TM Surface Wave Research Articles

Observation of Analog Flatland Cherenkov Radiations on Metasurfaces

AbstractRecent theoretical studies have suggested the existence of a lower‐dimensional version of the Cherenkov radiation, known as “flatland Cherenkov radiation” (FCR). FCR is generated by leakage from a surface‐wave waveguide while being entirely confined in a plane. Here, a metasurface platform is proposed for generating and observing FCR, which is characterized by alternated regions of capacitive and inductive surface impedance, supporting transverse electric (TE) and magnetic (TM) surface waves (SWs), respectively. For experimental demonstration, a microwave setup is presented, and measured results are compared with numerical simulations and theoretical predictions. The study shows that the phase velocities of different SWs can be controlled by structural designs, and suitably fast TE SWs can excite FCR in the form of slower TM SWs. FCR has unique properties such as directionality, tunability, and subwavelength confinement. The proposed platform has important potential to enable nanophotonic applications based on 2D optics, such as agile waveguiding and scanning.

Ghost surface polaritons in naturally uniaxial hyperbolic materials

We investigated ghost surface phonon polaritons localized in a naturally uniaxial hyperbolic material, where the longitudinal axis (optical axis) is at any angle with respect to the surface plane. Two ghost surface phonon polaritons (GSPs) were found in the two Reststrahlen frequency bands, respectively. They are two TM surface waves, and their electromagnetic fields not only attenuate but also oscillate with the distance away from the surface. Unlike conventional surface phonon polaritons, GSPs are virtual surface phonon-polariton modes without electrostatic limit. The numerical simulations of the GSP dispersion and polarization properties were based on the hexagonal boron nitride, and the numerical simulation of the attenuated total reflection (ATR) experiment demonstrates the existence of the GSPs and prove their excitability and observability.

A Low-Profile Dielectric Resonator Antenna With Compact-Size and Wide Bandwidth by Using Metasurface

A dielectric resonator antenna (DRA) with the loading of metasurface (MS) is proposed for low-profile, wide-bandwidth and compact-size. Firstly, an MS structure consisting of $6\times6$ periodic metallic patch cells is loaded above the DRA. It aims to excite an additional TM surface wave above the fundamental TE111 mode of the rectangular DRA. Then, the shorting walls are printed on two sides of the dielectric, thus moving down the operating frequency with respect to its TM surface wave mode. As such, the bandwidth of the antenna is significantly widened with compact-size under the operation of TE111 and TM surface wave modes. Finally, the proposed DRA with enhanced performance is fabricated and tested. The results show that an impedance bandwidth of the antenna is dramatically increased to about 17.2%, covering the frequency range from 1.75 to 2.08 GHz, which is about 9.6 times wider than the traditional DRA at the same thickness (1.8%). Besides, it still maintains the broadside radiation pattern with stable gain of around 6.6 dBi and fairly low cross polarizations of below −26 dB. Particularly, the overall size of the radiator still maintains as small as about $0.32\lambda _{0} \times 0.32\lambda _{0} \times 0.044\lambda _{0}$ . It should be noted that the analysis of the antenna is carried out by using Ansys HFSS software version 14.0 and ADS 2011.

Isolation Enhancement for W-Band Coplanar Array Antennas Based on Silicon Micromachining Technology

A W-band decoupling structure sandwiched between a pair of high-gain step-profiled horn array antennas using the silicon micromachining technology is proposed. To suppress the surface wave, 18 choke slots with a depth of one quarter wavelength at 94 GHz are arranged in a triangular-grid array and the isolation can be averagely improved by about 7 dB with a range of 2-20 dB. This decoupling structure and two W-band coplanar array antennas are fashioned and fully integrated together by the silicon micromachining technique. Five 400 μm thick and one 650 μm thick silicon wafers are utilized and the total thickness of the antennas is 2.65 mm. Thanks to this technology, light weight, compact size, and high integration of the decoupling structure and array antennas can also be achieved. Additionally, the two array antennas share a common ground plane within a small edge-to-edge spacing of 6.05 mm where TM surface waves exist. Experimental studies validate the performance of the proposed triangular-grid choke slot array.

Effect of nonlinear cap layer on TM-polarized surface waves in a graphene-based photonic crystal

In this paper, we investigated the effect of nonlinear cap layer and the chemical potential of the graphene on the p-polarized surface waves (SWs) in a one-dimensional graphene-based photonic crystal (GBPC). Three different cases were considered for the dielectric tensor of the nonlinear cap layer: (1) perpendicular uniaxial approximation, (2) parallel uniaxial approximation and (3) generic case. The results of the study indicated that the effect of nonlinear cap layer on TM SWs may be neglected due to the perpendicular approximation. On the other hand, in parallel approximation as well as generic form of dielectric function, the frequency of the TM SWs within the graphene-induced band gap (GIPBG) may be controlled by the nonlinear cap layer and the chemical potential of the graphene. Moreover, according to the results, in the GIPBG of GBPC with self-defocusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the same direction. However, with respect to the self-focusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the opposite direction. Consequently, by adjusting the chemical potential in the self-defocusing cap layer, the tunability range of the SW frequency may be extended and in the case of self-focusing, optical nonlinear effects may be eliminated.

Impedance Matching Design of a Low-Profile Wide-Angle Scanning Phased Array

In this paper, an effective method aimed at reducing the mutual impedance among array elements is developed to realize wide-angle impedance matching (WAIM) for planar phased arrays. According to the property of the coupling field, the inherent field distribution at apertures of each element is properly regulated so that the mutual impedance between two arbitrary elements can be substantially reduced. Based on the analysis of the impedance matrix for the equivalent microwave network, the required WAIM can be implemented with such minified mutual impedance. With the proposed method, a low-profile linear phased array with $1 \times 10$ uniform elements is designed and manufactured. For the presented array, the wide-angle scanning performance is attained from the joint effect of the spatial radiation and the surface-wave diffraction. To achieve WAIM, the inherent field of each element is deliberately adjusted according to the distribution of the guided TM surface wave, which acts as the dominant coupling field. Both simulated and experimental results indicate that the proposed phased array can steer its main beam from −81° to +81° in the azimuth plane, with peak realized gain fluctuation less than 3.5 dB. Particularly, besides the broad range of scan, all the active S-parameters are controlled less than −10 dB in the fixed operating band for all scanning angles.

Printed Leaky-Wave Antenna With Aperture Control Using Width-Modulated Microstrip Lines and TM Surface-Wave Feeding by SIW Technology

This letter presents a width-modulated microstrip line leaky-wave antenna (LWA) with substrate-integrated waveguide and microstrip feeding. In particular, the planar antenna system consists of an integrated surface-wave launcher and three identical rows of quasi-periodic width-modulated microstrip lines for TM leaky-wave excitation, which produces a tailored binomial-like aperture distribution on the guiding surface. The behavior of the antenna when changing the width-modulated lines for different aperture distributions is also analyzed and presented. The measured LWA demonstrates a fan beam pattern in the far field with realized gain values greater than 10 dBi and with a beam direction of about $-$ 20 $^\circ$ from broadside at 23 GHz. Also, far-field measurements and near-field data indicate that the half-power beamwidth is below 10 $^\circ$ , and the position of the main beam maximum is relatively stable, i.e., ranging from about $-$ 23 $^\circ$ to $-$ 15 $^\circ$ between 23 and 24 GHz. The measured prototype is also well matched over these frequencies and $|S_{11}| $-$ 20 dB at 23.5 GHz.

Influence of the electromagnetic parameters on the surface wave attenuation in thin absorbing layers

This paper describes the relationships between the surface wave attenuation properties and the electromagnetic parameters of radar absorbing materials (RAMs). In order to conveniently obtain the attenuation constant of TM surface waves over a wide frequency range, the simplified dispersion equations in thin absorbing materials were firstly deduced. The validity of the proposed method was proved by comparing with the classical dispersion equations. Subsequently, the attenuation constants were calculated separately for the absorbing layers with hypothetical relative permittivity and permeability. It is found that the surface wave attenuation properties can be strongly tuned by the permeability of RAM. Meanwhile, the permittivity should be appropriate so as to maintain high cutoff frequency. The present work provides specific methods and designs to improve the attenuation performances of radar absorbing materials.

A Compact Single Conductor Transmission Line Launcher for Telemetry in Borehole Drilling

A very compact and conformal launcher for single conductor transmission lines (SCTLs) at the HF-band is presented. Also the concept of using drill pipes as the conductor of SCTL is introduced for the first time to satisfy the need for cost-effective and real-time data communication in drilling process. It is shown that a TM surface wave can be launched effectively making use of the drilling mud around the drill pipe. Provision of TM surface wave launchers that can fit within the borehole at both ends makes it feasible to transmit data over the drill pipe from downhole to the surface and vice versa. The launcher is composed of an open ended helical conductor which concentrically surrounds the drill pipe with appropriate pitch and length forming a compact surface wave launcher. Keeping its dimension smaller than 0.005λ × 0.005λ × 0.03λ, the proposed launcher provides 2% fractional bandwidth at low HF-band.

A Closed-Form Representation of Isofrequency Dispersion Curve and Group Velocity for Surface Waves Supported by Anisotropic and Spatially Dispersive Metasurfaces

A general closed-form representation is introduced for representing the isofrequency dispersion curve (IDC) of an anisotropic, spatially, and frequency dispersive metasurface (MTS) constituted by a dense periodic texture of metallic elements printed on a grounded substrate. The formulation is restricted to printed elements isolated from each other (namely, patches and not slots) whose geometry exhibits at least two axes of symmetry. The expression is valid for the dominant TM surface wave (SW) until the limit of the Floquet-Bloch (FB) region and generalizes our previous formulation to arbitrary direction of propagation. This generalization permits a closed-form representation of the IDCs and of the group velocity as a function of two parameters only; these are the equivalent quasi-static capacitances along the symmetry directions of the geometry. The limit of validity of the closed-form representation has been defined and the formulation has been tested by full-wave analysis. The present formulation simplifies the design of MTS antennas and flat transformation optics devices.

Response to “Comment on ‘Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma’” [Phys. Plasmas 23, 044701 (2016)

We reply to the Comment of Moradi [Phys. Plasmas 23, 044701 (2016)] on our paper [Phys. Plasmas 20, 122106 (2013)]. It is shown that TM surface waves can propagate on the surface of a semi-bounded quantum magnetized collisional plasma in the Faraday configuration in the electrostatic limit. In addition, in the Faraday configuration, one can neglect the coupling of TM and TE modes in the two limiting cases of weak magnetic field (low cyclotron frequency) and strong magnetic field (high cyclotron frequency).

Comment on “Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma” [Phys. Plasmas 20, 122106 (2013)

In a recent article [Niknam et al., Phys. Plasmas 20, 122106 (2013)], Niknam et al. investigated the propagation of TM surface waves on a semi-bounded quantum magnetized collisional plasma in the Faraday configuration (in this case, the magnetic field is parallel to the both of the plasma surface and direction of propagation). Here, we present a fresh look at the problem and show that TM surface waves cannot propagate on surface of the present system. We find in the Faraday configuration the surface waves acquire both TM and TE components due to the cyclotron motion of electrons. Therefore, the main result of the work by Niknam et al. is incorrect.

Transition Function for Closed-Form Representation of Metasurface Reactance

Metasurfaces are thin metamaterials used for manipulating propagation of plane waves and surface-waves (SWs). They can be characterized by homogenized–boundary conditions, which, in absence of losses, can be represented through an equivalent reactance. In this paper, we introduce a general representation of isotropic frequency-dependent reactance which is valid along the dispersion curve of the relevant TM SW. This representation is written in terms of a transition function derived from a manipulation of the Cardano’s formula for third-degree algebraic equations. Throughout a large portion of the dispersion curve, this transition function depends on one parameter only, which is an equivalent quasi-static capacitance. Approaching the Floquet–Bloch region, where many higher order Floquet modes are excited, two additional parameters should be extracted from the full-wave data to complete the transitional representation of the reactance until the upper boundary of the Brillouin region. The final formula is valid for a generic isotropic reactance and for an anisotropic reactance when the direction of propagation is along a symmetry axis of the unit cell element.

Propagation of TM-surface waves on semi-bounded quantum plasma through porous medium

The propagation of surface waves on a semi-bounded quantum plasma through a porous medium is investigated. The quantum hydrodynamic equations and Maxwell’s equations are linearized and used with the boundary conditions to derive the dispersion relation for the surface wave on a quantum electron plasma half-space. For the electrostatic limit [speed of light tends to infinity (c → ∞)], the dispersion relation is analytically studied. The results show that the quantum effects that is characterized by coupling (plasmonic) parameter, porosity and viscosity enhance the propagation velocity of these waves, while the medium permeability slows down the propagation velocity of these waves.

Design of Scalar Impedance Holographic Metasurfaces for Antenna Beam Formation With Desired Polarization

This paper presents the design of a novel planar scalar impedance holographic metasurface, which is capable of beam forming with a desired electric field polarization and high gain. It is demonstrated that the surface can be constructed with patches of simple geometry and design. A detailed analysis of the mechanism of scalar impedance holographic metasurfaces is discussed. The scalar impedance holographic metasurface is designed at a dominant TM surface wave mode frequency. It is observed that the TM surface wave mode has an impurity of TE polarized electric fields of small magnitude. The presence of this impurity is exploited to design a holographic metasurface for beam forming with a desired polarization. This modified-HAIS is capable of forming a beam at a nonphase crossover frequency, unlike the conventional HAIS. The design procedure of the surface, with simulation and measurement results, is presented.

Theoretical Limitations for TM Surface Wave Attenuation by Lossy Coatings on Conducting Surfaces

In this work, we theoretically analyze the limitations for TM surface wave attenuation on lossy coated conducting surfaces containing electric and/or magnetic loss. We use both an analytical approach as well as numerical simulations, and find excellent agreement between them. We also find that the loss can be described by a simple approximate expression for a wide range of material properties. Furthermore, we analyze lossy slabs with simple equivalent circuit boundaries on top, such as may be provided by frequency selective surfaces or other patterned structures. We find that such composite lossy coating can exceed the attenuation of a simple lossy slab, but with limited bandwidth. We also find that only by increasing permeability, and not permittivity, can the peak absorption frequency be lowered for a given thickness without reducing the relative absorption bandwidth.

Impact of a DC magnetic field on evanescent wave intensity amplification for a magnetocompensated antiferromagnet

The impact of a dc magnetic field on evanescent TE and TM waves at the interface of transparent media comprising a semiconductor layer and a semi-infinite antiferromagnet is investigated using Otto geometry as an example. It is shown that switching a dc magnetic field orthogonal to a sagittal plane allows maximum amplification of the intensity of propagating evanescent TM or TE waves in both a layer and in semi-infinite space. The optimum conditions correspond to the formation of a peculiar TM or TE surface wave.

Positively and negatively large Goos–Hänchen lateral displacements from a single negative layered structure

We study the electromagnetic beam reflection from layered structures that include the so-called ε-negative and the μ-negative materials, also called single negative materials. We predict that such structures can demonstrate a giant lateral Goos-Hänchen shift of the resonant excitation of surface waves at the interface between the conventional and single negative materials, as well as due to the excitation of leaky modes in the layered structures. Then we replace the conventional layer with a left-handed layer (a material with both ε<0 and μ<0). We show that the Goos-Hänchen shift can be positive and negative depending on the type of this layer (conventional or LH material), which can support TE or TM surface waves.

Surface waves on the interface between a left-handed and a right-handed medium

The frequency regions where a surface wave (SW) exists on a dielectric/metamaterial interface are determined for the case when the metamaterial’s refractive index is negative. With allowance for the conditions of TE and TM SW existence in the structure, the characteristic frequencies that can be controlled with the help of the external magnetic field are calculated. On the basis of dispersion dependences for SWs, it is shown that the TM (TE) wave is forward (backward), and the backward wave is substantially slowed in the structure.

Effect of uniaxial anisotropy of left-handed layers on created surface waves in a one dimensional photonic crystal

We investigate theoretically the creation conditions of TE and TM polarized surface waves created at the interface between a homogeneous medium and one dimensional photonic crystal (1D PC). The 1D PC is composed of uniaxially anisotropic left-handed (LH) and isotropic right-handed (RH) layers. We show that the characteristics of surface waves created in the 1D PC are significantly different from those created in the structure composed of isotropic LH and RH layers. We also prove that the coexistence of TE and TM surface waves at the interface is possible in the same frequency domain. Moreover, it is shown that in this structure backward and forward surface waves are created in wider ranges of frequency and angle of incident light, in comparison with the structure in which the left-handed layers are isotropic.