Diversity metrics such as envelope correlation coefficient (ECC), mean effective gain (MEG), channel capacity loss (CCL), and total active reflection coefficient (TARC) for the proposed frequency range are also used to evaluate the performance of the constructed MIMO antenna. The wideband characteristics with a compact configuration make the design MIMO module a suitable candidate for mm-wave applications. The congruence between simulation and measurement confirms the validity of the suggested design.

A compact multiband flexible antenna with a full ground plane for off body communication

Abstract A compact, multiband flexible antenna for off Body Communication (OBC) at 2.45 GHz and UWB low and high bands are presented as required by the IEEE 802.15.6TM standard, 2012. The antenna exhibits a directional radiation pattern and provides good gain and a low specific absorption rate (SAR). The proposed antenna has a compact footprint of 44 × 32 ×1.5 mm3. The proposed antenna is fabricated by placing a conductive fabric on a 1.5 mm thick polydimethylsiloxane (PDMS) polymer to enhance high flexibility and durability. A full ground made of conductive textile is used on the underside of the dielectric to reduce the load directed towards the antenna caused by the layers of human tissue underneath and to minimize back radiation from the human body. The proposed antenna design combines square and circular rings to achieve multi-band characteristics. Edge chamfering, slotting, and stub addition bandwidth expansion techniques are used to achieve wide bandwidth. The proposed antenna demonstrates exceptional resistance to the human body's load and physical deformation. The proposed antenna is a compact single-layer substrate flexible FGP (FGP) antenna operable in the WLAN (2.45 GHz), lower (3.2-4.6 GHz), and higher UWB (6.2-11 GHz) bands specified by IEEE. 802.15.6.

Research on thermal resistance Performance: Broadband solar absorber based on laminated circular ring − disk microstructure

This paper presents a laminated circular-ring-disk (CRDS) solar microstructure absorber constructed based on heat-resistant metals. This absorber achieves an ultra-broadband absorption with a bandwidth of 2171.68 nm in the near-ultraviolet to mid-infrared band, and has three absorption peaks with absorption rates exceeding 96 %, with peak wavelengths of 342.09 nm, 1215.40 nm, and 2032.86 nm respectively. With the finite-difference time-domain method (FDTD), we detected that the average absorption efficiency of this absorber under Atmospheric mass of 1.5(AM 1.5) conditions is as high as 96.05 %, and the average energy loss is only 3.95 %. Meanwhile, the research results of the electric field distribution of the CRDS microstructure show that CRDS effectively promotes the surface plasmon resonance effect between the laminated metal materials. Combined with the research on the top micro-absorption structure materials, we finally determined the structural parameters of the CRDS structure absorber and selected heat-resistant metals nickel (Ni), chromium (Cr), and titanium (Ti). On this basis,we focused on the thermal radiation performance of the absorber and found that it has good adaptability to high-temperature environments. Finally, by comparing the Transverse Electric Wave(TE) and Transverse Magnetic Wave(TM) polarization conditions with the sweep parameter diagrams of 0°-60°, we found that the absorber has excellent angle insensitivity. In view of the above discussions, the CRDS microstructure absorber has good thermal stability, angle insensitivity, and can achieve ultra-broadband perfect absorption from the near-ultraviolet to the mid-infrared band, and has broad application prospects.

Weight functions for [formula omitted]-stresses in inner/outer double edge cracked circular rings

Weight functions (WF) for calculating the elastic T-stresses for inner edge cracked and outer edge cracked ring specimens are derived in this paper. Six forms of WF are considered, each of which requires only two reference T-stress solutions obtained using finite element method (FEM). Uniform and linear crack-face pressures are chosen as the two reference loading configurations. Quadratic and cubic crack-face pressures are chosen to validate the T-stresses obtained from WF, for both the ring specimens. When compared to T-stresses obtained from FEM, a percentage error of less than 3% is obtained for both the specimens, and hence the derived WF can be used for determining the T-stress solutions for any loading configurations. The derived WF is then used to determine the T-stresses in inner edge cracked and outer edge cracked circular rings subjected to uniform diametrical compression over arcs of the outer boundary. The effect of load distribution angle on the T-stresses is also found for the two rings for various inner to outer radii ratios.

The Proper Motion of the High Galactic Latitude Pulsar Calvera

Calvera (1RXS J141256.0+792204) is a pulsar of characteristic age 285 kyr at a high Galactic latitude of b = +37°, detected only in soft thermal X-rays. We measure a new and precise proper motion for Calvera using Chandra High Resolution Camera observations obtained 10 yr apart. We also derive a new phase-connected ephemeris using 6 yr of NICER data, including the astrometric position and proper motion as fixed parameters in the timing solution. Calvera is located near the center of a faint, circular radio ring that was recently discovered by LOFAR and confirmed as a supernova remnant (SNR) by the detection of γ-ray emission with Fermi Large Area Telescope. The proper motion of 78.5 ± 2.9 mas yr−1 at position angle 241.°3 ± 2.°2 (in Galactic coordinates) points away from the center of the ring, a result which differs markedly from a previous low-significance measurement, and greatly simplifies the interpretation of the SNR/pulsar association. It argues that the supernova indeed birthed Calvera <10 kyr ago, with an initial spin period close to its present value of 59 ms. The tangential velocity of the pulsar depends on its uncertain distance, v t = (372 ± 14)d 1 kpc km s−1, but is probably dominated by the supernova kick, while its progenitor could have been a runaway O or B star from the Galactic disk.

High sensitivity of a perfect absorber based on octagonal-star and circular ring patterned graphene metasurface

High sensitivity of a perfect absorber based on octagonal-star and circular ring patterned graphene metasurface

Reverse design of load-bearing broadband metamaterial absorber assisted by deep learning

Abstract In response to the current challenges of narrow absorption bandwidth, weak load-bearing capacity, and low design efficiency in absorbing structures, this study focuses on the reverse design of load-bearing broadband metamaterial absorber. A parameterized model of load-bearing metamaterial absorber was developed by integrating the composite sandwich structure with the electromagnetic resonant layers. The resonant layer was constructed using the combination of Vicsek-fractal and circular rings, with resistive films employed to broaden the absorption bandwidth. A deep learning-based forward prediction model was established to accurately predict the absorbance of the metamaterial absorber. The SHapley Additive exPlanations (SHAP) framework was utilized to analyze the forward prediction network, revealing the influence of various design parameters on the absorbance at center frequencies across the L to K band spectrum. Additionally, the Group Teaching Optimization Algorithm (GTOA) was introduced into the design process, leading to the development of an automated reverse design method for metamaterial absorber that can achieve specific design objectives. Using the GTOA-based reverse design method, a metamaterial absorber capable of effectively absorbing vertically incident electromagnetic waves within the 3-20 GHz frequency range was designed. The designed absorbing structure was fabricated, and its absorption performance was measured using the arch method. The measurement results were found to be in good agreement with the simulation data. The absorbing mechanism of the designed metamaterial absorber was analyzed based on the calculation of equivalent electromagnetic parameters and the electromagnetic resonance observed at the resonant frequency. It was determined that the primary absorbing effect is induced by electric resonance triggered by electromagnetic waves. The proposed metamaterial absorber can be applied to radar stealth design for military targets such as naval vessels. The research methodology and approach demonstrate significant generalizability and engineering applicability.

Design and characterization of a circular ring monopole antenna and its MIMO configuration for sub-6 GHz, sub-7 GHz and mm-wave 5G applications

Abstract In this paper, a circular ring monopole antenna, along with its MIMO configuration for sub-6 GHz, sub-7 GHz and mm-wave 5G applications is presented. The single element spans a wide range of frequencies in the sub-6 GHz and mm-wave regions, including a triple-band covering 1.9–6 GHz, 23.3–33.5 GHz, and a super-wide band starting from 37.5 GHz. A two-element MIMO antenna, derived from the single element, has been developed to operate in both frequency regions. It meets the -10 dB criterion with a bandwidth of 4.8 GHz (3.2 to 7.3 GHz) in the sub-6 GHz/sub-7 GHz spectrum. Additionally, the antenna exhibits a super-wide band in the mm-wave region starting at 30.4 GHz. The design covers key bands such as n78, LTE band 46, n96, 39 GHz band, 41 GHz band and more, assigned for 5G sub-6 GHz, sub-7 GHz and mm-wave applications. Improved isolation from 12 dB to 18.5 dB is achieved through a simple decoupling line structure between elements. The proposed MIMO antenna (75 × 56.4 × 1.52 mm³) exhibits a peak gain of 9.8 dBi, high isolation (18.5 dB), low envelope correlation coefficient (ECC &lt;0.016 ), high diversity gain (DG &gt; 9.995), and efficiency (&lt; 97%).

Theoretical and experimental study on the mechanical measurement of rock tensile fracture by ring radial compression

Conventional Brazilian disc splitting tests are hampered by stress concentration at the loading points, leading to test outcomes that do not truly represent the engineering failure strength of rocks. To enhance the accuracy of these tests, the specimen shape has progressed from the Brazilian disc to a circular ring. This study presents a theoretical analysis of the compression deformation process in circular rings, followed by platform-radial compression tests conducted on various types of rocks and metals, employing the digital speckle correlation method alongside an improved mechanical extensometer. The findings indicate that circular ring specimens failed under a combination of tensile and compressive stresses. The main crack originates along the loading direction on the inner wall of the ring and propagates outwards, resulting in the failure of the entire ring structure. While maximum tensile strain may serve as an indicator of rock failure, tensile stress alone should not be considered a definitive criterion for failure.

Ultra-broadband absorber and perfect thermal emitter for high-efficiency solar energy absorption and conversion

This study proposes a pyramid-shaped solar absorber designed with multi-layered Ti-SiO2 ring stacked. The structure achieves an average absorption efficiency of 98.03 % over the range of 280–4000 nm, and under AM1.5 spectral conditions, the weighted average absorption efficiency reaches 97.66 %, the bandwidth with an absorption efficiency greater than 90 % reaches 3750 nm. To explore the reason for achieving ultra-broadband absorption with this structure, the electromagnetic field distribution at three absorption peaks was calculated. The results revealed that the resonance between the polarization direction of the three-layer circular ring stacked structure and the plasmon resonance at the junction of Ti and SiO2 contribute to the model's capability for ultra-broadband high-efficiency absorption. At the same time, the thermal emissivity of the structure was calculated at high temperatures of 1000 K and 2000 K, both exceeding 97 %. Furthermore, due to the fully symmetrical design, the absorber is polarization-independent. It was found through calculations that whether in TM mode or TE mode, as the incident angle varies from 0° to 60°, the average absorption efficiency of the absorber changes only by 11.16 %, thereby verifying the structure's excellent insensitivity to incident light angles. In summary, all these characteristics indicate that the model has excellent application prospects in fields such as solar energy collection and photothermal conversion.

Influence of chirality on buckling of inextensible rings subject to dead loading

A variational approach is studied to understand buckling of inextensible rings made from chiral filaments and subject to dead loading. In opposite to previous literatures in which only in-plane bifurcation is allowed, i.e., the ring deforms only in its plane, in this work we consider both in-plane and out-of-plane bifurcation, i.e., the ring deforms both in its plane and out of its plane. For circular rings made from filaments without chirality, we find that they lose instability via out-of-plane bifurcation at critical values of loading smaller than those published. For circular rings made from filaments with chirality, they lose instability via coupling between in-plane and out-of-plane bifurcation at critical values of loading smaller than those at which bifurcation would happen without chirality. The destabilizing effect of chirality, however, can be reduced by increasing the twisting rigidity relative to the bending rigidity.

Massive scalar clouds and black hole spacetimes in Gauss-Bonnet gravity

We study static black holes in scalar-Gauss-Bonnet (sGB) gravity with a massive scalar field as an example of higher curvature gravity. The scalar mass introduces an additional scale and leads to a strong suppression of the scalar field beyond its Compton wavelength. We numerically compute sGB black hole spacetimes and scalar configurations and also compare with perturbative results for small couplings, where we focus on a dilatonic coupling function. We analyze the constraints on the parameters from requiring the curvature singularity to be located inside the black hole horizon r_hrh and the relation to the regularity condition for the scalar field. For scalar field masses m r_h \gtrsim 10^{-1}mrh≳10−1, this leads to a new and currently most stringent bound on sGB coupling constant \alphaα of \alpha/r_h^2\sim 10^{-1}α/rh2∼10−1 in the context of stellar mass black holes. Lastly, we look at several properties of the black hole configurations relevant for further work on observational consequences, including the scalar monopole charge, Arnowitt–Deser–Misner mass, curvature invariants and the frequencies of the innermost stable circular orbit and light ring.

Anisotropy of object nonrigidity: High-level perceptual consequences of cortical anisotropy.

We present a surprising anisotropy in perceived object nonrigidity, a complex, higher-level perceptual phenomenon, and explain it unexpectedly by the distribution of low-level neural properties in primary visual cortex. We examined the visual interpretation of two rigidly connected rotating circular rings. At speeds where observers predominantly perceived rigid rotation of the rings rotating horizontally, observers perceived only nonrigid wobbling when the image was rotated by 90°. Additionally, vertically rotating rings appeared narrower and longer compared to their physically identical horizontally rotating counterparts. We show that these perceived shape changes can be decoded from V1 outputs by incorporating documented anisotropies in orientation selectivity. We then show that even when the shapes are matched, the increased nonrigidity persists in vertical rotations, suggesting that motion mechanisms also play a role. By incorporating cortical anisotropies into optic flow computations, we show that the kinematic gradients (Divergence, Curl, Deformation) for vertical rotations align more with physical nonrigidity, while those for horizontal rotations align closer to rigidity, indicating that cortical anisotropies contribute to the orientation dependence of the perception of nonrigidity. Our results reveal how high-level percepts are shaped by low-level anisotropies, which raises questions about their evolutionary significance, particularly regarding shape constancy and motion perception.

Robustly Flexible, Highly Transparent, and Polymerization-Regulated Polyimide Aerogel Membranes as Efficient Thermal Insulators for Solar Collection.

Efficient thermal insulators that can maintain their efficacy at extreme temperatures are in pressing demand, particularly in fields such as energy saving, aerospace, and sophisticated equipment. Herein, a novel and facile polymerization-regulated optimal strategy is adapted to realize the comprehensive performance of polyimide (PI) aerogel membranes with mechanical robustness, high flexibility, hydrophobicity, light transmittance, and efficient thermal insulation. Benefiting from the hydrolysis of monomers and chemical imidization reaction process verified by a thermo-chemo-mechanically coupled theoretical model, the viscosity of precursors, shrinkage rate, and microstructure of aerogels are precisely controlled, leading to a low thermal conductivity range of 0.023-0.044 W/(m·K). The fabricated PI aerogel membranes, which undergo a remarkable transformation from their initial brittle and opaque nature to a state of high flexibility and transparency, exhibit a 3.0 times increase in tensile strength (4.6 MPa) and a 8.4 times improvement in elongation at break (20.6%) over previous studies while demonstrating an exceptional light transmittance of 92.5% across a wide spectral range from 500 to 2500 nm. Additionally, the PI aerogel membranes possess superior mechanical properties and a wide temperature resistance range extending from -196 to 300 °C. These flexible PI aerogel membranes can be effectively adjusted to meet the practical application of a circular ring solar thermal collector, which displayed a high solar heat collection temperature of 135 °C at a thickness of 0.5 mm. The coordination between the thermophysical properties and mechanical properties of the PI aerogel membranes in this work holds great promise for application requirements of thermal insulators in optical elements under harsh environments.

Model and Energy Bounds for a Two-Dimensional System of Electrons Localized in Concentric Rings.

We study a two-dimensional system of interacting electrons confined in equidistant planar circular rings. The electrons are considered spinless and each of them is localized in one ring. While confined to such ring orbits, each electron interacts with the remaining ones by means of a standard Coulomb interaction potential. The classical version of this two-dimensional quantum model can be viewed as representing a system of electrons orbiting planar equidistant concentric rings where the kinetic energy may be discarded when one is searching for the lowest possible energy. Within this framework, the lowest possible energy of the system is the one that minimizes the total Coulomb interaction energy. This is the equilibrium energy that is numerically determined with high accuracy by using the simulated annealing method. This process allows us to obtain both the equilibrium energy and position configuration for different system sizes. The adopted semi-classical approach allows us to provide reliable approximations for the quantum ground state energy of the corresponding quantum system. The model considered in this work represents an interesting problem for studies of low-dimensional systems, with echoes that resonate with developments in nanoscience and nanomaterials.

Negative Thermal Expansion Realized by an Incomplete Bimaterial Ring

Incomplete bimaterial ring (a circular ring with a gap) capable of producing negative macroscopic thermal expansion is proposed and its behavior is analyzed. The ring exhibits negative thermal expansion (NTE) (in the plane of the ring) when the outer ring has higher thermal expansion coefficient than the inner one. When the thermal expansion coefficients are equal (monomaterial incomplete ring), the effective (macroscopic) planar thermal expansion becomes zero. (The complete thermal expansion will be positive but small.) It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the role of the gap is played by the open ends. These structures will have higher stiffness than the incomplete bimaterial ring. The thermal expansion of the ring is characterized by the effective (macroscopic) coefficient of linear thermal expansion. The effective coefficient of linear thermal expansion depends on the temperature increase, making the thermal expansion nonlinear. Planar and 3D NTE structures are considered.

Prototype of Circular Split Ring Resonator-Based Sensor for Estimating Soil Moisture as a Function of Soil Particle Distribution

Prototype of Circular Split Ring Resonator-Based Sensor for Estimating Soil Moisture as a Function of Soil Particle Distribution

A visible transparent infrared microwave compatible stealth metasurface with low infrared emissivity

Abstract This article proposes a visible transparent infrared microwave-compatible stealth metasurface with low infrared emissivity, aiming to integrate visible transparency, low infrared radiation, and broadband microwave absorption. The entire structure consists of a dual layer of infrared shielding layer (IRSL) and microwave absorption layer (MAL). Among them, IRSL adopts a frequency selective surface (FSS) structure with high-duty cycle dielectric-metal-dielectric (DMD) to obtain low infrared emissivity and high microwave transmittance. MAL combines the equivalent circuit method (ECM) and particle swarm optimization algorithm (PSO) to design a circular ring metasurface for broadband microwave absorption. To achieve better absorption performance, a transition layer (TL) is introduced to improve impedance matching between IRSL and MAL. Meanwhile, the use of transparent materials throughout the entire structure has the characteristic of visible transparency. In summary, this article proposes a multiband compatible stealth metasurface design method that can meet the stealth requirements of modern battlefields.

Analysis of broadband linear polarization-converting meta-materials and their sensing and detection functions

In this paper, we present a broadband perfect-reflective linear polarization-converting metamaterial, which achieves perfect-reflective linear polarization conversion over a broadband frequency range of 28.15 GHz–60.80 GHz, and the narrow-band perfect-polarization-converting peaks appearing at the high frequency of 67.121 GHz can be used for microwave solution concentration detection. The design consists of a surface metal resonator structure, a Roggers 5880 dielectric layer and a copper metal backing. The surface metal resonator is a combination of a circular open ring, a square open ring, and a centrally located cross-metal cross ring nested in a modified, highly anisotropic structure. The perfect polarization transition peak at the high frequency band can be used for the solution detection function, which can detect the concentration of salt solution, glucose solution, and alcohol solution. When the refractive index of the solution sample to be tested changes gradually from 1.0 to 1.4, the polarization conversion peak shows obvious frequency shift, and the peak polarization conversion rate is always kept above 99%. The polarization principle was analyzed using surface electromagnetic field distribution and related theories, and the sample structure was processed and tested. The designed super-surface polarization conversion structure has potential applications in the field of microwave detection and microwave communication.

Development of a new analytical model for circular concrete ring segments with dry joints under combined effects

AbstractPrevious models of circular ring segment joints have been inadequate in describing their loading capacity due to the lack of consideration for the interaction between shear force and bending moment. Consequently, these models have led to over‐ or underestimation of the joints' capacity. The increasing use of dry joint connection technology in wind turbine towers and prefabricated segmental bridge constructions necessitates the development of advanced computational models for these connections. This study presents a new model that considers the effects of bending moment, shear force, and torsion on the loading capacity of circular ring segment joints. Numerical simulations were conducted to validate the developed model under different load combinations, and the results demonstrate excellent agreement between the model predictions and numerical simulations.