Evanescent Surface Modes Research Articles

Experimental studies on surface-wave isolation by periodic wave barriers

Periodic structures often fabricated at the micro/nano-scale have opened new vistas in acoustic and electromagnetic wave manipulations due to band-gap properties. This study shows theoretically and experimentally that the propagation of destructive surface waves can also be controlled artificially using periodic wave barriers that modify the global properties of the background soil. To depict the attenuation property of surface waves, this study provides a complete dispersion analysis, the complex dispersion relation. Results show that, remarkably, the attenuation zone for surface waves includes not only the band gap but also other evanescent surface modes. This result agrees well with that in the experimental transmission spectra for both periodic trench barriers and periodic pile barriers. Due to their broadband attenuation performance, periodic wave barriers are expected to apply to vibration isolation in a wide range of systems.

Spectral control of elastic dynamics in metallic nano-cavities

We show how the elastic response of metallic nano-cavities can be tailored by tuning the interplay with an underlying phononic superlattice. In particular, we exploit ultrafast optical excitation in order to address a resonance mode in a tungsten thin film, grown on top of a periodic MgO/ZrO2 multilayer. Setting up a simple theoretical model, we can explain our findings by the coupling of the resonance in the tungsten to an evanescent surface mode of the superlattice. To demonstrate a second potential benefit of our findings besides characterization of elastic properties of multilayer samples, we show by micromagnetic simulation how a similar structure can be utilized for magneto-elastic excitation of exchange-dominated spin waves.

Propagating Modes Generated by the Coupling of Evanescent Surface Modes in Metamaterial Slab Waveguides

Here, we report that evanescent surface modes at the interfaces between ε-negative and μ-negative metamaterials can be made into a propagating one via the introduction of symmetric slab structures. The slab induces strong coupling between double interfaces comprising the slab and also between two evanescent surface modes localized at each interface. The novel propagating mode has its origin in this strong coupling so that it becomes cut off when the core size (i.e., distance between double interfaces) becomes large enough to make the coupling effects negligible.

SCATTERING AND RADIATION CHARACTERISTICS OF STEP DISCONTINUITY IN LEFT-HANDED SLAB WAVEGUIDE OPERATING IN EVANESCENT SURFACE MODE

The scattering and radiation characteristics of a step discontinuity in left-handed (LH) slab waveguide operating in evanescent surface mode of TE and TM polarization are analyzed by a method, which combines the rigorous mode-matching method with the multi-mode network theory. In the analysis the radiation problem is transformed into a propagation problem so as to tremendously simplify the calculation procedure. The dispersion properties of the grounded planar LH slab waveguide for both ordinary and evanescent surface modes are examined, from which the left-hand property of the operating mode is testified. The relative scattered power and radiation pattern of the step are given for the first time, from which the backward radiation of the stepped LH guide is clearly demonstrated. The frequency scanning characteristics of the step under consideration in this paper are just opposite to that of the ordinary antenna, which makes the considered structure promising candidate for new type of planar antennas.

A NEW LEAKY WAVE ANTENNA BASED ON CHANNEL GUIDE FILLED WITH LEFT-HAND MATERIAL FOR MILLIMETER-WAVE APPLICATIONS

A new leaky wave antenna based on channel guide filled with left-handed material (LHM), operating in evanescent surface mode of TM polarization, is presented for millimeter wave applications. A transverse equivalent network that yields a dispersion relation in closed form is employed to analyze the leakage characteristics of the antenna. Numerical results are presented for the phase and leakage constants of the antenna in terms of different geometric parameters and dielectric distributions. Besides, the frequency dependences of the leaky characteristics for the present antenna are given, from which the backward radiation is clearly demonstrated.

Scattering and radiation characteristics of step discontinuity in a double‐negative (DNG) slab waveguide operating in the evanescent surface mode

AbstractThe scattering and radiation characteristics of a step discontinuity in a double‐negative (DNG) slab waveguide operating in the evanescent surface mode are analyzed by a method which combines the rigorous mode‐matching method with multimode network theory. In the analysis, the radiation problem is transformed into a propagation problem so as to tremendously simplify the calculation procedure. The dispersion properties of the grounded planar DNG slab waveguide for ordinary and evanescent surface modes are examined, from which the left‐hand property of the operating mode is verified. The relative scattered power and radiation pattern of the step discontinuity are given for the first time, from which the backward radiation of the stepped DNG guide is clearly demonstrated. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1085–1088, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21607

Wave Propagation in Grounded Dielectric Slabs with Double Negative Metamaterials

In this paper, the wave propagation in a grounded dielectric slab with double negative (DNG) metamaterials is studied. Dramatically different evanescent surface modes (electromagnetic fields exponentially decay both in air and inside the slab) are observed. They are highly dependent on medium parameters. An infinite number of complex surface modes are found to be existing which have proper field distribution in the air region. The investigations on the Poynting vectors show that they do not carry away energy in both transverse and longitudinal directions.

COMPLETE MODE SPECTRUM OF A GROUNDED DIELECTRIC SLAB WITH DOUBLE NEGATIVE METAMATERIALS

The properties of a grounded dielectric slab with double negative (DNG) metamaterials are investigated in this paper. Dramatically different dispersion curves of evanescent surface modes (electromagnetic fields exponentially decay both in air and inside the slab) are observed. They are highly dependent on the medium parameters. As the counterpart of the improper complex leaky modes in a double positive (DPS) medium, the complex modes in a DNG medium are proved to be exclusively proper. They have exponentially decaying fields in the air region and are termed complex surface modes. It is found that there are an infinite number of complex surface modes and they cannot be suppressed. The Poynting vectors of complex surface modes are studied and it is proved that their integrals along the transverse direction are simply zero. The complete mode spectrum of the dielectric slab for both DPS and DNG media are tabled and compared. Surface wave suppression is discussed and its necessary and sufficient conditions are presented.

Surface wave dynamics for a substrate with an adiayer

A monolayer adsorbed on a substrate can modify significantly the surface wave dynamics of the latter and more particularly the motions of the first substrate shells. Within the approximation of quasi-continuum description for the substrate dynamics and a static description of the monolayer, the surface wave dispersion curves and the surface vibrations are analytically determined in a 2D approach. In contrast to the usual theory of the Rayleigh mode which predicts an evanescent non-dispersive surface mode for a free surface elastic medium, the superficial shells of the substrate with static admonolayer exhibit either pseudo-oscillating or evanescent modes according to the value of the wave vector; the range of this behaviour depends significantly on the relative stiffness of the intrasubstrate and substrate-monolayer force constant tensors.

Optical observation of evanescent surface magnons in thin magnetic films

A new type of nonpropagating surface-wave-like magnon has been detected in yttrium iron garnet films (YIG) in a magnetostatic wave (MSW) device structure using Brillouin light scattering. The measurements were carried out on a YIG film stripline device operated at 2–4 GHz. With an applied magnetic field parallel to the stripline, magnon signals were observed at fields above the surface wave band edge. Theory shows that highly localized, evanescent surface modes can exist at such fields, but only when a ground plane is present; the bandwidth in field or frequency is inversely proportional to the separation between the film and the ground plane. The observed evanescent wave band limits are in good agreement with the theoretical values.