Excitation Of Surface Waves Research Articles

Ultra-high sensitivity Bloch surface wave biosensor design and optimization

In this paper, lithium niobate is used as a grating-coupling layer and Bragg reflector defect layer to couple the incident light and break the periodicity of the photonic crystal, which results in localized electric field enhancement and the excitation of Bloch surface waves. By adjusting the incident angle of the light, the structure can achieve two detection modes: surface diffraction detection and guided mode Bloch detection. The average detection sensitivities for the two modes are 452°/RIU and 3170°/RIU, respectively, with maximum detection sensitivities of 480°/RIU and 4380°/RIU. The designed guided mode Bloch detection has the highest sensitivity currently known.

Polarization-insensitive composite gradient-index metasurface array for microwave power reception

A composite gradient-index metasurface (C-GM) array for microwave power reception (MPR) operating at 5.8 GHz center frequency was introduced. The array is insensitive to the polarization of incident plane waves and possesses cosine gradient modulation characteristics, which can convert the incident plane waves into surface waves focused at the center of the array. The focused surface wave energy is then collected by an omnidirectional antenna and fed back to a single rectifier for radio frequency (RF) to direct current (DC) conversion, resulting in DC output. Simulation results show that the array can fully excite surface waves under different polarized plane wave excitations, and the omnidirectional antenna has good matching characteristics with the array, achieving an energy collection efficiency of 66.52%. The array was fabricated and measured, achieving an energy reception efficiency of 59.91% and an RF-DC conversion efficiency of 34.83%, which is consistent with the simulation results. The proposed C-GM array can capture higher electromagnetic power by simply increasing its size, without the need for additional rectifiers or complex matching networks, making it a flexible and efficient MPR solution for different application scenarios.

A new planar feeding method of dielectric rod antenna using dielectric resonator

This article proposes a new method for exciting surface waves in dielectric rod antennas using dielectric resonator antennas. The method involves housing a rectangular dielectric resonator antenna with a dielectric constant of 10.2 inside a hollow cylindrical dielectric rod antenna made of Teflon. By exciting the {TE}_{111}^{y} and {TE}_{113}^{y} modes of the dielectric resonator antenna, a surface wave can be launched along the Teflon tube. This method offers the advantage of integrating the dielectric rod antenna with planar circuits, where maximum radiation in the direction normal to the board is desirable. Compared to other planar feeding methods, this technique leads to lower back lobe and sidelobe levels. I fabricated the proposed structure and conducted tests to measure its performance. The measured results show an impedance bandwidth of 22% from 7.35 to 9.4 GHz and a maximum gain of 14 dB. Additionally, the simulated radiation efficiency of the proposed antenna in the entire band is above 90%.

Numerical Simulation of Surface and Internal Wave Excitation due to an Air Pressure Wave

Numerical Simulation of Surface and Internal Wave Excitation due to an Air Pressure Wave

Recent advances of transition radiation: Fundamentals and applications

Transition radiation is a fundamental process of light emission and occurs whenever a charged particle moves across an inhomogeneous region. One feature of transition radiation is that it can create light emission at arbitrary frequency under any particle velocity. Therefore, transition radiation is of significant importance to both fundamental science and practical applications. In this paper, we provide a brief historical review of transition radiation and its recent development. Moreover, we pay special attention to four typical applications of transition radiation, namely the detection of high-energy particles, coherent radiation sources, beam diagnosis, and excitation of surface waves. Finally, we give an outlook for the research tendency of transition radiation, especially its flexible manipulation by exploiting artificially-engineered materials and nanostructures, such as gain materials, metamaterials, spatial-temporal materials, meta-boundaries, and layered structures with a periodic or non-periodic stacking.

Excitation of surface waves in 3D ion beam neutralization

Neutralization of beams with 2D and 3D geometries by the electrons emitted from an external source is studied using particle-in-cell simulations. Our work reveals that the high-energy electrons excite Trivelpiece–Gould (TG) surface waves in the beams with 3D axisymmetric geometries. These high-energy electrons are generated because of a large amplitude electrostatic solitary wave (ESW) that forms near the electron source and has an electric potential amplitude more than three times the electron thermal energy. We also find that surface wave excitation only happens when the beam radius is large enough at the ion source to attract enough electrons that could form the large amplitude ESW. A comparison of the 3D TG surface wave dispersion relation with an expression for 2D surface waves reveals that they become excited in 3D axisymmetric but not in 2D planar beam because of a higher phase speed requirement in the latter case.

Frequency-dependent surface wave suppression at the Dirac point of an acoustic graphene analog

The dispersion of bound acoustic surface waves over hexagonal lattices of resonant cavities has been shown to be analogous to the dispersion of charge transport in carbon graphene. Of particular interest is the frequency range close to the acoustic Dirac point where novel physics is predicted to occur. In this study, we measure the dispersion curves of a single-layer acoustic graphene analogue with high resolution one-dimensional spatial scansand show how the curves can be suppressed (near and at the Dirac point) by strong variations in the impedance boundary conditions between the free field and surface wave regimes under certain experimental conditions. By systematically varying these impedance boundary conditions using different surface wave excitation techniques, we demonstrate that increased Rayleigh scattering and diffractive excitation can increase the dispersed surface wave pressure amplitude to an extent that the impedance-based wave suppression is circumvented. The improved conditions for observing acoustic Dirac points for two samples with two distinct operational frequency ranges are reported. The single-layer acoustic graphene analogue results discussed here are important for advancing the field of acoustic twistronics.

The dual mechanism underlying laser excitation of bulk and surface elastic waves in ablative regime

It is usually considered that plasma pressure impulse is the only mechanism corresponding to the laser excitation of bulk and elastic surface waves in an ablative regime. We report the first observation of a dual mechanism where the laser-induced shockwave impacts the target and generates secondary bulk and surface elastic waves some dozens of nanoseconds after the primary ones are generated by the plasma pressure impulse. We propose that the superimposing of the two wave groups can cause additional frequency components that should be considered in research and applications employing elastic waves generated by strong laser ablation.

Controlling surface waves with temporal discontinuities of metasurfaces

Abstract Static reactive metasurfaces allow excitation and propagation of surface waves. In this paper, we theoretically elucidate how surface-wave propagation along a reactive boundary is affected by temporal discontinuities of effective parameters characterizing the boundary. First, we show that by switching the value of the surface reactance, the velocity of surface waves is fully controlled, and the power of reflected and transmitted surface waves can be amplified. Second, we indicate that when a boundary supporting waves with transverse-electric polarization is switched to the one allowing only transverse-magnetic polarization, the propagating surface wave is “frozen” and converted to a static magnetic-field distribution. Moreover, efficiently, these fields can be “melted”, restoring propagating surface waves when the boundary is switched back to the initial state. Finally, we demonstrate that temporal jumps of the boundary reactance couple free-space propagating waves to the surface wave, in an analogy to a spatial prism. All these intriguing phenomena enabled by temporal discontinuities of effective properties of reactive metasurfaces open up interesting possibilities for the generation and control of surface waves.

Spin-decoupled excitation and wavefront shaping of structured surface waves via on-chip terahertz metasurfaces.

Surface waves (SWs) are of great importance in terahertz (THz) photonics applications due to their subwavelength properties. Hence, it is crucial to develop surface wavefront shaping techniques, which is urgent in modern information technologies. In this paper, a new scheme is proposed to realize SW excitation and spin-decoupled wavefront shaping with an ultracompact planar meta-device working in the THz range. The meta-device is composed of two parts: meta-atoms (in the center) and plasmonic metals (on the left and right sides). By carefully setting the geometry size and rotation angle of each meta-atom, the encoded spin-decoupled phase distributions for both left circularly polarized (LCP) and right circularly polarized (RCP) incident THz waves are determined. In this way, circularly polarized (CP) incident THz waves can be converted to SWs propagating along plasmonic metals with unique wavefront profiles, i.e., Bessel and focusing profiles. Full-wave simulations and THz near-field scanning experiments were performed to verify the functionalities of the meta-device, both of which are in great agreement with theoretical predictions. Our findings may provide more solutions to design THz integrated photonic devices and systems.

Retrieving the subwavelength cross-section of dielectric nanowires with asymmetric excitation of Bloch surface waves.

Optical microscopy with a diffraction limit cannot distinguish nanowires with sectional dimensions close to or smaller than the optical resolution. Here, we propose a scheme to retrieve the subwavelength cross-section of nanowires based on the asymmetric excitation of Bloch surface waves (BSWs). Leakage radiation microscopy is used to observe the propagation of BSWs at the surface and to collect far-field scattering patterns in the substrate. A model of linear dipoles induced by tilted incident light is built to explain the directional imbalance of BSWs. It shows the potential capability in precisely resolving the subwavelength cross-section of nanowires from far-field scattering without the need for complex algorithms. Through comparing the nanowire widths measured by this method and those measured by scanning electron microscopy (SEM), the transverse resolutions of the widths of two series of nanowires with heights 55 nm and 80 nm are about 4.38 nm and 6.83 nm. All results in this work demonstrate that the new non-resonant far-field optical technology has potential application in metrology measurements with high precision by taking care of the inverse process of light-matter interaction.

Design of planar wideband surface‐wave excited substrate integrated waveguide horn antenna loaded with metamaterials

AbstractIn this paper, a wideband planar substrate integrated waveguide (SIW) horn antenna based on surface wave excitation through loading metamaterials is designed. Strong coupling effect is realized between the employed bilayer metamaterial unit with the top layer as a π‐shaped‐slotted patch while the bottom layer as the complementary cross‐shaped‐slotted patch. The equivalent permittivity of the extended substrate in front of the planar horn aperture can be effectively reduced to unity and impedance mismatching for conventional planar SIW horn antenna can be reduced in a wide bandwidth. Results indicate that the working frequency of the antenna is 12.3–15.8 GHz with the relative impedance bandwidth of 24.6%.

Algorithms and Measuring Complex for Classification of Seismic Signal Sources, Determination of Distance and Azimuth to the Point of Excitation of Surface Waves

Machine learning and digital signal processing methods are used in various industries, including in the analysis and classification of seismic signals from surface sources. The developed wave type analysis algorithm makes it possible to automatically identify and, accordingly, separate incoming seismic waves based on their characteristics. To distinguish the types of waves, a seismic measuring complex is used that determines the characteristics of the boundary waves of surface sources using special molecular electronic sensors of angular and linear oscillations. The results of the algorithm for processing data obtained by the method of seismic observations using spectral analysis based on the Morlet wavelet are presented. The paper also describes an algorithm for classifying signal sources, determining the distance and azimuth to the point of excitation of surface waves, considers the use of statistical characteristics and MFCC (Mel-frequency cepstral coefficients) parameters, as well as their joint application. At the same time, the following were used as statistical characteristics of the signal: variance, kurtosis coefficient, entropy and average value, and gradient boosting was chosen as a machine learning method; a machine learning method based on gradient boosting using statistical and MFCC parameters was used as a method for determining the distance to the signal source. The training was conducted on test data based on the selected special parameters of signals from sources of seismic excitation of surface waves. From a practical point of view, new methods of seismic observations and analysis of boundary waves make it possible to solve the problem of ensuring a dense arrangement of sensors in hard-to-reach places, eliminate the lack of knowledge in algorithms for processing data from seismic sensors of angular movements, classify and systematize sources, improve prediction accuracy, implement algorithms for locating and tracking sources. The aim of the work was to create algorithms for processing seismic data for classifying signal sources, determining the distance and azimuth to the point of excitation of surface waves.

Excitation and reception of magnetostatic surface spin waves in thin conducting ferromagnetic films by coplanar microwave antennas. Part I: Theory

A fully self-consistent model for the excitation and reception of magnetostatic surface waves in thin ferromagnetic films by a set of coplanar antennas was developed and implemented numerically. The model assumes that the ferromagnetic film is highly conducting and is interfaced with non-magnetic metallic films, but is also suitable for modeling magneto-insulating films. Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction can be included at both interfaces of the ferromagnetic layer. The model calculates the coupling impedances between the different strips constituting the coplanar antennas. In some situations, this leads to a frequency non-reciprocity between counter-propagating waves even in the case of no asymmetry in the spin-wave dispersion relation. Several intermediate results of the model were checked numerically and the final output of the model, given as the scattering parameters, S11, S12, and S21 of the antenna system, were in good agreement with previous experimental studies.

Surface waves propagating along the interface between parabolic graded-index medium and photorefractive crystal with diffusion nonlinearity

The new types of surface waves propagating along the interfaces between photorefractive crystal and parabolic graded-index medium are described theoretically. The optical parameters of contacting media are chosen that the depth of field localization is less than the thickness of the graded-index layer. Exact solutions to the boundary problem in different range of the effective refractive index are obtained. The surface waves attenuating with oscillations into the photorefractive crystal can propagate with arbitrary values of the effective refractive index and with its fixed values corresponding to the discrete spectrum. The effect of the optical characteristics of the crystals on field distribution is analyzed. The surface wave corresponding to the ground mode of the discrete spectrum monotonically attenuating on both sides of the interface is found. The angle of incidence need not be small to excite surface waves with a non-oscillating profile. The period of spatial oscillations must be greater than the field penetration depth into the photorefractive crystal to excite the surface waves monotonically attenuating in the depth of the crystal.

Ultrasonic nondestructive evaluation of additively manufactured wear coatings

This work pertains to the nondestructive evaluation of additively deposited coatings using ultrasound measurements. The specific objective was to evaluate using ultrasound surface wave measurements the quality of Stellite 21 coatings deposited on Inconel 718 substrates by the directed energy deposition (DED) additive manufacturing (AM) process. The surface wave speed and diffuse backscatter amplitude of the ultrasound waves were correlated with both cracking and warpage of the coating. This research is important, because, the integrity of DED-processed coatings currently requires a combination of destructive metallographic studies and X-ray computed tomography analysis, which are both expensive and time consuming. Instead of using a normal incidence configuration for the ultrasound measurements, the surface-wave approach allows the inspection of the near surface coating integrity. Three different frequencies were used to excite surface waves because each frequency has a different penetration depth. The signals obtained were used to quantify and compare the surface wave speed and surface wave-diffuse ultrasonic backscatter amplitude from five different DED-processed Stellite coated samples. Considering destructive metallurgical characterization as a reference, surface wave measurements were found to be effective for examining coating integrity. Further, the backscatter amplitude of the surface waves was correlated with the crack density and warpage. These flaws also change the stress state of the Stellite coating and consequently the surface wave propagation speed and its scattering behavior.

Direct Numerical Inversion Methods for the Design of Surface Wave-Based Metasurface Antennas: Fundamentals, Realizations, and Perspectives

A recent synthesis paradigm for tailoring the far-field radiation of leaky wave (LW) radiating metasurface (MTS) antennas is reviewed and experimentally validated. The considered antennas are realized with electrically small patches printed on a planar grounded dielectric slab. The patch layer is modeled as an impedance sheet whose spatial variation is initially designed to provide the desired LW effect from a prespecified surface wave (SW) excitation.

Bragg–Cherenkov resonance and polaron-like decoupling of the Wigner solid on superfluid helium

Nonlinear polaron-like dynamics of the two-dimensional Wigner solid (WS) on superfluid 4He are theoretically analyzed in different models and transport regimes for their similarities and distinctions. The Bragg-Cherenkov (BC) resonant excitation of surface waves and WS decoupling from surface dimples were usually considered in terms of a dc transport model. At the same time, field-velocity characteristics of the WS are measured under ac conditions and presented for time-averaged quantities. Here the nonlinear equation of motion of the WS coupled to surface dimples is studied for ac conditions using two different approaches based on fixing the driving field or the output current. Both approaches are shown to give similar results for the first harmonics of major transport properties. In the ac theory, the BC resonances for dimple inertia and the momentum relaxation rate have asymmetrical shapes, which is in contrast with the results of dc models. Even a quite low driving frequency is shown to affect the amplitude of the BC resonance and decoupling of the WS. Above the BC threshold, the effective mass of surface dimples as a function of the velocity amplitude strongly oscillates indicating multiple recoupling processes.

Absorption characteristics of large acoustic metasurfaces.

Metasurfaces formed of arrays of subwavelength resonators are often tuned to 'critically couple' with incident radiation, so that at resonance dissipative and radiative damping are balanced and absorption is maximized. Such design criteria are typically derived assuming an infinite metasurface, whereas the absorption characteristics of finite metasurfaces, even very large ones, can be markedly different in certain frequency intervals. This is due to the excitation of surface waves, intrinsic to resonant metasurfaces and especially meta-resonances, namely collective resonances where the surface waves form standing-wave patterns over the planar metasurface domain. We illustrate this issue using a detailed model of a Helmholtz-type acoustic metasurface formed of cavity-neck pairs embedded into a rigid substrate, with geometric and dissipation effects included from first principles (R. Brandão and O. Schnitzer, Wave Motion, 97, 102583, 2020). This article is part of the theme issue 'Wave generation and transmission in multi-scale complex media and structured metamaterials (part 1)'.

On the origin of high harmonic fast wave edge losses in NSTX

Many mechanisms have been proposed to explain the high harmonic fast wave edge losses in the National Spherical Torus Experiment (NSTX) (Perkins et al 2012 Phys. Rev. Lett. 109 045001). Here, we discuss a newly discovered edge loss mechanism (Tierens et al 2021 Plasma Phys. Control. Fusion 64 035001) which involves the resonant excitation of surface waves on filaments. We show that this edge loss mechanism can explain the main parameter dependencies observed in NSTX experiments.