Resonance Modes Research Articles

Proximal High-Index Metamaterials based on a Superlattice of Gold Nanohexagons Targeting the Near-Infrared Band.

Plasmonic nanoparticles can be assembled into a superlattice, to form optical metamaterials, particularly targeting precise control of optical properties such as refractive index (RI). The superlattices exhibit enhanced near-field, given the sufficiently narrow gap between nanoparticles supporting multiple plasmonic resonance modes only realized in proximal environments. Herein, the planar superlattice of plasmonic Au nanohexagons (AuNHs) with precisely controlled geometries such as size, shape, and edge-gaps is reported. The proximal AuNHs superlattice realized over a large area with selective edge-to-edge assembly exhibited the highest-ever-recorded RI values in the near-infrared (NIR) band, surpassing the upper limit of the RI of the natural intrinsic materials (up to 10.04 at λ = 1.5µm). The exceptionally enhanced RI is derived from intensified in-plane surface plasmon coupling across the superlattices. Precise control of the edge-gap of neighboring AuNHs systematically tuned the RI as confirmed by numerical analysis based on the plasmonic percolation model. Furthermore, a 1D photonic crystal, composed of alternating layers of AuNHs superlattices and low-index polymers, is constructed to enhance the selectivity of the reflectivity operating in the NIR band. It is expected that the proximal AuNHs superlattices can be used as new optical metamaterials that can be extended to the NIR range.

Ultrafast Laser Manipulation of In-Lattice Plasmonic Nanoparticles.

Plasmonic nanoparticles enable manipulation and enhancement of light fields at deep subwavelength scales, leading to structures and devices for diverse applications in optics. Despite hybrid plasmonic materials display remarkable optical properties due to interactions between components in nanoproximity, scalable production of plasmonic nanostructures within a single-crystalline matrix to achieve an ideal plasmon-crystal interface remains challenging. Here, a novel approach is presented to realize efficient manipulation of in-lattice plasmonic nanoparticles. Employing ultrafast-laser-driven plasmonic nanolithography, metallic nanoparticles with controllable morphology are precisely defined in the crystalline lattice of yttrium aluminum garnet (YAG) crystal. Through direct ion implantation, hybrid plasmonic material composed of nanoparticles embedded in a sub-surface amorphous YAG layer is created. Subsequently, femtosecond laser pulses guide formation and reshaping of plasmonic nanoparticles from the amorphous layer into the single-crystalline matrix along direction of light propagation, facilitated by a plasmon-mediated evolution of laser energy deposition. By tailoring resonance modes and optimizing the coupling between structured particle assemblies, a range of applications including polarization-dependent absorption and nonlinearity, controllable photoluminescence, and structural color generation is demonstrated. This research introduces a new approach for fabricating advanced optical materials featuring in-lattice plasmonic nanostructures, paving the way for the development of diverse functional photonic devices.

Design and Theoretical Analysis of a Low Demodulation Deviation PhC Dual-Parameter Sensor Based on Quasi-BIC and Guided Mode Resonance

Design and Theoretical Analysis of a Low Demodulation Deviation PhC Dual-Parameter Sensor Based on Quasi-BIC and Guided Mode Resonance

Evaluation of power system instability probability considering output randomness of grid-connected converter

Abstract In recent years, there has been a notable increase in the installed capacity of new energy sources. Nevertheless, the random nature of the output power of G-CCs may potentially result in power system instability. This paper presents a closed-loop interconnection model comprising a G-CC as a feedback subsystem and a VSC-HVDC system as a feedforward subsystem. The instability condition of the closed-loop system is derived from the open-loop mode resonance theory. Subsequently, a mathematical model is developed to represent the random output of the G-CC. This approach allows the probability of open-loop mode resonant instability of the power system to be evaluated, as well as the risk of sub-synchronous resonant instability caused by the output randomness of the G-CC. Finally, validation is performed by building a simulation example system and a time-domain simulation system in MATLAB.

T-matrix of piezoelectric shunt inclusions on a thin plate

Developing piezoelectric-based plate-like metamaterials necessitates an effective modeling method to elucidate the omnidirectional wave properties of piezoelectric coupled inclusions on a thin plate. The commonly used methods, such as the transfer-matrix method and finite element method, are inadequate for analyzing the transmission and reflection of omnidirectional waves in a two-dimensional elastic medium. Unlike the existing methods, the multiple scattering method employs Bessel functions as the displacement-basis methods which can accurately describe the propagation and scattering characteristics of omnidirectional waves. This paper develops a novel T-matrix formulation to support the multiple scattering method, representing the input-output relationship between incident and reflected waves from a piezoelectric shunt inclusion on a host thin plate. The piezoelectric shunt inclusion comprises a varying-thickness substrate bonded with piezoelectric shunting patches. The T-matrix of the piezoelectric shunt inclusion is formulated by integrating the wave-based method with Rayleigh-Ritz method. The derived T-matrix is then used to semi-analytically analyze the far-field scattering and reflection properties of a single inclusion. Numerical results capture the scattering properties resulting from trapped mode resonances of the piezoelectric shunt inclusion. Additionally, the capability of the piezoelectric shunt damping to design and tune multiple critical coupling conditions for axisymmetric modes of thin plates is parametrically investigated by varying the values of inductors and resistors.

Impact of tip curvature and edge rounding on the plasmonic properties of gold nanorods and their silver-coated counterparts.

Colloidal solutions of gold nanorods and silver-coated gold nanorods were prepared. The seeded growth synthesis protocols were improved by adding a flocculation purification step. The resulting populations of pure gold nanorods and Au@Ag core-shell cuboids were characterized by very low dispersion in size and shape. UV-vis-near-infrared absorption measurements were performed on several batches of well-calibrated nano-objects, supported by calculations based on the discrete dipole approximation, allowed to highlight the impact of various morphological features on the optical response. In addition to the well-known effect of the nanorod aspect ratio on the shift of the longitudinal surface plasmon resonance mode, special attention was paid to changing either the rounding of the nanorod end-caps or that of the edges of the coating silver shell. Nanorods and cuboids were modeled as superellipsoids. This approach enabled us to model precisely their complex shapes using just a few simple parameters and analyze the evolution of their extinction spectra as a function of the rounding of their tips and edges. Such nano-objects are widely used for various applications in fields such as biomedical, biosensing, or surface-enhanced Raman spectroscopy, thus making it crucial to precisely assess the impact of each morphological feature for optimizing their performance.

Construction of Chiral-Magnetic-Dielectric Trinity Structures with Different Magnetic Systems for Efficient Low-Frequency Microwave Absorption.

The fabrication of carbon nanocoil (CNC)-based chiral-dielectric-magnetic trinity composites holds great significance in low-frequency microwave absorption fields. However, it is not clear that how the different magnetic systems affect the magnetic and frequency responses of the composites. Herein, four types of magnetic metals, FeCo, CoNi, FeNi, and FeCoNi, are selected to be combined with the chiral templates respectively, resulting in four types of chiral-dielectric-magnetic composites with similar morphology. The CNC templates endow all the composites with excellent dielectric loss. Further permeability analysis and the micro-magnetic simulation confirm that the frequency response region can be well adjusted by changing the magnetic systems with specific magnetic resonance modes and magnetic domain motion. Due to the synergistic effect between magnetism, chirality, and dielectricity, the FeNi-based composites exhibit the best low-frequency microwave absorption performance. The minimum RL of -60.7 dB is achieved at 6.7 GHz with an ultra-low filling ratio of 10%, and the EAB value in low-frequency region is extended to 3.7 GHz. This study provides further guidelines for the design of the chiral-dielectric-magnetic trinity composites in low-frequency microwave absorption.

Broadband rectification of microwave current in magnetic tunnel junctions with perpendicular magnetic anisotropy

We experimentally studied the effect of broadband rectification of microwave current in magnetic tunnel junctions with perpendicular magnetic anisotropy with using the method of spin-transfer ferromagnetic resonance in a planar external magnetic field. It was found that the parameters of broadband rectification (frequency range, rectified voltage value and the region of existence of the ferromagnetic resonance mode) depend on the size of the sample and its shape. The maximum value of the rectified voltage was on a round elliptical sample of 100×150 nm. At the same time, the widest operating frequency range of approximately 2 GHz was observed on strongly elliptical MTJs with the size of 75×250 nm.

Efficient second-harmonic generation in a lithium niobate metasurface governed by high-Q magnetic toroidal dipole resonances.

Lithium niobate (LN) is an excellent nonlinear optical material due to its large nonlinear coefficient, low loss, and broad optical transparency window. So, it is widely used in the generation of nonlinear harmonics. Magnetic toroidal dipole (MTD) resonance is a special optical resonance mode, which can effectively localize the light field inside the device, thus enhancing the nonlinear effects of the materials. In this work, we numerically study the second-harmonic generation (SHG) effect of the LN metasurface based on the MTD mode with a high quality factor (Q-factor). The designed LN nanorod dimer metasurface supports high Q-factor MTD guided mode resonances (GMRs), which are excited by varying the center spacing of the two nanorods, and the Q-factor can be controlled by the offset distance. The excited MTD can effectively confine the electric field within the device, which enables the LN metasurface SHG conversion efficiency to reach 1.15 × 10-2. In addition, by adjusting the structural parameters, it is possible to effectively modulate the wavelength and conversion efficiency of the SHG. Our results provide a new route for high-quality nonlinear light sources.

Waveguide-Enhanced Nanoplasmonic Biosensor for Ultrasensitive and Rapid DNA Detection.

DNA is fundamental for storing and transmitting genetic information. Analyzing DNA or RNA base sequences enables the identification of genetic disorders, monitoring gene expression, and detecting pathogens. Traditional detection techniques like polymerase chain reaction (PCR) and next-generation sequencing (NGS) have limitations, including complexity, high cost, and the need for advanced computational skills. Therefore, there is a significant demand for enzyme-free and amplification-free strategies for rapid, low-cost, and sensitive DNA detection. DNA biosensors, especially those utilizing plasmonic nanomaterials, offer a promising solution. This study introduces a novel DNA-functionalized waveguide-enhanced nanoplasmonic optofluidic biosensor using a nanogold-linked sorbent assay for enzyme-free and amplification-free DNA detection. Integrating plasmonic gold nanoparticles (AuNPs) with a glass planar waveguide (WG) and a microfluidic channel, fabricated through cost-effective, vacuum-free methods, the biosensor achieves specific detection of complementary target DNA sequences. Utilizing a sandwich architecture, AuNPs labeled with detection DNA probes enhance sensitivity by altering evanescent wave distribution and inducing plasmon resonance modes. The biosensor demonstrated exceptional performance in DNA detection, achieving a limit of detection (LOD) of 33.1 fg/mL (4.36 fM) with a rapid response time of approximately 8 min. This ultrasensitive, rapid, and cost-effective biosensor exhibits minimal background nonspecific adsorption, making it highly suitable for clinical applications and early disease diagnosis. The innovative design and fabrication processes offer significant advantages for mass production, presenting a viable tool for precise disease diagnostics and improved clinical outcomes.

Characterization of strongly coupled quartz tuning fork sensors for precision force measurement in atomic force microscopy

Miniaturized quartz tuning forks (QTFs) have been adopted as force sensors for non-contact atomic force microscopy (AFM). However, the coupled oscillation behaviors of the QTF prongs are not well understood, preventing quantitative measurement of the nanoscale tip-sample interaction forces. This article presents a lumped model that accurately delineates the coupled mechanical oscillations of QTF prongs, establishing rigorous relationships between experimental observables and tip-sample interaction forces. The first-order resonance spectra of a commercial QTF were fully characterized by correlating its piezoelectric response with the actual mechanical oscillation measured with a Fabry-Pérot interferometer. In order to uniquely determine the modeling parameters (i.e., the effective masses, spring constants, and damping constants), the experimental results were compared with the lumped model predictions while masses were added to one prong. The results reveal that the QTF’s center of mass is highly damped, preventing the observation of a symmetric resonance mode. In addition, the mass loading experiment demonstrates that the mechanical oscillations of the QTF prongs are strongly coupled, accounting for 59% (84%) of the effective stiffness at the in-plane (out-of-plane), antisymmetric resonance mode. We believe that the obtained QTF characterization results will pave the way for quantitative measurements of non-contact interaction forces in QTF-based AFM platforms, significantly improving the precision and reliability of nanoscale force measurements.

Development and Optimization of Micro‐Nanotopographical Platforms for Surface Enhanced Raman Scattering Biomolecular Detection

AbstractTopologically designed micro‐ and nanostructured surface‐enhanced Raman scattering (SERS) substrates propel the advancements of innovative applications, including environmental and forensic point‐of‐care miniaturised devices via enhancing the localised electric fields for accurate analyte sensing. Herein, a method for designing, optimising and fabricating fine‐tuneable concentric hexagonal, triangular and rectangular SERS‐active micronano‐substrates is developed, with each unit yielding significant enhancement. Numerical simulations of the 3D near‐field electric field guided the optimal design process. While the coaxial SERS substrates consistently outperformed their solid counterparts, the hexagonal micro‐nano topologies exhibited ×21 higher signal than coaxial square arrays and a 12‐15‐fold increase over the triangle structures. Alternation of the topological designs from square to triangle lattice yielded more uniform plasmonic modes propagating along the 60°‐directions with various resonance modes playing key roles in light reflectance. This enables the engineering of platforms with tailor‐enhanced signals by changing the arrangement of micro‐nano patterned coaxial arrays. The fabricated SERS substrates are validated by detecting traumatic brain injury biomarkers, effectively yielding the characteristic fingerprint spectra of each neuro‐molecule. The straightforward development of sub‐micrometre tuneable SERS‐active architectures enables anelegant route for high‐throughput biochemical sensing, laying a platform for amplified bimolecular detection of disease biomarkers and integration in bioanalytical systems.

Modal analysis and frequency matching study of subway bogie frame under ambient excitation

A wealth of practical cases indicates that the fatigue failure of subway bogies primarily stems from the modal resonance of the structure. If the modal characteristics of the entire vehicle, including equipment and bogies, are mismatched, rail vehicles may experience abnormal vibrations and noise. Therefore, it is imperative to conduct modal analysis and matching design for subway vehicle bogies to ensure smooth operation, reduce structural vibrations and noise, and enhance vehicle safety and ride comfort. Modal identification methods under the ambient l excitations during vehicle operation were employed to identify the modal parameters of the bogie structure before and after wheel reprofiling and under different load conditions. According to the test results, wheel reprofiling has minimal impact on the modal parameters of the structure, but with an increase in load, the modal frequencies of each order generally increase. This is associated with boundary constraint states, such as the increased stiffness of the bogie air spring with an increase in vehicle load. By comparing the test results with simulation analysis results of the bogie structure under free and constrained states, it is evident that simulating realistic boundary constraint conditions is crucial to ensure the accuracy of the finite element model. Based on frequency isolation criteria and vibration isolation theory, a frequency planning basis for the bogie structure was established. The study found that as the vehicle load increases, changes in the boundary conditions of the bogie affecting the elastic modal frequencies of the structure may have a certain impact on matching design, and may even better comply with the requirements of frequency management equations. This provides a new direction for subsequent scholars researching modal matching design.

Stability and Spin Waves of Skyrmion Tubes in Curved FeGe Nanowires.

In this work, we investigate the influence of curvature on the dynamic susceptibility in FeGe nanowires, both curved and straight, hosting a skyrmionic tube texture under the action of an external bias field, using micromagnetic simulations. Our results demonstrate that both the resonance frequencies and the number of resonant peaks are highly dependent on the curvature of the system. To further understand the nature of the spin wave modes, we analyze the spatial distributions of the resonant mode amplitudes and phases, describing the differences among resonance modes observed. The ability to control the dynamic properties and frequencies of these nanostructures underscores their potential application in frequency-selective magnetic devices.

New mechanism for fermion localization in the presence of anti-curvature tensor

This study aims into brane-world scenarios within the framework of f(R, A) gravity called Ricci-inverse modified theory, exploring the dynamics of spin-1/2 fermions coupled non-minimally to background scalar field functions. Through theoretical analysis and numerical techniques, we investigate the localization of both massless and massive fermionic modes on the brane. Our findings shows intricate phenomena, including unexpected configurations of the effective potentials and the identification of resonance modes in massive fermionic spectra. These insights shed light on the interplay between modified gravity and matter in extra-dimensional models, offering promising avenues for experimental validation and furthering our understanding of fundamental physics.

Purcell Enhancement and Spin Spectroscopy of Silicon Vacancy Centers in Silicon Carbide Using an Ultrasmall Mode-Volume Plasmonic Cavity.

Silicon vacancy (VSi) centers in 4H-silicon carbide have emerged as a strong candidate for quantum networking applications due to their robust electronic and optical properties, including a long spin coherence lifetime and bright, stable emission. Here, we report the integration of VSi centers with a plasmonic nanocavity to Purcell enhance the emission, which is critical for scalable quantum networking. Employing a simple fabrication process, we demonstrate plasmonic cavities that support a nanoscale mode volume and exhibit an increase in the spontaneous emission rate with a measured Purcell factor of up to 48. In addition to investigating the optical resonance modes, we demonstrate an improvement in the optical stability of the spin-preserving resonant optical transitions relative to the radiation-limited value. The results highlight the potential of nanophotonic structures for advancing quantum networking technologies and emphasize the importance of optimizing emitter-cavity interactions for efficient quantum photonic applications.

Design and Modelling of MEMS Vibrating Internal Ring Gyroscopes for Harsh Environments.

This paper presents a design, model, and comparative analysis of two internal MEMS vibrating ring gyroscopes for harsh environmental conditions. The proposed design investigates the symmetric structure of the vibrating ring gyroscopes that operate at the identical shape of wine glass mode resonance frequencies for both driving and sensing purposes. This approach improves the gyroscope's sensitivity and precision in rotational motion. The analysis starts with an investigation of the dynamic behaviour of the vibrating ring gyroscope with the detailed derivation of motion equations. The design geometry, meshing technology, and simulation results were comprehensively evaluated on two internal vibrating ring gyroscopes. The two designs are distinguished by their support spring configurations and internal ring structures. Design I consists of eight semicircular support springs and Design II consists of sixteen semicircular support springs. These designs were modelled and analyzed using finite element analysis (FEA) in Ansys 2023 R1 software. This paper further evaluates static and dynamic performance, emphasizing mode matching and temperature stability. The results reveal that Design II, with additional support springs, offers better mode matching, higher resonance frequencies, and better thermal stability compared to Design I. Additionally, electrostatic, modal, and harmonic analyses highlight the gyroscope's behaviour under varying DC voltages and environmental conditions. Furthermore, this study investigates the impact of temperature fluctuations on performance, demonstrating the robustness of the designs within a temperature range from -100 °C to 100 °C. These research findings suggest that the internal vibrating ring gyroscopes are highly suitable for harsh conditions such as high temperature and space applications.

Enhancing phase modulation and group delay in reflective Huygens metasurfaces via a Fabry-Perot cavity

Huygens metasurfaces exhibit excellent optical properties such as 2π phase modulation and slow light effects. However, they face challenges including wide bandwidth and low group delay due to their high radiation losses. Here, we propose a reflective Huygens metasurface coupled with an F-P cavity. We demonstrate that F-P resonance modes can couple with magnetic-quasi-bound-state (M-QBIC) and electric-quasi-bound-state (E-QBIC) in the Huygens metasurface through constructive interference, significantly enhancing the quality factors of both QBICs. Through structural parameter optimization, our reflective Huygens metasurface achieves 4π phase modulation and a high group delay of up to 166 ps. Compared to the non-coupled Huygens metasurface with the same structural asymmetry, the group delay of the F-P coupled reflective Huygens metasurface is enhanced by up to 30 times. Our design reduces the fabrication precision requirements for Huygens metasurfaces, enabling similar group delays to be achieved in low-symmetry coupling structures as in highly symmetric non-coupling structures. Additionally, the performance of this metasurface shows robustness to changes in incident light polarization. This design highlights the potential for achieving high-quality factors, large phase modulation, and large group delay, offering new avenues for the design of highly sensitive tunable devices, efficient nonlinear optical devices, and narrowband slow light devices.

Large-angle analytical solution of magnetization precession in ferromagnetic resonance

Abstract Dynamics of magnetization M driven by microwave are derived analytically from the nonlinear Landau-Lifshitz-Gilbert equation. Analytical M and susceptibility are obtained self-consistently under a positive circularly polarized microwave field, h=(hcosωt,hsinωt,0), with frequency ω, which is perpendicular to a static field, H=(0,0,H). It is found that the orbital of M is always a cone along H. However, with increasing h the polar angle θ of M initially increases, then keeps 90° when h≥h 0=αω/γ in ferromagnetic resonance (FMR) mode, where α is Gilbert damping constant and γ is gyromagnetic ratio. These effects result in a nonlinear variation of FMR signal as h increases to h≥h 0, where the maximum of resonance peak decreases from a steady value, linewidth increases from a decreasing trend. These analytical solutions provide a complete picture of the dynamics of M with different h and H.

Partially embedded metabarrier to suppress surface waves in granular mediaa).

The gravity-induced depth-dependent elastic properties of a granular half-space result in multiple dispersive surface modes and demand the consideration of material heterogeneity in metabarrier designs to suppress surface waves. Numerous locally resonant metabarrier configurations have been proposed in the literature to suppress Rayleigh surface waves in homogeneous media, with little focus on extending the designs to a heterogeneous half-space. In this work, a metabarrier comprising partially embedded rod-like resonators to suppress the fundamental dispersive surface wave modes in heterogeneous granular media known as first order PSV (PSV1; where P is the longitudinal mode and SV is the shear-vertical mode) and second order PSV (PSV2) is proposed. The unit-cell dispersion analysis, together with an extensive frequency-domain finite element analysis, reveals preferential hybridization of the PSV1 and PSV2 modes with the longitudinal and flexural resonances of the resonators, respectively. The presence of the cutoff frequency for the longitudinal-resonance hybridized mode facilitates straightforward suppression of the PSV1 mode, while PSV2 mode suppression is possible by tailoring the hybridized flexural resonance modes. These PSV1 and PSV2 bandgaps are realized experimentally in a granular testbed comprising glass beads by embedding 3D-printed resonator rods. Also explored are novel graded metabarriers capable of suppressing both PSV1 and PSV2 modes over a broad frequency range for potential applications in vibration control and seismic isolation.