Transverse Magnetic Surface Waves Research Articles

Dipolar Huygens-Kerker radiation for surface waves.

Exotic dipolar radiation with zero light emission in one direction but maximal light emission in the opposite direction was envisioned by Huygens in 1690, and it could emerge in vacuum if the ratio between the source's electric and magnetic dipole moments fulfills the Kerker condition as revealed by Kerker in 1983. Due to its intricate connection with both the Huygens principle and Kerker condition, this radiation phenomenon is suggested to be termed as dipolar Huygens-Kerker radiation, and at this moment, the ratio is termed as the Huygens-Kerker ratio. However, the dipolar Huygens-Kerker radiation remains underexplored in non-vacuum matters, inside which the source locates, especially for surface waves. Here we find that the dipolar Huygens-Kerker radiation of surface waves in principle could occur in non-vacuum matters and is essentially featured with the same normalized radiation pattern, which is closely related to the inclination factor that appears in the Fresnel-Kirchhoff diffraction theory. Moreover, the corresponding Huygens-Kerker ratio is intrinsically determined by the phase velocity of excited surface waves. To be specific, the Huygens-Kerker ratio is proportional to the phase velocity for transverse-magnetic surface waves but becomes inversely proportional to the phase velocity for transverse-electric surface waves.

Comment on: “Tunable surface waves supported by graphene-covered left-handed material structures” [Opt. Commun. 489 (2021) 126874

In a recent article (Yaqoob et al., 2021), Yaqoob et al. studied the tunable electromagnetic surface wave propagation on the graphene-covered left-handed material (LHM) slab backed by the perfect electric conductor (PEC). They derived the dispersion relations for both transverse electric (TE) and transverse magnetic (TM)-polarized surface waves, and then used the relations for two types of LHMs according to the spectral range, i.e., GHz- and THz-LHM. The present Comment points out although the system under consideration (i.e., graphene-covered LHM) is itself physically challenging, the results for THz-LHM are also rather unreal because the frequency regime to accomplish the calculations falls within the high THz frequency band. In such a frequency band, the conductor substrate no longer behaves like a PEC and thus the results are rather unreal when considering THz-LHM. We note that the metal, for example, gold or silver may be modeled as a PEC, but only for a few THz. Moreover, when considering GHz-LHM, we obtain new forms of dispersion relations for both TE and TM surface waves. We find that our dispersion relations do not agree with the results obtained by Yaqoob et al.

Wide Bandwidth and Enhanced Gain of a Low-Profile Dipole Antenna Achieved by Integrated Suspended Metasurface

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 $0.07\lambda $ ( $\lambda $ is the wavelength in free space at the center operating frequency) shows the realized boresight gain of 8.5–11.5 dBi over $\vert \text{S}_{11}\vert \le -10$ dB impedance bandwidth of 33.6% (or 4.15–5.85 GHz).

Theoretical design and analysis of wideband active hard electromagnetic surfaces using non-Foster circuit loaded anisotropic metasurfaces

The electromagnetic (EM) hard surface which can both support transverse electric and transverse magnetic surface wave modes has the important ability to reduce the EM blockage of metallic obstacles. We propose a method to design an electrically thin hard surface with wide bandwidth by loading with non-Foster elements. The wideband hard surface composed of an anisotropic impedance coating can be considered as a kind of active metasurface. We develop a method to determine the values of the loading non-Foster circuit which can minimize the dispersion of the unit cells. For this method, we derive accurate values for the loading non-Foster elements through theoretical analysis. We also determine the fundamental limitations on the bandwidth due to stability requirements. To verify our theoretical design, we simulate the transmission performance between the two ports on opposite sides of a metallic rhombus-shaped obstacle coated with the non-Foster based metasurface. The simulated results show that the blockage has been largely reduced over a broad bandwidth from 0.2 GHz to 1.5 GHz. Finally, we provide a discussion on how the resistive part of the non-Foster circuit can affect the performance of the wideband hard surface coating.

Theory of magnetically controlled low-terahertz surface plasmon-polariton modes in graphene–dielectric structures

This paper investigates the electromagnetic behavior of transverse magnetic (TM) surface plasmon-polaritons guided by a magnetostatically biased, laterally infinite graphene surface at the interface between two dielectric materials. We present the theory for the reflectance calculation of a graphene-based attenuated total reflection (ATR) device, and analyze the conditions for the observation of surface polaritons in the 500 GHz–5 THz frequency range. In the absence of magnetostatic field B0, TM surface excitations in graphene are generated only by TM-polarized incident waves. In the presence of B0, the surface conductivity of graphene becomes a tensor, allowing surface polaritons to be excited by transverse electric (TE) polarized incident waves as well. Features in the ATR reflectance curves for TM- or TE-polarized incident radiation for several B0 are identified as corresponding to TM surface waves for the range of frequency examined. It is observed that the surface excitations produced by TE incident light display stronger confinement than the surface polaritons excited by TM incident light. Knowledge of the electromagnetic properties of graphene–dielectric structures may be valuable for modern applications in the field of tunable plasmonic graphene electronics at the far-infrared.

Strong sub-terahertz surface waves generated on a metal wire by high-intensity laser pulses.

Terahertz pulses trapped as surface waves on a wire waveguide can be flexibly transmitted and focused to sub-wavelength dimensions by using, for example, a tapered tip. This is particularly useful for applications that require high-field pulses. However, the generation of strong terahertz surface waves on a wire waveguide remains a challenge. Here, ultrafast field propagation along a metal wire driven by a femtosecond laser pulse with an intensity of 1018 W/cm2 is characterized by femtosecond electron deflectometry. From experimental and numerical results, we conclude that the field propagating at the speed of light is a half-cycle transverse-magnetic surface wave excited on the wire and a considerable portion of the kinetic energy of laser-produced fast electrons can be transferred to the sub-surface wave. The peak electric field strength of the surface wave and the pulse duration are estimated to be 200 MV/m and 7 ps, respectively.

Surface Waves in Oversized G-Band Slow-Wave Structures with Rectangular Corrugations

Surface waves in oversized G-band slow-wave structure with rectangularly corrugated wall are analyzed numerically. The inner corrugation generates cylindrical surface wave. The outer corrugation also generates transverse magnetic surface wave. The upper cut-offs of surface waves are controlled by corrugation amplitude. In excitation of the surface waves by an annular electron beam, the slow cyclotron interaction as well as the Cherenkov interaction occur due to there-dimensional beam perturbations. The slow cyclotron interaction merges with the Cherenkov interaction at lower magnetic field. The merged growth rate is enhanced by 13% as compared to the isolated Cherenkov growth rate. The surface waves on inner and outer corrugations can have different frequencies and can be excited selectively by adjusting the beam radius of the electron beam.

Surface wave resonances supported on a square array of square metallic pillars

A family of transverse-magnetic surface waves is shown to be supported at microwave frequencies by a square array of subwavelength square cross-section metal pillars on a conducting ground plane. These surface waves are experimentally characterised with a collimated microwave beam apparatus that utilises a pair of two-dimensional parabolic mirrors positioned on the sample surface. The dispersion of the modes, each associated with a quantisation of the electromagnetic field in the depth of the slits, is fully characterised and compared with the predictions of finite element modelling.

Analysis and simulation of generating terahertz surface waves on a tapered field emission tip

Finite difference-time domain simulations and analytical solutions show that terahertz transverse-magnetic surface waves are generated on a tapered field emitter tip by an oscillating terahertz current at the apex, where this current may be caused by photomixing with two lasers in laser-assisted field emission. The tip is modeled as a paraboloid so the analytical solution for the electromagnetic fields may be determined in paraboloidal coordinates using a basis of regular and irregular Coulomb wave functions. The simulations and analytical solutions show that there are quasistationary region and transitional region as the surface waves are generated by the oscillating current at the apex and then propagate on the tapered field emitter tip.

Plasma Wave Electronics: A Revival Towards Solid-State Terahertz Electron Devices

Researches on the interactions between drifting carrier plasma waves and electromagnetic waves were intensively studied theoretically and experimentally in 1960s to 1990s but faded out with inconclusive results. This study presents a series of fundamental works carried out by our group in order to re-evaluate the possibility of realizing a solid-state amplifier operating in THz region based on the drifting plasma wave interactions. Firstly, we described a new method to analyze the properties of semiconductor drifting plasma in a semiconductor-insulator structure based on the Transverse Magnetic (TM) mode analysis. The components of waves, the electromagnetic fields and the ω- and k- dependent effective permittivity which are used to describe the dielectric response of the semiconductor plasma to the TM surface wave excitation are derived. Then, the properties of semiconductor drifting plasma in a two-dimensional electron gas (2DEG) structure using the developed TM mode analysis are presented. Here, the electromagnetic fields and the ω- and k- dependent effective permittivity of the 2DEG drifting plasma are also determined. The analyzed device structure and formulation procedures to explain the interactions between drifting plasma waves in semiconductor and electromagnetic waves propagating through the interdigital slow-wave structure is then presented. Next, some preliminary experimental studies of plasma wave interactions using interdigital-gated n-AlGaAs/GaAs high-electron-mobility-structure carried out are presented. Finally, we concluded the findings or contributions of our work and some remarks for future research.

Field solution of nonlinear magnetic surface wave for a planar superconductor-antiferromagnet transmission line

A sinusoidal field solution for a nonlinear transverse magnetic surface wave in a symmetric planar transmission line made of a superconducting film and two antiferromagnets is derived. This solution enables us to investigate the propagation characteristics in the infrared frequency region. Propagation characteristics such as the attenuation constant and the phase constant are numerically analyzed as a function of the frequency, the temperature, and the thickness of a superconductor as well. In the temperature-dependent attenuation constant, it is found that there exists a characteristic temperature at which the attenuation constant attains a maximum. This characteristic temperature decreases with increasing frequency. In addition, it is seen that both the attenuation constant and the phase constant decrease with increasing thickness of a superconducting film. Finally, numerical result in the total power flow reveals that there exists a cutoff propagation constant. Electromagnetic wave can propagate through the line when the propagation constant is greater than this cutoff value.

Dyadic Green’s functions and guided surface waves for a surface conductivity model of graphene

An exact solution is obtained for the electromagnetic field due to an electric current in the presence of a surface conductivity model of graphene. The graphene is represented by an infinitesimally thin, local, and isotropic two-sided conductivity surface. The field is obtained in terms of dyadic Green’s functions represented as Sommerfeld integrals. The solution of plane wave reflection and transmission is presented, and surface wave propagation along graphene is studied via the poles of the Sommerfeld integrals. For isolated graphene characterized by complex surface conductivity σ=σ′+jσ″, a proper transverse-electric surface wave exists if and only if σ″>0 (associated with interband conductivity), and a proper transverse-magnetic surface wave exists for σ″<0 (associated with intraband conductivity). By tuning the chemical potential at infrared frequencies, the sign of σ″ can be varied, allowing for some control over surface wave properties.

Surface wave suppression in antenna systems using magnetic metamaterial

In the presence of normal substrates, it is well known that there exists strong transverse magnetic (TM) surface wave coupling between antenna ports on a shared ground plane. Through the analysis of surface wave propagation, such coupling is proposed to be substantially decreased via the use of magnetic metamaterials. The design and the characterization of the metamaterials are presented, and it is shown that within a certain frequency band, the material behaves as an anisotropic magnetic plasma, suppressing the propagation of a TM surface wave. Experimental measurements further confirm such a suppression, and an isolation improvement of 15 dB between an aperture spaced 9.2 cm apart is observed, in agreement with numerical simulations.

Surface Wave Distribution over Electromagnetic Bandgap (EBG) and EBG Reflective Shield for Patch Antenna

Surface wave distribution over electromagnetic bandgap (EBG) plate is measured and suppression of surface wave propagation over the EBG is investigated. We used a micro current probe that detects Hfield strength of the propagating transverse magnetic (TM) microwave up to 6 GHz. By scanning with the probe over the EBG, we visualized surface wave distribution at various frequencies. This visualized map shows that the EBG plate suppresses the surface wave propagation within the bandgap frequency. We utilized this effect for the antenna reflective shield. By combining the EBG with a microstrip patch antenna, this EBG works as a reflective shield and the front-to-backward radiation ratio of antenna is increased. In this experiment, we fabricated three types of shield board: mushroom type of EBG that has hexagonal textured patches connected with via-holes, textured surface without via-holes, and plane metal. By comparing the surface wave distributions and beam patterns of antenna with various shields, we found that the visualized map of TM surface wave gives us direct and intuitive information and helpful tips in designing the EBG reflective shield for patch antenna.

Quasi-periodic planar metamaterial substrates

We report our experimental and theoretical studies on a metamaterial substrate consisting of a quasi-periodic metallic planr pattern and a flat metal sheet, interconnected through metallic vias. We show that this structure possesses multiple in-phase reflection frequency regimes and spectral gaps for transverse-magnetic surface waves, whereas the transverse-electric surface waves are suppressed in all frequencies. In particular, an antenna put on top of this planar structure radiates with very high directivity (D=240) at some frequencies. This phenomenon is mainly governed by the inhomogeneity of the structure, which is a collective effect of perfect magnetic and electric conductors operating simultaneously at the frequency.

Nonlinear behavior of magnetic surface waves on the interface between ferromagnet and antiferromagnet

In this article the nonlinear frequency characteristics of the transverse magnetic surface waves at microwave frequencies on the interface between a ferromagnet and an antiferromagnet have been studied. The results show that the magnetic surface waves have passband(s) and stopband(s), which are interchangeable through the variation of the wave power. It is shown that the nonlinear surface waves excited on the interface can be backward surface waves with group velocities opposite to their phase velocities in direction. The passband widths of the forward surface waves are about five times larger than those of the backward surface waves in the situation.

Electromagnetic surface modes of a dielectric superlattice: the supercell method

We present a study of the reliability of the supercell method in calculations of surface electromagnetic modes. For a truncated superlattice constituted of nonabsorbing dielectric layers, we demonstrate that the numerical solutions obtained by this method for transverse-electric waves agree with those based on the Bloch theory for the semi-infinite superlattice. A slab of superlattice with at least nine unit cells yields satisfactory convergence to an analytic dispersion relation for the surface modes. In addition, we apply the supercell method to study in detail the dependence of transverse-electric and transverse-magnetic surface waves on the cut-off position in the cell next to the surface. As a specific case, we choose a TiO2/SiO2 superlattice—layers with relatively high dielectric contrast in the visible spectrum. We find the surface modes strongly dependent on the position of the surface. In fact, they appear only for certain terminations. By plotting the field amplitudes, we show that there exist different possibilities for the guidance of surface waves. The variation of the penetration depth of these modes is also discussed.

A fast, accurate, and efficient method for pole extraction in microstrip problems

AbstractIn this article, a fast and novel method is proposed to determine accurately and efficiently the singularity due to the surface wave as found in the electric field integral equation. The method involves a simple reorganization of the classical expressions for both the transverse electric (DTE) and the transverse magnetic surface wave modes (DTM) into some piecewise linear forms suitable for the Newton‐Raphson algorithm. Extensive numerical comparison is made with some of the classical methods used for pole extraction. The numerical results, as presented, confirm efficiency and fast quadratic convergence.

Hybrid modes, substrate leakage, and losses of slotline at millimeter-wave frequencies

Guided, hybrid propagation in a slotline at microwave and millimeter-wave frequencies is discussed. The analysis is carried out rigorously in the space domain, involving the variational solution of a singular integral equation for an E, field tangential to the slot. Data are obtained for field distributions, dispersion, and characteristic impedance, and are compared with data available in the literature. Results are reported on power lost by the propagation mode in the conductors and in the dielectric substrate. The analysis highlights the onset of leakage into a sufficiently thick substrate due to the excitation of a TM (transverse magnetic) surface wave. This sets a high-frequency limit for lossless operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theory of the response of schottky-barrier diodes to transverse magnetic surface waves

Both the reflectivity and quantum efficiency response functions of a Schottky-barrier diode are calculated for the case when the device is exposed to transverse magnetic surface electromagnetic waves. The surface plasma resonance is shown to occur in both responses Numerical results are presented for a Au/nSi diode.