Supercoupling of surface waves withε-near-zero metastructures

This study examines the analytical and numerical solution of electromagnetic surface waves supported by a resistive metasurface-covered grounded metamaterial structure. To simulate the metamaterial, the Kramers–Kronig relation based on the causality principle is used, while the modeling of the resistive metasurface has been done by implementing the impedance boundary conditions. The analytical expressions for the field phasors of surface waves are developed for the transverse magnetic (TM) polarized mode and transverse electric (TE) polarized mode. The characteristic equations are computed for both modes, and the unknown propagation constant is evaluated numerically in the kernel. After computation, the dispersion curves, electric field profiles, effective mode index (N_{eff}), and phase speeds (v_{p}) are presented for both the TM and TE polarized modes. To study the tunability of surface waves, the influence of the thickness of the metamaterial slab (d), effective permittivity of the metamaterial (varepsilon_{1}), thickness of the resistive metasurface (t), and effective permittivity of the metasurface (varepsilon_{r}) on all the numerical results has been studied. However, the geometrical parameters are found to be more sensitive to the effective mode index (N_{eff}) and phase speed (v_{p}) of the surface waves. The results are consistent with the published results, which reflects the accuracy of the work. It is concluded that the appropriate choice of parameters can be used to achieve surface waves with the desired characteristics in the GHz range. The present work may have potential applications in surface waveguide design, surface wave speed controllers, surface communication devices, and light trapping configurations.

LiNbO, is examined as to its suitability for ex- tended time delays using the wraparound concept. In this connection the propagation characteristics of surface waves on rotated (about the X axis) I' cuts are investigated for propaga- tion directions such that the sagittal plane is in the neighbor- hood of the YZ plane. These crystal cuts and directions of propagation are of considerable interest inasmuch as they contain planes of propagation which exhibit large electrome- chanical coupling and favorable anisotropy (extended beam collimation). These same orientations also contain directions of propagations in which leaky wave modes can appear. Leaky-wave propagation is possible for directions of propaga- tion which do not lie in the YZ plane for a range of rotated Y cuts, wherein the outward surface normal makes an angle of between -5 and -85 (or equivalently - 175 to -95) with respect to the positive Y axis of the crystal measured toward the positive Z axis. Electric probe measurement of piezo- electric surface waves have been made on rotated Y cuts which support leaky-wave propagation. Velocity profiles on three rotated Y-cut planes were obtained for each of the surface- wave, shear-wave, and leaky-wave solutions. general, the surface-wave mode is evanescent in the transverse direction so long as its velocity is less than the lowest bulk shear-wave velocity in the substrate material.5 Since the sur- face wave propagation velocity on a cylindrical surface in- creases as the ratio of the radius to wavelength approaches unity,' the lowest shear wave will be the lowest velocity mode at some point and the evanescent condition is no longer satis- fied. Mode conversion is then a distinct possibility, unless the particle displacements of the two modes are orthogonal to each other, thus preventing mode coupling. On the other hand, there exists an upper limit on the radius of curvature if mode conversion, leading to significant attenua- tion, developes along all or part of the propagation path in the curved region. In that case, and for purely practical reasons, the curved path length must be minimized by reducing the curvature radius as much as is possible, subject only to the lower limit criteria discussed previously. The large functional bandwidth and favorable anisotropy inherent in YZ LiNbOj renders it an attractive candidate for wide band information storage. It is shown in this paper that the angle between the helical propagation path (sagittal plane) and the YZ plane in LiNhO, must be small if significant losses on the curved portions of the path are to be avoided. These additional losses arise from the coupling between the surface wave and the lowest bulk shear wave in one quadrant of rotated Y cuts, where the velocity of the latter is lower than that of the surface wave and the particle motions of the two waves have a common component and are therefore coupled. EXPERIMENTAL DATA

Tunable surface waves supported by graphene-covered left-handed material structures

The ability to freely manipulate the wavefronts of surface plasmon polaritons (SPPs) or surface waves (SWs), particularly with multifunctional integration, is of great importance in near-field photonics. However, conventional SPP control devices typically suffer from low efficiency and single-function limitations. Although recent works have proposed metasurfaces that achieve bifunctional SPP manipulation, their implementation relies on the excitations of circularly polarized (CP) light with different helicities. Here, we propose a generic approach to designing bifunctional SPP meta-devices under single-helicity circularly polarized incidence. Constructed using carefully selected and arranged meta-atoms that possess both structural resonance and a geometric phase, this kind of meta-device can exhibit two distinct SPP manipulation functionalities in both co- and cross-polarized output channels under one CP incidence. As proof of this concept, we designed a bifunctional meta-device in the microwave regime and numerically demonstrated that it can convert a normally incident left circularly polarized (LCP) beam into SWs, exhibiting both a focused wavefront in the co-polarized output channel and a deflected wavefront in the cross-polarized output channel. Our findings substantially enrich the capabilities of metasurfaces to manipulate near-field electromagnetic waves, which can find many applications in practice.

In this paper, the two-dimensional Fourier transform and wave decomposition technique are used to transform Maxwell’s equation in transversely isotropic (TI) formation into two independent sets of transmission line equations about transverse magnetic (TM) wave and transverse electric (TE) wave. According to both transmission line theory and superposition principle, an improved transmission line method is advanced to simplify the computational process of TM wave and TE wave only by introducing the transmission line Green’s functions of the current source. Thus, the new algorithm and the new expressions of current source electromagnetic (EM) dyadic Green’s functions in frequency-wavenumber domain are established for realizing the efficient simulation of marine controlled-source electromagnetic (MCSEM) responses in the horizontally layered TI formation. On this base, the basic solutions of the transmission line Green’s functions and EM boundary conditions are utilized to derive the recursive formula of the generalized reflections and amplitudes of the TE and TM waves, and the analytic solutions of the Green’s functions in each bed are obtained. Then, by using Fourier inverse transform and Bessel integral formula, the MCSEM responses in frequency-spatial domain are expressed in the Sommerfeld integral form. A combination of the cubic spline interpolation with the Lommel integral is used to efficiently compute the MCSEM responses. Finally, we validate the modeling algorithm and investigate the influences of changes in operation frequency and anisotropic coefficient on the MCSEM response in the TI formation.

Realizing and manipulating strong light–matter coupling in two-dimensional monolayer semiconductors is important in the research of cavity quantum electrodynamics and the development of photonic/plasmonic devices. Here, we investigate the coupling between the transverse-electric (TE) polarized wave supported by a Si3N4/Ag heterostructure and the two excitons in a WS2 monolayer (i.e., the A- and B-excitons) attached on such a heterostructure. It is found that the dissipation rate of the TE wave can be modified by simply varying the thickness of the Ag film. By appropriately designing the thickness of the Ag film, the strong coupling between the TE wave and the two excitons in the WS2 monolayer can be simultaneously realized, leading to hybridization of the two excitons. We numerically simulate the angle-resolved reflection spectra for the WS2/Si3N4/Ag heterostructure and reveal hybridization of the two excitons mediated by the TE wave. In experiments, we introduce Au nanorods as scatters for the TE wave, which enhance the in-plane electric field and achieve stronger photon–exciton coupling. We experimentally measured the angled-resolved scattering spectra for an Au nanorod placed on the WS2/Si3N4/Ag heterostructure and demonstrated the strong coupling between the TE wave and the two excitons, which results in the hybridization of the two excitons. Our findings open horizons for realizing and manipulating strong light–matter interaction in two-dimensional materials and pave the way for the construction of photonic/plasmonic devices by exploiting dielectric–metal heterostructure.

Internal waves are ubiquitous oceanographic features that occur in various forms across the world’s oceans. They manifest themselves as interface waves across ocean density layers that represent the interplay between buoyancy and gravitational forces, and are typically classified as linear and nonlinear internal waves. Nonlinear internal waves are characterized by isopycnal displacements that can exceed 30 m, and current velocities that approach 1 m/s. Internal wave energy converters, if developed, could have the advantage of no surface expression and provide for the availability of renewable ocean energy in regions of scant surface wave energy resources.
 Here, internal wave energies were computed at two locations: the New Jersey continental shelf and the coast of Central California. The available energy resource calculated for internal waves was then compared against surface gravity wave resources at each of these locations. Results suggest that the internal wave energy flux is comparable to that of surface waves on the New Jersey continental shelf during the summer of 2006 but is two orders of magnitude lower than that of surface waves in Central California during the summer of 2017. When expressed in terms of forces on a cylindrical structure, internal wave forces are an order of magnitude lower than that of surface waves on identically sized cylinders. However, the forces of the two resources are comparable when the diameter of the cylinder is doubled for the internal wave calculations. This suggests that while a larger energy converter would be required to harness internal wave energy, the larger size could be a reasonable tradeoff for advantages such as the lack of surface expression and the availability of energy in regions of limited surface wave energy resources.
 These results could potentially pave the way for longer-time scale characterization of internal waves and the development of devices to harness this energy resource (thereby powering the Blue Economy), while augmenting the portfolio of marine renewable energy resources. Further, the dominance of internal wave energy resources during summer seasons when the water column is stratified can augment the surface wave energy resource that can be diminished during the summer season.

In this paper, we reviewed some recent studies on planar metamaterials and demonstrated two new way to realize high directive antenna for the first time: 1) Quasi-periodic metamaterial surface can suppress transverse-electric (TE) surface waves and support directive emissions. 2) Periodic metamaterial surface can be applied in realizing one-dimensional subwavelength Fabry-Perrot (FP) metamaterial cavity which support directive emissions. We show both experimentally and theoretically that these phenomena mainly originate from the dispersive reflection phase and surface wave dispersions.

The reflection, the transmission, and the scattering properties of transverse electric surface waves incident on single and multiple discontinuities in a dielectric slab waveguide are analyzed. Boundary conditions acting together with the orthogonality provide singular coupled integral equations on the discrete and continuous wave amplitudes at the discontinuities. This system of singular integral equations is solved by iteration via the conventional Neumann series which are found rapidly converging. Illustrative examples such as the step, the abruptly ended, and the air‐gap junctions are treated.

A low-profile metasurface-based dipole antenna is proposed, analyzed, and implemented for the wideband operation with improved gain. The metasurface is suspended by separating it from the ground plane with an air gap and positioning it right beneath a horizontally oriented dipole. The wide operating bandwidth is attributed to the simultaneous excitation of the transverse electric surface wave resonance of the suspended metasurface (SMS) and the adjacent metasurface-based dipole resonance. The small propagation constant of transverse magnetic surface wave in the operating band enlarges the SMS aperture along the dipole direction for higher gain compared to a conventional low-profile antenna. The proposed antenna design with an overall thickness of 0.07λ (λ is the wavelength in free space at the center operating frequency) shows the realized boresight gain of 8.5-11.5 dBi over |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ -10 dB impedance bandwidth of 33.6% (or 4.15-5.85 GHz).

We considered surface waves at the interface between a metal and a photorefractive medium in local drift and nonlocal diffusion mechanism. We used particle vibration model and the method of numerical simulation of MATLAB to investigate the formation and energy variation of surface waves and stability of localized surface wave. The type of surface wave is decided by the value of the propagation constant. It will form the delocalized surface wave when sign of the propagation constant is negative, and we will get the shock surface waves and localized surface waves for the positive propagation constant. The energy of the surface waves in photorefractive medium increases monotonically with the propagation constant. We evoluted the localized surface waves applying the split step Fourier method for the stability of localized surface wave. The localized surface wave is propagating stably at the interface between a metal and a photorefractive medium.

Excitation of surface waves by a relativistic electron beam propagating over a conducting cylindrical medium (metal or highly ionized plasma) is investigated theoretically. Dispersion relations describing the linear interaction of surface electromagnetic waves with a monoenergetic electron beam are derived, and the growth rates and spatial amplification factors of excited waves are determined. Condition for the nonlinear trapping of the beam electrons by a surface wave is used to determine the maximum amplitude of the excited wave and the optimal radiator length. The electric field of a surface wave excited by an electron beam is estimated for a particular case.

Metasurface (MTS) antennas are based on the transformation of a cylindrical-wavefront surface wave (SW) into a general wavefront leaky wave (LW). The MTS aperture is constituted by a grounded dielectric slab printed with an electrically dense distribution of subwavelength patches realizing space-variable, homogenized tensor impedance boundary conditions (IBCs). One of the challenges in this type of antenna is related to obtaining dual polarization operations by using the same impedance modulation. In this article, we explore and compare three simple approaches to obtain two beams with orthogonal polarizations by feeding two ports. A first known method is based on exciting both a transverse electric (TE) and a transverse magnetic (TM) SW mode on the same modulated impedance. A second method exploits the concept of impedance modulation sharing, according to which two distinct modulations, designed to radiate different polarizations when properly illuminated by distinct offset feeding points, are superimposed on the same aperture. A third method consists in duplexing an outward (radially diverging) and an inward (converging to the center) SW. Simple analytical formulas are presented for the synthesis of the impedance that allows for the control of the inward/outward waves to ensure balanced radiation performances in terms of aperture efficiency for the two polarizations. A comparison in terms of performances between the latter two approaches is presented.

The accurate source depth of earthquake is important for understanding plate-tectonic processes and structure of seismic faults, identifying natural earthquake and non-natural earthquake. The amplitude formula of seismic surface wave shows that the amplitude of surface wave is closely related to the focal mechanism, the azimuth from epicenter to station and the source depth. When the focal mechanism and the observation position are determined, the excitation energy of surface wave is sensitive to source depth. The surface wave amplitude spectrum can be applied to determine the focal depth. The amplitude energy of shallow earthquake shows the “notch” phenomenon in band of frequency between 0.01 and 0.08 Hz in amplitude spectra, i.e. the attenuation of amplitude energy. The position of the frequency-dependent “notch” is related to the source depth. In this study, the relationship between the position of the “notch” and the source depth is analyzed by theoretical seismogram. We obtain the amplitude spectrums of the far-field at different source depths and then locate the source depth by means of comparing with observed seismic waveforms. By the amplitude spectrum of theoretical surface wave, small changes in the source depth can cause the variation of the amplitude spectrum so that the source depth of shallow earthquake can be accurately determined. The focal mechanism is coupled with the source depth. In order to analyze the influence of the disturbance of source mechanism to source depth determination, the focal mechanism of Jiuzhaigou earthquake was inversed, with disturbance of 10 degrees to strike, dip and rake. The results show only rather small changes in locating depth. In order to eliminate the influence of low frequency noise, shear wave and surface wave of short-period on amplitude spectra, this study adopts the AK135 velocity model to remove the dispersion. In this study, the seismic source depth of the Jiuzhaigou M 7.0 earthquake of 8 August 2017 in Sichuan province, China, was determined at 8.2 km by the energy attenuation characteristics of Rayleigh amplitude spectrum.

Surface waves have been extensively studied in earthquake seismology. Surface waves are trapped near an infinitely large surface. The displacements decay exponentially with depth. These waves are also named Rayleigh and Love waves. Surface waves are also used for nondestructive testing of surface defects. Similar waves exist in finite width three-dimensional plates. In this case, displacements are no longer constant in the direction perpendicular to the wave propagation plane. Wave energy could still be trapped near the edge of the three-dimensional plate, and hence the term edge waves. These waves are thus different to the two-dimensional Rayleigh and Love waves. This paper presents a numerical model to study dispersion properties of edge waves in plates. A two-dimensional semi-analytical finite element method is developed, and the problem is closed by a perfectly matched layer adjacent to the edge. The numerical model is validated by comparing with available analytical and numerical solutions in the literature. On this basis, higher order edge waves and mode shapes are presented for a three-dimensional plate. The characteristics of the presented edge wave modes could be used in nondestructive testing applications.