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Deep-subwavelength periodic metallic structures, which are also called plasmonic metamaterials, have received much attention due to their ability of supporting spoof surface plasmons polariton (SPP) modes. However, it is still difficult to obtain the dispersion relations of different modes for complicated plasmonic metamaterials with finite thickness. To solve the problem, we make further development of a field-network joint dispersion analysis method that was proposed recently so that the method can be used to analyze the spoof SPP structures with a certain thickness. The developed method not only allows us to predict the dispersion relations of complicated spoof SPP structures with finite thickness but also can be used to find a series of intrinsic high-order modes of the periodic metallic structures. As an example, we present the theoretical dispersion curves of the fundamental and high-order modes for a complicated spoof SPP structure, which have good agreements with the simulated results. Meanwhile, the calculated near fields also match the simulated and measured results well. [ABSTRACT FROM AUTHOR]

The dispersion and dielectric attenuation characteristics of a double-staggered grating waveguide (DSGW) are two crucial features related to the output characteristics of a sheet-beam traveling-wave amplifier and have been previously studied by using theoretical analysis and simulations. In this work, these two characteristics are both experimentally studied. Two ${H}$ -band (220–325 GHz) DSGW circuit prototypes with and without dielectric attenuators made of the BeO-TiO2 composite ceramic were machined by using nanocomputer numerical control milling. Experimental studies of the dispersion property were performed successfully where the measurement results were in good agreement with those predicted by simulations, exhibiting a wide passband of 70 GHz (230–300 GHz). The measured transmission coefficient has been decreased from −5 to −55 dB after the introduction of dielectric attenuators, experimentally verifying the feasibility of the adopted methodology. The effects of the variations of dispersion relation and transmission loss on the beam-wave interaction stability were also investigated. [ABSTRACT FROM AUTHOR]

We numerically calculate using the 2-D electromagnetic solver SUPERFISH the dispersion relation for electromagnetic modes supported by finite-length, overmoded, corrugated, cylindrical slow wave structures (SWSs) with azimuthal symmetry by first enforcing electric, and thereafter magnetic boundary conditions on both the left and right boundaries of the SWS. We construct the dispersion relation as a set of dispersion curves related to azimuthally symmetric TM0n modes of the finite-length SWS and compare it with the analytically calculated dispersion relation. It is shown as a result of the numerical calculations that the analytically calculated dispersion curves of higher order TM0n modes of the infinite-length SWS are not the dispersion curves defining each single TM0n mode, but rather are combinations of dispersion curves defining those high-order TM0n modes with some parts of dispersion curves defining lower order TM0n-k) modes, where k = 1 . . . (n−1). [ABSTRACT FROM AUTHOR]

The plasmonic surface is made of metallic surface with deep sub-wavelength decorations, which are designed to mimic the surface plasmon polaritons at lower frequency. Recently, high-order modes in some special structures are analyzed. In order to analyze the dispersion problem of high-order modes of complex lossless structures faster and simpler, a convenient and simple method using the average input wave impedance obtained by a field-network joint solution is proposed. Meanwhile, based on Forster's reactance theorem, high-order modes of the complex structure always exist. Then, the dispersion curves of the high-order modes calculated using proposed method are in perfect match with the simulated results, which can verify the effectiveness and correctness of the proposed method. Additionally, the simulated and experimentally measured electric field distribution of high-order modes have great agreement. Using the proposed method, one can quickly obtain dispersion curve of a plasmonic structure to verify or estimate structure design. Hence, the proposed method may make a big step forward for obtaining the special dispersion relations.

In this article, by substituting the dielectric tensor in Maxwell’s equations and using the boundary conditions in a longitudinally magnetized plasma-filled coaxial elliptical waveguide, the dispersion relation in the considered configuration is derived. We study the energy and dynamic of an injected external electron with initial energy using radiation of an electromagnetic source in the considered waveguide having the considered hybrid mode. The trajectory and kinetic energy of an injected electron in the considered waveguide along the propagating axis and hybrid field components are plotted. The obtained differential equations are numerically solved by the fourth-order Runge–Kutta method, and the results are graphically presented. The effects of different parameters on the trajectory and kinetic energy of injected electrons are investigated. [ABSTRACT FROM AUTHOR]

The metallic grating structure is usually used in the Cherenkov maser. In order to further improve the gain and bandwidth of the sheet beam metallic grating waveguide system, the beam can be with initial transverse and axial velocity instead of pure axial velocity. In this situation, the sheet helical beam will interact with several space harmonics waves simultaneously, and then, the combined cyclotron and Cherenkov resonances can be utilized. Based on the linear theory, the “hot” dispersion equation of the sheet beam metallic grating cyclotron maser is derived and calculated. Through the numerical calculations, the contribution of each resonance, and the influence of beam voltage, the magnetic field and transverse to axial velocity ratio on the gain and bandwidth are analyzed. Besides, the effects of the beam voltage and magnetic field on the growth rate are also simulated, which can further verify the accuracy of the theoretical calculations. This analysis shows the potential of the sheet helical beam with a metallic grating waveguide system, which can be further studied and applied in the future. [ABSTRACT FROM AUTHOR]

A magnetically insulated line oscillator (MILO) was studied using the simulation software packages high-frequency structure simulator (HFSS) and Computer Simulation Technology-Particle Studio (CST-PS). HFSS was used to find dispersion characteristics of the slow-wave structure and predict resonant-mode frequencies. CST-PS was used to analyze the operation of the device with space charge included. At an applied voltage of 500 kV, CST-PS predicted 1.25-gigawatt (GW) microwave generation at 1.2 GHz while drawing 57 kA. These simulations are consistent with previously published experimental results for a similar MILO. The CST-PS model was used to predict MILO operation as a function of injected voltage, and a separate study was performed to evaluate the effects of an independent, externally applied axial magnetic field. These simulation efforts are in support of upcoming experiments at the University of Michigan, where the MILO investigated in this article will be tested on a new linear transformer driver facility. [ABSTRACT FROM AUTHOR]

This article presents a small-signal theory of a tape helix traveling-wave tube (TWT) with distributed cold tube loss, including the recently discovered space charge effects on the circuit mode that was obtained from the exact dispersion relation of the corresponding lossless tube. The classical values of Pierce’s parameter ${C}$ and ${Q}$ are modified in this new formulation, while the cold tube loss will enter in a similar way as in Pierce. Realistic examples are given, including tubes with uniform circuit loss and with a spatial sever, and compared with the Pierce’s classical theory. [ABSTRACT FROM AUTHOR]

Based on a kinetic model, a linear theory of the 2-D sheet beam metallic grating cyclotron maser has been derived and analyzed numerically. The TE mode dispersion relation and the periodicity of the normalized amplitudes of spatial harmonics of the cyclotron maser with rectangular gratings are obtained. Through numerical calculations, the dependence of the growth rate on the gap distance between the metallic grating surface and the beam, the external magnetic field strength, the beam current, the transverse-to-axial velocity ratio, the axial velocity spread, and the beam voltage are analyzed. This article presents an analysis of interaction using the fundamental TE mode in the 2-D metallic grating sheet beam system. The fundamental TE mode in the 2-D metallic rectangular waveguide grating structure is the fundamental TMx mode in the 3-D rectangular waveguide grating structure and this method can be extended to the practical 3-D interaction system that operates at other TMx modes and has a good potential for the study of the combined resonances in cyclotron masers with grating structures. [ABSTRACT FROM AUTHOR]

In this paper, the finite-element method (FEM) is applied for an exact solution of the dispersion of hybrid electromagnetic waves excited in a novel combined elliptical waveguide. This special configuration is included of an elliptical metallic waveguide filled with a dielectric material, whereas two axial hollows with circular cross section have been created in it. A hollow is placed in one of focuses of the elliptical waveguide and second hollow is located in another focus or shifted from it. Two straight relativistic electron beams with the same currents and velocities in opposite directions are injected inside the hollows. Here, we apply an accurate approach in which the electromagnetic fields described by the FEM and satisfies boundary conditions at the interfaces of different regions. Then, the time growth rate of slow waves amplified by the electron beam is numerically calculated. The excited waves are in microwave range. The effects of accelerating voltage and current density of electron beams, and geometrical parameters such as radius and location of electron beam, on the frequency spectra, the growth rate, and profiles of axial electric and magnetic fields of excited slow waves are studied. Our research shows, the novel waveguide studied in this paper is superior to other waveguide structures in wave amplification with applying minimum input electrical power. [ABSTRACT FROM AUTHOR]

An analytical model is developed with the aim to investigate the propagation of dust-acoustic (DA) waves in a multicomponent thermal dusty plasma system including ion species as well. Dust particles are considered positively charged by electron and ion currents, thermionic and UV photo-ionic processes. The model is applied to laboratory plasma as well as Martian atmospheric plasma to explain the nature of dust potential variation as well as characteristics of DA propagation modes within the linear and nonlinear regimes for given plasma parameters. In the nonlinear regime, the KdV equation is derived, and the equation is seen to support the propagation of compressive solitons in laboratory plasma system and rarefactive solitons in the case of Martian atmospheric plasma. The inclusion of ion species in the system is seen to have an important role in determining the propagation speed, the amplitude, and the corresponding width of solitons. The thermionic work function W, photon yield factor Y, and low value of flux density of UV photon beam $J$ do not have an appreciable impact on dispersion relation and DA soliton structures. On the contrary, noticeable changes occur in the case of the dust surface potential obtained in both laboratory and Martian plasmas. [ABSTRACT FROM AUTHOR]

Several models have been employed for second-harmonic generation (SHG) in optical fibers. Their common drawback is the low conversion efficiency of SHG. When cladding modes had been studied as pump signals through tilted fiber grating coated by nonlinear layers, an efficiency of the order 0.14% was reached. In this paper, a detailed investigation is carried out to study SHG in absorbing optical fibers, where a new schematic is proposed by adding a thin metallic film between the fiber cladding and the nonlinear layer to excite some plasmonic modes. These modes possess enhanced field amplitudes within the nonlinear layer, leading to a higher SHG efficiency up to 22% and 4% in case of using silver and gold, respectively. Solutions of the dispersion relation, intermodal phase matching, coupling between core and cladding modes, and field distributions are fully studied. The grating parameters are optimized to reach the maximum possible efficiency. [ABSTRACT FROM AUTHOR]

In this paper, dispersion relations (DRs) of photonic crystals (PhCs) are computed by multilayer perceptron (MLP) and extreme learning machine (ELM) artificial neural networks (ANNs). Bi- and tri-dimensional optimized structures presenting distinct DRs and photonic band gaps (PBGs) were selected for case studies. Optical properties of a set of PhCs with similar geometries and different dimensions were calculated by an electromagnetic solver in order to provide input data for ANN training and testing. We demonstrate that simple- and fast-training ANN models are capable of providing accurate DRs’ curves in a very short time. [ABSTRACT FROM AUTHOR]

The Sentinel-1 constellation can provide numerous high-resolution C-band synthetic aperture radar (SAR) data with long-term continuity and freely, thus showing a cost-effective solution for the coastal monitoring at high or moderate spatial resolutions. The major goal is to improve estimates of shallow water depth for SAR applications. We present an algorithm that is based on the linear dispersion relation between water depth and swell parameters like swell wavelength, direction, and period to estimate shallow water depth using multitemporal SAR data with a short repeating cycle. This is accomplished via circular convolution and Kalman filter that provides both the estimates and a measure of their uncertainty at each location. The introduced algorithm is tested on four Sentinel-1 interferometric wide swath (IW) mode SAR images over the coastal region of Fujian Province, China. The retrieved water depth both from multitemporal SAR images and different single SAR images show general agreement with water depth from an official electronic navigational chart. All comparisons indicate that the proposed method is feasible and multitemporal SAR data have great potential in bathymetric surveying. [ABSTRACT FROM AUTHOR]

Plane-wave (PW) ultrasound imaging allows for ultrafast image acquisition rates, thus enabling new biomedical applications, such as ultrasound-based blood flow and tissue motion characterization. We propose two novel Fourier domain techniques for PW ultrasound image reconstruction that can be used as an alternative to conventional delay-and-sum beamforming. In particular, we show how to modify two classic algorithms used for geophysical data processing (namely, Stolt’s and slant-stack depth migration under zero-offset constant-velocity assumptions), so that their new versions can be used for PW ultrasound data processing. To demonstrate the merits and limitations of our approach, we provide qualitative and quantitative comparisons with other Fourier domain methods reported in the ultrasound literature. Our evaluation results are based on the image resolution, contrast, and similarity metrics obtained for several public-domain experimental benchmark data sets. [ABSTRACT FROM AUTHOR]

For a realistic case of an electron beam interacting with the electromagnetic fields supported by a thin perfectly conducting tape helix, we derive the exact dispersion relation, from which an unambiguous determination of Pierce’s space-charge parameter ${Q}$ is made. In the process of doing so, we discover that the circuit mode in the equivalent three-wave theory of Pierce must be modified at high beam current, an aspect not included in Pierce’s original analysis. We quantify this circuit mode modification by a new parameter that we call ${q}$ , introduced here for the first time in traveling-wave tube theory. In a realistic example, we find that the effect of ${q}$ is equivalent to a modification of the circuit phase velocity by as much as two percent, which is a significant effect—equivalent to a detune of two percent. [ABSTRACT FROM AUTHOR]

As it is well known that the simplified classical Pierce’s three-wave theory can provide scaling insights into traveling-wave tube (TWT) operation for its close-form solutions, and thus becomes a useful guide for TWT design. However, the classical Pierce’s three-wave theory shows poor agreement with Lagrangian theory, so determining how to achieve a more accurately Pierce’s three-wave theory from Pierce’s four-wave theory becomes an open problem. In this paper, a more accurately revised Pierce’s three-wave dispersion relation is deduced by using an approximate treatment on the nonlinear term of the dispersion relation of Pierce’s four-wave beam-wave interaction theory. Meanwhile, the boundary conditions of classical Pierce’s three-wave theory are revised by theoretical analysis. Thus, the revised Pierce’s three-wave theory is established. The Pierce small-signal theories are compared to each other and Lagrangian theory on a set of TWT parameters which are based on a single pitch section of C- and Ku- bands TWTs. It is found that the revised Pierce’s three-wave theory agrees extremely well with Lagrangian theory and gains more accuracy than the classical Pierce’s three-wave theory in the small-signal beam-wave interaction region. Finally, the phase difference between Pierce’s four-wave theory and revised Pierce’s three-wave theory is discussed. [ABSTRACT FROM AUTHOR]

Due to the abilities of remarkable field confinements and enhancements, plasmonic surfaces supporting spoof surface plasmon polaritons (SPPs) are important artificial structures with many potential applications. In this paper, we propose analytical derivation to the dispersion formulation of metallic surface with complicated subwavelength decorations using a field-network joint solution, which offers a new scheme to obtain the dispersion relations of plasmonic surfaces. Based on the proposed method, we could predict not only the dispersion relationship between the frequency and wavenumber but also the approximate near-field distribution on the plasmonic surface rapidly and accurately. As an example, we analyze a series of complex-decorated metallic plasmonic surfaces, with comparisons to the full-wave simulation and experiment. The analytical, numerical, and experimental results show that these plasmonic surfaces support electromagnetic surface modes that are similar to the SPPs at the optical frequency. Meanwhile, the calculated dispersion curve and field form have great matching to the simulation and measured results. [ABSTRACT FROM AUTHOR]

Video imagery of surface waves recorded from a small off-the-shelf quadcopter with a self-stabilizing camera gimbal is analyzed to estimate the surface current field. The nadir looking camera acquires a short image sequence, which is geocoded to Universal Transverse Mercator coordinates. The resulting image sequence is used to quantify characteristic parameters (wavelength, period, and direction) of short (0.1–1 m) surface waves in space and time. This opens the opportunity to fit the linear dispersion relation to the data and thus monitor the frequency shift induced by an ambient current. The fitting is performed by applying a spectral energy-based maximization technique in the wavenumber–frequency domain. The current field is compared with measurements acquired by an acoustic Doppler current profiler mounted on a small boat, showing an overall good agreement. The root-mean-square error in current velocity is 0.09 m/s with no bias. [ABSTRACT FROM PUBLISHER]

The findings of this paper prove that the direct implementation of fourth-order operators in the alternatingdirection-implicit finite-difference time-domain algorithm is not the most consistent way to improve its accuracy. Instead of applying the standard expressions, a methodology that exploits the scheme's dispersion relation is introduced, so that spacetime errors are balanced as equally as possible. After applying a matching-terms approach, new operator coefficients are extracted that depend on cell shape and time-step size. The resulting scheme offers an order of magnitude smaller error over practically all frequencies of interest, verifying the successful implementation of dispersion-reducing practices in this unconditionally stable technique. [ABSTRACT FROM AUTHOR]

It is useful to determine the stopband of a bed of nails that can be used for packaging applications. The traditional methodology to identify the cell characteristics is to use the eigenmode solver, which is a numerical method that cannot be validated using a measurement setup. Here, we introduce a mathematical procedure to extract the dispersion relation out of the scattering parameters. The scattering parameters express the transmission and the reflection at the ports, which are functions of the phase constant of the propagating modes inside the device under test. A measurement setup is established by placing several successive cell rows inside a $Ku$ -band rectangular waveguide. The proposed algorithm is validated through examples of well-known dispersion relations. The extracted dispersion relation with the introduced methodology is in good agreement with the one obtained from the eigenmode solver. The ride gap waveguide is used as an application example. [ABSTRACT FROM AUTHOR]

The propagation of ionic perturbations in a dusty plasma is considered through a three-species kinetic simulation approach, in which the temporal evolution of all three elements, i.e., electrons, ions, and dust particles are followed based on the Vlasov equation coupled with the Poisson equation. Two cases are focused upon: first, a fully electron-depleted dusty plasma, i.e., a plasma consisting of ions and dust particles. The second case includes dusty plasmas with large electron-to-ion temperature ratios. The main features of the ionic waves in these two settings, including the dispersion relation and the Landau damping rate, are studied. It is shown that the dispersion relation of the ionic waves perfectly matches the dispersion relation of Langmuir waves and hence is called Langmuir-like ionic waves and can be considered as Langmuir-like ionic waves. These waves can be theoretically predicted by the dispersion relation of the dust-ion-acoustic waves. The transition of ionic waves from dust-ion-acoustic to Langmuir-like waves is shown to be sharp/smooth in first/second case. The Landau damping rates based on simulation results are presented and compared with theoretical predictions wherever possible. [ABSTRACT FROM PUBLISHER]

The dispersion relations of two lowest-order surface plasmon (SP) modes are derived for a structure consisting of a thin silver layer around a reduced cladding fiber. Mode splitting is formed by reducing metal thickness. Fulfillment of phase matching condition is investigated by inspection of the SPs’ and fiber modes’ dispersion diagrams. Propagation lengths, field patterns, and resonance wavelengths are determined with high accuracy. The sensitivity of 7.13 × 10−6 RIU is obtained for ambient refractive index range of 1.333–1.375. Short-range SP modes cannot be excited in this structure even in IR region. Dependence of SP cutoff conditions on the core radii, metal thickness, ambient refractive index, and operating wavelength are explored. It is proved that the proposed method is going to be useful for proper structural design of single plasmonic mode operation in SP resonance based fiber optic refractive index sensors. [ABSTRACT FROM PUBLISHER]

Four different two-band E(k) relations for band-to-band tunneling in the literature are examined. Three of them are continuous functions, from Franz, Kane, and Flietner, respectively. One is piecewise, consisting of two linear lines from the band edges in a k^{2} versus E plot. It is shown that while all three continuous models converge to the same function when the effective masses of the two bands are equal, they give different k^2 or mass-barrier products when the masses are unequal. In particular, Flietner’s model can result in a mass-barrier even higher than the piecewise linear model when the masses are highly mismatched. In addition to the four published models, a fifth, generalized power- n~E(k) model is introduced, which covers both Franz’s model and the piecewise linear model as two special cases. [ABSTRACT FROM AUTHOR]

Swell propagation in shallow water sets specific relationships between water depth and swell parameters like swell wavelength and period. These relationships allow coastal bathymetry to be retrieved if swell parameters are measured. Synthetic aperture radar (SAR) is able to image swell waves, and spectral analysis of SAR images is a well-known approach for measuring swell parameters. However, owing to nonlinearities in SAR imaging, speckle and noise, spectral analysis can result in significant bathymetric errors. The paper individuates the conditions in which linear imaging is achieved and presents an algorithm able to preserve the accuracy of the calculated bathymetry against image speckle and noise. The proposed approach includes: 1) image resizing and filtering before spectral analysis; 2) limitations to the domain of the spectral analysis; and 3) spatial smoothing of the estimated parameters. The algorithm is tested on L-band ALOS PALSAR data collected over coastal regions in the Gulf of Naples, Italy, showing that swell can be properly tracked from open sea to shoreline. Dense coverage and submetric accuracy is thus achieved. [ABSTRACT FROM PUBLISHER]

By using the coupled-mode theory-based transfer matrix, we analyze the optical properties of direct and indirect coupling of cascaded cavities in the resonator-waveguide system. The dispersion relation of the system, bandgap opening mechanisms, and anticrossing behavior are investigated theoretically and numerically. We also derive the transmission coefficients of the direct and indirect coupling system with multiple cavities and demonstrate the interaction between the modes, which leads to Fano resonance with an asymmetric transmission line shape. All the results obtained by the transfer matrix method are confirmed by the finite-difference time-domain method in photonic crystals. [ABSTRACT FROM PUBLISHER]