Frequency Splitting Research Articles

Valley-dependent conductivity and dispersion relation of surface magnetoplasmons

Electron hydrodynamics attracts increasing interest in solid state physics, offering a universal long-wavelength description of collective modes in a two-dimensional system. In two-dimensional materials with broken inversion symmetry and two degenerate valleys, a perpendicular magnetic field lifts the valley degeneracy via a Zeeman effect due to the orbital magnetic moments arising from electron rotations, relevant for developing valleytronic devices. In this work, we use a two-component hydrodynamic model to investigate the valley-dependent conductivity tensor and valley-dependent dispersion relation of surface magnetoplasmons under the modulations of the perpendicular magnetic field, Berry curvature and topological orbital magnetic moment. It is shown that the valley splitting of conductivity is large and tunable in the presence of the valley Zeeman effect. Valley splitting of frequency appears on the order of terahertz, which is preferable for realizing sub-wavelength nonreciprocal magneto-optical devices in the terahertz range.

Simultaneous wireless power and data transfer based on 4FSK modulation using the four splitting frequencies of series–parallel combined resonant circuit-based system

Simultaneous wireless power and data transfer based on 4FSK modulation using the four splitting frequencies of series–parallel combined resonant circuit-based system

Coherent rotation of a single spin via adiabatic half passage in the presence of a ferromagnetic vortex

We experimentally and numerically study possible implementations for rotations of a single nitrogen-vacancy defect spin state in proximity to a magnetic vortex core. Dynamically controlled magnetic vortex cores have been suggested as a means to provide nanoscale, rapidly-tunable magnetic fields for spin qubit addressability and control. However, driven and thermal non-equilibrium dynamics of the vortex core complicate prospects for high-fidelity gate operations. We find that the complicated profile of the driven vortex core fringe field leads to significant, but unpredictable enhancement of both Zeeman splitting and Rabi frequency. Furthermore, the gyrotropic dynamics of the vortex core lead to a complicated evolution of the spin state. We demonstrate that the fidelity of rotations can be improved using an adiabatic passage protocol in which the vortex provides an enhancement of spin splitting and Rabi frequency while unwanted vortex dynamics are suppressed.

Modeling analysis of combustion instability in an annular combustor equipped with circumferentially segmented perforated liner

Hazardous azimuthal thermoacoustic modes often occur in lean-premixed annular combustors. One practical control method is the application of perforated liners with bias flow. However, circumferentially uniform perforated liners are not competent to control them, because the perforated plate covered by a single azimuthally uniform backing cavity cannot provide sufficient acoustic pressure difference across the perforated plate to bring in adequate acoustic damping. In this work, we developed a three-dimensional thermoacoustic model to consider the effects of a novel passive control damper of the circumferentially segmented perforated liner. Emphasis is placed on the effects of the segmented liner on controlling the azimuthal modes. It is found that the azimuthal mode in the premixed annular combustor can be either plenum-dominant or combustor-dominant, with the frequency of the latter one larger than the former. The stabilities of the two kinds of modes behave differently with the change of time delay. The results of the lined combustor cases indicate that the circumferentially segmented perforated liner generally improves the control effectiveness compared with the circumferentially uniform perforated liner thanks to the rigid plates inserted in the backing cavity. At the locally inserted position, the rigid plate enforces a rigid boundary condition that changes the azimuthal pressure mode shape in the backing cavity. As a result, more acoustic damping through the pressure difference across the plate is produced. Symmetry-breaking effects are found if the segmentation is asymmetric or two-fold symmetric. The behavior of the splitting frequencies caused by the segmented liner is also studied, and the symmetric segmented liner turns out to be a better choice because the resulting azimuthal mode is degenerate with two equivalent suppressed growth rates. In order to further enhance the control effect, one significant effective measure is to increase the depth of the backing cavity.

Magnetodielectric Material Characterization Using Stepped Impedance Resonators

Two resonance-based methods for magnetodielectric (MD) material characterization are presented in this article using stepped impedance resonators (SIRs). A single SIR (SSIR) is initially used to create two spatially separated sensing areas for permittivity and permeability measurements predicated on the resonance frequency variation. Next, a differential-based sensing method, based on resonance frequency splitting, is introduced for permittivity and permeability differential measurements. For this purpose, four spatially separated sensing areas are established on a single resonance structure using a double SIR (DSIR). The presented sensors provide a reliable sensing method for MD characterization and comparison. The proposed sensing methods are validated through numerical analysis based on electromagnetic (EM) simulation and experimental measurement of materials with different intrinsic EM properties.

Photonic Band Inversion and Absorption Enhancement in Dirac Semi‐Metal Tamm Plasmon Multilayer System

AbstractTopological photonics is becoming increasingly important due to its possibility to manipulate light with topological phases. Constrained by tunable material, the concept of the topological phase of light is less employed for the realization of terahertz (THz) devices. Incorporating tunable plasmonic materials with topological photonic structures can promote topological protection at the THz frequency. Here the topological phase transition in the terahertz bands is demonstrated by integrating Dirac semi‐metal with topological photonic crystal. This work proposes photonic band inversion induced frequency splitting and absorption enhancement in bulk Dirac semi‐metal (BDS) based Tamm plasmon multilayer system. The enhancement in absorption is achieved by designing a one‐dimensional topological edge state such that the combination with the Tamm plasmon state provides topological protection to the entire BDS–photonic crystal heterostructure. The proposed structure undergoes band inversion, a topological transition in the photonic band structure. These results may facilitate the realization of terahertz topological effects and contribute to the goal of topological protection in sensing applications.

Frequency splitting characteristics analysis of capacitive wireless power transfer

Frequency splitting characteristics analysis of capacitive wireless power transfer

Stable Atomic Magnetometer in Parity-Time Symmetry Broken Phase.

Random motion of spins is usually detrimental in magnetic resonance experiments. The spin diffusion in nonuniform magnetic fields causes broadening of the resonance and limits the sensitivity and the spectral resolution in applications like magnetic resonance spectroscopy. Here, by observation of the parity-time (PT) phase transition of diffusive spins in gradient magnetic fields, we show that the spatial degrees of freedom of atoms could become a resource, rather than harmful, for high-precision measurement of weak signals. In the normal phase with zero or low gradient fields, the diffusion results in dissipation of spin precession. However, by increasing the field gradient, the spin system undergoes a PT transition, and enters the PT symmetry broken phase. In this novel phase, the spin precession frequency splits due to spatial localization of the eigenmodes. We demonstrate that, using these spatial-motion-induced split frequencies, the spin system can serve as a stable magnetometer, whose output is insensitive to the inevitable long-term drift of control parameters. This opens a door to detect extremely weak signals in imperfectly controlled environments.

Design and Experiment for N = 3 Wineglass Mode Metal Cylindrical Resonator Gyroscope Closed-Loop System

This paper studies a kind of gyro structure of N = 3 Wineglass Mode Metal Cylindrical Resonator Gyroscope (WMMCRG). Compared with traditional Cylindrical Vibrating Gyroscope (CVG), the designed structure has higher scale factor and lower frequency split. This paper provides a more specific processing method and the parameters of resonator materials. A closed-loop controlling system with low error and low noise is designed for WMMCRG. The system is composed of three independent closed-loop systems: drive closed-loop, sensing closed-loop, and quadrature error correction closed-loop. Through the test of the high-precision turntable, under the premise of the same material and processing technology, the bias instability, bias stability, zero bias, Angular Random Walk (ARW), and frequency split of WMMCRG is 1.974°/h, 10.869°/h, 10.3323°/s, 16 (°)/√h, 0.02 Hz, respectively.

Doublet structure in the optical spectrum of a semiconductor laser with optoelectronic feedback in a square-wave regime

We observe an optical spectrum consisting of a doublet in the output of a semiconductor laser diode with optoelectronic feedback in a dynamical regime in which a self-sustained square-wave modulation is observed, depending on injection current and feedback strength. The doublet frequency splitting is strongly correlated with the duty cycle of the square wave; both parameters as well as the relative magnitude of the peaks are observed to vary with the feedback level. A rate equation model reproduces the spectral doublets. The appearance of the doublet is attributed to active medium gain saturation and refractive index dependence on the carrier density.

δ Scuti pulsations in the bright Pleiades eclipsing binary HD 23642

ABSTRACT We announce the discovery of pulsations in HD 23642, the only bright eclipsing system in the Pleiades, based on light curves from the Transiting Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and attribute them to δ Scuti pulsations in the secondary component. We find four ℓ = 1 doublets, three of which have frequency splittings consistent with the rotation rate of the star. The dipole mode amplitude ratios are consistent with a high stellar inclination angle and the stellar rotation period agrees with the orbital period. Together, these suggest that the spin axis of the secondary is aligned with the orbital axis. We also determine precise effective temperatures and a spectroscopic light ratio, and use the latter to determine the physical properties of the system alongside the TESS data and published radial velocities. We measure a distance to the system in agreement with the Gaia parallax, and an age of 170 ± 20 Myr based on a comparison to theoretical stellar evolutionary models.

A frequency split trimming technique for axisymmetric shell structures

Axisymmetric shell structures are characterized by the presence of flexural modes which occur in degenerate pairs. However, since no practically realized structure is perfectly axisymmetric, the frequencies constituting a mode pair become unequal and causes what is commonly termed as “frequency split” between the modes. In applications such as vibratory gyroscopes, it is desired that the frequencies of the working pair of modes be equal. This work proposes an easily implementable (particularly in the industry) technique which reduces frequency split of a target mode pair. To address the frequency split trimming problem, this work investigates a model that describes the planar dynamics of a vibrating ring (which is prototypical to axisymmetric shell structures), with added mass segments. The effects of mass, as well as span, of an added segment on the ring’s natural frequencies and mode shapes are brought out. Novelties of the proposed trimming technique are that it employs added mass in the form of segments and that it has a negligible effect on the axes of the structure’s mode shapes. The technique is extended to general axisymmetric bodies, and it is validated experimentally for the case of a hemispherical resonator.

Dominated mode switching and nanoparticle detection at exceptional points

We present a theoretical investigation of dominated mode switching and nanoparticle detection at a wavelength of 2 µm that uses coupled whispering gallery mode (WGM) resonators operating at exceptional points (EPs). The simulations show that with assisted gain and loss the system can be steered to operate at EPs by adjusting the nanoparticle-introduced backscattering. The unbalanced contributions of the clockwise and counterclockwise modes can be observed when the system approaches the EPs, and the dominated mode is switchable by transiting the system from one EP to another. Owing to the square root topology of EPs, the enhanced frequency splitting can be obtained when the system is subjected to a perturbation, which results in a more than five times sensitivity enhancement compared to a traditional sensor. Furthermore, a simulation also reveals that an increased gain–loss contrast in the resonators contributes to an enhanced frequency splitting, and thus a higher sensitivity enhancement factor. Our investigations validate the feasibility of a WGM resonator operating at EPs for unidirectional laser emitting and nanoparticle sensing.

Nitrogen management to minimize yield-scaled ammonia emission from paddy rice in the Middle and Lower Yangtze River Basin: A meta-analysis

Paddy fields in China contributed to one third of the global cropland ammonia (NH3) emission inventory, while rice accounted for half of cereal consumption, necessitating exhaustive considerations of the balance between NH3 emissions abatement and food demand. The concept of yield-scaled emission intensity (emissions per unit crop production) has the potential to guide sustainable intensification strategies, yet its application to NH3 emissions remains poorly understood. Here, by constructing novel crop-specific models for single rice production and NH3 emissions in the Middle and Lower Yangtze River Basin (LYRB) as a case study, the relationships between fertilizer N application and yield-scaled NH3 were estimated. Contrary to our hypothesis of a tipping point, our results showed that yield-scaled NH3 curves could not directly identify optimal nitrogen (N) rates. However, the benefit of lower N fertilizer rate on NH3 abatement consistently outweighed the risk of yield loss. The exponential relationships between yield-scaled NH3 and N surplus allowed us to estimate the N surplus criterion as 15.6 kg N ha−1 (or 190 kg N ha−1 fertilizer N rate) for the LYRB. Under the N surplus criterion, NH3 emissions can be reduced by 23–27% without severely impacting rice yield, compared to the N rate required for the highest yield. Moreover, five major controlling factors for yield-scaled NH3 were estimated by random forest models, ranked in order of importance as N rate, total N, K rate, mean annual precipitation, and soil organic carbon. Among the agricultural practices (irrigation, tillage, and fertilizer management), deep placement was the most effective measure to reduce yield-scaled NH3, showing 48% reduction potential, followed by proper N splitting frequency (43%). Overall, this study highlights the efficacy of N application optimization and targeted farm management in mitigating NH3 emission while maintaining crop productivity.

Analysis of the Type 4 Effectome across the Genus Rickettsia

Rickettsia are obligate intracellular bacteria primarily carried by arthropod hosts. The genus Rickettsia contains several vertebrate pathogens vectored by hematophagous arthropods. Despite the potential for disease, our understanding of Rickettsias are limited by the difficulties associated with growing and manipulating obligate intracellular bacteria. To aid with this, our lab conducted an analysis of eight genomes and three plasmids from across the genus Rickettsia. Using OPT4e, a learning algorithm-based program designed to identify effector proteins secreted by the type 4 secretion system, we generated a putative effectome for the genus. We then consolidated effectors into homolog sets to identify effectors unique to Rickettsia with different life strategies or evolutionary histories. We also compared predicted effectors to non-effectors for differences in G+C content and gene splitting. Based on this analysis, we predicted 1571 effectors across the genus, resulting in 604 homolog sets. Each species had unique homolog sets, while 42 were present in all eight species analyzed. Effectors were flagged in association with pathogenic, tick and flea-borne Rickettsia. Predicted effectors also varied in G+C content and frequency of gene splitting as compared to non-effectors. Species effector repertoires show signs of expansion, degradation, and horizontal acquisition associated with lifestyle and lineage.

Realizing symmetry-guaranteed pairs of bound states in the continuum in metasurfaces

Bound states in the continuum (BICs) have received significant attention for their ability to enhance light-matter interactions across a wide range of systems, including lasers, sensors, and frequency mixers. However, many applications require degenerate or nearly degenerate high-quality factor (Q) modes, such as spontaneous parametric down conversion, non-linear four-wave mixing, and intra-cavity difference frequency mixing for terahertz generation. Previously, degenerate pairs of bound states in the continuum (BICs) have been created by fine-tuning the structure to engineer the degeneracy, yielding BICs that respond unpredictably to structure imperfections and material variations. Instead, using a group theoretic approach, we present a design paradigm based on six-fold rotational symmetry (C6) for creating degenerate pairs of symmetry-protected BICs, whose frequency splitting and Q-factors can be independently and predictably controlled, yielding a complete design phase space. Using a combination of resonator and lattice deformations in silicon metasurfaces, we experimentally demonstrate the ability to tune mode spacing from 2 nm to 110 nm while simultaneously controlling Q-factor.

A New Manufacturing Methodology under Limited Machining Capabilities and Application to High-Performance Hemispherical Resonator

High-performance component production requires nearly homogeneous materials, ultra-precise machining and a high surface integrity. However, conventional design and manufacturing methodologies, which continuously increase the geometric tolerance to meet the performance requirements, lead to cost increases that even exceed the existing machining capabilities. This paper presents a general manufacturing methodology for high-performance components under realistic conditions, such as the current capability for material forming and machining. In order to achieve an excellent component performance, this methodology includes parameter extraction, sensitivity analysis, and trimming processes that consider the effect of material removal resolution and processing uncertainties. Simulations performed on the hemispherical resonator demonstrate how the proposed methodology is applied to fabricate extremely high-performance resonators. An efficient modal tuning strategy is proposed based on a sensitivity analysis of the tuning process parameters subject to material removal resolution and uncertainties. The tuning results prove the feasibility of this new methodology for high-performance components manufacturing. The elimination of the frequency split can finally be achieved with surface tuning iteratively. The proposed methodology provides an effective solution to achieve high-performance components under limited machining capabilities.

Complex nonlinear dynamics of polarization and transverse modes in a broad-area VCSEL

Lasers can exhibit nonlinear and chaotic dynamics driven by the interaction of multiple lasing modes, and investigating the different scenarios of mode competition and bifurcations of their dynamics is of great interest on a fundamental level as well as in view of applications. We study the dynamics of a broad-area vertical-cavity surface-emitting laser (VCSEL) in solitary continuous-wave operation with a comprehensive investigation of its polarization state, lasing spectra, near-field distributions, and temporal dynamics. Fluctuations at the frequency of birefringence splitting and other frequency components develop in a series of bifurcations. The bifurcations coincide with changes of the transverse lasing modes and/or the polarization state, demonstrating the importance of both the spatial and polarization degrees of freedom for mode competition. As a consequence, the inherent nonlinear dynamics of broad-area VCSELs is significantly more complex than the dynamics of VCSELs with a single spatial mode.

Design of Helmholtz resonator group in a lightweight aluminum alloy wheel for reducing tire acoustic cavity resonance noise

Tire acoustic cavity resonance (TACR) noise is one of the significant sources causing vehicle interior noise at low-frequency band. Since the rotating and loading conditions can split TACR frequencies, TACR noise exhibits a relatively narrow frequency band, which becomes a challenge to attenuate this type of noise. To deal with this problem, the reduction method of the Helmholtz resonator (HR) group installed inside a lightweight aluminum alloy wheel is adopted in this paper. By the combination welding of spoke and rim in aluminum alloy wheel of a passenger vehicle, the internal annular hollow area is generated as the installation space for this HR group. Great advantages of this manufacturing process are the lightweight and easy installation performances for the wheel. According to the theoretical analyses based on the superposition of traveling waves and its experimental validations, the frequency bands of TACR noise for a rotating tire are determined. To reduce the noise, HR group consisting of 5 different sizes is designed by the Finite Element Method (FEM). Meanwhile, the sound-reducing tire-wheel assembly incorporated with the designed HR group is manufactured and tested by the bench and vehicle experiments. A remarkable reduction can be observed at the peak and specified frequency range of TACR noise. Moreover, the performance also proves to be stable and robust under various road and speed conditions. This paper provides a comprehensive and feasible process strategy for the development of noise-reducing wheel.

Research of Frequency Splitting Caused by Uneven Mass of Micro-Hemispherical Resonator Gyro.

In practical engineering, the frequency splitting of Hemispherical Resonator Gyro (HRG) caused by uneven mass distribution seriously affects the precision of HRG. So, the inherent frequency is an important parameter of micro-Hemispherical Resonator Gyro (m-HRG). In the processing of hemispherical resonator, there are some morphological errors and internal defects in the hemispherical resonator, which affect the inherent frequency and the working mode of m-HRG, and reduce the precision and performance of m-HRG. In order to improve the precision and performance of m-HRG, the partial differential equation of the hemispherical resonator is solved, and the three-dimensional model using ANSYS software accurately reflected the actual shape is established in this paper. Then, the mode of hemispherical resonator in ideal state and uneven mass distribution state are simulated and analyzed. The frequency splitting mechanism of the hemispherical resonator is determined by calculation and demonstration, and the frequency splitting of the hemispherical resonator is suppressed by partial mass elimination. The results show that the absolute balance of energy can ensure the high-quality factor and the minimum frequency splitting of the hemispherical resonator. Therefore, during the processing of hemispherical resonator, the balance of mass should be achieved as much as possible to avoid various surface damage, internal defects and uneven mass distribution to guarantee the high-quality factor Q and minimum frequency splitting of hemispherical resonator.