Electric Surface Waves Research Articles

TE Surface Waves in a Plasma Sandwich Structure

Transverse electric surface waves are analyzed in a plasma medium bounded by a left-handed material. A dispersion relation is obtained by applying the boundary conditions for the tangential eld components. Numerical investigations show the dependence of e ective wave index on the propagation frequency for di erent thicknesses and number densities of the plasma medium and also for di erent values of the lling factor of left-handed material.

Supercoupling of surface waves withε-near-zero metastructures

It is known that $\ensuremath{\epsilon}$-near-zero (ENZ) structures may provide exciting possibilities for light-matter interaction, including the phenomenon of supercoupling, i.e., channeling of wave energy through ultranarrow conduits connecting two waveguides. Here, we extend this concept to the surface waves using structures with effective ENZ properties, exploring how surface waves can tunnel through such structures with essentially no reflection, even in the presence of sharp bends. Such ENZ metastructures support tunneling of waves with longitudinal wave numbers near zero. The surface waves may include examples of transverse electric (TE) surface waves along the grounded dielectric slabs (e.g., in the microwave regime) and TE surface-plasmon polariton waves along the negative-permeability interfaces. The ENZ metastructures can transfer the surface wave energy from one side to another by an anomalous squeezing effect, which is effectively independent of the length and the shape of the ENZ metastructures. The interaction of electromagnetic waves with such systems offers exciting possibilities for the design of flat photonic devices and components.

Nearly perfect resonant absorption of TE-polarized light at metal surfaces coated with arrayed dielectric stripes

A quasi-transverse electric (TE) surface wave mode exists at a metal surface coated with an ultrathin high-index dielectric layer. As the coating is in dielectric stripe arrays, nearly perfect absorption of TE-polarized incidence light is observed in simulations, due to resonances of the quasi-surface waves at each segment of the dielectric-coated metal surfaces. In analysis, the Fabry-Perot-like nature of the resonances is clarified, and effects of symmetry on different behaviors of the odd- and even-order resonance modes are discussed. While the absorption peak is tunable, perfect absorption appears near cut-off wavelength of the surface mode.

Hybrid Graphene-Microfiber Waveguide for Chemical Gas Sensing

Graphene has been attracting great interest as the basis of novel photonic devices and sensors due to its many unique optical and electric properties that are quite different from conventional film materials. In this paper, we propose and demonstrate a novel hybrid graphene-microfiber waveguide structure and its application to chemical gas sensing for the first time to our knowledge. As the complex refractive index of the extremely thin graphene film (<;1 nm) can be easily modified by chemical gas molecules distributing on its surface, the transverse electric mode surface wave intensity is sensitive to gas concentration. Such an intensity modulation induced by gas molecules can be detected via the coupling of evanescent field between the graphene waveguide and the microfiber. A sensitivity of 0.31 dB/100 ppm and good reversibility are observed experimentally for acetone vapor gas sensing. It is believed that this hybrid waveguide structure could open a new window to realize a variety of graphene-based photonic sensors, for potential applications in the fields of biology, medicine, and chemistry.

Propagation of a TE surface mode in a relativistic electron beam–quantum plasma system

The dispersion properties of a transverse electric (TE) surface waves propagating along the interface between a magneto-quantum plasma–relativistic beam system and vacuum are studied by using the quantum hydrodynamic model. The general dispersion relations are derived and analyzed in some special cases of interest. Moreover, the effects of density gradients for the beam and plasma on the dispersion properties of surface waves are investigated. The kind of dispersion relations depends strongly on the ambient magnetic field B o via the gyro-frequency ω c , the quantum parameters, and the width of the plasma layer as well as the relativistic factor for the electron beam. It is found that the quantum effects play a crucial role to facilitate the propagation of TE surface waves.

NONLINEAR TE SURFACE WAVES IN A LAYERED ANTIFERROMAGNET — SUPERCONDUCTOR WAVEGUIDE STRUCTURE

This paper describes the theoretical characteristics of TE nonlinear transverse electric surface waves propagating at microwave frequencies in a layered structure of superconductor film bounded by an antiferromagnet substrate and a linear ferrite cover. The effects of the operating angular frequency and temperature of superconductor on the dispersion characteristics have been examined. The power flow has also been studied as a function of the reduced phase and attenuation constants.

Reflection, transmission, and stability characteristics of optical beams incident upon nonlinear dielectric interfaces

A recently developed equivalent-article theory is illustrated by presenting the first analytic stability result for trapped transverse electric nonlinear surface waves at an interface separating two nonlinear dielectric media. The theory permits us to make quantitative predictions on beam reflection, transmission, and breakup with accurate estimates of the amount of incident beam power converted into propagating self-focused channels and scattered as radiation. Contact is made with earlier numerical studies of Gaussian beam incidence upon a linear–nonlinear interface and of the stability properties of trapped nonlinear surface waves.

Characteristics of Reflected Bulk Acoustic Waves in Rotated Y-Cut Quartz

An analysis of the reflection of hulk acoustic waves from the hottom surface in a 90-propagating rotated Y-cut quartz reflected bulk wave (KBW) device is presented. It is shown that the reflected waves from the bottom surface consist of a shear bulk acoustic wave and an inhomogeneous electric surface wave. It is demonstrated that the inhomogeneous electric surface wave radiates energy away from the region where the hulk wave is incident. This energy is then radiated into another set of shear hulk acoustic waves. As a result, the totally reflected beam is smeared and becomes wider than the receiving trans- ducer. The actual energy loss associated with the inhomogeneous elec- tric surface wave is calculated using power balance equations. Good agreement between experimental and theoretical device insertion loss is demonstrated. HE REFLECTION and refraction of elastic waves from a piezoelectric crystal-vacuum boundary is a problem of recurring interest. Very recently, there has been a renewed interest ( l)-(5) in utilizing reflected bulk acoustic waves (RBW) to transmit energy in quartz mi- crowave acoustic devices. RBW's are excited by an in- terdigital transducer (IDT), beamed into the substrate re- flected off the crystal's bottom surface. Since they are redirected to the upper surface they can be intercepted by an output IDT. In crystal orientations that support the sur- face skimming bulk wave (SSBW), RBW's are considered (5) to be a higher frequency extension of SSBW's. They are obtained by exciting the IDT at a frequency higher than that required for SSBW operation and therefore rep- resent a simple series of the complex plate mode spectrum (2). 131. Studies (l), 141, (5) show that RBW's offer the possibility of creating a new class of planar bulk wave devices which have some distinct advantages over SAW or SSBW devices, or both. These advantages include a higher frequency of operation, a broader bandwidth, and the capability of tailoring the device frequency-tempera- ture characteristics by changing transducer separation and crystal thickness.

Effect of thin films on the surface of a dielectric on the spectrum and energy of surface waves in the transition radiation of relativistic charged particles

The authors study the excitation of electric surface waves by a charged particle which intersects, at low angle, the surface of a dielectric. The field and energy of the electric surface waves are determined. It is shown that the deposition of thin dielectric films on the surface of a dielectric leads to a shift of the spectrum of electric surface waves. By varying the dielectric permittivity and thickness of the film, one can shift the boundary frequency of the spectrum of electric surface waves towards longer wavelengths.

Scattering of surface waves on transverse discontinuities in planar dielectric waveguides

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.

Investigation of Leaky-Wave Propagation in Rotated Y Cuts of LiNbO3

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

Electric coupling properties of acoustic and electric surface waves

A discussion is given of electric coupling across in interface between various kinds of surface waves on solids. This leads to a unified treatment of the propagation and coupling properties of such phenomena as electrostatic energy carrier waves on semiconductors. Rayleigh waves on piezoelectric media and Bleustein-Gulyaev waves. The influence of an electric drift field and of a transverse magnetic field is included and much attention is paid to amplification and related phenomena. The central quantity in the treatment is the effective dielectric constant ϵ eff with which a half-space of material can be characterized. Ingebrigssen's approximation of this quantity for the case of Rayleigh waves is analyzed and shown to be realistic in many interesting situations. New effects, derived in this paper are: 1) a tendency of Bleustein-Gulyaev waves to turn “leaky”. i.e., to radiate acoustic energy away from the interface when electrically coupled to a semiconducting adjacent medium which is subjected to an electric drift field and to a transverse magnetic field; 2) a tendency of acoustic surface waves to acquire low phase velocities if this magnetic field becomes large and has the proper direction; 3) an interdigital electrode structure on a non-plezoelectric semiconductor which is subjected to a d.c. electric drift field may exhibit a negative a.c. conductance. The relevance of ϵ eff for the electrical excitation of surface waves is also shown to be considerable and some difficulties associated with previous treatments of the excitation problem are discussed in terms of ϵ eff.