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Super-Oscillatory Metalens at Terahertz for Enhanced Focusing with Reduced Side Lobes
摘要： In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, ef?ciency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high re?ection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately ?11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations.
关键词： metamaterials,evolutionary algorithm,metasurfaces,terahertz,metalens,terahertz focusing,subwavelength focusing,super-oscillatory lens
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - Chennai, India (2018.3.22-2018.3.24)] 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - Dual-band Bandpass Filter Using Complementary Split Ring Resonators for X-Band Applications
摘要： This paper is focused on Complementary Split Ring Resonator (CSRR) to design a dual band bandpass filter (BPF) for X-Band frequencies using metamaterial concept. To achieve the functionalities of metamaterials, rectangular shaped complementary split ring resonators are etched in the ground plane along with λ/4 microstrip lines on the top. The inner and the outer rings are joined at the center through a gap. The length of the inner ring and the outer ring are calculated to make the BPF operating at 8.2 GHz and 9 GHz in X-Band. The width of the inter-connecting gap is changed to control the passband edges. An equivalent circuit model is proposed for the designed dual-band BPF to understand the working of the basic cell along with a microstrip line. By varying the length and width of the CSRR and changing the microstrip line dimensions two resonances are can be adjusted and finally fixed at our desired resonating frequencies. The results of EM simulation and the circuit simulation are compared to confirm the validity of the proposed design.
关键词： Bandpass filter,Complementary Split Ring Resonators,Dual-band filter,Metamaterials
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Bangalore, India (2018.9.19-2018.9.22)] 2018 International Conference on Advances in Computing, Communications and Informatics (ICACCI) - Compact Tunable Dual-band Bandpass Filter using Edge-open Split Ring Resonators for X-Band Applications
摘要： In this paper, a dual-band bandpass ?lter(BPF) is designed using edge-open Split Ring Resonators(SRR) which is obtained by modifying the conventional SRRs. The inner ring and the outer ring of the edge-open SRRs are connected to stubs to get dual passbands with improved ?lter characteristics. The rings of the SRR are loaded with varactor diodes to tune the individual passbands of the proposed BPF. The ?rst passband can be tuned independently by varying the capacitance of the varactor diode D1 while the second passband remains unchanged by ?xing the capacitance of the varactor diode D2 and vice versa. Hence, the proposed ?lter helps in tuning both the passbands independently of about 0.6GHz for the ?rst passband & 0.3GHz for the second passband and achieves compactness in size of about 20mm x 14mm. The ring equivalents of each rings and the obtained S-parameter results of the proposed BPF while tuning the individual passbands are discussed in this paper.
关键词： Split Ring Resonators,Varactor Diodes,Tunable ?lter,Metamaterials,Dual band bandpass ?lter
更新于2025-09-09 09:28:46
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Characterization of additively manufactured cellular alumina dielectric structures
摘要： Additive manufacturing (AM, also known as 3D printing) can produce novel three-dimensional structures using low-loss dielectric materials. This enables the construction of dielectrics with complex shapes that enable innovative microwave applications such as resonators, filters, and metamaterial lenses. This paper addresses the production and characterization of cellular structures of various designed densities created with a low loss ceramic material, alumina (aluminum oxide), via vat photopolymerization. The permittivity of these printed structures is variable over roughly an octave, with a range of relative permittivites from 1.78 to 3.60, controlled via part geometry.
关键词： electromagnetic metamaterials,dielectric materials,ceramics,printing,design for manufacture
更新于2025-09-09 09:28:46
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Relaxed micromorphic model of transient wave propagation in anisotropic band-gap metastructures
摘要： In this paper, we show that the transient waveforms arising from several localised pulses in a micro-structured material can be reproduced by a corresponding generalised continuum of the relaxed micromorphic type. Specifically, we compare the dynamic response of a bounded micro-structured material to that of bounded continua with special kinematic properties: (i) the relaxed micromorphic continuum and (ii) an equivalent Cauchy linear elastic continuum. We show that, while the Cauchy theory is able to describe the overall behaviour of the metastructure only at low frequencies, the relaxed micromorphic model goes far beyond by giving a correct description of the pulse propagation in the frequency band-gap and at frequencies intersecting the optical branches. In addition, we observe a computational time reduction associated with the use of the relaxed micromorphic continuum, compared to the sensible computational time needed to perform a transient computation in a micro-structured domain.
关键词： anisotropy,transient dynamic response,elastic metamaterials,relaxed micromorphic model
更新于2025-09-09 09:28:46
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Tunable triple-band graphene refractive index sensor with good angle-polarization tolerance
摘要： In this article, we design a triple-band graphene refractive index sensor with good angle-polarization tolerance, which is composed of graphene elliptic-circular nanodisk resonators periodically arranged on a dielectric substrate. The numerical results indicate that the resonant wavelengths of three modes of graphene resonators show consecutively linear tunability when the refractive index of the surrounding medium varies, and the sensitivity is up to 11.56 μm/RIU. The sensing range can be further adjusted by controlling the doping level of graphene. In addition, the proposed graphene sensor maintains polarization insensitivity over a wide angular range (0-60°), showing very good angle-polarization tolerance. This work enables us to achieve a tunable triple-band sensor and provides potential value for label-free biomedical sensing.
关键词： graphene,surface plasmon resonance,refractive index sensor,metamaterials
更新于2025-09-09 09:28:46
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Tunable near-infrared perfect absorber based on the hybridization of phase-change material and nanocross-shaped resonators
摘要： Ge2Sb2Te5 (GST) is a kind of non-volatile chalcogenide phase-change material, which has a significant difference in permittivity between its amorphous and crystalline states in the infrared range. On account of this remarkable property, the combination of GST and metamaterials has great potential in tunable meta-devices. In this paper, a perfect absorber based on a nanocross-resonator array stacked above a GST spacer layer and an Au mirror (i.e., a metal-dielectric-metal configuration) is designed and experimentally demonstrated. A thin indium tin oxide (ITO) protective layer is inserted between the GST spacer and the Au resonator to avoid heat-induced oxidation of the GST layer during phase transition. We found that the ITO layer not only can protect the GST layer from deterioration, but also allows a significant blue shift in the absorption peak from 1.808 lm to 1.559 lm by optimizing the thickness of the two dielectric layers without scaling down the size of the metal structure, which provides a more feasible idea in pushing the absorption peak to higher frequency. The LC circuit model is presented to explain this blue-shift phenomenon, which is mainly attributed to the engineering of the dielectric environment of the parallel plate capacitance. In addition, such good performance in dynamitic modulation makes this perfect absorber a robust candidate for optical switching and modulating in various situations.
关键词： metamaterials,near-infrared,nanocross-shaped resonators,phase-change material,tunable,perfect absorber,GST
更新于2025-09-09 09:28:46
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Photonic topological phases in dispersive metamaterials
摘要： We analyze the photonic topological phases in dispersive metamaterials which satisfy the degenerate condition at a reference frequency. The electromagnetic duality allows for the hybrid modes to be decoupled and described by the spin-orbit Hamiltonians with pseudospin 1, which result in nonzero spin Chern numbers that characterize the topological phases. In particular, the combined Hamiltonian of the hybrid modes complies with a fermionic-like pseudo time-reversal symmetry that ensures the Kramers degeneracy, leading to the topological protection of helical edge states. The transverse spin generated by the evanescent surface waves is perpendicular to the wave vector, which exhibits the spin-momentum locking as in the surface states for three-dimensional topological insulators. The topological properties of the helical edge states are further illustrated with the robust transport of a pair of counterpropagating surface waves with opposite polarization handedness at an irregular boundary of the metamaterial.
关键词： spin-momentum locking,pseudospin 1,Kramers degeneracy,dispersive metamaterials,helical edge states,spin Chern numbers,spin-orbit Hamiltonians,photonic topological phases
更新于2025-09-04 15:30:14
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Semi-implicit FDTD TW scheme for modelling effective surface plasmons
摘要： A semi-implicit finite-difference time-domain thin-wire (TW) scheme with a relaxed stability condition is proposed for modelling effective surface plasmons in waveguide metamaterials. Its formulation is based on introducing the Newmark-Beta method into the TW formulation based on the contour-path integral of Maxwell’s equations around a wire. The resultant scheme is magnetically implicit. Its stability, accuracy and efficiency are assessed in the application to a wire-added parallel-plate waveguide perturbed with a small gap.
关键词： Newmark-Beta method,surface plasmons,semi-implicit FDTD,thin-wire scheme,waveguide metamaterials
更新于2025-09-04 15:30:14
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Active Thermal Control of 5 nm Gap Terahertz Antennas
摘要： Metallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width-to-length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled-mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.
关键词： metamaterials,active modulation,terahertz spectroscopy,nanogaps,thermal expansion
更新于2025-09-04 15:30:14