Propagation Characteristics Of Modes Research Articles

Temperature-assisted electromagnetic surface modes in graphene-based temperature sensitive metafilms

Graphene has the potential to manipulate surface modes in frequency bands from THz to mid-IR regions. Typically, due to single-atom thickness and low charge-carrier density, the thermal response of graphene is ineffective. Temperature-sensitive materials (TSMs) can play an active role in enhancing the thermal response of graphene-based devices. In the present work, graphene-based temperature-sensitive metafilms have been proposed for thermally tunable propagation of electromagnetic surface modes. A detailed analytical and numerical solution for temperature-dependent electromagnetic surface (even and odd) modes supported by the graphene-based temperature-sensitive metafilm has been studied. The Kubo’s formulation has been used to model optical conductivity (σ g ) while the hybrid Drude’s model is implemented to realize the indium antimonide (InSb) as temperature-sensitive material. To simulate the metafilm, the waveguide modal analysis approach was implemented, while the realization of the graphene sheets was achieved by the use of impedance boundary conditions (IBCs). The propagation characteristics for even/odd surface modes were analyzed under different values of temperature (T), chemical potential (µ c ), and thickness of metafilm (d). Further, the numerical results for even and odd surface modes under two phases of InSb [Insulator phase (T = 200 K) and metallic phase (T = 300 K)] were compared under different values of chemical potential (µ c ) and TSM film thickness (d). It is concluded that the propagation characteristics of surface modes are sensitive to the external temperature and can be tailored by tuning the temperature, chemical potential (µ c ), and TSM film thickness (d). Moreover, the degeneracy of the even and odd modes can be controlled by varying the temperature and TSM film thickness. The work is suitable for designing temperature-assisted dual channel waveguides, THz optical switches, THz optical logic designs, and flexible thermal-optical sensors.

Propagation characteristics of low frequency electromagnetic modes in collisional beam plasma system

Propagation characteristics of low frequency electromagnetic modes in collisional beam plasma system

Propagation Characteristics of Stress Waves and Failure Modes of Gray Sandstone with a Gypsum-Filled Joint Under Impact Load

Propagation Characteristics of Stress Waves and Failure Modes of Gray Sandstone with a Gypsum-Filled Joint Under Impact Load

Mechanical behaviors and failure characteristics of coal-rock combination under quasi-static and dynamic disturbance loading: a case based on a new equipment

The dynamic disasters of deep mining coal and rock mass are frequent and easy to be instable. Aiming at the deformation of coal-rock roadway under the coupled static and dynamic load, a new equipment which can simulate the actual situation dynamic environment is used to carry out the coupled static-dynamic loading test of coal-rock combination. The failure law and mechanical behavior of combination are studied. Test results show that weak structure significantly affects mechanical response of coal-rock combination. The coal part with lower strength firstly reaches the crack initiation stress. The strength of the combination is dominated by the coal part. The post-peak stage of the stress–strain curve under the coupled static and dynamic load presents a stepped reduction, which shows yield process. The dynamic load level has a significant effect on the mechanical behaviors of the combination. The elastic modulus decreases under dynamic loading. The peak stress of the combination is positively correlated with the dynamic load level in a certain range, and the peak strain was negatively correlated. The energy accumulation and dissipation are closely related to the failure of the samples. The strain energy is more concentrated in the area where the failure occurs first. The AE energy under dynamic load is developed from the traditional “four-stages” characteristic under static load to three stages. The interval release stage appears because of the appearance of intermittent disturbance load makes the AE energy of the sample change intermittently. The dynamic instability of samples accompanies a sudden increase in AE energy rate, hysteresis loop area and strain. Compared with the shear failure of single lithology sample, the failure mode of the combinations is mainly tensile, and it turns into tensile-shear failure under dynamic load. The fragmentation of samples is different under different failure modes. The fragmentation index can characterize the failure mode and crack propagation characteristics of coal-rock combination. The research provides reference for large deformation dynamic disasters of surrounding rock.

Multi-Conductor Cable Modeling With Inclusion of Measured Coaxial Wave Propagation Characteristics

The prediction of voltage stresses in transformer and machine windings requires the ability to calculate pulse propagation effects on the feeding cable with sufficient accuracy. The use of commonly available cable models in electromagnetic transient (EMT) programs can lead to voltage wave fronts with too weak damping at very high frequencies. This work shows a method for improving the accuracy of such models by usage of measured coaxial mode propagation characteristics. The information is introduced into a wide-band multi-conductor cable model at high frequencies by a merging procedure, with only a minor impact on the non-coaxial modes of propagation. The application of the developed model is demonstrated for cases where the metallic sheaths are grounded at one end only, or are cross-bonded.

A Floquet engineering approach to optimize Schottky junction-based surface plasmonic waveguides

The ability to finely control the surface plasmon polariton (SPP) modes of plasmonic waveguides unveils many potential applications in nanophotonics. This work presents a comprehensive theoretical framework for predicting the propagation characteristics of SPP modes at a Schottky junction exposed to a dressing electromagnetic field. Applying the general linear response theory towards a periodically driven many-body quantum system, we obtain an explicit expression for the dielectric function of the dressed metal. Our study demonstrates that the dressing field can be used to alter and fine-tune the electron damping factor. By doing so, the SPP propagation length could be controlled and enhanced by appropriately selecting the intensity, frequency and polarization type of the external dressing field. Consequently, the developed theory reveals an unexplored mechanism for enhancing the SPP propagation length without altering other SPP characteristics. The proposed improvements are compatible with existing SPP-based waveguiding technologies and could lead to breakthroughs in the design and fabrication of state-of-the-art nanoscale integrated circuits and devices in the near future.

Defect identification in variable thickness waveguides using SH0 guided wave

Guided waves, especially Lamb waves, propagating in plate-like structures with constant thicknesses have been investigated intensively in the past decades in the context of structural health monitoring (SHM) and non-destructive testing (NDT). However, structures with variable thicknesses are also very common in practice, such as ship hulls whose thickness varies for satisfying various load conditions, and defect identification for such structures is also of importance. In this paper, we compare the propagation characteristics of both Lamb modes and SH0 mode in variable thickness plates and propose to use the SH0 mode for defect identification in such waveguides because of its non-dispersive property. First, the non-dispersive property of the SH0 mode in waveguides with variable thickness is demonstrated in theory. Then, a wave prediction method is adopted to illustrate the differences between the Lamb modes and the SH0 mode when propagating in waveguides with constant or variable thickness. Finally, experiments are conducted on a variable thickness plate to verify the non-dispersive property of the SH0 mode and further compare the results with those of the Lamb modes. Recently developed thickness-poled omnidirectional shear horizontal piezoelectric transducers (OSH-PTs) are used to produce pure SH0 waves. It is observed that the velocity of the Lamb modes may change significantly and the group velocity of the S0 mode even decreases by 55.1% during propagation, which hampers Lamb modes from defect identification in variable thickness plates. By contrast, the SH0 mode is non-dispersive thus promising for damage detection, and its effectiveness for defect localization in such structures is validated experimentally.

Non-Hermitian coupling of orbital angular momentum modes in optical waveguides

We investigate the optical coupling of orbital angular momentum (OAM) modes in a multimode waveguide assisted by a lossy single-mode waveguide. By utilizing coupled mode theory, we show that the coupling coefficients between two OAM modes with opposite rotation directions become imaginary-valued in cylinder waveguides, which further gives rise to polarization-locked wave dynamics. Any injections with different polarizations finally evolve into linear polarization (LP) modes, as the output modes are synthetized by antisymmetric supermodes of two OAM modes. In addition, non-Hermitian asymmetric couplings are induced in elliptical waveguides, which stem from the interaction between synthetical gauge fields and dissipation. By increasing the ellipticity of waveguides, the degree of asymmetric coupling increases, and the system experiences a phase transition, which can be reflected from propagation characteristics of OAM modes. The study provides a promising approach for controlling modal coupling of OAM modes and may find potential applications in OAM generation and polarization conversion.

Macro Meso Response and Stress Wave Propagation Characteristics of MCT High-Voltage Switch Under Shock load

In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor (MCT) high-voltage switch under the synergic action of mechanical load and high voltage, the separated Hopkinson pressure bar (SHPB) test system was used to simulate different impact load environments, and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system, the instantaneous electrical signals of MCT high-voltage switch were collected. Combined with numerical simulation and theoretical analysis, the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined. The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels. The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage, recoverable functional damage, non-recoverable damage and structural damage. Due to the gap between the metal gate and the oxide layer, the insulating oxide layer was charged. After placing for a period of time, the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared, which induced the recoverable functional damage failure of the device. In addition, obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch, leading to unrecoverable damage of the device.

Influence of electron temperature anisotropy on wave mode propagation and power deposition characteristics in helicon plasma

As the core issue in helicon discharge, the physical mechanism behind the high ionization rate phenomenon is still not fully understood. Based on the warm plasma dielectric tensor model which contains both the particle drift velocity and temperature anisotropy effect, by employing the general dispersion relation of electromagnetic waves propagating in magnetized and uniform plasma with typical helicon discharge parameter conditions, wave mode propagation characteristic and collisional, cyclotron and Landua damping induced wave power deposition properties of azimuthally symmetric mode are theoretically investigated. Systematic analysis shows the following findings. 1) Under typical helicon plasma parameter conditions, i.e. wave frequency <i>ω</i>/(2π)=13.56 MHz, ion temperature is one tenth of the electron temperature, and for a given magnetic field <i>B</i><sub>0</sub> (or wave frequency <i>ω</i>), there exists a critical wave frequency <i>ω</i><sub>cr</sub> (or magnetic field <i>B</i><sub>0,cr</sub>), above which (or below <i>B</i><sub>0,cr</sub>) the damping of the <i>n = </i>1, 2, 3 cyclotron harmonics begins to increase sharply. 2) For the electron temperature isotropic case, the attenuation constants of different harmonics start to increase significantly and monotonically at different thresholds of magnetic field, while the phase constant abruptly increases monotonically from the beginning of the parameter interval. On the other hand, for the electron temperature anisotropic case, both the phase constant and attenuation constant have peaking phenomenon, i.e. the attenuation constant begins to increase sharply at a certain value of <i>B</i><sub>0</sub> and meanwhile the phase constant presents a maximum value near the same value of magnetic field, thus the phase constant starts to keep constant at a certain value of <i>B</i><sub><i>0</i></sub> and meanwhile the attenuation constant has a maximum value near this same value of magnetic field. 3) For the wave power deposition properties, under electron temperature anisotropy conditions, power deposition due to collisional damping of Trivelpiece-Gould (TG) wave plays a dominant role in a low field (<i>B</i><sub>0 </sub>= 48 Gs) (1 Gs = 10<sup>–4</sup> T); by considering the electron finite Larmor radius (FLR) effect, the power deposition of TG wave presents a maximum value at a certain point of parallel electron temperature<i> T</i><sub>e,</sub><sub>//</sub>; with the decrease of <i>T</i><sub>e,⊥</sub>/<i>T</i><sub>e,</sub><sub>//</sub>, the maximum value of power deposition increases gradually. All these findings are very important in further revealing the physical mechanism behind the high ionization rate in helicon plasma.

Estimating dispersion relations of ultrasonic guided waves in bone using a modified matrix pencil algorithm

Guided wave ultrasound technology is well recognized for non-destructive testing. The technology is increasingly applied in bone characterization and imaging to evaluate bone strength and fracture risk. Cortical bone with porous microstructure induces substantial dispersion and attenuation effects on ultrasonic guided waves (UGW). Estimating frequency-dependent propagation characteristics of co-excited wave modes is significant to studying UGW propagation and developing wave-based approaches. This work implements a modified matrix pencil method to simultaneously compute modal wavenumber and attenuation coefficient from dispersive bone UGW signals with improved convergence rate and noise reduction ability. The dispersion estimation is formulated as a matrix pencil or generalized eigenvalue problem with Loewner matrices. The extracted eigenvalues are estimated complex wavevectors, in which the wavenumber and attenuation can be deduced from the real and imaginary components respectively. The performance of the proposed algorithm is demonstrated with low signal-to-noise-ratio synthetic and experimental datasets acquired using axial-transmission measurement settings. The computed dispersive features are validated via comparison with the theoretically calculated dispersion curves by semi-analytical finite-element simulation. The dispersive wave properties are accurately reconstructed in a computationally efficient manner and can be further utilized for bone parametric analyses and subsequently clinical bone health assessment.

An Asymptotic Method for Taking into Account the Influence of the Boundary Layer of a High-Speed Flow on the Propagation Characteristics of Sound Modes in a Cylindrical Duct with Rigid Walls

An Asymptotic Method for Taking into Account the Influence of the Boundary Layer of a High-Speed Flow on the Propagation Characteristics of Sound Modes in a Cylindrical Duct with Rigid Walls

Anisotropy of the Uniaxial Pressure Influence on Lamb and SH Wave Characteristics in a Rotated Cut of LiNbO₃ Crystal.

Theoretical study of the effect of uniaxial pressure on the propagation characteristics of plate modes as Lamb and SH waves in a lithium niobate plate is carried out. A change in the effective crystalline symmetry, as well as the effective elastic constants under the pressure influence, has been derived. The controlling coefficients describing the pressure influence on the plate modes' phase velocities are calculated for the various applications of uniaxial pressure. The uniaxial pressure influence on the hybridization of the elastic waves is discussed.

Multiport all-logic optical switch based on thermally altered light paths in a multimode waveguide.

A generic multiport optical switch capable of generating all-logic outputs is demonstrated by altering the mode profiles and propagation characteristics in a multimode waveguide through a combination of microheaters. The principles and design rules are introduced. As proof of concept, a 3-bit all-logic switch is fabricated on a polymer waveguide platform. The experimental results are in good agreement with the simulations based on a heat solver and the eigenmode expansion method. The device shows polarization insensitive and colorless operation from 1520 to 1600 nm with an extinction ratio between "On" and "Off" states larger than 11.9 dB in all cases. The maximum heat power is 43.9 mW (for (1, 0, 0) state). The simple, compact, and easily scalable device can be used to construct 1×N and M×N switch networks, showing promising applications in on-chip photonic signal processing and computation.

Modal propagation characteristics and transient analysis of multiconductor cable systems buried in lossy dispersive soils

In surge analysis, an important issue is the influence of the imperfect earth on the propagation characteristics of the conductors. In this paper, the wave propagation characteristics and the transient performance of underground multiconductor cable systems in flat, vertical and trefoil arrangement are investigated. The Longmire and Smith frequency-dependent (FD) soil model as well as a generalized earth formulation are considered, taking into account in the analysis the impact of earth conduction effects on both the series impedance and shunt admittance of the cable conductors and sheaths. Comparisons are carried out with approximate earth formulations, neglecting the influence of imperfect earth on shunt admittances. Finally, resonance frequency analysis and transient simulations are performed for the different cable arrangements to evaluate the importance of FD soil modeling and earth formulation per cable arrangement.

Investigation of Wave Propagation Behavior of Partially Two-Layered Plates

Abstract In this study, the acoustic emission characteristics of a rectangular plate with a partially covered free damping viscoelastic layer excited by an acoustic source (Hsu-Nielsen) has been investigated. A partially covered plate configuration consisting of a base plate (aluminum) and free damping layer (polyethylene) is considered. An acoustic emission source generated different acoustic modes, which caused the plate to have in-plane and out-plane displacements. These plate displacements will be captured by acoustic sensors. To obtain the general form of plate displacements theoretically, Von Karman theory and a Kelvin-Voigt model were used and the equations of motion were derived using Galerkin’s method. The effects of nonlinear terms of the strain-displacement relation on wave propagation characteristics of plates were investigated. The main frequency ranges of signals and the propagation speed of acoustic modes and their attenuation are very important for source locating. These parameters depend on the acoustic source and transmitted medium. So, theoretically predicting the main frequency range of signals because of the acoustic source and propagation characteristics of different acoustic modes has an important role in an acoustic source–locating algorithm. For this purpose, acoustic emission experiments were carried out using two R15α sensors. Frequency domains of theoretical and experimental results were analyzed. A comparison of the obtained results showed good agreement between the experimental and theoretical Lamb velocities and main frequency ranges.

A persistent quiet-Sun small-scale tornado

Context. Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it. Aims. We investigate the nature and characteristics of waves within this quiet-Sun vortex flow, over the course of an uninterrupted 48-min observing time interval, in order to better understand its physics and dynamics. Methods. We used a cross-wavelet spectral analysis between pairs of Hα and Ca II 8542 Å intensity time series at different wavelengths and, hence, atmospheric heights, acquired with the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope, as well as the derived Hα Doppler velocity and full width at half maximum time series. We constructed halftone frequency-phase difference plots and investigated the existence and propagation characteristics of different wave modes. Results. Our analysis suggests the existence of Alfvénic type waves within the vortex flow that propagate upwards with phase speeds of ∼20–30 km s−1. The dominant wave mode seems to be the fast kink wave mode, however, our analysis also suggests the existence of localised Alfvénic torsional waves, which are related to the dynamics of individual chromospheric swirls that characterise the substructure of the vortex flow. The Hα V–I phase difference analysis seems to imply the existence of a standing wave pattern that is possibly arising from the interference of upwards propagating kink waves with downwards propagating ones that are reflected at the transition region or the corona. Moreover, the results provide further evidence that the central chromospheric swirl drives the dynamics of the vortex flow. Conclusions. This is the first exhaustive phase difference analysis within a vortex flow that explores the nature and dynamics of different wave modes within it. The question, however, of whether, and how, the dissipation of the derived wave modes occurs remains open, and given that such structures are ubiquitous on the solar surface, it’s also important to investigate whether they might ultimately play a significant role in the energy budget of the upper layers of the solar atmosphere.

A segmented heterostructure cladding fiber designed for extreme large mode area

A segmented heterogeneous cladding (SHC) fiber was proposed in this work to obtain extreme large mode area. The mode propagation characteristics of the SHC fiber was analysed in detail, including loss coefficient, effective mode area and transverse mode discrimination et al. The research results show that the fiber parameters such as the central angle θ of cladding 2, the wavelengthλ, the fiber core radius r and the refractive index n2 of cladding 2 all have effects on loss coefficient and effective mode area, but transverse mode discrimination is almost unaffected. When r is 150 μm, the mode area is up to 34,343 μm2. The principle of single mode operation for the SHC fiber laser was also suggested. Thus, the SHC fiber can be designed for extreme large mode area and applied in high power fiber lasers.

Asymmetric propagation of spoof surface plasmons along doubly corrugated metal surfaces

Spoof surface plasmons (SSPs) on the doubly corrugated metal surfaces can find a variety of applications, such as waveguides, filters, sensors, communications, and other high-performance active devices in terahertz (THz) and microwave bands. However, these studies so far are mostly on the perfect symmetric structure. In this paper, the asymmetric doubly corrugated metal surfaces are proposed to support and propagate SSP modes, which is inherently free from the conventional structure. The analytical dispersion theory of SSP modes on the structure is presented by a simplified field expansion method, which is also verified by a finite integration method. Based on the given modal analysis, the dispersion relations, propagation losses, and field profiles of the SSP modes with various geometric parameters for both 2D and 3D structures are investigated and analyzed in THz frequencies. By introducing an asymmetry of different upper and lower groove depths, the asymptotical frequency of the symmetric SSP mode at the Brillouin boundary can be largely tuned compared with the conventional symmetric structure. However, the asymptotical frequency of anti-symmetric SSPs on the structure is almost unmovable for the given structural parameters. The symmetric SSP mode demonstrates a larger propagation loss on the structure with the increased degree of asymmetry, while the anti-symmetric mode is inversely lower. By increasing the gap size between these two asymmetric corrugated metal surfaces, the propagation losses decrease for both symmetric and anti-symmetric SSP modes. SSP modes experience a larger distance on the asymmetric structure with an increased unit period and, thus, the damping losses are also enlarged. The effect of 3D structure parameters on the propagation characteristics of SSP modes with a closed sidewall is also considered for practical applications. The presented studies on the SSP modes of the asymmetric doubly corrugated metal surfaces provide new avenues to develop plenty of devices such as low-loss waveguides and filters and many other compact active devices at THz frequencies.

On the Identification of Elastic Moduli of In-Service Rail by Ultrasonic Guided Waves.

Non-destructive rail testing and evaluation based on guided waves need accurate information about the mode propagation characteristics, which can be obtained numerically with the exact material properties of the rails. However, for rails in service, it is difficult to accurately obtain their material properties due to temperature fluctuation, material degradation and rail profile changes caused by wear and grinding. In this study, an inverse method is proposed to identify the material elastic constants of in-service rails by minimizing the discrepancy between the phase velocities predicted by a semi-analytical finite element model and those measured using array transducers attached to the rail. By selecting guided wave modes that are sensitive to moduli but not to rail profile changes, the proposed method can make stable estimations for worn rails. Numerical experiments using a three-dimensional finite element model in ABAQUS/Explicit demonstrate that reconstruction accuracies of 0.36% for Young’s modulus and 0.87% for shear modulus can be achieved.