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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Constant-Intensity Waves in Non-Hermitian Media
摘要： When waves propagate through a non-uniform potential landscape their interference typically gives rise to a complex intensity pattern. In this chapter we review our work on how to entirely suppress these intensity variations by adding system-specific gain and loss components to the potential. The resulting constant-intensity (CI) waves are entirely free of interference fringes and get perfectly transmitted across any such non-Hermitian scattering landscape that is put in their way. We discuss how to generalize this concept to more than one dimension and to the non-linear regime where these special wave states open up the way to study the phenomenon of modulation instability in non-uniform potentials. Experimental implementations of these unique wave states are envisioned not just in optics, but also in other fields of wave physics such as in acoustics.
关键词： Acoustics,Modulation instability,Optics,Constant-intensity waves,Wave propagation,Non-Hermitian media
更新于2025-09-10 09:29:36
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Amplitude-activated mechanical wave manipulation devices using nonlinear metamaterials
摘要： We report device implications for acoustic metamaterials with various nonlinear oscillator microstructures as passive amplitude-activated mechanical wave filters and waveguides using simulations on their representative one-dimensional discrete element models. Linear and various nonlinear hardening and softening stiffness cases and combinations thereof are considered for the local oscillators. The propagation and attenuation characteristics of harmonic waves in a tunable frequency range are found to correspond to the excitation amplitude and nonlinearity-dependent shifts in the local resonance bandgap for such nonlinear acoustic metamaterials. Three passive acoustic devices—(i) amplitude-activated selective filter, (ii) amplitude band pass or band rejection filter, and (iii) direction-biased waveguide—are demonstrated numerically. Constituent frequency components in bifrequency excitations are shown to be retained or diminished to varying degrees within acoustic metamaterials with either hardening or softening local oscillators depending on their individual amplitudes. Using trilinear hardening or softening oscillators instead switches the response between attenuation and propagation respectively, outside of a tunable bandwidth of amplitude for the same excitation frequency. Whereas, amplitude-dependent, passive direction-bias in propagation characteristics for a given excitation frequency is demonstrated in a metamaterial waveguide composed of units with tuned combinations of linear and nonlinear hardening oscillators deployed in sequence. These predictions indicate the possibility of realizing acoustic metamaterials having passive adaptive, amplitude-activated dynamics using tailored combinations of nonlinear oscillators to elicit prescribed wave transformations across them.
关键词： Nonlinearity,Wave propagation,Acoustic metamaterial
更新于2025-09-10 09:29:36
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Propagation properties of chirped Airy hollow Gaussian wave packets
摘要： Based on the analytic expression of the chirped Airy hollow Gaussian (CAiHG) wave packets derived from the (3+1)-dimensional ((3+1) D) Schr?dinger equation, their propagation properties are investigated in detail for the first time. The results show that a focusing of the chirped Airy Gaussian pulses is found, which leads to the same focusing of the propagation trajectory and the maximum scattering force. The distribution factor can modulate the convergence of the side wave rings at . During the propagation process, with the increase of the , when the is negative, the side wave rings rise along the main wave axis but their moving is opposite when the is positive. When the beam order , the intensity, the angular momentum and the gradient force gradually tend to the center but they move radially when . The direction of the peripheral gradient force points to the center but the direction is opposite in the center. The beam orders only affect the magnitude of the normalized maximum scattering force but have little effects on their distribution.
关键词： Chirping,Mathematical model in optics,Wave propagation
更新于2025-09-10 09:29:36
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[IEEE 2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET) - Kiev (2018.7.2-2018.7.5)] 2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET) - Modeling of Electromagnetic Wave Scattering and Propagation in the Presence of a Pre-Fractal PEC Strip Grating
摘要： Classes of one-dimensional self-similar fractals with variable Hausdorff–Besicovitch dimension are presented. They can be used in the pre-fractal modelling in electromagnetic and acoustic wave theory: wave scattering by pre-fractal gratings and wave propagation in pre-fractal systems of microstrip lines.
关键词： self-similar fractals,wave scattering,wave propagation,pre-fractal modelling,fractal dimension
更新于2025-09-09 09:28:46
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Large-scale gravity wave perturbations in the mesopause region above Northern Hemisphere midlatitudes during autumnal equinox: a joint study by the USU Na lidar and Whole Atmosphere Community Climate Model
摘要： To investigate gravity wave (GW) perturbations in the midlatitude mesopause region during boreal equinox, 433 h of continuous Na lidar full diurnal cycle temperature measurements in September between 2011 and 2015 are utilized to derive the monthly profiles of GW-induced temperature variance, T (cid:48)2, and the potential energy density (PED). Operating at Utah State University (42? N, 112? W), these lidar measurements reveal severe GW dissipation near 90 km, where both parameters drop to their minima (～ 20 K2 and ～ 50 m2 s?2, respectively). The study also shows that GWs with periods of 3–5 h dominate the midlatitude mesopause region during the summer–winter transition. To derive the precise temperature perturbations a new tide removal algorithm suitable for all ground-based observations is developed to de-trend the lidar temperature measurements and to isolate GW-induced perturbations. It removes the tidal perturbations completely and provides the most accurate GW perturbations for the ground-based observations. This algorithm is validated by comparing the true GW perturbations in the latest mesoscale-resolving Whole Atmosphere Community Climate Model (WACCM) with those derived from the WACCM local outputs by applying this newly developed tidal removal algorithm.
关键词： Ionosphere (wave propagation),meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
更新于2025-09-09 09:28:46
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Propagation of Electromagnetic Waves through an Invisible Gradient-Index Lens with Negative Refractive Index
摘要： A radially inhomogeneous (gradient-index) lens made of material with a negative refractive index, invisible from the viewpoint of geometrical optics, is proposed and designed. The design includes derivation and solution of an equation for determining the refractive index profile, as well as derivation of an expression allowing calculation of the ray trajectories in the lens. Propagation of a plane wave through a cylindrical modification of the proposed lens both for the case of E-polarization and for the case of H-polarization is analyzed numerically using the hybrid projection method. The results obtained for the RCS of the lens are compared to the similar performance of a positive-index lens described in the previous publications.
关键词： numerical methods,RCS,geometrical optics,invisible lens,Electromagnetic wave propagation,negative refractive index,gradient-index lens
更新于2025-09-09 09:28:46
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[IEEE 2018 Days on Diffraction (DD) - St.Petersburg, Russia (2018.6.4-2018.6.8)] 2018 Days on Diffraction (DD) - Some approaches to harmonic wave propagation in elastic solids with random microstructure
摘要： We address two approaches to the problem of the one-dimensional wave propagation in elastic solids with random microstructure characterized by random elastic and mass properties. They are the method of integral spectral decomposition and the Fokker–Planck–Kolmogorov equation for describing the apparatus of continuous Markov processes. Merits and deficiencies of each approach are discussed. The studied approaches are shown to cover a number of problems of the harmonic wave propagation in heterogeneous or stochastic media. Therefore by means of a preliminary analysis of a particular problem and accounting for the strong and weak side of each approach one can find an appropriate solution strategy.
关键词： Fokker–Planck–Kolmogorov equation,random microstructure,harmonic wave propagation,elastic solids,integral spectral decomposition
更新于2025-09-09 09:28:46
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[IEEE 2018 IEEE International Conference on Intelligent Transportation Systems (ITSC) - Maui, HI, USA (2018.11.4-2018.11.7)] 2018 21st International Conference on Intelligent Transportation Systems (ITSC) - Automotive Radar Multipath Propagation in Uncertain Environments
摘要： Future use of high-resolution near range radar sensors for vehicle environment perception is facing challenges in terms of detection and correct assignment of multipath reflections (false-positives) from surfaces and obstacles. This paper presents a novel geometric model to determine the relative positions from surrounding targets and reflection surfaces assuming that every object moves on a circular path to a mutual center. Principles of electromagnetic wave propagation under consideration of incident wave angles at potential reflection surfaces are described. Radar measurements illuminating an experimental target and a highway barrier as reflection surface, which reproducibly generates several multipath reflections, were carried out in a deterministic test environment and validate our presented methods. The installation of absorption material at intense reflection areas was conducted as countermeasure to reduce the intensity of false-positive detections. Furthermore, a realistic urban driving scenario using a real vehicle as target object and a building wall was reconstructed to proof field relevance.
关键词： electromagnetic wave propagation,false-positive detections,multipath propagation,Automotive radar,geometric model
更新于2025-09-04 15:30:14
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Perturbing the polarisation of Riemann–Silberstein electromagnetic vortices
摘要： In optics the electric ?eld E usually receives more attention than the magnetic ?eld B because it interacts more strongly with matter. But for the propagation of waves in free space E and B should be given equal weight. From the two real vector ?elds E and B one ?rst constructs the vector field F = E + iB and then the complex scalar field F.F. It is this complex scalar field that contains the Riemann–Silberstein (RS) vortex lines. The optical vortices in monochromatic waves that are usually discussed are stationary in space, but these RS vortices are normally in constant motion. However, exceptionally, if the plane waves whose interference gives the ?eld are circularly polarised and are all of the same hand, it is known that the RS vortices are stationary. We study here what happens when this polarisation condition is gradually relaxed, using a 4-wave model. RS vortices are Lorentz invariant and this makes it possible to de?ne a coordinate frame in which there is spatial repetition, so that results can be exhibited in a repeating 3D unit cell. As the perturbation grows, a given point on an RS vortex at ?rst traces out an elliptical orbit; then a critical value is reached where reconnections and disconnections occur at two de?nite times during the cycle. The changes thereafter are like those seen in a general RS vortex ?eld.
关键词： phase singularities,reconnection,wave propagation,wave vortices,Riemann–Silberstein vortices
更新于2025-09-04 15:30:14
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On the propagation of Voigt waves in energetically active materials
摘要： If Voigt-wave propagation is possible in a dissipative anisotropic dielectric material characterised by the permittivity dyadic e, then it is also possible in the analogous energetically active material characterised by the permittivity dyadic e? , where e? is the hermitian conjugate of e. This symmetry follows directly from a theoretical analysis of the necessary and suf?cient conditions for Voigt-wave propagation in anisotropic materials. As a consequence of this symmetry, a porous dissipative material that exhibits Voigt-wave propagation can be used to construct a material that allows the propagation of Voigt waves with attendant linear gain in amplitude with propagation distance, by means of in?ltration with an electrically or optically activated dye, for example. This phenomenon is captured by the Bruggeman formalism for homogenised composite materials based on isotropic dielectric component materials that are randomly distributed as oriented spheroidal particles.
关键词： active materials,homogenised composite materials,Bruggeman formalism,anisotropic dielectric materials,Voigt-wave propagation
更新于2025-09-04 15:30:14